Welcome to the 21st International Conference on Atomic Processes in Plasmas. APIP will be held at the Headquarters of the International Atomic Energy Agency (IAEA), in the Vienna International Centre, Vienna Austria from 15 – 19 May 2023.
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The behavior of tungsten impurity in fusion plasmas is one of the important issues to be studied to achieve high-temperature plasmas for fusion reactions since tungsten used as plasma-facing material is sputtered by plasma particles and is expected to reduce electron temperature due to large radiation power. Many studies have been done to examine atomic properties and spectral models for tungsten ions, however, tungsten ions with 4f open subshells are not well studied yet due to the complexity of the atomic structure. Extreme ultraviolet (EUV) spectra of tungsten ions have been measured in various fusion devices and electron beam ion traps (e.g. [1,2]), and examined by comparison of theoretically calculated spectra by collisional-radiative (CR) models (e.g. [3,4]). The unresolved transition array (UTA) measured at 4.5-7nm wavelength region for plasma with electron temperature ~1keV is produced by numerous overlapped 4d-4f and 4p-4d transitions of tungsten ions. The wide two-peak feature of the UTA profile is not fully understood yet, even though recombination processes are included in the CR models [4,5] for Wq+ with q=25-39. On the other hand, the peaks measured at 2-4nm are well understood and are produced by many n=4-5 and n=4-6 transitions of Wq+ with q=22-30. They are useful to estimate charge state distributions [4,5]. For ions with q<22, no peaks are found in this region and we need some identifier for such lower charged ions. We extend our study to EUV spectra at 10-30nm where n=5-5 transitions are found for mid-charged tungsten ions by CR model calculations.
We have performed plasma experiments to measure tungsten spectra by pellet injection with Large Helical Device (LHD) for wide wavelength regions. Measured spectra at 10-30nm can be used to evaluate calculated spectra by CR models for mid-charged tungsten ions. Details of the comparison will be presented at the conference.
[1] R. Neu et al., Plasma Phys. Control. Fusion 38, A165 (1996)
[2] H. A. Sakaue et al., AIP Conf. Proc. 1438, 91 (2012)
[3] T. Putterich, R. Neu, R. Dux et al., Plasma Phys. Control. Fusion 50, 085016. (2008)
[4] I. Murakami, H. A. Sakaue, C. Suzuki et al., Nucl. Fusion 55, 093016 (2015)
[5] I. Murakami, D. Kato, T. Oishi et al., Nucl. Mater. Energy 26, 100923 (2021)
Light and metallic impurity identification in the 225-302 Å range from the SURVIE spectrometer in the WEST Tokamak
C. Desgranges(1), J.L. Schwob(2), P. Mandelbaum(3), R. Guirlet(1), Y. Boumendjel(1), O. Peyrusse(4), P. Manas(1), N. Fedorczak(1) and the WEST team(*)
(1) CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France
(2) Racah Institute of Physics, The Hebrew University, 91904 Jerusalem, Israel
(3) Azrieli College of Engineering, 91035 Jerusalem, Israel
(4) Aix-Marseille Université, CNRS, Laboratoire LP3, UMR7341, F-13288 Marseille, France
The WEST tokamak aims at testing actively cooled solid W monoblock Plasma Facing Units mounted in shape of a flat crown forming the lower divertor. These tests aim at long plasma discharges, with thermal loads of the same order of magnitude as those expected for the ITER vertical part of the lower divertor (10 MW/m2). This solid W actively cooled lower divertor has been under test since December 2022. More than 60 seconds stable L-mode X-point plasma discharges have already been realised. The main gas used for WEST plasmas is deuterium. The plasma impurity content must be as low as possible because it dilutes the fuel and more importantly cools the plasma, decreasing its performances.
Two VUV spectrometers are used to characterise plasma contamination due to impurities coming from plasma facing components. One is equipped with two mobile detectors and dedicated to physics studies, the other one (called SURVIE) is a survey spectrometer equipped with a single fixed detector. Here the focus will be put on this latter spectrometer. Its spectral range is 225-302 Å. Its fixed line of sight crosses the plasma centre almost in the midplane
A thorough line identification of the VUV spectra has been performed since 2018 in various configurations : ohmic, with LHCD heating, with ICRH heating, with both LHCD and ICRH heating. These lines are identified mainly from the Kelly tables [1] and the NIST database [2].
At the start of the experimental campaigns, during ohmic phase, Chlorine (Cl XII to Cl XIV) as well as Oxygen (O IV), Titanium (Ti X, XVIII and XX), Nitrogen (N IV and V) and Boron (B V) lines dominate the spectra. Chlorine comes from a plastic plate which fell down behind a vacuum vessel protection panel and was never completely eliminated in the subsequent campaigns. The presence of Nitrogen and Titanium is due to a number of limiter tiles made of BN fixed to the limiter frame by titanium rings. When the plasma leans on these tiles, consequently B, N and Ti lines appear.
An ohmic plasma including a large Argon injection allowed identification of Argon lines (Ar XIII, XIV and XV).
Then during plasmas heated by LH power only , it is observed that Copper (Cu XIII, XVIII and XIX) is dominant and lines from W VII-VIII to W XLV appear and increase with LHCD power.
In the case of ICRH power alone, silver lines (Ag XVI, XVIII and XIX) appear and increase with ICRH power. Silver is due to the Silver coating of ICRH antennae front face.
The lower ionisation stages of impurities give indications on the plasma edge temperature and sources, the higher ones on the impurity content of plasma core. From these two types of information, impurity transport can be evaluated.
Furthermore this line identification helps on the one hand to determine the impurity production processes and consequently to adapt the plasma's magnetic equilibrium ; on the other hand it helps to assess the plasma conditioning state and performance.
References :
[1] R. L. Kelly, Journal of Physical and Chemical Reference Data Vol. 16 (1997) supplement N°1
[2] https://www.nist.gov/pml/atomic-spectra-database
(*) http://west.cea.fr/WESTteam
High-resolution x-ray crystal spectroscopy has been a workhorse on numerous tokamaks to measure the ion temperature and toroidal rotation profiles from the Doppler broadening and shift, respectively, of intrinsic or seeded impurity line radiation emission. SPARC will be a first-of-its-kind tokamak that will similarly employ this diagnostic. The unique high electron temperature and high neutron flux environment of SPARC has been driving factors for the engineering design. Presented is the performance of the envisaged system of spectrometers optimized to view the Ne-like Xe 3D line (λ$\approx$2.72 Å) for low-temperature operations ($T_{e0}$$\approx$4-10 keV) and the He-like Kr w resonance line (λ$\approx$0.94 Å) for high-temperature operations ($T_{e0}$>10 keV). The Flexible Atomic Code (FAC) has been utilized to calculate line intensities, including satellites and polluting tungsten lines. The throughput has been calculated ensuring integration times on the order of the expected energy confinement time, $\sim$100ms. This workflow has been validated against measured spectra from an absolutely calibrated von Hamos as well as a Johann spectrometer installed on Alcator C-Mod to good agreement. While the number of lines-of-sight is highly constrained, the staged installation of beamlines over the first campaigns minimizes error in calculated fusion power from the reconstructed profiles.
Understanding the basic plasma parameters of temperature and density, as well as their gradients in the scrape-off layer (SOL), is a topic critical for providing information about the performance of a divertor concept. The stellarator Wendelstein 7-X features a novel resonant island divertor with an adjustable rotational transform of ι = 2π (5/6, …, 5/4). In order to study the performance of this divertor concept, an active spectroscopy system on a thermal helium beam [1] was developed and installed on the device [2]. The system consists of four identical Czerny-Turner spectrometers imaging two stellarator-symmmetric upper and lower divertor modules, allowing for tomographic reconstruction of impurity radiation in the island divertor region. The helium beam diagnostic operates using the technique of line ratio spectroscopy, applying a collisional-radiative model (CRM) to relate the observed line radiation to the underlying plasma parameters [3]. Despite successful operation during previous experiments, there have been systematic disagreements observed between the helium beam and other edge diagnostics. In order to investigate the uncertainties of the helium beam diagnostic and the vulnerabilities of the underlying atomic data set, a complete Bayesian treatment has been undertaken with the Minerva Bayesian modeling framework [4]. First, it has been shown through a sensitivity study that the diagnostic method is robust against random measurement errors and systematic calibration errors on the scales achievable with the current diagnostic setup. From this, it is concluded that the majority of the uncertainty in the reconstructed temperature and density arises from systematic uncertainties in the underlying CRM rather than from measurement errors, and that a narrow subset of these processes is disproportionately responsible for plasma profile reconstruction uncertainties [5]. A new R-matrix data set for helium has been calculated and its differences from previous data sets will be discussed, as well as the implications on plasma parameter reconstructions. Finally, corrections for finite magnetic field effects are discussed and the relevant regimes for neglecting these effects are shown.
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[2] T. Barbui, et al. Nuclear Fusion 60.10 (2020): 106014
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[5] Flom, E. et al. Nuclear Mat. & Eng. 2023.
Acknowledgements: This work was funded in part by the U.S. Department of Energy under grant DE-SC00014210 and DE-SC00013911. This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.
High-Z materials such as tungsten and molybdenum have become leading solutions for plasma-facing materials. There are uncertainties in both erosion and transport of these elements requiring further research. The spectral emission of these high-Z species in combination with Collisional Radiative (CR) modeling can provide necessary information for plasma transport modeling. The Python program, ColRadPy, has been developed to solve collisional-radiative and ionization balance equations which can be applied to fusion, laboratory, and astrophysical plasmas [1]. The program provides generalized coefficients that can be used in existing plasma modeling codes and spectral diagnostics.
A spectral survey of tungsten emission in the ultraviolet region was conducted in two experiments, DIII-D tokamak and Compact Toroidal Hybrid (CTH) torsatron, to assess the potential benefits of UV emission for tungsten erosion diagnosis. A total of 53 neutral tungsten spectral lines were observed, including 32 lines not previously reported at fusion conditions [2]. Metastable level populations of neutral tungsten can impact both emission and erosion measurements, which can be significant at ITER relevant divertor electron densities. Observation of spectral lines in the UV region allows for relative metastable fractions and electron temperature to be diagnosed at the erosion location. The observed neutral tungsten emission lines can be used to measure gross tungsten erosion. The simultaneous observation of neutral tungsten and singly charge tungsten lines can estimate net erosion and the fraction of tungsten that is re-deposited.
Spin-changing collisional rate coefficients for metastable levels allow for the detailed exploration of the dynamics of metastable levels [3]. Long-lived metastable states in neutral tungsten can impact erosion measurements, so time-dependent collisional radiative modeling is used to analyze their role in tungsten emission and ionization. The large number of non-quasistatic atomic states in neutral tungsten can take milliseconds to reach equilibrium, affecting erosion measurements, so a scheme for measuring relative metastable fractions is proposed through simultaneous observation of multiple ultraviolet spectral lines of neutral tungsten. The Chodura sheath is a region of low electron density produced by magnetic fields impinging on plasma facing surfaces at shallow angles. The Chodura sheath also is important due to its potential impact on time-dependent neutral tungsten [4]. A simple model is developed to account for the effects of the Chodura sheath on the time-dependence of neutral tungsten. The study provides a roadmap for modeling the spectral emission from complex species like tungsten and yields accurate tungsten erosion.
[1] C. A. Johnson et al. 2019 Nucl. Mater. Energy 20 100579
[2] C. A. Johnson et al. 2019 PPCF 61 095006
[3] R. T. Smyth et al. 2018 Phys. Rev. A 97 052705
[4] C. A. Johnson et al (2020, November 9–13) Diagnosing metastable populations in fusion edge plasmas using collisional-radiative modeling constrained by experimental observations 62nd Annual Meeting of the APS Division of Plasma Physics
Upper and lower graphite divertor in EAST tokamak have been updated to tungsten divertors in 2014 and 2021 respectively to investigate the tungsten divertor operation and to realize high-performance long pulse discharge. Therefore, studies on the tungsten behavior are crucially important for improving the plasma performance. For the purpose four fast-time-response [1-2] and four space-resolved [3-4] extreme ultraviolet (EUV) spectrometers have been installed on EAST to observe line emissions from tungsten ions and their intensity radial profiles in wavelength ranges of 5-520Å.
Photon emission coefficient (PEC) data for W45+ at 62.336 and 126.998Å, W43+ at 61.334 and 126.29Å have been used to estimate density profiles of W45+ and W43+ ions in the bulk plasma [3,5]. Tungsten unresolved transition arrays (W-UTA) in the long wavelength range of 168-225Å, 225-268Å and 278-332Å observed from typical EAST ELMy H-mode plasmas are analyzed for the study of edge tungsten behaviors. As a result, three lines of 186.28 Å, 190.48 Å and 192.02 Å with relatively strong intensities emitted from W8+ ions could be confirmed by comparing with the time behaviors of well-known line emissions from W6+ at 216.219 and 261.387 Å [6,7], W7+ at 200.367 Å and 200.483 Å [8] and W27+ at 49.403Å [1-4]. Therefore, the ionization per photon coefficients, S/XB, for the lines from weekly ionized ions are therefore required to estimate the tungsten influx at plasma edge. Additionally, visible spectrometer with spatial viewing range covering the whole EAST poloidal cross section have been newly developed for the attempt of investigating the radial profile of line emissions of M1 transitions from W26+-W28+ and W8+-W12+ ions which have been observed in LHD [9] and EBIT [10] respectively. Calculation of full radial profiles of impurity density and influx will be attempted using the PEC and S/XB data of the observable lines.
Reference
[1] L. Zhang et al., Rev. Sci. Instrum. 86 (2015) 123509
[2] Z. Xu et al., Nucl. Instrum. Meth. A 1010 (2021) 165545
[3] L. Zhang et al., Nucl. Instrum. Meth. A 916 (2019) 169
[4] Y.X Cheng et al., Rev. Sci. Instrum. 93 (2022) 123501
[5] Y.X Cheng et al., IEEE T Plasma Sci. 50(2022):691-699
[6] J. Clementson et al., J. Phys. B 43 (2010) 144009
[7] C.F. Dong et al., Nucl. Fusion 59 (2019) 016020
[9] D. Kato et al., Nucl. Fusion 61 (2021) 116008
[10] Q. Lu et al. Phys. Rev. A 103 (2021) 022808
This work was supported by the National MCF Energy R&D Program (Grant No. 2022YFE03180400) and Chinese Academy of Sciences President’s International Fellowship Initiative (PIFI) (Grant No. 2020VMA0001).
Most of the realistic kinetic calculations for tokamak plasmas require now to incorporate the effect of partially ionized high-Z elements, arising either from uncontrolled influxes of metallic impurities like tungsten in high input power regimes or from mitigation by massive gas injection of runaway electrons generated after plasma disruptions [1,2]. The usual electron-ion Fokker-Planck collision operator must be therefore modified, according to the atomic physics. as well as the cross-sections for some synthetic diagnostics, like bremsstrahlung, whose importance for characterizing the plasma state is considerable [3]. This represents a challenge, in order to perform fast but also accurate calculations, regardless the types of elements present in the plasma and their local level of ionization, while covering a wide range of electron energies in a consistent way, from thermal to highly relativistic limits. In this context, a unified modelling of the atomic physics has been developed, based on a multi-Yukawa potential representation calibrated against advanced quantum relativistic calculations [4]. Besides the possibility of an accurate description of inner and outer atomic shells, it is possible to derive analytical formulations for elastic and inelastic scattering which can be easily incorporated in kinetic codes [3,5-7]. The impact of the number of exponentials in the description of the atomic potential is discussed, and compared with the Thomas-Fermi or Thomas-Fermi-like atomic models.
This work was partially funded by National Science Centre, Poland (NCN) grant HARMONIA 10 no. 2018/30/M/ST2/00799.
References
[1] V. Ostuni, et al., Nucl. Fusion, 62 (2022) 106034.
[2] L. Hesslow, et al., Phys. Rev. Letter, 118 (2017) 255001.
[3] Y. Peysson, et al., in proceedings of IAEA FEC 2020 - The 28th IAEA Fusion Energy Conference, 10-15 May 2021, Nice (E-Conference), France.
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Abstract
The Doppler Shift Spectroscopy (DSS) diagnostics, since its inception as a diagnostics technique in Neutral Beam Injectors (NBI), has proved to be an indispensable tool for characterizing positive and negative ion beams and optimising the ion sources performance [1-2]. For positive ion beams, beam parameters such as beam energy, beam species mix, beam impurity fractions, beam divergence and injected power fraction are routinely estimated using this technique [3-5]. In case of negative ion beams, this technique is primarily used to assess the beam inhomogeneity and beam stripping fractions which are very important parameters for understanding the negative ion source performance [2,6].
In positive ion beams, the ion source plasma discharge contains multi specie ions: H+,H2+ and H3+ which are accelerated to the same energy (E) during extraction of beam. During neutralization phase, they undergo variety of collisions such as charge exchange, dissociative charge exchange, dissociative ionization etc with the background H2 gas to form positive, neutral and negative ion species at different energies. Some of these species are also be formed in excited state , whose emissions are recorded and analysed in this technique. The beam or ion species mix is usually obtained from the ratios of the observed intensities corresponding to each energy group of excited neutrals which are correlated to various production processes via an extensive emission model. Similar technique are also used for DSS analysis of negative ion beams for the applications mentioned above. It may be noted that the present modelling efforts consider the uncertainties related to the available measured cross section database for both positive and fast negative ion beams.
Further in both positive and negative ion beams, the beam divergence is estimated using a rigorous line profile analysis [1,6-7]. In our recent study, it is observed that the conventional deconvolution techniques when applied to a low divergent large focal length beams ( e.g. ITER-HNB/DNB , JET NBI etc.) yielded errors larger than 30%. A novel line profile method has been developed to account for such errors.
In this presentation, the details of a comprehensive collisional radiative modelling applicable to positive and negative ion beams and the line profile method developed for estimating divergence of low divergent large focal length beams are presented and discussed. The challenges and limitations of this technique are highlighted.
References
1. W. F. Burrel C F, Cooper W S, Steele, “Doppler Shift Spectroscopy of powerful neutral beams”, Rev. Sci. Instrum, 51, 1451 (1980).
Argon seeding in a tokamak has several benefits such as, achieving lower-H-mode thresholds [1, 2], reducing heatloads on plasma-periperals through radiative power dissipation at the plasma boundary [3] etc. Trace argon is also injected for diagnostic purposes [4, 5]. Nonetheless, argon accumulation in the core and its high radiation through line and continuum emissions result in confinement degradation and fuel dilution and it is an important concern for the present and future tokamaks such as ITER [3]. Therefore, it is important to understand argon impurity dynamics in fusion plasmas thereby controlling argon concentration and accumulation inside the plasma column.
Vaccuum Ultraviolet (VUV) and visible line emissions from partially ionized argon impurity ions are simultaneously observed in the Aditya-U [6] ohmically heated plasma with trace argon impurity injection (~ 1017 particles) during the current flat top phase of the discharge. These line emissions, observed using abolutely calibrated high resolution visible and VUV spectrometer systems are used to understand argon impurity dynamics in the plasma [7]. Argon transport coefficients (diffusivity and convective velocity) are calculated from the integrated use of these two spectroscopic diagnostics and the 1D impurity transport code STRAHL.
During the experiments, space resolved visible line emissions of Cl-like argon ions and line integrated VUV line emissions from Be-like and B-like argon ions have been observed. The Ar1+ line emissions in the visible range at 472.68 nm (3p44s 2P1.5 - 3p44p 2D1.5), 473.59 nm (3p44s 4P2.5 - 3p44p 4P1.5), 476.48 nm (3p44s 2P0.5 - 3p44p 2P1.5), 480.60 nm (3p44s 4P2.5 - 3p44p 4P2.5) and VUV emissions of Ar13+ at 18.79 nm (2s22p 2P1.5 - 2s2p2 2P1.5) and Ar14+ at 22.11 nm (2s2 1S0 - 2s2p 1P1) are identified using NIST database. From the experiments, radial emissivity profile of Ar1+ spectral emission and brightness ratio of Ar13+ and Ar14+ ions have been calculated simultaneously. In order to estimate the argon impurity transport coefficients, the experimental emissivity profile and brightness ratio need to be simultaneously compared with those simulated using the impurity transport code, STRAHL. Since the photon emissivity coefficeints (PEC), required to obtain the emissivty profiles of the observed transitions, are not directly available, they have been generated using NIST and ADAS databases. For all the observed transitions of Ar1+, Ar13+ and Ar14+ ions used in the study the appropriate fundamental data related to electron impact excitation rate coefficients are obtained from the ADAS database, by properly matching the energy levels between NIST and ADAS database. These data were then used in ADAS generalised collisional-radiative (GCR) data production routine which provided the required PECs for the range of electron density and temperature. The calculated PECs were then used in STRAHL code to simulate the emissivity profile of Ar1+ spectral emission and brightness ratio of Ar13+ and Ar14+ ions and compared with experimental values to estimate argon transport coefficients. Argon diffusivity ~ 12 m2/s in the edge (ρ > 0.85) and ~ 0.3 m2/s in the core region have been observed. The diffusivity values in the edge and core are found to be higher than the neo-classical values, which suggests that the argon transport is mainly anomalous in the Aditya-U tokamak. Moreover, it has been observed that an inward pinch of ~ 10 m/s is required to match the experimental and simulated data. The measured peaked profile of total argon density suggests impurity accumulation in these discharges. The detailed results on experimental measurements, calculation of PEC profiles and argon transport coefficients will be discussed in the paper.
References
1. Ongena J., et al 2001 Plasma Phys. Control. Fusion 43, A11.
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Structural transitions in solids induced by intense femtosecond pulses from X-ray
free-electron laser are in the focus of this talk. Depending on the dose absorbed, the
irradiation can trigger an ultrafast electronic or structural transition in these materials. For very
high doses, transition from the solid to warm-dense-matter or to plasma state follows.
Dedicated theoretical modeling tools reveal complex multistage evolution of the irradiated
systems, confirmed by experimental measurements performed at X-ray free-electron-laser
facilities. Challenges remaining for the modeling and possible further model developments are
discussed.
K-shell x-ray emission spectroscopy is a standard tool used to diagnose the plasma conditions created in high-energy-density physics experiments such as short-pulse heated buried microdot targets. In the simplest approach, the emissivity-weighted average temperature of the plasma can be extracted by fitting an emission spectrum to a single temperature condition. Recent work has shown that temperature distributions resulting from spatial gradients and the time evolution of the sample can be extracted from time-integrated x-ray spectra [1], however the intensity of the optically thick emission lines needed to be modified to fit the experimental spectra. In this work, we explore the effects of various treatments of optically thick emission lines in the analysis of buried layer microdot targets including escape factors and full radiation transport calculations. In doing so, we aim to identify the origin of the multipliers required to fit such experimental spectra and improve the characterization of the plasma conditions in the buried layer targets used for x-ray opacity studies.
[1] M. J. MacDonald et al., Rev. Sci. Instrum. 93, 093517 (2022).
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
Laser-driven shock compression coupled to brilliant X-rays probes opens new research opportunities in the field of matter at extreme conditions allowing to answer questions relevant for planetary science. At beamline ID24 at ESRF (Grenoble, France) a High-Power laser was coupled to time-resolved X-ray Absorption Spectroscopy (XAS)[1]. The unique advantage represented by coupling XAS together with a High-Power laser is the ability to microscopically probe a sample regardless its state. This because, XAS technique-besides being element selective- is sensitive to short-range order and to the electronic configuration. We present here the laser-driven shock compressed XAS data of iron collected at ID24 up to 250 GPa and 4000K along the Hugoniot curve and of liquid iron measured during the shock release, that means probing at later times after the shock was out of the Fe layer. We were able to locate our shocked Fe measurements on the phase diagram by anchoring the VISAR interferometer outputs to ESTHER hydrodynamic simulation code. The acquired XAS range was long enough to retrieve the first coordination shell radius and to so retrieve its volume. The laser energy upgrade foreseen in 2023, will allow to reach and microscopically probe WDM states and thus provide an experimental constrain to theoretical models.
[1] Sevelin-Radiguet, N., Torchio, R., Berruyer, G., Gonzalez, H., Pasternak, S., Perrin, F., Occelli, F., Pepin, C., Sollier, A., Kraus, D., Schuster, A., Voigt, K., Zhang, M., Amouretti, A., Boury, A., Fiquet, G., Guyot, F., Harmand, M., Borri, M., Groves, J., Helsby, W., Branly, S., Norby, J., Pascarelli, S. & Mathon, O. (2022). J. Synchrotron Rad. 29, 167-179.
Atomic structure profoundly impacts the material and radiative properties of dense plasmas. Accurate atomic models are critical to understanding the structure and evolution of stellar interiors, inertial fusion plasmas, and traditional and nuclear explosives. Even at a few times solid density, however, interactions between neighboring ions in a plasma may substantially modify the atomic wavefunctions. Calculations of these many-body quantum interactions are exceedingly difficult, requiring approximations to be made in most atomic structure models, yet few datasets exist to verify their accuracy. We present inner-shell x-ray absorption spectra of mid-Z witness layers in a laser-driven spherical implosion compressed to Gbar pressures. We map the energy shift of inner-shell transitions during disassembly and the relationship to the evolving thermodynamic conditions. Impacts on atomic structure models are discussed.
This talk describes how the steady state atomic kinetics approximation can underestimate the electron temperature determined from K-shell lines in ps-time-scale transient plasmas. In particular we model the inferred temperature evolution of solid FeS targets used in opacity experiments at the Orion laser facility determined from the ratio of the sulfur He-alpha to Ly-alpha lines. Initially we model the constant density steady state scenario and then expand this to include the time dependent density effects. The Orion experiments use short-pulse lasers to heat a thin microdot of FeS buried in a plastic target to temperatures of more than 1 keV and densities of approximately 1-2 g/cm3 after the FeS quickly equilibrates with the density of plastic. Using atomic kinetics calculations based on the temperature and density history from a radiation hydrodynamic simulation of the target evolution, we show how the peak temperature inferred from the sulfur line ratios is both lower and temporally lags the input temperature history. We then discuss how opacity effects impact the analysis and consider whether other materials may be optimal temperature diagnostic for different temperature ranges.
When an ultra-intense (>10$^{18}$ W/cm$^2$) laser pulse interacts with a suitable target in the plasma state, relativistic electrons are accelerated. These electrons can emit high-energy photons (keV-MeV energy range) mainly through bremsstrahlung [1,2], mediated by the atoms and ions inside the target, and through synchrotron-like emission [3]. These emission processes can be exploited for diagnostics in experiments and for developing laser-based high-energy photon sources. These sources could complement conventional ones by providing unique properties like compactness, ultrafast duration, small source size, high energy and high flux. Advanced targets, like a double-layer target (DLT), can enhance the number and energy of relativistic electrons produced in the interaction and consequently boost emission. Specifically, a DLT is made of a solid substrate covered with a low-density layer which favours the laser-plasma coupling [4]. This contribution presents the results of numerical simulations investigating, in particular, bremsstrahlung in laser interaction with DLTs. The modelling of this atomic emission process in laser-plasma interaction needs proper investigation and discussion of the cross-section choice and use. Indeed, particle-in-cell codes, widely used tools to study laser-plasma interaction, can be coupled in different ways with Monte Carlo approaches [5,6] to simulate bremsstrahlung. After considering the rationale and criticalities of some of these simulation approaches based on open-source codes, we use these tools with the support of analytical models to study the leading processes and properties of bremsstrahlung in DLTs [7]. We look at the impact of the DLT and laser parameters on the emission properties. We also consider the competition with synchrotron-like emission and the effect of including other atomic processes, like target ionization, in the simulations. Our 2D and 3D simulations show how DLTs can enhance the number of high-energy emitted photons and tune emission according to their properties (thickness, density, atomic number). These results make bremsstrahlung in DLTs worthy of investigation in future experimental campaigns and potential applications like photon activation analysis [8] and laser-driven tomography.
[1] J.D. Kmetec et al. Physical Review Letters 68, 1527 (1992)
[2] F. Albert et al. Plasma Physics and Controlled Fusion 58, 103001 (2016)
[3] A. Di Piazza et al. Reviews of Modern Physics 84, 1177 (2012)
[4] L. Fedeli et al. Scientific Reports 8, 3834 (2018)
[5] C.D. Chen et al. Physics of Plasmas 20, 052703 (2013)
[6] B. Martinez et al. Physics of Plasmas 26, 103109 (2019)
[7] A. Formenti et al. Plasma Physics and Controlled Fusion 64, 044009 (2022)
[8] F. Mirani et al. Communications Physics 4, 185 (2021)
One of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed $3C$ and $3D$. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio $R_{\mathrm{exp}} = f_{3C}/f_{3D}=3.51(2)_{\mathrm{stat}}(7)_{\mathrm{sys}}$ agrees with state-of-the-art calculations of $R_{\mathrm{th}}=3.55(2)$, as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of $3C$ and $3D$ transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.
X-ray studies of atomic processes involving highly charged ions at EBIT/S
Ł. Jabłoński, D. Banaś and M. Pajek
Institute of Physics, Jan Kochanowski University, 25-406 Kielce, Poland
The electron beam ion traps and sources (EBIT/S) producing highly charged ions (HCI) offer unique experimental conditions to study various atomic processes [1], including electron impact ionization/excitation, recombination and radiative and nonradiative deexcitation of trapped and extracted HCI from EBITs. Here the experiments on X-ray emission from EBIT plasma involving highly charged Xeq+ (q up to 40) ions are discussed, in particular, in context of radiative (RR) and dielectronic (DR) recombination of ions with electrons (see Fig. 1). In experiments with extracted slow Xeq+ ions interacting with metallic beryllium the relaxation of Rydberg hollow atoms (RHA) [2], formed at a surface, was studied. We demonstrate experimentally that in ultrafast relaxation of RHA the two-electron processes, such as interatomic Coulombic decay (ICD) [3,4] and internal dielectronic excitation (IDE) [5], play important role. The present results clearly demonstrate that that x-ray spectroscopy, applied to measure the radiation emitted from HCI produced at, allows to reveal fine details of various atomic processes involving highly exited heavy ions.
References
1. H. Winter and F. Aumayr, J. Phys. B 32, R39 (1999).
2. J.P. Briand et al., Phys. Rev. Lett. 65, 159 (1990).
3. L.S. Cederbaum et al. Phys. Rev. Lett. 79, 4778 (1997).
4. R.A. Wilhelm et al., Phys. Rev. Lett. 119, 103401 (2017).
5. R. Schuch et al., Phys. Rev. Lett. 70, 1073 (1993).
Photoionization plays a key role in the production of highly charged ions in active galactic nuclei (AGNs). The inner shell photoionization leads to highly excited states that are the subject of radiative and Auger cascade. An electron from a higher shell fills the inner-shell vacancy while simultaneously causing the removal of another electron from the atomic system during the Auger decay. As a result of the Auger cascade, the produced ions have higher charge states than the initial ion. However, the final ion population eventually stabilizes in states that are below the ionization threshold of the corresponding ion.
The aim of the current work is to study multiple photoionization of the $2p$ subshell of the Fe$^{+}$ $3d^{6}4s$ configuration. The investigation of multiple photoionization for the iron atom and ions was the subject of our earlier work [1, 2], and this study represents a continuation of that research. The Fe$^{+}$ ion is an important diagnostic tool for the study of AGNs. The Fe$^{+}$ emission is thought to arise from gas in the broad line region. The spectral lines of the Fe$^{+}$ ion were also identified from the inner torus wall. On the other hand, the higher ionization stages of Fe were observed in spectra from AGNs [3].
Multiple photoionization cross sections are studied for all 63 energy levels of the Fe$^{+}$ $3d^{6}4s$ configuration. The study also includes partial photoionization cross sections to the configurations of produced ions. The photoionization of the $2p$ subshell of the Fe$^{+}$ $3d^{6}4s$ configuration leads to the autoionizing Fe$^{2+}$ $2p^{5}3d^{6}4s$ configuration which has 360 energy levels.
Decay of the Fe$^{2+}$ $2p^{5}3d^{6}4s$ configuration through a cascade of radiative and Auger transitions produces 9 final configurations which population exceeds 0.01%: Fe$^{2+}$ $3d^{5}4s$, Fe$^{3+}$ $3d^{5}$, Fe$^{3+}$ $3d^{4}4s$, Fe$^{4+}$ $3d^{4}$, Fe$^{4+}$ $3d^{3}4s$, Fe$^{4+}$ $3p^{5}3d^{5}$, Fe$^{5+}$ $3d^{3}$, Fe$^{5+}$ $3d^{2}4s$, Fe$^{5+}$ $3p^{5}3d^{4}$. The study of the cascade includes only electric dipole transitions. The produced configurations can lead to further decay through radiative transitions of higher multipoles.
The main populations of the cascade decay reside in states of the Fe$^{4+}$ and Fe$^{5+}$ ions. The yield of the Fe$^{6+}$ ion is lower than 0.01% for all levels of the Fe$^{2+}$ $2p^{5}3d^{6}4s$ configuration from which the cascade starts. It has to be noted that the largest ion yields depend on the level of the Fe$^{2+}$ $2p^{5}3d^{6}4s$ configuration. The largest population of the Fe$^{4+}$ ion amounts to $\sim$72% for the ground level of the Fe$^{2+}$ $2p^{5}3d^{6}4s$ configuration. The lowest ion yield of $\sim$30% corresponds to the highest levels of the initial configuration of the cascade. On the other hand, the largest population of $\sim$57% for the Fe$^{5+}$ ion is produced from the level with index 160 while the lowest population of $\sim$24% is a result of cascade decay from the level with index 9. What is more, the yield of the Fe$^{3+}$ ion varies from $\sim$1.7% (index 1) to $\sim$24.6% (index 137).
The strongest branch of the cascade when population of levels is proportional to their statistical weights lead to Fe$^{5+}$: Fe$^{2+}$ $2p^{5}3d^{6}4s$ $\rightarrow$ Fe$^{3+}$ $3p^{4}3d^{6}4s$ (44%) $\rightarrow$ Fe$^{4+}$ $3p^{5}3d^{4}4s$ (36%) $\rightarrow$ Fe$^{5+}$ $3d^{3}$ (34%).
References
[1] S. Kučas et al., Astron. Astrophys. 643, A46 (2020).
[2] S. Kučas et al., Astron. Astrophys. 654, A74 (2021).
[3] F.C. Cerqueira-Campos et al., Mon. Not. R. Astron. Soc. 500, 2666 (2020).
Collisional cross sections and collisional-radiative (CR) models are of upmost importance for plasma diagnostics in the entire community, from low-temperature athmospheric pressure plasmas and fusion applications to astrophysical studies. Large efforts have been undertaken to provide collisional data by experiments, simulations, and analytic calculations. However, the validation of collisional data and CR models is very challenging and requires high-quality spectroscopic measurements and complex data analysis methods [1-2]. Here, we present our effort to validate collisional data relevant for fusion applications by modeling the results of fast spectroscopic diagnostics in a highly reproducible plasma experiment.
The Resonant Antenna Ion Device (RAID) [3], operated at EPFL, Switzerland, is a linear plasma device that produces a steady-state Helicon discharge, sustaining electron densities ne of few $10^{17}$ to $10^{19}$ m$^{-3}$ and temperatures Te of 1 to 10 eV in hydrogen (deuterium), helium, and argon. The plasma is highly reproducible and well diagnosed by means of Langmuir (LP) and B-dot probes, as well as optical emission specttroscopy (OES), Thomson scattering (TS), laser induced fluorescence (LIF), and two photon absorption LIF (TaLIF).
A Laser Collisional Induced Fluorescence (LCIF) diagnostic in helium plasmas [4] that enables simultaneous monitoring of various (>10) optical transitions (n = 3 and 4 → n = 2), was recently developed at RAID [5]. The local pumping of the 1s3s 1D level hereby minimizes the effect of integration along the line of sight. In the future, we suggest to utilize a tunable ps-laser pulse (28 ps, 193 nm to 2300 nm) which will allow us to pump different He levels with high temporal resolution. An absolute calibration of the detection system can directly yield the (combined direct and cascade) apparent population rate of the probed levels (except 1P) resulting from the pumping process, while the measurement of the fluorescence life time enables quantitative inference about the opacity of the plasma and the (collisional) quenching in various plasma conditions. Comparison of the experimental results with predictions from a CR model allows understanding the role of complex (de)population processes like opacity. Ultimately, we intend to develop a method that allows simultaneous fitting of the experimental spectra obtained from different pumping schemes, while varying the reaction rates for the dominant collision processes by using a probabilistic approach based on Bayesian data analysis, similar to [1-2]. With the extensive spectral data sets provided by the LCIF diagnostics and the independently obtained plasma parameters from TS and LIF, we will push this analysis to a level that will enable us to put experimental constraints on the collisional cross sections for helium to improve present-day plasma diagnostics in the fusion community.
This work was partially supported by the Swiss National Fund grant No 200020_204983.
References:
[1] D. Dodt et al., 2010 New J. Phys. 12, 073018
[2] E. Flom et al., 2022 Nuclear Materials and Energy 33, 101269
[3] I. Furno et al., 2017 EPJ Web Conf. 157, 03014
[4] E V Barnat and K Frederickson, 2010 Plasma Sources Sci. Technol. 19, 055015
[5] M. Baquero-Ruiz et al., 25th Europhysics Conference on the Atomic and Molecular Physics of Ionized Gases (ESCAMPIG), 2022.
Emission lines from He-like ions are an essential diagnostics tool of high-resolution X-ray spectra from satellite missions, such as Chandra and XMM-Newton. Due to the simplest close-shell structure of these ions, observable spectra contains the strongest and easiest identifiable emission lines in a variety of astrophysical objects. The physical insight of these lines can be used to probe the dynamics of hot coronal plasmas, cool photo-ionized plasmas, as well as out-of-equilibrium-plasmas like ones present in the winds of X-ray binaries, and supernova remnants. Recently, the Perseus cluster's X-ray spectrum was analyzed using Hitomi's Soft X-ray Spectrometer micro-calorimeter to measure turbulent motion at its center. The broadening and Doppler shift of He-like lines of FeXXVIII was used in this regard. However, obstacles emerged in the analysis due to inaccuracies in atomic data employed in standard plasma modelling codes. This motivates not only a careful analysis of the theoretical methods, but also an experimental benchmark of the line formation mechanisms.
X-ray measurements of He-like OVII were carried out at the FLASH- Electron Beam Ion Trap (EBIT), Heidelberg. The decay of the forbidden $z$ line population was directly observed with an electron beam energy scheme defined by a triangular wave. We observed the He-like dielectronic recombination (DR) KLn structure, as well as resonant excitations (RE) superimposed to collisional excitations (CE) of H-like and He-like ions at the collisional excitation threshold. The $2p$ line emission ($x+y+w$) was isolated with a sufficient fast scan that makes the $z$ emission constant, allowing its subtraction from the overall emission. The experimental method was verified with a home-made collisional-radiative code. Results of the line formation are compared with calculations of FAC, based on isolated-resonant approximation, and R-matrix method, as well as current state-of-the art R-matrix calculations.
In an electron beam ion trap (EBIT) the ion plasma is confined in a spatially narrow region centered around the electron beam compressed to about 10$^{10}$-10$^{12}$ cm$^{-3}$ densities. The ion cloud in its equilibrium generally consists of a narrow distribution of charge states. This can be finely tuned by adjusting the electron beam energy and current, the axial magnetic field, and the amount of neutral atoms in the trap region. The almost mono-energetic electrons are responsible for electron impact ionization and recombination processes and contribute to the confinement of the ions.
In the EBIT of the National Institute of Standards and Technology (NIST) the non-Maxwellian plasma has been modeled by collisional-radiative calculations [1] to reliably predict the spectral emission of the ion cloud [2-3]. In recent experiments we have found that in some cases, the charge state distribution of the ions is strongly affected by metastable energy levels that accumulate considerable ion population. Ag-like and Ni-like heavy ions are examples of such systems, where the lowest excited states are highly metastable. The effect strongly depends on the density of the electrons; therefore, it can serve as a sensitive diagnostic of plasmas where metastable ions are present. Measured spectral features and details of model calculations will be presented.
[1] Y. Ralchenko and Y. Maron, J. Quant. Spec. and Rad. Trans. 71 (2001) 609
[2] R. Silwal, Dipti, E. Takacs, J.M. Dreiling, S.C. Sanders, A.C. Gall, B.H. Rudramadevi , J.D. Gillaspy, Y. Ralchenko, J. Phys. B. At. Mol. and Opt. Phys. 54 (2021) 245001
[3] C. Suzuki, Dipti, Y. Yang, A.C. Gall, R. Silwal, S. Sanders, A. Naing, J.N. Tan, E. Takacs, Y. Ralchenko, J. Phys. B. At. Mol. and Opt. Phys. 54 (2020) 015001
Saturated absorption spectroscopy is a tool that can be used to suppress the Doppler broadening of observed atomic and molecular transition lines in order to measure their precise wavelengths. Obtaining a saturated absorption condition by laser excitation is an essential technique for use in saturated absorption spectroscopy. We are introducing the laser excitation process into the collisional radiative model of hydrogen atoms to uncover how much saturation can be achieved under realistic plasma conditions and laser power density. Results show that the simulated spectra were able to successfully model Lamb dips and peaks utilizing this method, with the simulated plasma and laser parameters showing good agreement with the ones used in the experiment. This model has additionally helped to give further insight into how plasma parameters can affect the spectral characteristics of Lamb dips and peaks by noting the dependence of the simulated spectral saturation on these parameters.
The study of hyperfine structures in many-electron highly charged ions (HCIs) can provide a deeper understanding of strongly correlated electrons and serve as a benchmark for advanced theoretical calculations. Additionally, the possibility of using HCIs as atomic clock candidates emphasizes the importance of hyperfine structures in many-electron HCIs [1]. However, there has been limited progress in hyperfine spectroscopy of many-electron HCIs due to experimental challenges. We successfully performed hyperfine-structure resolved laser spectroscopy of HCIs in an electron beam ion trap plasma. In the meeting, we present the hyperfine structures in the 4d95s1 metastable states of Pd-like 127I7+ by laser-induced fluorescence (LIF) spectroscopy of magnetic-dipole (M1) transitions along with the detailed modeling and theoretical hyperfine structure calculations [2].
The evolution of charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn as a function of the density of the H$_2$ buffer gas surrounding the LPP is investigated. Without a H$_2$ buffer gas, energetic 1 - 5 keV Sn ions in charge states of 4+ up to 8+ are detected. In this keV regime, lower Sn charge states, i.e., below 4+ are absent. When H$_2$ is introduced into the system, low-charged energetic Sn ions can be produced by a series of consecutive electron capture processes. However, as electron capture by Sn$^{2+}$ ions from H$_2$ is endothermic, no significant population of singly charged Sn ions is expected in the keV regime. At H$_2$ pressures of 6x10$^{-4}$ mbar and higher, however, we only detect Sn$^{2+}$ and Sn$^+$ ions.
To explain the production of keV Sn$^+$ ions, electron capture by metastable Sn$^{2+*}$ ions has been proposed [1]. Semi-classical calculations on Sn$^{3+}$- H$_2$ collisions [2] indicate that one-electron capture by Sn$^{3+}$ ions populates Sn$^{2+}$ ions in metastable states. Model simulations (using theoretical 2-state Landau-Zener cross sections to account for capture by each of the three metastable $^3$P$_J$ levels) to track the charge states of Sn ions while traversing the H$_2$ gas agree with our measured data. This underpins the key role of metastable Sn$^{2+*}$ ions as a gateway to the production of Sn$^+$ ions. From an LPP-based EUV source perspective, the production of energetic Sn$^+$ ions in the buffer gas is of high relevance, as it shifts the charge state balance from Sn$^{2+}$ towards Sn$^+$ ions, which have a larger stopping cross section than Sn$^{2+}$ ions [3].
[1] Rai et al., 2023 to appear in Plasma Sources Sci. Techn.
[2] Rai et al., 2022, Phys. Rev. A. 106, 012804
[3] Abramenko et al., 2018, Appl. Phys. Lett. 112, 164102
The X-ray Imaging and Spectroscopy Mission (XRISM) is a Collaborative Mission jointly developed by NASA and the Japanese Space Agency (JAXA), with the European Sapace Agency (ESA) participation. It will have Two instruments: Resolve - a soft X-ray (0.3-12 keV) spectrometer providing non-dispersive high-resolution X-ray spectroscopy; and Xtend - a 40 arcminute field of view soft X-ray imager. XRISM is scheduled to launch from Japan in May of 2023. The mission is to recover science lost with the demise of Hitomi in 2016. After a 9-month calibration and performance verification phase, the rest of the mission lifetime will be for General Observers worldwide. In this talk I will review the capabilities of XRISM, and some of the science goals for the observations to be carried out during the performance verification phase. I will highlight the fundamental atomic physics knowledge needed in order to interpret XRISM observational data, and also how this impacts the XRISM science.
I will present the results of experiments at LCLS where we created and diagnosed iron plasma at temperature exceeding 1keV, and at solid iron (atomic) densities, with bulk electron densities greater than 2×10^24/cm^3. Using photon energies between 7100eV and 9000eV and pulse lengths less than 100 femtoseconds, we focussed the LCLS beam to a 120nm focal spot. A 2micron thin iron sample was placed in this focus and irradiated with intensities in excess of 10^20 W/cm^2.
In this way, the heated iron foil reaches conditions (i.e. electron density and temperature) comparable to the stellar core condition in stars on the main sequence between 0.1 and 100 solar masses. The temperature we reached are relevant to emission seen from Galaxy clusters.
We compare the x-ray emission from the iron sample with atomic-kinetic calculation (i.e. SC-FLY). The analysis confirm the charges states and temperatures reached, and give a measure of the Ionization Potential Depression and collision rates in these dense plasmas.
Neutron star (NS) mergers are at the origin of gravitational waves (GW) detected by LIGO/Virgo interferometers. Such events produce a large amount of elements heavier than iron by a rapid neutron capture (r-process) nucleosynthesis. Among these elements, those belonging to the fifth row of the periodic table, in particular from Zr ($Z$ = 40) and Cd ($Z$ = 48), are the greatest contributors to the opacity affecting the kilonovae, after the lanthanides and actinides. In the present work, new atomic structures and radiative parameters (wavelengths and oscillator strengths) are reported for a large number of spectral lines in two selected elements, namely Nb ($Z$ = 41) and Ag ($Z$ = 47) from neutral to triply ionized states. These results were obtained through large-scale atomic structure calculations using the pseudo-relativistic Hartree–Fock method implemented in Cowan code. The results obtained were used to calculate the expansion opacities characterizing the kilonova signal observed resulting from the collision of two NS, for typical conditions corresponding to time after the merger t = 1 day, the temperature in the ejecta T $\le$ 15000 K, and a density of $\rho$ = $10^{−13}$ $\mathrm{g.cm^{−3}}$ . Comparisons with previously published experimental and theoretical studies have shown a good agreement. In terms of quantity and quality, the results presented in this work are the most complete currently available, concerning the atomic data and monochromatic opacities for niobium and silver and are useful for astrophysicists to interpret kilonova spectra.
Recent measurements at the Sandia National Laboratory of the x-ray transmission of iron plasma much higher than predicted by theory have cast doubt on modelling of iron x-ray radiative opacity at conditions close to the solar convective zone-radiative zone boundary. An increased radiative opacity of the solar mixture, in particular iron, is a possible explanation for the disagreement in the position of the solar convection zone-radiative zone boundary as measured by helioseismology and predicted by modelling using the currently accepted elemental composition based on photosphere analysis. Here we present data from radiation burn-through experiments which do not support a large increase in the opacity of iron at conditions close to the base of the solar convection zone and provide a constraint on the possible values of both the mean opacity and the opacity in the x-ray range of the Sandia experiments. the data agree with opacity values from current state-of-the-art opacity modelling and hence do not support an increase in iron opacity as a partial explanation for the discrepancy in the predicted solar convective-radiative zone boundary position.
Since solar abundance was renewed in 2005, solar models and helioseismology disagree. One hypothesis is that calculated iron opacity used in the solar model is underestimated. In 2015, we measured Fe opacity at solar interior temperatures using Z machine at Sandia National Laboratories and revealed significant disagreement with calculated opacities. If true, it can partially resolve the discrepancy, but the more-than-expected disagreement aroused a controversy in the community. Since then, we performed more than 20 experiments and refined the analysis methods to improve the accuracy of the result. We will present how the iron opacity and its uncertainty changed with the analysis refinements and the increased number of experiments and discuss its impact on the solar problem.
The magnetic field is extremely important for understanding the properties of the solar corona. However, there are still difficulties in the direct measurement of the coronal magnetic field. The magnetic-field-induced transition (MIT) in Fe X, appearing in coronal spectra, was discovered to have prospective applications in coronal magnetic
field measurements. In this work, we obtained the extreme ultraviolet spectra of Fe X in the wavelength range of 174–267 Å in the Shanghai High-temperature Superconducting Electron Beam Ion Trap, and examined the effect of MIT in Fe X by measuring the line ratios between 257.262 Å and the reference line of 226.31 Å (257/226) at different magnetic field strengths for the first time. The electron density that may affect the 257/226 value was also obtained experimentally and verified by comparing the density-sensitive line ratio (175.266 Å/174.534 Å) measurements with the theoretical predictions, and there was good agreement between them. The energy separation between the two levels of 3s2 3p4 3d 4D5/2 and 4D7/2, one of the most critical parameters for determining the MIT rate, was obtained by analyzing the simulated line ratios of 257/226 with the experimental values at the given electron densities and magnetic fields. Possible reasons that may have led to the difference between the obtained energy splitting and the recommended value in previous works are discussed. Magnetic field response curves for the 257/226 value were calculated and compared to the experimental results, which is necessary for future MIT diagnostics.
The ultrafast absorption of laser energy in condensed matter results in strongly out-of-equilibrium material conditions, which evolve into warm dense matter (WDM). Understanding the fundamental processes of ultrafast energy relaxation and structural evolution in these extreme systems is crucial for a wide range of fields, from laser nano-surgery to laser-fusion research.
The generally accepted concept for the response of systems irradiated by femtosecond laser pulses is that the optical pulse directly excites electrons, which quickly thermalize, establishing a finite electronic temperature in a few tens of femtoseconds, while the lattice remains cold. The two subsystems then equilibrate through electron-phonon coupling, which is the basic premise of the two-temperature model (TTM). This framework has been widely applied to calculate optical and thermophysical properties of laser-irradiated matter, develop advanced models for thermal and nonthermal melting, and interpret data from various experiments. However, the electronic system's detailed dynamics might be more complex than described by the simple TTM.
This contribution presents measurements of XFEL absorption of WDCu, and the optical reflectivity of WDAu irradiated with femtosecond laser pulses. The measurements for the WD noble metals (~ 1 eV/atom) reveal the rich dynamical features of nonthermal electrons and vacancies and their interactions with the lattice. The improved modeling of electron dynamics, which includes the recombination of nonthermal electrons and the dynamic shift of the excited valence band, successfully reproduces the key features observed in the measurements. These findings shed light on improving our understanding of the ultrafast population balance between conduction and localized electrons in materials and related transport properties under extreme temperature and pressure conditions.
This work received support from the National Research Foundation of Korea (NRF2019R1A2C2002864, NRF-2020K1A3A7A09080397).
Quantum degeneracy and thermal effects challenge atomic models of warm dense matter (WDM), a regime where partial ionization, interatomic bonding, and band structure can modify plasma response properties. We use real-time time-dependent density functional theory (TDDFT), a multi-center first-principles approach, to benchmark the predictions of an improved average-atom (AA) framework for WDM. Our comparisons of dynamic structure factors in warm dense deuterium, carbon, and aluminum help constrain models of electron-ion collision frequencies that broaden and shift the plasmon feature often analyzed in x-ray scattering diagnostics. However, TDDFT also predicts other effects that remain difficult for AA to capture. First, we find that collective behavior in warm dense iron blue shifts transitions into thermally depleted $d$ states. Also, we uncover subtle signatures of atomic order in isochorically heated aluminum arising from non-idealities in the density of states. But despite its higher accuracy relative to AA, TDDFT still relies on some poorly characterized and difficult to improve approximations. We will conclude with a preview of some potential advantages that emerging quantum computing technologies may offer for modeling atomic processes in plasmas. This work has important implications for WDM modeling and characterization, most immediately the possibility of novel diagnostic techniques for high temperatures and/or systems out of thermal equilibrium.
We propose a consistent approach to determine the screening potential in dense plasmas with inhomogenous free electron micro-space distribution. Based on a local density and temperature-dependent ion-sphere model, the Saha equation approach is extended to the regime of strongly coupled plasmas by taking the free-electron-ion interaction, free-free-electron-interaction, inhomogenous free-electron micro-space distribution, and free-electron quantum partial degeneracy into account, in the free energy calculation. The ionization balance is determined by solving an extended Saha equation. All the quantities, including he bound orbitals with ionization potential depression, free-electron distribution, and bound and free-electron partition function contributions, are calculated self-consistently in the theoretical formalism. It has been shown that the ionization equilibrium is evidently modified by considering the above non-ideal characteristics of the free electrons [1].
To explicitly taking the exchange-correlation effect of free electrons into account, we incorporate the effective static approximation of local field correction (LFC) within our IPD framework through the connection of dynamical structure factor. The effective static approximation poses an accurate description for the asymptotic large wave number behavior with the recently developed machine learning representation of static LFC induced from the path-integral Monte Carlo data. Our calculation shows that the introduction of static LFC through dynamical structure factor brings a nontrivial influence on IPD at warm/hot dense matter conditions. The correlation effect within static LFC could provide up to 20% correction to free-electron contribution of IPD in the strong coupling and degeneracy regime. Furthermore, a new screening factor is obtained from the inhomogenous density distribution of free electrons calculated within the self-consistent model, with which excellent agreements are observed with other methods and experiments at warm/hot dense matter conditions[2].
References
[1] Jiaolong Zeng, Yongjun Li, Yong Hou, and Jianmin Yuan, Non-ideal effect of free electrons on ionization equilibrium and radiative properties in dense plasmas. Phys. Rev. E to be published
[2] Xiaolei Zan, Chengliang Lin, Yong Hou, and Jianmin Yuan, Local field correction to ionization potential depression of ions in warm or hot dense matter. Phys. Rev. E 104, 025203 (2021).
Matter under extreme high-energy-density (HED) conditions (e.g., at superhigh pressures from billions to trillions of atmospheres) are often encountered in stars and inertial confinement fusion targets. Such extreme HED matter can now be created on energetic laser/XFEL facilities and pulsed-power machines in laboratories. Accurate knowledge of extreme HED matter is essential to better understanding planetary science and astrophysics, as well as reliably designing fusion energy targets. Over the past decade, research has revealed that traditional plasma-physics models often fail to describe the physics of matter under HED conditions since strong coupling and electron degeneracy play a crucial role in such quantum many-body systems.
Probing HED matters in an experiment mostly relies on x rays since it is one of the possible sources that can penetrate dense matters. X-ray–induced fluorescence and/or absorption are often used to infer what happens inside extreme HED matter. On the theoretical/computational side, ab initio methods such as density functional theory (DFT) and time-dependent DFT [1] can provide a self-consistent way to predict the properties of HED matter (with systematic improvement possible). Combining both x-ray spectroscopy experiments and ab initio calculations, we have investigated some new HED physics phenomena over the past few years, which include the Fermi-surface rising in warm dense matter [2] and interspecies radiative transition in super-dense matter [3]. To understand these precision x-ray spectroscopy measurements, we have derived a DFT-based kinetic model to explore the extreme atomic physics of HED matters at Gbar pressures [4], which enables us to eliminate the controversial continuum-lowering models for dense plasmas. In this talk, I will share what we have learned so far in exploring HED matter, as well as what we are still struggling to understand.
1. Y. H. Ding et al., Phys. Rev. Lett. 121, 145001 (2018).
2. S. X. Hu, Phys. Rev. Lett. 119, 065001 (2017).
3. S. X. Hu et al., Nature Communications 11, 1989 (2020).
4. S. X. Hu et al., Nature Communications 13, 6780 (2022).
We show data and first analysis of a recent (Feb 2022) experiment on the spectroscopic investigation of XFEL-heated Cu foil targets. Cu foils were irradiated by the tightly focused XFEL beam (~1μm focus, up till 300μJ in energy, European XFEL), which heats the target to approximately 100 eV during its duration (~25 fs). The XFEL photon energy was varied in the range 8.8-9.8 keV to scan resonances and K edges of various charge states; three spectrometers were observing the emission Kα and Kβ lines and their satellites. The experimental data are compared to the SCFly simulations and the details are analyzed by using the FAC atomic code.
First of the many interesting phenomena, the shift of the Kα satellite lines is discussed. Each of the Kα lines from ions with different occupancy of the L sheel is shifting both due to the charge state of the emitting ion (i.e. number of electrons in M shell) and due to electron temperature via plasma screening. Both these shifts are experimentally observed and well described by using the FAC calculations. The observed shifts of the absorption K edges are also observed and agrees well to the Stewart-Pyatt model newly included in the FAC code, when the temperature parameter is adjusted to account for the strongly non-thermal electron distribution.
The radiative properties of an atom or an ion surrounded by a plasma, are modified through various mechanisms. Depending on plasma conditions the electrons supposedly occupying the upper quantum levels of radiators no longer exist as they belong to the plasma free electron population. All the charges present in the radiator environment, electrons and ions, contribute to the lowering of the energy required to free an electron in the fundamental state. This mechanism is known as ionization potential depression (IPD). The knowledge of IPD is fundamental as it affects both the radiative properties of the various ionic states and their populations. Its evaluation deals with highly complex n-body coupled systems, involving particles with different dynamics and attractive ion-electron forces. Two distinct models, namely the Stewart–Pyatt (SP) [1] and Ecker–Kröll (EK) [2] models, are widely used to estimate the IPD.
More recently, an approach based on classical molecular dynamics simulation has been developed providing an alternative way to calculate the IPD [3]. Ions and electrons are treated as classical particles and a minimum of quantum properties are taken into account through a regularized potential allowing to model collisional ionization and recombination processes. The related numerical code, BinGo-TCP, has been designed to describe neutral mixtures composed of ions of the same atom with different charge states, and electrons. Within the limits of classical mechanics, all charge-charge interactions are accounted for in the particle motion.
In this work, after a brief reminder of the modeling basis, the importance of the choice of the IPD modelling will be emphasized through a study of the influence of the IPD on the magnitude of the cross-section of ionization by free-electron impacts in the high-density domain [4]. Additionally, we will discuss the ionization energy distributions obtained with BinGo-TCP due to the fluctuating environment of the ions.
[1] Stewart J C and Pyatt K D 1966, Astrophys. J. 144, 1203
[2] Ecker G and Kröll W 1963, Phys. Fluids 6, 62
[3] Calisti A, Ferri S and Talin B 2015, J. Phys. B: At. Mol. Opt. Phys. 48, 224003
[4] Benredjem D, Pain J.-C, Calisti A and Ferri S 2022, J. Phys. B: At. Mol. Opt. Phys. 55, 105001
The collective behavior of a plasma is favored by the long range of electric and magnetic fields, and is well known to be able to excite waves with an oscillating electric field. For example, Langmuir waves are ubiquitous in many types of laboratory, fusion, and astrophysical plasmas. By using a classical equipartition theorem for a plasma in equilibrium, one can attribute half of the energy of the wave to the oscillating field, and the other half to kinetic energy, and one can then estimate that the modulus of the electric field of the wave is an order of magnitude smaller than the mean plasma microfield, for example, in a plasma with a temperature T = 1 eV, and a density N = 10^21 m^-3. In a non-thermal plasma, however, the waves can be amplified by an instability, which allows the modulus of the oscillating electric field to reach values greater than the mean plasma microfield.
We here study the spectroscopic signature of an oscillating field E ⃗_L=E ⃗_W cos(ω_p t+φ), where ω_p=√(Ne^2/(mϵ_0 )) is the electronic plasma frequency, with e and m being the charge and the mass of the electron, and ϵ_0 the permittivity of free space. We calculate the first Lyman and Balmer lines of hydrogen for densities between 10^19 m-3 and 10^23 m^-3, and a temperature of 10^4 K, conditions for which the ion dynamics affect the central part of the spectral lines. Our aim is the simultaneous diagnostic of the plasma and Langmuir wave parameters. By treating the electron contribution with a constant collision operator, we calculate the simultaneous effect of ion dynamics and an oscillating electric field using a numerical simulation of ion motion, coupled with a numerical integration of the Schrödinger equation. For intense electric field calculations, we show how the dynamic fields transfer the intensity of the central part of the line to an increasing number of satellites at multiples of the plasma frequency.
Standard atomic physics models in PIC simulation either neglect excited states, predict atomic state population in post processing only, or assume quasi-thermal plasma conditions.
This is no longer sufficient for high-intensity short-pulse laser generated plasmas, due to their non-equilibrium, transient and non-thermal plasma conditions, which are now becoming accessible in XFEL experiments at HIBEF (EuropeanXFEL), SACLA (Japan) or at MEC(LCLS/SLAC).
To remedy this, we have developed a new extension for our PIC simulation framework PIConGPU to allow us to model atomic population kinetics in-situ in PIC-Simulations, in transient plasmas and without assuming any temperatures.
This extension is based on a reduced atomic state model, which is directly coupled to the existing PIC-simulation and for which the atomic rate equation is solved explicitly in time, depending on local interaction spectra and with feedback to the host simulation. This allows us to model de-/excitation and ionization of ions in transient plasma conditions, as typically encountered in laser accelerator plasmas.
This new approach to atomic physics modelling will be very useful in plasma emission prediction, plasma condition probing with XFELs and better understanding of isochoric heating processes, since all of these rely on an accurate prediction of atomic state populations inside transient plasmas.
The Linear Response Method (LRM) uses tabulated data obtained with a small number of radiation fields to replace inline steady-state non-local thermodynamic equilibrium (NLTE) collisional-radiative calculations for (nearly-) arbitrary radiation fields. The tabulated data includes first-order derivatives with respect to the frequency-dependent radiation, i.e. linear response coefficients. Straightforward application of the LRM provides radiative properties and equation-of-state information as a function of plasma conditions and radiation field as required for radiation-hydrodynamics calculations. This approach has successfully been used in simulations of inertial confinement fusion hohlraums and other high energy density applications.
The response coefficients themselves contain information which can improve simulations in other ways. One approach provides a simple quantitative measure of how far a given set of conditions is from LTE. This allows a code to transition between LTE and NLTE data and numerical treatments at the most appropriate time. A more far-reaching improvement comes from integrating the response coefficients into radiation transport calculations, making them implicit and consistent with both the material temperature and the radiation field. We discuss these improvements and their implementations.
This work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
A detailed understanding of the principles underlying ion-atom and ion-molecule collisions is essential for plasma modelling and diagnostics. Recent advances in experimental techniques have resulted in detailed and highly accurate kinematically complete measurements. However, theory lags far behind and cannot describe the experiments on differential ionisation. In particular, the description of experimental data on energy and angular distributions of electrons produced in intermediate-energy ion collisions with simple atomic and molecular targets has remained an insurmountable problem for over five decades. We have developed a coupled-channel method that provides the first accurate solution to the problem. The method is based on an expansion of the total scattering wave function using a two-centre pseudostate basis. This allows one to take into account all underlying interdependent processes, namely, direct scattering and ionisation, and electron capture into bound and continuum states of the projectile. Wave packets are used to discretise the continuous spectrum of the target and projectile. The method is applied to calculate the doubly differential cross section as a function of the energy and angle of electrons emitted in proton-induced ionisation of H, He and H$_2$. Excellent agreement between the obtained results and the experimental data is found. This paves the way for an accurate description of the recent kinematically complete experiments.
The problem of low-energy electron-impact rotational excitation of H2 has been studied in great detail over the last 60 years, due to its importance in low-temperature hydrogen plasmas and gases. Be- low 10 eV, rotational excitation comprises up to 20% of the total cross section, and below the v = 0 → 1 threshold (≈ 0:5 eV) it is the dominant contribution to electron energy loss. Accurate cross sections for the rotational transitions of H2 are vital for modelling the emission spectra of astrophysical clouds, or for constructing collisional-radiative (CR) models of fusion-relevant plasmas. Up to 0.5 eV, the N = 0 → 2 and 1 → 3 rotational excitation cross sections are well known, with good agreement between the results of electron swarm experiments, which are reproduced by several calculations. At higher energies, however, the situation is less ideal, with substantial disagreement between various measurements and calculations.
The theoretical techniques applied to this problem in the past have utilised a variety of approximations to the treatment of coupling between rovibrational levels, from the adiabatic-nuclei (AN) approximation in which the coupling is neglected, to the most accurate rovibrational close-coupling approach. However, the common factor in all previous studies is the use of model potentials in place of coupling to the closed electronically-inelastic channels. The various choices of potential can lead to differences in the calculated cross sections far more significant than the errors introduced by the AN approximation, particularly since the greatest discrepancies are at energies more than 10 times the threshold energy, where the AN approximation is accurate. What is missing from the literature are theoretical studies of low-energy rotational excitation in which the coupling to closed electronic channels is accounted for rigorously. Within the AN approximation this is feasible provided one can solve the electronic scattering problem accurately. Here we apply the molecular convergent close-coupling (MCCC) method, which in recent years has been shown to completely solve the electronic scattering problem for H2 [1]. The results presented here are available online [2].
References
[1] Zammit et al. 2016 Phys. Rev. Lett 116 233201
[2] mccc-db.org
[3] Lane N F and Geltman S 1967 Phys. Rev. 160 53
[4] Henry R J W and Lane N F 1969 Phys.Rev. 183 221
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It has long been observed that the number of weak lines from many-electron atoms follows a power law distribution of intensity. While computer simulations have reproduced this dependence, its origin has not yet been clarified. Here we report that the combination of two statistical models—an exponential increase in the level density of many-electron atoms and local thermal equilibrium of the excited state population—produces a surprisingly simple analytical explanation for this power law dependence. We find that the exponent of the power law is proportional to the electron temperature. This dependence may provide a useful diagnostic tool to extract the temperature of plasmas of complex atoms without the need to assign lines.
Because of the generality of this statistical model, a similar principle may apply to other quantum complex system. Indeed, we find for the first time that the gamma-ray emission from heavy nuclei also satisfy a similar power-law intensity distribution. For the nuclei, the power-law exponent is always unity and the intensity parameter of the distribution is independent from nuclear property. We confirm these properties from the experimental results registered in a nuclear database.
Plasma technologies are a promising route in a wide range of applications concerning negative impacts of climate crisis (e.g. stress conditions on seeds inhibiting germination or normal growth of plants, epidemic proliferation) and even, for the conversion of greenhouse gases (GHG) into energetic gases.
In this work, an overview of plasma technologies currently applied to ameliorate our environment would be depicted; followed by projects developed at our Laboratory where optical emission spectroscopy (OES) resulted in an useful tool to better understand and optimize these techniques. Specifically, rotational and electronic temperatures and key chemical species (e.g. •O, O(1D), •OH, e-) are here described.
Particularly, four affordable and green plasma applications would be depicted: the use of non-thermal plasma to improve the germination and growth of endangered Mexican maize specie, the deactivation of virus type, the synthesis of carbon nanoparticles with thermal plasmas to construct environmental friendly supercapatteries and, finally, the treatment of toxic gases and the conversion of GHG into syngas.
Non-thermal plasma (NTP) possesses useful properties for interacting with biomaterials. Our NTP laboratory group focuses mainly on the study and generation of NTP and the explanation of its interactions with biological objects. For NTP generation, we mainly use the corona and related discharges. The NTP quality and intensity depend on the set up of electrode arrangement, power supply and can be adjusted to specific applications. Our devices range from very weak sources based on point-to-ring discharge, to relatively strong ones based on transient spark discharge. Additionally, we are developing portable, affordable and user-friendly NTP generation devices for practical applications in medicine, food production, or agriculture. Our laboratory investigates the interactions of NTP with biological materials, with a focus on microbial decontamination of sensitive materials such as the face masks and food products (improving food shelf life), treatment of infections such as onychomycosis (fungal nail infection), enhancement of seed quality and early plant growth, and modification of biosurfaces through the activation of biomolecular films.
Abstract:
In recent years, non-thermal atmospheric pressure plasma has attracted wide attention in
health care for the” processing” of medical tools and living tissues due to its many
advantages, such as non-destructive surgery, controlled, high-exactness removal of
diseased sections, high efficiency, simple systems, easy operation, non-toxic residue, and
low cost. In this work, the construction and characterization of an Atmospheric Pressure
Microwave Induced (APMI) Plasma Jet, that had been generated using microwave up to
2.4GHz for argon (Ar) and helium (He) gases and operated at low-temperature plasma
below 40 Cº for exceptional standardization protocol of this plasma source that meets
medical requirements. The plasma column has been characterized as a function of the Ar
and He flow rate. The influence of the higher gas flow rate lead to increase of the plasma
column length and reduction of the plasma jet temperature. The optical Emission
Spectroscopy (OES) method was employed to detect the active species inside the plasma
column and determine plasma parameters such as electron temperature (Te), electron
density (ne), plasma frequency (fp), Debye length (λD), and Debye (ND) number of the Ar
and He plasma jet. The plasma parameters, of the electronic excitation temperature and
density of electrons were determined by Boltzmann‟s plot method and Stark broadening
effect equation respectively. The inactivation efficiency of the APMI plasma jet is
evaluated against Gram-positive pathogenic bacteria (Staphylococcus aureus) and Gram-
negative (E. coli) with different time exposure. These samples were exposed to a plasma
column at different exposure times (5, 10, and 15 min) with an argon flow rate of 15 slm
and helium gas flow rate of 4 slm , the distance between the plasma column nozzle and
sample (bacteria) was 3 cm. The results presented that the plasma column temperature
was lower than 40 Cº, which will not cause damage to living tissues. The inactivation
efficiency is directly extended with increased exposure time and treatment with helium
plasma jets showed a higher efficiency in bacterial inhibition than argon plasma jets. The
result of the emission line spectrum showed the presence of reactive oxygen and nitrogen
species between lines 300 nm and 700 nm which formed from ambient air. These species
are the main key in the bacteria inactivation process. We confirmed that the inactivation
mechanism was unaffected by UV irradiation while the charged particles played a minor
role in the inactivation process.
The advent of x-ray free-electron lasers (XFELs) has enabled a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interactions. The femtosecond timescales of these interactions lead to the creation of transient high-energy-density plasmas, where both electrons and ions may be far from local thermodynamic equilibrium (LTE). Predictive modelling of such systems remains challenging because of the substantially different timescales on which electrons and ions thermalize, and because of the vast number of atomic configurations that are required to describe the resulting highly-ionized plasmas. Here we present work discussing the evolution of systems driven to high energy densities using CCFLY, a non-LTE, Fokker-Planck collisional-radiative code. We use CCFLY to investigate the evolution dynamics of a solid-density plasma driven by an XFEL, and explore the relaxation of the plasma to local thermodynamic equilibrium on femtosecond timescales in terms of the charge state distribution, electron density, and temperature.
Reference
S. Ren, Y. Shi, Q.Y. van den Berg, M. Firmansyah, H.-K. Chung, E.V. Fernandez-Tello, P. Velarde, J.S. Wark, S.M. Vinko, arXiv:2208.00573 (2023).
We propose a model of ion-electron plasma (or nucleus-electron plasma) that accounts for the electronic structure around nuclei (i.e. ion structure) as well as for ion-ion correlations. The model equations are obtained through the minimization of an approximate free-energy functional, and it is shown that the model fulfills the virial theorem. The main hypotheses of this model are 1) nuclei are treated as classical indistinguishable particles 2) electronic density is seen as a superposition of a uniform background and spherically-symmetric distributions around each nucleus (system of ions in a plasma) 3) free energy is approached using a cluster expansion 4) resulting ion fluid is modeled through an approximate integral equation.
In this presentation we will describe the set of hypotheses of this model, sketch the derivation of the model equations and comment on them. We will show how this model fulfills the virial theorem, allowing a sound definition of the related thermodynamic quantities. Finally, we will show results from numerical calculations, comparison with other models such as VAAQP or INFERNO, and discuss the limitations of the model.
The spectrometer calibration station at LLNL is used to characterize and calibrate the many crystals used in the various geometries of the x-ray spectrometers regularly used at the National Ignition Facility (NIF). Such absolute calibration is essential for every experiment in order to extract meaningful results and properly diagnose the plasmas. We present the calibration of three NIF spectrometers, the Imaging Spectroscopy Snout (ISS) used at magnification of 12X, its homologue dedicated to low magnification (ISS-LM) and the NIF X-ray Spectrometer (NXS).
The ISS can be equipped with up to four different transmission Quartz crystals in Cauchois geometry, each offering different energy ranges from ~7.5 keV to ~12 keV with high spectral resolutions while the ISS-LM is using Silicon transmission crystals. Meanwhile, the NXS utilizes different crystal materials in an elliptical Bragg-reflection geometry allowing for a choice in spectral range ~1.5 keV to ~20 keV, each with a wide bandwidth and low spectral resolution. This work will present and compare the measurements of crystal’s responses in eV.μsr/mm2 for Qz(100) and Si (111) in both ISS and NXS geometries as well as results for PET (002) in NXS configuration. The inferred integrated reflectivity will also be presented and compared, in some cases, to theoretical calculations made with pyTTE program.
This work performed under the auspices of the U.S. Department of Energy by General Atomicsunder Contract 89233119CNA000063 and by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
LLNL-ABS-840130.
High energy density physics (HEDP) is an interesting interdisciplinary field and it plays the important roles in astrophysics and controlled fusion science. The HEDM generated by intense heavy ions beam has the properties of large volume, uniform state, any material and high reproducibility, which provides a unique experimental solution for HEDP research in lab. In China, a new high intensity heavy ions accelerator facility (HIAF) is under construction and it will provide a very powerful ions beam to access the HEDM.
Energy deposition of ions in plasmas is a key topic to generate the HEDM and a high precision knowledge is called for. Based on the HIRFL (Heavy Ions Research Facility at Lanzhou), an experimental setup is built to carry out the research of low energy ions – plasmas interaction. The energy losses of protons and Helium ions in hydrogen plasmas are measured and the theoretical models are compared experimentally, where some new effects are figured out.
In this conference, we will introduce the recent results of low energy ions in plasmas, and the status of HIAF will be given too.
K-shell transitions of He-like species have been widely used to diagnose high-energy-density plasmas, including those in the inertial-confinement fusion experiments. Recently, Stark broadening of the krypton He-beta line was used for inferring the electron density in NIF compressed capsules [1,2] and suggested for diagnostics in Laser MegaJoule experiments [3]. Here, we report on the Stark lineshape modeling of Kr He-beta based on computer simulations that include electron penetration effects [4], resulting, in particular, in the consistent evaluation of the plasma polarization shift. Measuring the latter can serve as an independent method of plasma density diagnostics. Furthermore, Li-like satellites, contributing to the overall shape of the He-beta complex, were also calculated.
[1] L. Gao et al., https://doi.org/10.1103/PhysRevLett.128.185002
[2] K. W. Hill et al., https://doi.org/10.1088/1361-6587/ac9017
[3] G. Pérez-Callejo et al., https://doi.org/10.1103/PhysRevE.106.035206
[4] E. Stambulchik and C. A. Iglesias, https://doi.org/10.1103/PhysRevE.105.055210
The discrepancies between theoretically calculated and experimentally measured Iron opacities at the Sandia National Laboratory Z-pinch machine are hitherto still unexplained even after nearly a decade of effort. Theoretical opacities have neglected higher-order processes such as two-photon processes, i.e., two-photon ionization or Raleigh and Raman scattering and thus could be a potential additional source of opacity that may lessen the disagreement with experimental measurements. We will present a summary of our two-photon ionization calculations in which we conclude that two-photon absorption cannot explain the bound-free discrepancy between experiment and theory, and then move on to show previously unreported calculations for the elastic (Raleigh) and inelastic (Raman) scattering contributions for the measured 2-4 Ne-like Iron lines.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-XXXXX
X-ray free electron lasers (XFEL) provide some unique capabilities in high energy density physics due to their ability to create solid density plasmas on very short time scales. The plasmas produced from these systems are typically far from LTE due to the large radiation field and short time scales. In recent years, collisional-radiative (CR) atomic kinetics codes have been adapted to handle these extreme conditions with promising results. Some of these modifications include extension of atomic data sets appropriate for solid density plasmas, treatment of continuum lowering and electron degeneracy. To reduce computational time, most models assume that the free electrons are instantaneously thermalized such that their distribution can be characterized by a Maxwellian or Fermi-Dirac distribution. This assumption breaks down for very short pulses and high XFEL photon energy, and an improved treatment of the electron distribution is required. We discuss the treatment of the electron distribution in the CR modeling framework and modifications to account for continuum lowering and degeneracy effects. We also show simulation results of an XFEL heated copper experiment. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.