Abstract:
JET deuterium experiments in an advanced tokamak scenario with an internal transport barrier (ITB) exhibit unstable electromagnetic (EM) perturbations in the sub-TAE frequency range. In JET pulse number (JPN) 92054, a high-beta plasma ($\beta_N = \beta_T B_T a / I_P \sim 4.38 [\%Tm/MA]$) with high power neutral beam injection (NBI), $P_{NBI} = 25.1 MW$, contained EM...
Based on the experimental parameters in HL-2A tokamak, the linear stability and nonlinear dynamics of BAE with reversed safety factor $q$ profile are investigated by using kinetic-MHD code M3D-K. It is found that the ($m/n=3/2$) BAE is excited by co-passing energetic ions with $q_{min}=1.5$ in linear simulation, and the mode frequency is consistent with experimental meuasurement. The...
Ion cyclotron resonance frequency (ICRF) heating has been chosen as one of the fundamental auxiliary heating systems in many present-day fusion devices, as well as the upcoming ITER. Energetic ions generated by ICRF heating with energies up to several hundred-keV or several MeV can drive a variety of Alfven eigenmodes, such as reversed-shear, toroidal and ellipticity Alfven eigenmodes (RSAE,...
Edge localized modes (ELMs) are periodic magnetohydrodynamic (MHD) instabilities driven by sharp pressure gradients and current densities at the plasma boundary that will likely lead to transient, and intolerable, energy and particle losses in ITER. Although the ELM nature is still under intense investigation, their behavior and their consequences in a burning plasma with a significant...
In recent years, there has been significant progress with global electromagnetic gyrokinetic codes in modelling Alfvén Eigenmodes (AEs) and other energetic particle (EP) driven instabilities in realistic equilibria, for example, simulations with the gyrokinetic code ORB5 [1] of Energetic Particle Modes (EPMs) and Energetic-particle-driven Geodesic Acoustic Modes (EGAMs) in ASDEX Upgrade (AUG)...
Tungsten accumulation is one of the main challenges for successful operation of ITER and future reactors. For this reason, various techniques have been developed recently in order to mitigate such accumulation. One of such methods is the application of wave heating, in particular electron cyclotron resonance heating (ECRH) deposited close to the plasma center.
Recent 3D equilibrium...
Verification and validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreements for the growth rate and mode structure of the n=1...
Recent DIII-D experiments show that sawteeth can be strongly affected by anisotropic fast ions from Neutral Beam Injection (NBI) in both negative and positive triangularity plasma configurations. Fast ions from co-current NBI are stabilizing for the sawtooth stability, resulting in longer sawtooth periods. On the other hand, fast ions from counter-current NBI are destabilizing, leading to...
The D-T fusion cross-section in magnetically confined plasmas is increased by 50% when the spins of both nuclei are polarized along the magnetic field[1], offering promise for a significant increase in fusion energy output with no additional requirement on plasma confinement. Theoretically [1], depolarization mechanisms from field inhomogeneities or collisions are weak in the core of a tokamak...
Linear numerical simulations using FAR3d indicate that negative triangularity (NT) shaping of plasma in DIII-D lowers the growth rate of energetic particle (EP) driven Alfvén eigenmodes (AEs) as compared to the positive triangularity (PT) shaping of plasma [1]. Recently, there is a renewed interest in the NT shaping for its benefits of reduced microturbulence, better thermal confinement and...
This presentation examines the energetic particle transport induced by saturated kink modes and sawtooth crashes in JET deuterium plasmas. It is known that kink mode-resonant transport[1-3] and phase-space redistribution from sawtooth crashes[4-5] can drive strong fast ion transport with dependencies on particle pitch and energy. Measurements with JET's Faraday cup fast ion loss detector array...
We study the effect of a sawtooth crash on the dynamics of MeV-class fast deuterons, as produced by ion cyclotron heating, and alpha particles in the energy range 35-3500 keV, resembling helium ash and newly-born fusion alphas. The simulations are performed using the hybrid code MEGA [1], which solves visco-resistive MHD equations for the bulk plasma and drift-kinetic equations with...
Energetic particle transport due to the energetic-particle-driven magnetohydrodynamic (MHD) instabilities in existing fusion devices has been intensively studied in order to find a way to control/reduce the energetic deuterium-tritium fusion born alpha particle transport in a future fusion reactor. In the hydrogen Large Helical Device (LHD) plasma experiment, a study of energetic ion...
Kinetic-magnetohydrodynamic hybrid simulations were performed to investigate the linear growth and the nonlinear evolution of off-axis fishbone mode (OFM) destabilized by trapped energetic ions in tokamak plasmas. The spatial profile of OFM is mainly composed of $m/n = 2/1$ mode inside the $q=2$ magnetic flux surface while the $m/n = 3/1$ mode is predominant outside the $q=2$ surface, where...
It is known that MHD instability driven by energetic particles called EIC is excited in high ion temperature mode with high power perpendicular NBI heating in LHD [1]. The EIC has been observed by measuring temperature fluctuations and local magnetic field fluctuations, but the overall structure of the EIC is not well understood.
In this study, we introduce a data assimilation method based...
An imaging neutral particle analyzer (INPA) [1] provides energy and radially resolved measurements of the confined fast-ion (FI) population ranging from the high-field side to the edge on the midplane of the DIII-D tokamak. In recent experiments, a neutral beam modulation technique is employed to diagnose FI flow in the INPA-interrogated phase-space driven by multiple, marginally unstable...
Edge localized modes (ELMs) are inherent to a transport barrier at the tokamak plasma edge. While there have been extensive theoretical as well as simulational studies on the ELM characteristics, there are relatively few studies on the effects of ELMs on fast-ion transport [1]. Here, by employing the nonlinear gyrokinetic theory, we develop a theoretical analysis of the fast-ion transport...
Beam ion losses have been observed in AUG discharges during the plasma current ramp-up phase and during disruptions. The velocity-space of the escaping, and ccelerated, beam ions has been measured with the poloidal FILD array available at AUG [1]. Tomographic reconstruction techniques [2] applied to the FILD data revealed, with unprecedented detail, the velocity-space distribution of the lost...
Resonant magnetic field perturbation (RMP) coils are used in multiple fusion devices to mitigate magnetohydrodynamic (MHD) instabilities known as edge localised modes. The coils produce a radial magnetic field component that is small compared to the toroidal field strength, but breaks the axi-symmetry of the flux surfaces near the edge. This increases heat and particle transport at the plasma...
During the current quench in ASDEX Upgrade (AUG) disruptions, created by massive gas injection (MGI) to study runaway electron (RE) physics [1], Alfvénic activity is visible in the 300-800 kHz range. An example is presented in figure 1. These modes are analysed as potential runaway electron mitigation candidates [2]. With the help of a mode tracing algorithm, we classified the mode behaviour...
Kinetic instabilities in the MHz range have been observed during current quench in DIII-D disruption experiments (A. Lvovskiy et al., PPCF 60, 124003 (2018)). These instabilities are correlated with the RE loss happening at the beginning of disruption. In this work we use a MHD-kinetic code M3D-C1-K to simulate the excitation of this instability. It is found that this mode lies in the fast...
Fast-ion distribution functions in the MeV-range can be diagnosed by neutron emission spectroscopy (NES) and gamma-ray spectroscopy (GRS). For a given fast-ion distribution function and diagnostic energy bin, a measurement signal will have contributions originating from various fast-ion orbits [Ref1][Ref2]. These contributions depend on the sensitivity of the diagnostic in orbit phase space,...
Fast-ion losses and radiation expected in fusion reactors challenge conventional fast-ion diagnosis techniques that rely on delicate components such as scintillating plates and cameras. Passive measurement of coherent ion cyclotron emission (ICE) via magnetic pickup loops offers a robust diagnostic alternative but requires improved experimental resolution and more detailed theory. To this end,...
Linear wave properties of the low-frequency Alfven modes (LFAMs) observed in the DIII-D tokamak experiments with reversed magnetic shear [Nucl. Fusion 61, 016029 (2021)] are theoretically studied and delineated based on the general fishbone-like dispersion relation. By adopting the representative experimental equilibrium parameters, it is found that, in the absence of energetic ions, the LFAM...
We present results of simulation study of low-frequency Alfvenic modes in sub-TAE (Toroidal Alfven Eigenmodes) range in DIII-D, in particular, BAE (Beta-induced AE) and LFM (low-frequency mode) [1-3]. Using the Gyrokinetic Toroidal Code (GTC) [4], we have performed gyrokinetic simulations of BAE and LFM in DIII-D plasmas and identified LFM by comparing its properties to those of BAE [5]. Fast...
Operation in the quiescent regime with a large number of energetic particles (EEs) in specific energy range (~ 150–250 keV) have been achieved during the flattop of EAST low-density Ohmic discharges. Toroidal Alfvén eigenmodes (TAEs) excited by EEs are well demonstrated both in the deuterium plasmas and the helium plasmas. The resonance condition for EEs to drive TAEs is discussed and well...
Energetic particles (EPs), especially alpha particles, can excite collective shear Alfvén wave (SAW) instability in tokamak plasmas，and in turn affects the behavior of EPs, resulting in EPs transport loss. Notably, reversed shear Alfvén eigenmodes (RSAE) can be preferentially excited by core localized EPs [1], with their frequency and radial localization directly determined by local safety...
Quasi-axisymmetric (QA) device combines the advantages of both tokamak and stellarator, and thus, it can be considered as a disruption-free tokamak and it excites the interests of the fusion community. Alfvén eigenmode (AE) is an important issue for magnetic confinement fusion because it enhances energetic particle (EP) transport and degrades heating performance. Nowadays, a QA device named...
The long time-scale nonlinear simulation of energetic particle (EP) instabilities is critical to studies of fast ion transport since this allows inclusion of mode-coupling induced zonal flows/currents, and transfers of energy to longer and shorter scales. These processes, which are important in evaluating the impact of EP instabilities on heating efficiency, can evolve over much longer...
We present recent measurements and analyses of Alfven Eigenmode (AE) stability in JET D and T plasmas. Stable AEs are resonantly excited by an array of eight in-vessel, toroidally-spaced antennas with independent power and phasing. Databases of stable AE frequencies, net damping rates $\gamma < 0$, and toroidal mode numbers have been assembled for various isotope mixes, and trends are...
The seeming coupling between fast upwards frequency sweeping modes and tornado modes in a set of JET sawtoothing discharges was investigated. The frequency sweeping modes were identified as near-axis Alfvén cascade eigenmodes associated with a very flat yet strictly monotonic q-profile near the axis, in contrast with the common reversed-shear scenarios. The evolution of the modes’ frequency...
Spatial channelling (SC) is a phenomenon of the transfer of the energy and momentum across the magnetic field by destabilized eigenmodes [1-3]. Energy transfer deteriorates or improves plasma confinement, depending on the energy flux direction. In particular, inward SC of alpha-particle energy by fast magnetoacoustic modes (FMM) may have played a role in the improved confinement and...
The energetic particle-induced geodesic acoustic mode (EGAM) causes loss of injected beam ions on DIII-D [1, 2]. The EGAM is a global [3] n=0, m=0 predominantly electrostatic mode with typical fundamental frequencies between 20-40 kHz. (n and m are toroidal and poloidal mode numbers.) While EGAMs commonly appear in amplitude bursts, they can be continuous, sweep in frequency, or oscillate in...
The confinement of fast-ions, such as those generated by neutral beam injection (NBI), ion cyclotron resonance heating (ICRH) or fusion products, is of paramount importance for future fusion reactors to ensure a good plasma heating efficiency and the device integrity. Toroidicity induced Alfven Eigenmodes (TAEs) have been shown, both experimentally and numerically, to increase the radial...
Recent experiments at TCV have shown a strong mitigation of Toroidal Alfvén Eigenmodes (TAEs) in negative triangularity (NT) plasma compared to its counterpart experiment in positive triangularity (PT). In order to better understand the underlying physics mechanisms, non-linear simulations with positive ( δ = +0.4) and negative ( δ =- 0.4) triangularities have been carried out with the hybrid...
Confinement of fast ions belongs to most difficult challenges facing a stellarator fusion reactor. Theory suggests a number of optimization schemes aimed to improve it, see, e.g., overview [1]. In particular, the quasi-isodynamic approach is employed in Wendelstein 7-X and Helias reactors. However, first numerical studies have shown that some fraction of 3.5 MeV alphas in a quasi-isodynamic...
One of the challenges in gyro-kinetic shaping study is the impact of reversed magnetic shear to the trapped electron mode (TEM) instability, which can only be handled by global gyro-kinetic simulations with kinetic electron response. The configuration with reversed magnetic shear is widely used in recent experiments since it provides the formation of internal transport barrier (ITB) structures...
The destabilization of toroidal Alfven eigenmodes (TAEs) by alpha particles requires special conditions in current tokamaks, and DT operation of JET provides this rare opportunity [1]. The unambiguous observation of these modes is anticipated to be difficult, and the operation in DT is potentially limited by the availability of tritium and the allowable neutron wall activation, which might...
Recent theoretical and experimental studies have suggested possible effects of microturbulence on Alfven eigenmode (AE) saturation and energetic particle (EP) transport in fusion plasmas. Zonal flows can be nonlinearly generated by, and in turn, suppress both the AE and microturbulence. EP Scattering by the microturbulence can affect phase space dynamics in the nonlinear AE-EP interaction....
The success of burning plasma devices relies on their ability to confine fusion alpha particle products long enough for them to transfer a substantial fraction of their energies to the reacting thermal particles via collisions. It is, therefore, essential to develop efficient and robust capabilities to predict the level of energetic ion losses in tokamak experiments. This work...
An interface for kinetic stability analysis has been implemented in TRANSP, motivated by recent advances in the calculation of fast ion transport induced by MHD and Alfvénic Eigenmodes [1] in time-dependent simulations and by the need for predicting accurate evolution of fast ion pressure profiles for the interpretation, prediction and design of controlled plasma discharges. Similar efforts...
A thermal ion driven bursting instability with rapid frequency chirping, assessed to be an Alfvénic ion temperature gradient mode [1], has been observed in plasmas having reactor-relevant temperature in the DIII-D tokamak [2] (see the Fig. 1). The modes are excited over a wide spatial range from macroscopic device size to micro-turbulence size and the perturbation energy propagates across...
