Experiments on DIII-D support a new approach, confirmed by transport modeling, to achieving Q=10 in ITER using a scenario with low plasma current (~ 8 MA), high $\beta_{\rm p}$, and line-averaged Greenwald fraction ($f_{\rm Gw}$) above 1. At 8 MA the disruption risk and ELM challenge are greatly reduced, with the possibility that uncontrolled ELMs may be acceptable$^1$. Due to the need of...
The use of high temperature superconductors (HTS) in magnetic systems of fusion devices enables magnetic fields over 16 T, unachievable with low temperature superconductors (LTS), and promises significant reduction in cryogenic and energy budget [1-4]. HTS materials are considered by some researcher groups as the enabling material to make magnetic confinement systems more compact and more...
An accurate calculation of radial neoclassical transport is important for both tokamaks and stellarators. In tokamaks, deviations of the magnetic field from axisymmetry (caused, for example, by ripple due to the finite number of coils or by resonant magnetic perturbations) can result in significant neoclassical damping of the toroidal rotation [1]. In stellarators, their intrinsically...
The challenge
A power plant based on a tokamak architecture has a magnetic cage with thick shielding, so maintenance needs to be conducted through long narrow access ports (see figure 1). This means unprecedented dexterous handling of massive flexible components, which is difficult, slow and expensive. For this reason, industrial plant to date has always been arranged to allow the heaviest...
According to the European strategy to fusion energy, the development and the operation of a demonstration power plant (DEMO) is foreseen as the single step between ITER and a commercial tokamak fusion power plant (FPP). DEMO is required to feature all key systems and components of an FPP and to comply with a set of general goals [Donné, 2018]. These goals include a few hundred megawatts...
The 2018 National Academies of Sciences (NAS) Report of the Committee on a Strategic Plan for U.S. Burning Plasma Research and the more recent APS-DPP Community Planning Process (CPP) recommend that the U.S. should pursue innovative science and technology to enable construction of a Fusion Pilot Plant (FPP) that produces net electricity from fusion at reduced capital cost. Such a mission...
As the EUROfusion EU-DEMO design programme approaches the transition between the pre-conceptual and conceptual design phase the systems code PROCESS has been improved to incorporate more detailed plasma physics, engineering and integration models. Unlike many systems codes PROCESS combines the physics modelling with both technology and costs analysis. Key to the conceptual design phase are...
This paper presents solutions for critical problems in Japan’s DEMO (JA DEMO), which include common DEMO design issues beyond ITER-relevant technologies. The highlights of this design study are (i) system design for electric power generation, (ii) remote maintenance concept to attain a high plant availability, and (iii) novel concept for water-cooled pebble bed blanket and tritium recovery....
![RBt-space.][1]
![Q-dependence.][2]
![kappa-beta-space.][3]
Spherical Tokamak reactor (STR) is attractive due to its inherent capabilities such as disruption avoidance, natural elongation, natural divertor and high beta capability, apart from a smaller size, with presumably lower costs [ 1, 2]. There has been an extraordinary evolution from the early concepts like SMARTOR [ 3] with...
In this paper, we present a novel approach to simulate plasma turbulence in tokamak geometry. Even with most advanced supercomputers in these days, it is still very challenging to simulate turbulence and transport globally in the realistic tokamak geometry. One of challenges is the time scale disparity between ion and electron due to the large mass ratio between them.
We propose a new...
As the ITER staged approach plan is finalized, Korean fusion community has recently constructed a roadmap toward the Korean demonstration reactor (K-DEMO). Eight core technologies essential for the K-DEMO design are identified: 1) Core plasma technology, 2) System design and safety, licensing technology 3) Fusion materials technology, 4) Wall components technology, 5) Superconducting magnet...
Good vacuum health of any fusion machine is a stringent requirement for a quality plasma discharge. A pumping system of a fusion machine has to remove the gas load during two scenarios efficiently: the first one involves preparing the machine by baking of vessel and plasma-facing components to ~150 degree C to 200 degree C to achieve base vacuum level of < 1 E-8 mbar and the other is during...
Extraction of heat from the breeding blanket in tokamaks requires a network of heat carrying pipes from the blanket modules (BM) to the steam-generator (SG). Regardless of the type of the blanket concept, the operational requirements will mandate the RH compatibility and remote maintenance. The pipe-network will need to connect all BM in a given sector by sector-manifold, which in turn will...
The high field, high density tokamak FTU closed its 30-years of operation at the end of 2019. FTU is a circular machine (R0=0.93 m, a=0.29 m) with an Inconel Vacuum Vessel, Ni and Fe being its dominant elements, and Mo poloidal and toroidal limiters. The relatively high plasma densities, in combination with baking and boronization conditioning techniques, have ensured the possibility of...
A description of a micromodel of a salt blanket for conducting benchmark experiments with the melting of salt fluorides (0.52 NaF+0.48ZrF4) is given. The experiments are intended for verification of nuclear data libraries and codes applied to justify the nuclear and radiation safety of full-scale subcritical blankets of thermonuclear installations based on liquid-salt technologies,
Three dry...
The most effective numerical treatment of turbulence within a transport model of a tokamak plasma is as a multi-scale, multi-physics problem. Multi-scale since the typical time- and space-scales associated with turbulence are usually much smaller than the time- and space-scales of the plasma as a whole, which is the domain of a transport code; multi-physics since a range of possible physics...
The tokamak progress in 20th century accompanied by the replacement of their plasma-facing components (PFC) from high Z materials to low (Ref. 1). This made it possible to obtain a relatively pure (Zeff <1.5) fusion plasma. However, superconducting tokamaks of the 21th century discovered a new obstacle for fusion as limiting of the duration of the discharges (PH/S - limit [1]) due to the...
As part of the work on the creation of a pilot industrial hybrid reactor (PHP) in Russia, a demo fusion neutron source DEMO-FNS is being designed. Progress in the facilities development and tokamak fuel cycle (FC) modeling allowed for a number of systems to move from the conceptual design stage to the engineering stage. The report discusses technical proposals for key fuel cycle systems and...
We have analysed cross-scale interactions between trapped-electron-mode (TEM) and electron-temperature-gradient (ETG) turbulence by means of gyrokinetic simulations. We find that (i) TEM turbulence suppresses ETG turbulence and dominates electron heat transport, and (ii) the suppression of ETG by TEM can ubiquitously happen even when TEM-driven zonal flows are subdominant. Additionally, from...
Previous studies of the European Demonstration fusion reactor concept (DEMO) have shown that the expected amounts of radioactive waste at reactor end of life (EOL) can be of the order of 10$^4$ tonnes [refs 1,2,3]. These studies also suggested that comparable amounts of waste will be classified as low level waste (LLW) and intermediate level waste (ILW) 100 years after DEMO EOL. Since these...
Single crystal diamonds appear to be promising for VUV and soft X-ray (SX) radiation detection. The wide bandgap (5.5 eV) results in very low leakage currents and high sensitivity to radiation with wavelengths shorter than 225 nm (visible-blind detectors); furthermore, the high charge carrier mobility allows very fast time responses. More importantly, diamond is optimally suited for harsh...
Generally, DEMO requires larger toroidal field (TF) coils than ITER, resulting in two major difficulties, the tolerance in TF coil fabrication and installation and an increased inductance. This paper presents the possible solutions these on the basis of the design study on Japan’s DEMO (JA DEMO). It was confirmed that, in the case of adopting a mitigated tolerance by a factor of 2.5-5 compared...
The Russian concept of steady-state operating plasma-facing components (PFC) based on the use of a stagnant or slowly flowing liquid metal (LM) as a plasma-facing material enclosed in a capillary-porous system (CPS) (Ref. 1) integrates all the advantages of LM with the possibility of uniform distribution of its layer on the surface, regardless of its orientation in space, with high resistance...
WEST is an actively cooled full W tokamak aiming at power exhaust studies in long / steady-state pulses. WEST can operate in lower single null (USN), upper single null (USN) and double null configuration with an aspect ratio of 5-6. The lower divertor was partially made of ITER-like target in phase 1 (2016-2019), it will be fully made of ITER-like PFC in phase 2 starting autumn 2020 [1, 2]....
The improvement of nuclear power thermal reactors, the development and creation of fast reactors accompanied with the transition to a closed nuclear fuel cycle are being carried out at present time. In this regard, it is important to develop technologies for the management of spent nuclear fuel and radioactive waste, as well as the development of fusion and "fusion-fission" hybrid systems. The...
To resolve concerns for heat/electromagnetic loads from vertical displacement events (VDEs), we developed an equilibrium controller, which can predict and control VDEs to an arbitrary direction and allows us to cope with either upward or downward unmitigated VDEs. Here we improve the prediction rate by parameterizing a power supplies voltage saturation rate with a newly developed adaptive...
Effective thermal energy utilization from in-vessel components is important issue to develop the plant concept of a fusion DEMO, because there are several in-vessel components in a fusion power plant. How to use of divertor thermal energy is now a key for development of the plant concept for JA DEMO. Following two options are newly proposed as for the divertor thermal energy considering...
Here we report an innovative divertor pumping system using proton conductor pump, fuel proceesing system with isotopic recycling by this device, and its impact on the tritium fuel sufficiency of DEMO, particularly that enables commissioning without initial loading of significant quantity of tritium prior to its operation. Proton conductor pump is developed by the authors that actively...
Disruption is an essential issue for ITER because of potential damages from heat loads, halo current and runaway electrons.1 Owing to harmfulness of disruption, it is necessary to develop effective disruption mitigation methods to guarantee the success of ITER project. The shattered pellet injection (SPI) will be used to disruption mitigation and runaway current dissipation on ITER.2 It can...
One of the main goals of WEST is the assessment of power handling capabilities and lifetime of tungsten divertor components under high heat flux and high fluence operation in a full W tokamak environment [ 1 ]. In phase 1, covering the four experimental campaigns (named C1 to C4), WEST operated with a mix of actively cooled ITER like tungsten plasma facing units and inertial tungsten coated...
The new Divertor Tokamak Test facility has taken off. DTT [ ] (Fig.1) is a superconducting tokamak with 6 T on-axis maximum toroidal magnetic field carrying plasma current up to 5.5 MA in pulses with total length up to 100 s. The D-shaped device is up-down symmetric, with major radius R=2.14 m, minor radius a=0.65 m and average triangularity 0.3. The auxiliary heating power coupled to the...
A new drift-kinetic theory and computational approach to understand the plasma response to small magnetic islands associated with neoclassical tearing modes (NTMs) is presented. It demonstrates that drift effects associated with the passing particles support a pressure gradient across a sufficiently small magnetic island, leading to a suppression of the instability drive from the bootstrap...
Removal of corrosion impurities from the molten Pb-16Li, which is a candidate breeder and coolant for the liquid metal breeding blanket system, is indispensable for the safe and efficient operation of the future fusion reactors. The corrosive nature of Pb-16Li in high temperature environment is responsible for the generation of corrosion impurities from the structural material. The deposition...
CEA has been involved for seven years (2014-2020) in the pre-conceptual design study of the magnet systems EU DEMO [1, 2] and for 2 years (2018-2020) in the industrial exploratory study for the cryogenic system and cryo-distribution for EU DEMO. In the framework of these Eurofusion workpackages, significant engineering and technological results have come out from the studies and they have...
The confinement of fast particles in fusion devices is shown to be strongly affected by Alfvén activity [1] and in order to model the associated wave particle interaction, a proper identification of the excited Alfvén Eigenmodes (AEs) is needed in the first place. The shear Alfvén spectrum is highly dependent on the iota profile of the magnetic configuration [2], which in turn depends on the...
Here we report the result of validation of tritium recovery system for liquid PbLi breeding blanket with Vacuum Sieve Tray (VST), that is a tritium extraction from multiple droplets under a vacuum. The VST device is installed in Oroshhi-2 PbLi test loop at the National Institute for Fusion Science (NIFS) in 2019 followed by further modification, and the performance and reliability of the...
Bounce-kinetic model based on the modern nonlinear bounce-kinetic equations[1] has been used for gKPSP[2] gyrokinetic simulations and produced useful and promising results[3]. However, magnetically trapped particles were treated as deeply trapped in that TEM and ITG simulation. This paper reports on an extension including the barely trapped particles. This will allow simulations addressing the...
Low frequency modes belonging to the Alfvenic Kinetic Ballooning mode (KBM)[1] and the mixed polarization Beta-induced Alfven Acoustic Eigenmode (BAAE)[2] branches, have been recently observed experimentally [3] and confirmed numerically [4]. Due to the low frequency range of the core ion bounce motion, kinetic treatment of both circulating[5,6] and trapped particles[7,8] is required in order...
The research on the physical and mechanical properties of structural and functional ma-terials of future fusion reactors has been actively conducting for many years in the Republic of Kazakhstan [1, 2].
Specialized KTM tokamak is being developed in Kazakhstan to research the behavior of candidate materials of the first wall under the conditions of high heat flows comparable to those in future...
The shear of the radial electric field at the edge is widely accepted to be responsible for turbulence reduction in edge transport barriers and thought as a key ingredient of the improved confinement of H-mode plasmas. Nevertheless, a full understanding of how its profile builds up at the edge is still lacking. It can either be formulated as the result of a competition between several...
Abstract:
During the operation of the fusion reactor, the tritium breeder pebbles packed into the tritium breeding blanket formed a tritium breeder pebble bed. Under the influence of the severe environment such as irradiation swelling, thermal expansion, alternating stress, and so forth, the tritium breeder pebbles will be broken and pulverized, accompanied by changes in the...
The fusion neutron sources needed for FFH (Fusion-Fission Hybrid) devices are not available so far, and the blankets integrating the fusion and fission characteristics need to be projected and validated. The concrete validation of the FFH concept is needed. Starting from the figures of a neutron source needed for FFH, the paper is devoted to: i) the determination of parameters for a tokamak...
Technology Readiness Levels (TRLs) give a good idea of maturity of new technology and are used by industry and government organisations worldwide. Nine TRLs exist ranging from initial ideas at Level 1 where basic principles are observed to fully robust technologies validated for application in industry at Level 9. TRLs can be further subdivided into Readiness Levels for system, materials,...
We carried out global calculations of neoclassical (NC) impurity transport in helical plasmas including the effect of variation of electrostatic potential on the flux surface, $\Phi_1$, for the first time. An impurity hole plasma found in LHD experiment is analysed by the global simulation. Contrary to the conventional local approximation models, which indicate negative ambipolar radial...
With reduced neoclassical transport, turbulent transport becomes a critical issue for plasma confinement in optimized stellarators. Therefore, it is important to understand properties of microturbulence in stellarators, which is complicated by the 3D equilibrium. Furthermore, the interactions between neoclassical and turbulent transport in stellarators and the extrapolation to the reactor...
Gyrokinetics is the appropriate theoretical framework to study turbulence in magnetized plasmas. It takes advantage of scale separation between turbulence and background quantities (such as magnetic geometry and plasma profiles), and provides a reduction of phase-space dimensionality, which allows an important saving of computational resources. In tokamaks, the theoretical analysis and the...
The possibility to exploit the properties of medium and light impurities in contaminating plasmas is explored in many tokamaks devices [2-5]; since is crucial to fix the conditions that favor a strong increase of particle confinement while minimizing the amount of impurities needed, as well as to favor the so called "plasma detachment". The light doping action represents a good method to...
High-Temperature Superconducting (HTS) magnet is considered to be applied to the next-generation helical experimental device. Three types of large-current (6-18 kA) HTS conductors are being developed. One of the crucial requirements is to secure the high current density of 80 A/mm2 at a condition of 20 K temperature and 10 T magnetic field. In the first phase of the development, short samples...
The aspect ratio $A = R/a$ is a central parameter for tokamak design in many aspects. In particular, it is expected to critically impact plasma vertical stability and heating, disruption forces, tritium breeding, maintenance and cost [1]. Yet, there is some freedom in its choice. Most of present tokamaks, including ITER, operate at $A\sim3$, with notable exceptions like MAST ($A\sim1.5$) and...
Whereas it is widely believed that velocity shear could suppress plasma instabilities and stimulate the transition from low (L-) to high (H-) confinement modes, the underlying physics of plasma instability suppression is still not clear. Often it is assumed that the stabilization of plasma instability characterized by the growth rate $\gamma _{inst} $ occurs when by the velocity shear $|...
The ADITYA (R0 = 75 cm, a = 25 cm) ohmically heated circular limiter tokamak has been designed and built to produce plasma in a toroidal vacuum chamber of rectangular cross-section with 20 numbers of toroidal field coils capable of producing ~ 1.5 Tesla toroidal magnetic field at plasma centre. The ADITYA tokamak has been successfully operated for 3 decades with more than 30,000 discharges....
Data assimilation techniques are applied to the integrated transport simulation (TASK3D[A]) in Large Helical Device (LHD). We use the ensemble Kalman filter (EnKF) and the ensemble Kalman smoother (EnKS) as data assimilation methods for the estimation of state variables. The time series data of experimentally measured temperature and density profiles are assimilated into TASK3D[B]. The...
One of the objectives of the JET DTE2 experimental campaign will be related to investigation of alpha particle physics and alpha-driven instabilities (1) along with identifying their effect on plasma performance. Recent JET experiments have shown that the 3-ion ICRF heating schemes are an efficient way for generating a fast ion population in the plasma as a consequence of beam ions...
ITER will be equipped with a tungsten divertor, which is planned to operate over a significant period of time, from the Pre-Fusion Power Operation phase into the Fusion Power Operation phase [1]. As was shown in a number of linear devices as well as in tokamaks, tungsten (W) exhibits pronounced surface morphology changes under helium (He) plasma exposure, which can affect its thermal and...
Liquid metal blankets are advanced and have many attractive features such as low operating pressure, design simplicity, and a convenient tritium breeding cycle. However, the magnetohydrodynamic (MHD) effects are a key issue remaining to be solved, one of them is the coupling MHD effect[1-3] which normally exists in liquid metal blankets. The coupling MHD effect is that the flow state in one...
We investigate ion temperature gradient (ITG) mode in hydrogen-isotope plasmas under a radial electric field in Large Helical Device (LHD) using the global gyrokinetic code, XGC-S. The radial electric field is taken into account by additional $E \times B$ drift motion in the poloidal direction. The present multi-mode linear simulations indicate the following properties of ITG mode and...
Runaway electrons (RE) are one of the major concerns for ITER operations. In tokamak devices where fusion reactions take place at high rate and with large total current, the loss of plasma confinement can lead to runaway electrons formation (possibly up to 12 MA in ITER) via primary and secondary generation mechanisms [1,2]. The major issue with runaway electrons that form after the disruption...
Heat load control on plasma facing components (PFC) is a critical issue for fusion devices like ITER: power injection and exhaust systems should be regulated and high radiating plasma scenario at the edge are investigated. Future fusion reactors will have to rely on impurity seeding to enhance the radiative fraction in the range of ~90% in order to cool the edge plasma and prevent PFC damages....
Here we report progress in electrical and mechanical performances of mechanical joints of high-temperature superconducting (HTS) conductors and methods to evaluate those quality. Our research activities showed that (i) Joint resistance for bridge-type mechanical lap joint and mechanical edge joint have been reduced to be acceptable value for HTS helical coils in FFHR-d1 helical fusion reactor,...
As a promising strategy, quiescent H-mode (QH-mode) offers tokamak plasma scenarios without edge localized modes (ELMs) but with constant plasma density and radiated power. This type of ELM-free H-mode regime is often achieved at relatively low plasma density in experiments, and is found to be accompanied by the presence of edge harmonic oscillations (EHOs), which are believed to provide...
We report the results of experimental characterization of the depth dependent helium concentration in single crystal tungsten specimens, as compared to modeling predictions, following repeated helium plasma exposures in the reciprocating collector probe in WEST during the C4 helium campaign. This study was motivated by the opportunity to experimentally validate modeling predictions of the...
We clarify the toroidal flow generation mechanism by electron cyclotron heating (ECH) in stellarator/heliotrons comparing the HSX and LHD experiment results. Radial diffusion of energetic electrons by ECH produces a canceling return current, which then generates a $j_r\times B$ torque that can play an important role in the toroidal rotation in the ECH plasmas. We investigate the energetic...
Modest effects of deuterium line radiation trapping in MAST Upgrade tokamak Super-X and snowflake (SF) divertor plasmas are found using SOLPS-EIRENE and UEDGE code divertor plasma modeling (1, 2), and CRETIN code (3) radiation transport and collisional-radiative modeling. In MAST-U, both the Super-X and SF divertor plasmas are predicted to reach highly radiative (detached) regimes at lower...
Fuel retention and release from tungsten (W) Plasma Facing Components (PFCs) are key issues in the development of fusion as an energy source. Due to safety issues, a strict 700 g inventory tritium limit is required in the ITER vessel material. Moreover, the inventory of hydrogen isotopes (HIs) and their release back into the plasma can jeopardize its control due to too high radiated power at...
A neural network version of the Multi-Mode Model (MMM) (1), known as MMMnet, has been trained to reproduce the calculation of plasma turbulent diffusivities needed for transport simulations. Model-based control applications require response models with fast (e.g. for closed-loop offline simulations) to extremely fast (e.g. for real-time control and estimation) calculation times, making...
Nuclear performance evaluation is the core basis of tritium breeding blanket design and also the key input for thermo-hydraulic and thermo-mechanic numerical analysis. Whereas, the tritium breeding blankets have the features of complex structure, heterogeneous neutron flux distribution and a long energy span of neutron, which are considerable challenges for neutronienter image description...
The compact torus (CT) plasma is a self-organized plasmoid used for fuelling and providing external helicity and momentum. Recent research has shown that central fuelling greatly improves the tritium breeding ratio, which is a key parameter in tritium fusion devices [1]. As the most promising fuelling solution for future fusion devices, such as ITER and CFETR, CT plasma can achieve an...
Predicting the dynamics of a burning plasma over long time scales, i.e. comparable with the energy confinement time or even longer, is essential in order to understand modern fusion experiments. Extending first-principle-based gyrokinetic simulations to these time scales is a formidable task from a computational resource point of view. This makes predictive analyses very challenging and calls...
The lower hybrid current drive (LHCD) system in WEST plays a key role for achieving long pulse operation and high performance plasmas. Up to 5 MW LHCD power has been coupled in WEST plasmas in both Lower Single Null and Upper Single Null configurations, and pulse duration of 55 s has been sustained with 3 MW of LHCD [1]. The LHCD power is launched into the plasma by two multijunction launchers...
We investigate the merging processes of spherical tokamak (ST)-type plasmoids confined in a conducting vessel by means of a particle simulation. For this purpose, (i) we have developed a new particle simulation model to analyze physics not only near the contact point of two STs, i.e., the reconnection point, but also in the entire region of a poloidal surface. We find that (ii) plasma heating...
Water Detritiation System (WDS) is a critical safety system for ITER to reduce the tritium release to the atmosphere and help in the recovery of tritium for self-sustainability. The tritium released/leaked into plant area from the process systems is sent to Atmosphere Detritiation System (ADS), where it is converted to moisture by catalytic reaction with oxygen in air and then scrubbed with...
A natural way to control turbulence in magnetic fusion devices is to take advantage of zonal flows, which form spontaneously and can reduce the turbulence level. Zonal flows can even suppress turbulence completely in a certain parameter range where drift-wave instabilities would otherwise develop. But exploiting this effect, known as the Dimits shift, requires understanding of its physics,...
The China Fusion Engineering Test Reactor (CFETR) is the next device in the roadmap for the realization of fusion energy in China, which aims to bridge the gaps between the fusion experimental reactor (ITER) and the demonstration reactor (DEMO). For the fusion reactor, the neutronic and shielding assessment is indispensable for the performance and safety design of the reactor, which strongly...
Prof. Bruno Coppi and his collaborators have been developing a theory based on an experiment on the ignition of a fusion reaction in a compact tokamak under strong magnetic fields and high plasma density. To carry out this experiment, the tokamak IGNITOR project has been developed [1]. The concept of IGNITOR tokamak based on the using of a strong magnetic field (up to 13 T) and plasma current...
Experimental tests on a prototype system of a novel, rapid time-response disruption mitigation system (DMS) being developed as a back-up option for ITER, referred to as the Electromagnetic Particle Injector (EPI) have been able to verify the primary advantages of the concept, which are its ability to meet short warning time scales of <10ms while attaining the projected high velocities for deep...
The Joint-Texas Experimental tokamak (J-TEXT), formerly named TEXT/TEXT-U in the University of Texas at Austin in USA, has been reconstructed and obtained the first plasma in the Huazhong University of Science and Technology in the spring of 2007[1]. In J-TEXT tokamak, the upgraded resonant magnetic perturbation (RMP) system and the shattered pellet injection system were built, which allows...
Understanding the properties of micro turbulence driven transport and the regulation mechanism is critical in magnetic fusion plasmas. The local and quasilinear theory demonstrates diffusive microscopic turbulent transport, which follows the Fick’s law relating the transport linearly to the gradient, i.e. Q=-nχ∇T and predicts the gyro-Bohm scaling of transport. However, this conventional...
Experiments to stabilize the vertical position of the plasma were carried out in a small tokamak device, PHiX. By the experiments, we demonstrated for the first time in the world that the combined magnetic field generated with saddle coils (SCs) and toroidal magnetic field coils (TFCs) could stabilize the vertically unstable positions of the plasmas with nearly circular cross-sections. The...
The sometimes-apocalyptic statements on the steady increase in carbon dioxide are unleashing powerful political forces but have aroused little interest in scientific solutions—neither carbon-dioxide removal nor carbon-free energy sources. Science can move quickly in periods of societal crisis. The splitting of the nucleus to nuclear weapons required less than seven years, and a fission powered...
The early phases of tokamak plasma current ramp-up are often of very short duration and of little concern on current devices. On ITER, the combination of costly, actively cooled plasma-facing components (PFC) and relatively long timescales ($\sim 10 s$) before the transition to X-point configuration, means that power flux management is key if PFC lifetime is not to be compromised. This paper...
Here we report a neutronics study in a blanket mock-up using a compact fusion neutron source. With the optimized discharge condition, the neutron source stably produces fusion neutrons with the production rates > 10^5 n/s in a deuterium?deuterium (DD) operation (neutron energy: 2.45 MeV). The operation showed a non-linear increase with the applied voltage, in consistent with the cross section...
In November 2019, the physical start-up of KTM tokamak was carried out. One of the main research task of KTM tokamak is study of behavior of first wall candidate materials under influence of high heat flux, which is expected to be in future thermonuclear reactors [Ref.1]. KTM is an aspect ratio A=2, single null divertor configuration, plasma current Ipl=750 кА, toroidal magnetic field Bt=1 Т,...
The breeding blanket will be the component in charge of extracting and amplifying the neutronic power in future Fusion Power Plants. In addition, it has to warrant the reactor tritium self-sufficiency through efficient breeding and recovery. An additional function is the protection of the vacuum vessel (VV) and magnets against radiation [1.]. Various blanket concepts have been proposed along...
The electrochemical technique is shown to be effective to develop liquid blanket system, not only for the molten salt one but also for the liquid metal ones. (i)Oxygen impurity in lead lithium eutectic alloy was removed as CO2 gas by electrolysis in the molten salt contacting with the liquid metal, as well as (ii)nitrogen impurity in liquid lithium. Considering the electrochemical...
Runaway electrons (REs) are relativistic electrons produced during plasma breakdowns, ramp-ups and disruptions. They may reach several 10s of MeV and form multi-MA beams and pose a serious threat to the reliability and availability of future tokamak devices. During the initial commissioning phase of the WEST tokamak [Bucalossi 2014], a significant fraction of discharges contained runaway...
The Greenwald density limit ($\bar{n}_g$) defines a fundamental bound on the tokamak operating space, and so is of central importance to magnetic fusion. Recent experiments (1) reinforce the suggestion (2) that the density limit occurs due to an abrupt increase in edge particle transport, with edge cooling and MHD phenomena following as secondary consequences. Here, we present a theory of...
In drift-wave turbulence, cross-correlations between fluctuations produce turbulent fluxes, which have profound consequences for confinement and the underlying nonlinear turbulence dynamics. In this work, we use a new approach based on deep learning to obtain a reduced mean-field model for the drift-wave/zonal flow dynamics from simulations of the Hasegawa-Wakatani system. In particular, we...
Many tokamak experiments have demonstrated improved core confinement with high toroidal rotation shear. It is widely recognized that turbulence-driven zonal flow has a strong impact on confinement. It has been pointed out that zonal flow can be driven by the parallel compression$^{1,2}$, which is expected to be enhanced with equilibrium parallel rotation shear. Particularly, a gyrokinetic...
