Journal articles: 'Plasmi in tokamak'

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Liang, Chen, Zhuang Ma, Zhen Sun, Xiaoman Zhang, Xin You, Zhuang Liu, Guizhong Zuo, Jiansheng Hu, and Yan Feng. "Demonstration of object location, classification, and characterization by developed deep learning dust ablation trail analysis code package using plasma jets." Review of Scientific Instruments 94, no. 2 (February 1, 2023): 023506. http://dx.doi.org/10.1063/5.0123614.

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Based on deep learning, a Dust Ablation Trail Analysis (DATA) code package is developed to detect dust ablation trails in tokamaks, which is intended to analyze a large amount data of tokamak dusts. To validate and benchmark the DATA code package, 2440 plasma jet images are exploited for the training and test of the deep learning DATA code package, since plasma jets resemble the shape and size of dust ablation clouds in tokamaks. After being trained by 1920 plasma jet images, the DATA code package is able to locate 100% plasma jets, classify plasma jets with the accuracy of >99.9%, and output image skeleton information for classified plasma jets. The DATA code package trained by the plasma jet images is also used to analyze the dust ablation trails captured in the Experimental Advanced Superconducting (EAST) tokamak with the satisfactory performance, further verifying its applicability in the fusion dust ablation investigation. Based on its excellent performance presented here, it is demonstrated that our DATA code package is able to automatically identify and analyze dust ablation trails in tokamaks, which can be used for further detailed investigations, such as the three-dimensional reconstruction of dusts and their ablation trails.

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Pankratov, Igor M., and Volodymyr Y. Bochko. "Nonlinear Cone Model for Investigation of Runaway Electron Synchrotron Radiation Spot Shape." 3, no. 3 (September 28, 2021): 18–24. http://dx.doi.org/10.26565/2312-4334-2021-3-02.

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The runaway electron event is the fundamental physical phenomenon and tokamak is the most advanced conception of the plasma magnetic confinement. The energy of disruption generated runaway electrons can reach as high as tens of mega-electron-volt and they can cause a catastrophic damage of plasma-facing-component surfaces in large tokamaks and International Thermonuclear Experimental Reactor (ITER). Due to its importance, this phenomenon is being actively studied both theoretically and experimentally in leading thermonuclear fusion centers. Thus, effective monitoring of the runaway electrons is an important task. The synchrotron radiation diagnostic allows direct observation of such runaway electrons and an analysis of their parameters and promotes the safety operation of present-day large tokamaks and future ITER. In 1990 such diagnostic had demonstrated its effectiveness on the TEXTOR (Tokamak Experiment for Technology Oriented Research, Germany) tokamak for investigation of runaway electrons beam size, position, number, and maximum energy. Now this diagnostic is installed practically on all the present-day’s tokamaks. The parameter v┴/|v||| strongly influences on the runaway electron synchrotron radiation behavior (v|| is the longitudinal velocity, v┴ is the transverse velocity with respect to the magnetic field B). The paper is devoted to the theoretical investigation of runaway electron synchrotron radiation spot shape when this parameter is not small that corresponds to present-day tokamak experiments. The features of the relativistic electron motion in a tokamak are taken into account. The influence of the detector position on runaway electron synchrotron radiation data is discussed. Analysis carried out in the frame of the nonlinear cone model. In this model, the ultrarelativistic electrons emit radiation in the direction of their velocity v→ and the velocity vector runs along the surface of a cone whose axis is parallel to the magnetic field B. The case of the small parameter v┴/|v||| (v┴/|v|||<<1, linear cone model) was considered in the paper: Plasma Phys. Rep. 22, 535 (1996) and these theoretical results are used for experimental data analysis.

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Windridge, Melanie. "Smaller and quicker with spherical tokamaks and high-temperature superconductors." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2141 (February 4, 2019): 20170438. http://dx.doi.org/10.1098/rsta.2017.0438.

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Research in the 1970s and 1980s by Sykes, Peng, Jassby and others showed the theoretical advantage of the spherical tokamak (ST) shape. Experiments on START and MAST at Culham throughout the 1990s and 2000s, alongside other international STs like NSTX at the Princeton Plasma Physics Laboratory, confirmed their increased efficiency (namely operation at higher beta) and tested the plasma physics in new regimes. However, while interesting devices for study, the perceived technological difficulties due to the compact shape initially prevented STs being seriously considered as viable power plants. Then, in the 2010s, high-temperature superconductor (HTS) materials became available as a reliable engineering material, fabricated into long tapes suitable for winding into magnets. Realizing the advantages of this material and its possibilities for fusion, Tokamak Energy proposed a new ST path to fusion power and began working on demonstrating the viability of HTS for fusion magnets. The company is now operating a compact tokamak with copper magnets, R 0 ∼ 0.4 m, R / a ∼ 1.8, and target I p = 2MA, B t0 = 3 T, while in parallel developing a 5 T HTS demonstrator tokamak magnet. Here we discuss why HTS can be a game-changer for tokamak fusion. We outline Tokamak Energy's solution for a faster way to fusion and discuss plans and progress, including benefits of smaller devices on the development path and advantages of modularity in power plants. We will indicate some of the key research areas in compact tokamaks and introduce the physics considerations behind the ST approach, to be further developed in the subsequent paper by Alan Costley. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

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Garrido, I., A. J. Garrido, M. G. Sevillano, and J. A. Romero. "Robust Sliding Mode Control for Tokamaks." Mathematical Problems in Engineering 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/341405.

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Nuclear fusion has arisen as an alternative energy to avoid carbon dioxide emissions, being the tokamak a promising nuclear fusion reactor that uses a magnetic field to confine plasma in the shape of a torus. However, different kinds of magnetohydrodynamic instabilities may affect tokamak plasma equilibrium, causing severe reduction of particle confinement and leading to plasma disruptions. In this sense, numerous efforts and resources have been devoted to seeking solutions for the different plasma control problems so as to avoid energy confinement time decrements in these devices. In particular, since the growth rate of the vertical instability increases with the internal inductance, lowering the internal inductance is a fundamental issue to address for the elongated plasmas employed within the advanced tokamaks currently under development. In this sense, this paper introduces a lumped parameter numerical model of the tokamak in order to design a novel robust sliding mode controller for the internal inductance using the transformer primary coil as actuator.

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Saperstein, A. R., J. P. Levesque, M. E. Mauel, and G. A. Navratil. "Halo current rotation scaling in post-disruption plasmas." Nuclear Fusion 62, no. 2 (January 6, 2022): 026044. http://dx.doi.org/10.1088/1741-4326/ac4186.

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Abstract Halo current (HC) rotation during disruptions can be potentially dangerous if resonant with the structures surrounding a tokamak plasma. We propose a drift-frequency-based scaling law for the rotation frequency of the asymmetric component of the HC as a function of toroidal field strength and plasma minor radius (f rot ∝ 1/B T a 2). This scaling law is consistent with results reported for many tokamaks and is motivated by the faster HC rotation observed in the HBT-EP tokamak. Projection of the rotation frequency to ITER and SPARC parameters suggest the asymmetric HC rotation will be on the order of 10 Hz and 60 Hz, respectively.

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Garrido, Izaskun, Aitor J. Garrido, Jesús A. Romero, Edorta Carrascal, Goretti Sevillano-Berasategui, and Oscar Barambones. "Low EffortLiNuclear Fusion Plasma Control Using Model Predictive Control Laws." Mathematical Problems in Engineering 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/527420.

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One of the main problems of fusion energy is to achieve longer pulse duration by avoiding the premature reaction decay due to plasma instabilities. The control of the plasma inductance arises as an essential tool for the successful operation of tokamak fusion reactors in order to overcome stability issues as well as the new challenges specific to advanced scenarios operation. In this sense, given that advanced tokamaks will suffer from limited power available from noninductive current drive actuators, the transformer primary coil could assist in reducing the power requirements of the noninductive current drive sources needed for current profile control. Therefore, tokamak operation may benefit from advanced control laws beyond the traditionally used PID schemes by reducing instabilities while guaranteeing the tokamak integrity. In this paper, a novel model predictive control (MPC) scheme has been developed and successfully employed to optimize both current and internal inductance of the plasma, which influences the L-H transition timing, the density peaking, and pedestal pressure. Results show that the internal inductance and current profiles can be adequately controlled while maintaining the minimal control action required in tokamak operation.

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Podpaly, Y. A., J. E. Rice, P. Beiersdorfer, M. L. Reinke, J. Clementson, and H. S. Barnard. "Tungsten measurement on Alcator C-Mod and EBIT for future fusion reactors1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas." Canadian Journal of Physics 89, no. 5 (May 2011): 591–97. http://dx.doi.org/10.1139/p11-038.

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Tungsten will be an important element in nearly all future fusion reactors because of its presence in plasma facing components. This makes tungsten a good candidate for a diagnostic element for ion temperature and toroidal velocity measurement, and it makes understanding tungsten emissions important for tokamak power balance. The effect of tungsten on tokamak plasmas is investigated at the Alcator C-Mod tokamak using VUV, bolometry, and soft X-ray spectroscopy. Tungsten was present in Alcator C-Mod as a plasma facing component and through laser blow-off impurity injection. Quasi-continuum emission previously seen at other tokamaks has been identified. Theoretical predictions are presented of tungsten emission that could be expected in future Alcator C-Mod measurements. Furthermore, spectra of highly charged tungsten ions have been studied at the SuperEBIT electron beam ion trap. This emission could prove useful for spectroscopic diagnostics of future high-temperature fusion reactor plasmas.

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Federici, Fabio, Matthew L. Reinke, Bruce Lipschultz, Andrew J. Thornton, James R. Harrison, Jack J. Lovell, and Matthias Bernert. "Design and implementation of a prototype infrared video bolometer (IRVB) in MAST Upgrade." Review of Scientific Instruments 94, no. 3 (March 1, 2023): 033502. http://dx.doi.org/10.1063/5.0128768.

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A prototype infrared video bolometer (IRVB) was successfully deployed in the Mega Ampere Spherical Tokamak Upgrade (MAST Upgrade or MAST-U), the first deployment of such a diagnostic in a spherical tokamak. The IRVB was designed to study the radiation around the lower x-point, another first in tokamaks, and has the potential to estimate emissivity profiles with spatial resolution beyond what is achievable with resistive bolometry. The system was fully characterized prior to installation on MAST-U, and the results are summarized here. After installation, it was verified that the actual measurement geometry in the tokamak qualitatively matches the design; this is a particularly difficult process for bolometers and was done using specific features of the plasma itself. The installed IRVB measurements are consistent both with observations from other diagnostics, including magnetic reconstruction, visible light cameras, and resistive bolometry, as well as with the IRVB-designed view. Early results show that with conventional divertor geometry and only intrinsic impurities (for example, C and He), the progression of radiative detachment follows a similar path to that observed for large aspect ratio tokamaks: The peak of the radiation moves along the separatrix from the targets to the x-point and high-field side midplane with a toroidally symmetric structure that can eventually lead to strong effects on the core plasma inside the separatrix.

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Dlougach, Eugenia, Alexander Panasenkov, Boris Kuteev, and Arkady Serikov. "Neutral Beam Coupling with Plasma in a Compact Fusion Neutron Source." Applied Sciences 12, no. 17 (August 23, 2022): 8404. http://dx.doi.org/10.3390/app12178404.

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FNS-ST is a fusion neutron source project based on a spherical tokamak (R/a = 0.5 m/0.3 m) with a steady-state neutron generation of ~1018 n/s. Neutral beam injection (NBI) is supposed to maintain steady-state operation, non-inductive current drive and neutron production in FNS-ST plasma. In a low aspect ratio device, the toroidal magnetic field shape is not optimal for fast ions confinement in plasma, and the toroidal effects are more pronounced compared to the conventional tokamak design (with R/a > 2.5). The neutral beam production and the tokamak plasma response to NBI were efficiently modeled by a specialized beam-plasma software package BTR-BTOR, which allowed fast optimization of the neutral beam transport and evolution within the injector unit, as well as the parametric study of NBI induced effects in plasma. The “Lite neutral beam model” (LNB) implements a statistical beam description in 6-dimensional phase space (106–1010 particles), and the beam particle conversions are organized as a data flow pipeline. This parametric study of FNS-ST tokamak is focused on the beam-plasma coupling issue. The main result of the study is a method to achieve steady-state current drive and fusion controllability in beam-driven toroidal plasmas. LNB methods can be also applied to NBI design for conventional tokamaks.

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Mitrishkin, Yuri V., Valerii I. Kruzhkov, and Pavel S. Korenev. "Methodology of Plasma Shape Reachability Area Estimation in D-Shaped Tokamaks." Mathematics 10, no. 23 (December 5, 2022): 4605. http://dx.doi.org/10.3390/math10234605.

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This paper suggests and develops a new methodology of estimation for a multivariable reachability region of a plasma separatrix shape on the divertor phase of a plasma discharge in D-shaped tokamaks. The methodology is applied to a spherical Globus-M/M2 tokamak, including the estimation of a controllability region of a vertical unstable plasma position on the basis of the experimental data. An assessment of the controllability region and the reachability region of the plasma is important for the design of tokamak poloidal field coils and the synthesis of a plasma magnetic control system. When designing a D-shaped tokamak, it is necessary to avoid the small controllability region of the vertically unstable plasma, because such cases occur in practice at a restricted voltage on a horizon field coil. To make the estimations mentioned above robust, PID-controllers for vertical and horizontal plasma position control were designed using the Quantitative Feedback Theory approach, which stabilizes the system and provides satisfactory control indexes (stability margins, setting time, overshoot) during plasma discharges. The controllers were tested on a series of plasma models and nonlinear models of current inverters in auto-oscillation mode as actuators for plasma position control. The estimations were made on these models, taking into account limitations on control actions, i.e., voltages on poloidal field coils. This research is the first step in the design of the plasma shape feedback control system for the operation of the Globus-M2 spherical tokamak. The developed methodology may be used in the design of poloidal field coil systems in tokamak projects in order to avoid weak achievability and controllability regions in magnetic plasma control. It was found that there is a strong cross-influence from the PF-coils currents and the CC current on the plasma shape; hence, these coils should be used to control the plasma shape simultaneously.

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Shukla, Braj Kishore, Jatin Patel, Harshida Patel, Dharmesh Purohit, Hardik Mistry, and K. G. Parmar. "ECRH experiments on Tokamaks SST-1 & Aditya-U and ECRH upgradation plan for SST-1." EPJ Web of Conferences 277 (2023): 02005. http://dx.doi.org/10.1051/epjconf/202327702005.

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A 42GHz-500kW ECRH system [1-6] is used to carry out various experiments related to plasma breakdown and ECR heating on tokamaks SST-1 and Aditya-U. The system has been upgraded with new anode modulator power supply to launch two ECRH pulses to carry out breakdown and heating simultaneously. In SST-1, ECRH system is used routinely for plasma breakdown at fundamental harmonic, approximately 150kW power is launched for 70ms to 150ms duration and consistent plasma start-up is achieved in SST-1. In the recent experiments, second EC pulse is also launched at the plasma flat-top to heat the plasma, some heating signatures are seen but more experiments will be carried out to confirm the plasma heating with ECRH. In Aditya-U tokamak, simultaneous plasma breakdown and heating experiments are carried out successfully [2]. In the first pulse around 100kW power in fundamental O-mode is launched for 70ms duration for the breakdown at low-loop voltage and around 150kW ECRH power for 50ms duration is launched in second EC pulse to heat the plasma. In case of Aditya-U, plasma heating is observed clearly as soft X-ray signal increases sharply with ECRH. In AdityaU tokamak, deuterium plasma experiments have been carried out and ECRH launched at the flat-top of deuterium plasma current. In deuterium plasma also ECR heating is observed as soft X-ray signal increases with ECH power. For SST-1, ECRH system is being upgraded with another 82.6GHz system, this system would be used to carry out plasma heating and start-up at second harmonic. The 82.6GHz system is already connected with the SST-1 tokamak, the old 82.6GHz-200kW Gyrotron will be upgraded to 400kW system to carry out effective heating experiments on SST-1 at higher ECRH power. The paper discusses the recent results of ECRH experiments carried out on tokamaks SST-1 & Aditya-U and presents the upgradation plan of EC system for SST-1.

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Bishop, Chris M., Paul S. Haynes, Mike E. U. Smith, Tom N. Todd, and David L. Trotman. "Real-Time Control of a Tokamak Plasma Using Neural Networks." Neural Computation 7, no. 1 (January 1995): 206–17. http://dx.doi.org/10.1162/neco.1995.7.1.206.

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In this paper we present results from the first use of neural networks for real-time control of the high-temperature plasma in a tokamak fusion experiment. The tokamak is currently the principal experimental device for research into the magnetic confinement approach to controlled fusion. In an effort to improve the energy confinement properties of the high-temperature plasma inside tokamaks, recent experiments have focused on the use of noncircular cross-sectional plasma shapes. However, the accurate generation of such plasmas represents a demanding problem involving simultaneous control of several parameters on a time scale as short as a few tens of microseconds. Application of neural networks to this problem requires fast hardware, for which we have developed a fully parallel custom implementation of a multilayer perceptron, based on a hybrid of digital and analogue techniques.

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Segura, Javier Lopez, Nicolas Urgoiti Moinot, and Enzo Lazzaro. "Simulation of a high proton temperature plasma toroidal magnetic trap to be used in proton-11B fusion." Journal of Technological and Space Plasmas 1, no. 1 (November 20, 2019): 12–20. http://dx.doi.org/10.31281/jtsp.v1i1.6.

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Several tokamaks structures containing 500 keV protons to be used in P-B11 fusion were simulated. In order to find the optimal confinement configuration, the simulation was helped by an evolutionary algorithm running 145,000 simulations. The results are presented in this paper. According to the simulations the tokamak structure can be operated to reach ignition using the proposed plasma mode that includes the use of low electron temperature and high thermal energy protons in the plasma (500 keV).

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SAADAT, SH, M. SALEM, M. GHORANNEVISS, and P. KHORSHID. "Stochastic modeling of plasma mode forecasting in tokamak." Journal of Plasma Physics 78, no. 2 (November 11, 2011): 99–104. http://dx.doi.org/10.1017/s0022377811000456.

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AbstractThe structure of magnetohydrodynamic (MHD) modes has always been an interesting study in tokamaks. The mode number of tokamak plasma is the most important parameter, which plays a vital role in MHD instabilities. If it could be predicted, then the time of exerting external fields, such as feedback fields and Resonance Helical Field, could be obtained. Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average are useful models to predict stochastic processes. In this paper, we suggest using ARIMA model to forecast mode number. The ARIMA model shows correct mode number (m = 4) about 0.5 ms in IR-T1 tokamak and equations of Mirnov coil fluctuations are obtained. It is found that the recursive estimates of the ARIMA model parameters change as the plasma mode changes. A discriminator function has been proposed to determine plasma mode based on the recursive estimates of model parameters.

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Sadakov, Sergey, Fabio Villone, Guglielmo Rubinacci, and Salvatore Ventre. "Simple Parametric Model for Calculation of Lateral Electromagnetic Loads in Tokamaks at Asymmetric Vertical Displacement Events (AVDE)." Plasma 5, no. 3 (July 25, 2022): 306–23. http://dx.doi.org/10.3390/plasma5030024.

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This paper describes a family of relatively simple numerical models for calculation of asymmetric electromagnetic (EM) loads at all tokamak structures and coils at asymmetric vertical plasma displacement events (AVDE). Unlike currently known AVDE studies concentrated on plasma physics, these models have a practical purpose to calculate detailed time-dependent patterns of AVDE-induced EM loads everywhere in the tokamak. They are built to intrinsically assure good-enough EM load balance (opposite net forces and torques for the Vacuum Vessel and the Magnets with zero total for the entire tokamak), as needed for consequent simulation of the tokamak’s dynamic response to AVDE, as well as for the development of tokamak monitoring algorithms and tokamak simulators. To achieve these practical goals, the models work in a manner of parametric study. They do not intervene in details of plasma physics, but run at widely varied input assumptions on AVDE evolution and severity. Their outputs will fill a library of ready-for-use lateral EM loads for multiple variants of AVDE evolution and severity. The tokamak physics community can select any variant from the library, and engineers can pick ready-for-use AVDE loads. Investigated here, EM models represent one already known approach and one newly suggested. The latter attempts to reflect the helical pattern of halo currents in plasma and delivers richer outcomes and, thus, can be preferred as the single practical model for parametric calculations.

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Воронин, А. В., В. Ю. Горяинов, В. В. Забродский, Е. В. Шерстнев, В. А. Корнев, П. Н. Аруев, Г. С. Курскиев, Н. А. Жубр, and А. С. Тукачинский. "Измерение электронной температуры плазмы фольговым рентгеновским спектрометром, установленным на токамаках ТУМАН-3М и Глобус-М2." Журнал технической физики 91, no. 12 (2021): 1922. http://dx.doi.org/10.21883/jtf.2021.12.51758.188-21.

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Technical solution were presented for a foil spectrometer installed on the Globus-M2 and TUMAN-3M tokamaks for measuring the electron plasma temperature. Measurements have been carried out of the time dependence of the plasma temperature in the central region of tokamaks. Using of integrated photodetectors and unique beryllium foils with a thickness of 14–80 µm made it possible to increase the sensitivity of the spectrometer. An important quality of the foils used were the increased values of strength, plasticity, homogeneity, and the absence of surface and internal defects. The combined use of the spectrometer with Thomson scattering diagnostics made it possible to carry out regular temperature measurements in the Globus-M2 tokamak with a high spatial and temporal resolution. The influence of impurities is estimated on the measurement of the electron temperature of the plasma.

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Menard, J. E., B. A. Grierson, T. Brown, C. Rana, Y. Zhai, F. M. Poli, R. Maingi, W. Guttenfelder, and P. B. Snyder. "Fusion pilot plant performance and the role of a sustained high power density tokamak." Nuclear Fusion 62, no. 3 (February 7, 2022): 036026. http://dx.doi.org/10.1088/1741-4326/ac49aa.

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Abstract Recent U.S. fusion development strategy reports all 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 low capital cost. Compact tokamaks have been proposed as a means of potentially reducing the capital cost of a FPP. However, compact steady-state tokamak FPPs face the challenge of integrating a high fraction of self-driven current with high core confinement, plasma pressure, and high divertor parallel heat flux. This integration is sufficiently challenging that a dedicated sustained-high-power-density (SHPD) tokamak facility is proposed by the U.S. community as the optimal way to close this integration gap. Performance projections for the steady-state tokamak FPP regime are presented and a preliminary SHPD device with substantial flexibility in lower aspect ratio (A = 2–2.5), shaping, and divertor configuration to narrow gaps to an FPP is described.

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BATISHCHEV, O. V., M. M. SHOUCRI, A. A. BATISHCHEVA, and I. P. SHKAROFSKY. "Fully kinetic simulation of coupled plasma and neutral particles in scrape-off layer plasmas of fusion devices." Journal of Plasma Physics 61, no. 2 (February 1999): 347–64. http://dx.doi.org/10.1017/s0022377898007375.

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Fluid descriptions of plasmas, which are usually applied to a collisional plasma, can only be justified for very small Coulomb Knudsen numbers. However, the scrape-off layer (SOL) plasmas of experimental magnetic confinement fusion devices tend to have operational regimes characterized by a Coulomb Knudsen number around 0.1. In interesting detached regimes of an SOL plasma in a tokamak, when the plasma detaches from the limiters or divertors, this number may increase along with the local plasma gradients. Plasma gradients are also known to increase (and thus drive non-local effects) in inertial confinement fusion. Neutrals, which are being produced owing to plasma recombination at the plasma–divertor interface, may be in a mixed collisional regime as well. Thus simultaneous kinetic treatments of plasma and neutral particles with self-consistent evaluation of boundary conditions at the material walls are required. We present a physical model and a numerical scheme, and discuss results of purely kinetic simulations of plasmas and neutrals for actual conditions in the Alcator C-Mod and Tokamak-de-Varennes experimental tokamaks. Results for both steady-state and transient regimes of SOL plasma flow are presented. Our approach, unlike particle-in-cell and Monte Carlo methods, is free from statistical noise.

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Binderbauer, M. W., and N. Rostoker. "Turbulent transport in magnetic confinement: how to avoid it." Journal of Plasma Physics 56, no. 3 (December 1996): 451–65. http://dx.doi.org/10.1017/s0022377800019413.

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From recent tokamak research, there is considerable experimental evidence that superthermal ions slow down and diffuse classically in the presence of turbulent fluctuations that cause anomalous transport of thermal ions. Further more, research on field-reversed configurations at Los Alamos is consistent with the view that kinetic effects suppress instability growth when the ratio of plasma radius to ion orbital radius is small; turbulence is enhanced and confinement degrades when this ratio increases. Motivated by these experiments, we consider a plasma consisting of large-orbit non-adiabatic ions and adiabatic electrons. For such a plasma, it is possible that the anomalous transport characteristic of tokamaks can be avoided and a compact reactor design becomes viable.

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Melnikov, Alexander. "Evolution of Heavy Ion Beam Probing from the Origins to Study of Symmetric Structures in Fusion Plasmas." Symmetry 13, no. 8 (July 27, 2021): 1367. http://dx.doi.org/10.3390/sym13081367.

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The overview discusses development of the unique fusion plasma diagnostics—Heavy Ion Beam Probing (HIBP) in application to toroidal magnetic plasma devices. The basis of the HIBP measurements of the plasma electric potential and processing of experimental data are considered. Diagnostic systems for probing plasma in tokamaks TM-4, TJ-1, TUMAN-3M and T-10, stellarators WEGA, TJ-II and Uragan-2M are presented. Promising results of the HIBP projects for various existing modern machines, such as TCV, TCABR, MAST, COMPASS, GLOBUS-M2, T-15 MD and W7-X and the international fusion tokamak reactor ITER are given. Results from two machines with similar size and plasma parameters, but with different types of the magnetic con-figuration: axisymmetric tokamak T-10 and helically symmetric stellarator TJ-II are compared. The results of studies of stationary potential profiles and oscillations in the form of quasimonochromatic and broadband fluctuations, turbulent particle flux, fluctuations of density and poloidal magnetic field are presented. The properties of symmetric structures—zonal flows and geodesic acoustic modes of plasma oscillations as well as Alfvén Eigenmodes excited by fast particles from neutral beam injection heating are described. General trends in the behavior of electric potential and turbulence in magnetized fusion plasmas are revealed.

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Sadakov, Sergey. "A Few Points of the Engineering Logic Discussed in ITER EDA on Evaluation of Halo- and AVDE-Induced Loads in Tokamaks." Plasma 4, no. 3 (June 22, 2021): 366–75. http://dx.doi.org/10.3390/plasma4030025.

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All tokamaks are designed to withstand a certain number of energetic electromagnetic (EM) transients caused by uncontrolled terminations of plasma pulses, including symmetric and asymmetric plasma vertical displacement events: VDEs and AVDEs. These events generate significant pulsed EM loads in all conductive components and coils. Axially symmetric transient EM loads induced by VDEs without Halo current have been calculated well since the 1980s; however, Halo-related EM load components and lateral loads associated with AVDEs still cause discussions. The author worked on fast plasma and EM transients in tokamaks quite a while ago then deviated to other areas but has been keeping track of the topic since. He is aware of discussions of the modelling of Halo currents and of significant scatter present in current estimates for AVDE-induced lateral loads and contends that some points of engineering logic formulated earlier on this topic may help reduce these uncertainties. This article summarises a few points of the engineering understanding developed in informal discussions within the ITER EDA team with the purpose to preserve these points for all tokamak developments.

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Donnelly, I. J., and B. E. Clancy. "Kinetic theory of Alfvén waves in plasmas with force-free currents." Journal of Plasma Physics 45, no. 2 (April 1991): 213–28. http://dx.doi.org/10.1017/s0022377800015658.

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Equations are derived for the kinetic-theory analysis of small-amplitude Alfvén waves in cylindrical plasmas carrying force-free currents. The equations, which include ion Larmor-radius effects to second order, are applicable to reversed-field pinches as well as to tokamaks. Fourier mode amplitudes are derived for model antennas with radial current feeds, and a quantitative analysis is made of the antenna resistance and the wave density fields in a small tokamak during Alfvén-wave heating. The effect of the plasma current on the wave thermal energy flux is discussed.

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Montani, Giovanni, Nakia Carlevaro, and Brunello Tirozzi. "On the Turbulent Behavior of a Magnetically Confined Plasma near the X-Point." Fluids 7, no. 5 (April 29, 2022): 157. http://dx.doi.org/10.3390/fluids7050157.

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We construct a model for the turbulence near the X-point of a Tokamak device and, under suitable assumptions, we arrive to a closed equation for the electric field potential fluctuations. The analytical and numerical analysis is focused on a reduced two-dimensional formulation of the dynamics, which allows a direct mapping to the incompressible Navier-Stokes equation. The main merit of this study is to outline how the turbulence near the X-point, in correspondence to typical operation conditions of medium and large size Tokamaks, is dominated by the enstrophy cascade from large to smaller spatial scales.

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Yashin, Alexander, Alexander Belokurov, Leonid Askinazi, Alexander Petrov, and Anna Ponomarenko. "The Influence of Fast Particles on Plasma Rotation in the TUMAN-3M Tokamak." Atoms 10, no. 4 (October 1, 2022): 106. http://dx.doi.org/10.3390/atoms10040106.

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In most present-day tokamaks, the majority of the heating power comes from sources such as neutral-beam injection (NBI) and other types of auxiliary heating which allow for the transfer of energy to the plasma by a small population of externally introduced fast particles. The behavior of the fast ions is important for the overall plasma dynamics, and understanding their influence is vital for the success of any future magnetic confinement devices. In the TUMAN-3M tokamak, it has been noted that the loss of fast particles during NBI can lead to dramatic changes in the rotation velocity profiles, as they are responsible for the negative radial electric field on the periphery.

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Zhang, W., Z. W. Ma, H. W. Zhang, W. J. Chen, and X. Wang. "Influence of aspect ratio, plasma viscosity, and radial position of the resonant surfaces on the plasmoid formation in the low resistivity plasma in Tokamak." Nuclear Fusion 62, no. 3 (January 20, 2022): 036007. http://dx.doi.org/10.1088/1741-4326/ac46f8.

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Abstract In the present paper, we systematically investigate the nonlinear evolution of the resistive kink mode in the low resistivity plasma in Tokamak geometry. We find that the aspect ratio of the initial equilibrium can significantly influence the critical resistivity for plasmoid formation. With the aspect ratio of 3/1, the critical resistivity can be one magnitude larger than that in cylindrical geometry due to the strong mode–mode coupling. We also find that the critical resistivity for plasmoid formation η crit decreases with increasing plasma viscosity in the moderately low resistivity regime. Due to the geometry of Tokamaks, the critical resistivity for plasmoid formation increases with the increasing radial location of the resonant surface.

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Буланин, В. В., В. К. Гусев, Г. С. Курскиев, В. Б. Минаев, М. И. Патров, А. В. Петров, Ю. В. Петров, and А. Ю. Яшин. "Применение метода многочастотного допплеровского обратного рассеяния для исследования альфвеновских мод в токамаке." Письма в журнал технической физики 45, no. 21 (2019): 44. http://dx.doi.org/10.21883/pjtf.2019.21.48474.17982.

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The results of the study of toroidal Alfven modes (TAE) using the multi-frequency Doppler backscattering (DBS) in the Globus-M tokamak are presented. The article is focused on the presentation of the Alfven mode registration method for multichannel probing. The possible causes of the observed oscillations of the poloidal plasma rotation velocity at the Alfvén oscillation frequencies are discussed in detail. The data on the spatial distribution of Alfvén modes revealed by multi-frequency DBS are given. The recommendations for the further development of the DBS with the aim of a more detailed study of TAE in tokamaks were determined.

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27

Ondac, Peter, Jan Horacek, Jakub Seidl, Petr Vondrácek, Hans Werner Müller, Jirí Adámek, and Anders Henry Nielsen. "COMPARISON BETWEEN 2D TURBULENCE MODEL ESEL AND EXPERIMENTAL DATA FROM AUG AND COMPASS TOKAMAKS." Acta Polytechnica 55, no. 2 (April 30, 2015): 128–35. http://dx.doi.org/10.14311/ap.2015.55.0128.

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<p style="text-indent: 0px; margin: 0px;">In this article we have used the 2D fluid turbulence numerical model, ESEL, to simulate turbulent transport in edge tokamak plasma. Basic plasma parameters from the ASDEX Upgrade and COMPASS tokamaks are used as input for the model, and the output is compared with experimental observations obtained by reciprocating probe measurements from the two machines. Agreements were found in radial profiles of mean plasma potential and temperature, and in a level of density fluctuations. Disagreements, however, were found in the level of plasma potential and temperature fluctuations. This implicates a need for an extension of the ESEL model from 2D to 3D to fully resolve the parallel dynamics, and the coupling from the plasma to the sheath.</p>

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28

Sadowski, Marek J. "Selected methods of electron-and ion-diagnostics in tokamak scrape-off-layer." Nukleonika 60, no. 2 (June 1, 2015): 199–206. http://dx.doi.org/10.1515/nuka-2015-0039.

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Abstract This invited paper considers reasons why exact measurements of fast electron and ion losses in tokamaks, and particularly i n a scrape-off-layer and near a divertor region, are necessary in order to master nuclear fusion energy production. Attention is also paid to direct measurements of escaping fusion products from D-D and D-T reactions, and in particular of fast alphas which might be used for plasma heating. The second part describes the generation of so-called runaway and ripple-born electrons which might induce high energy losses and cause severe damages of internal walls in fusion facilities. Advantages and disadvantages of different diagnostic methods applied for studies of such fast electrons are discussed. Particular attention is paid to development of a direct measuring technique based on the Cherenkov effect which might be induced by fast electrons in appropriate radiators. There are presented various versions of Cherenkov-type probes which have been developed by the NCBJ team and applied in different tokamak experiments. The third part is devoted to direct measurements of fast ions (including those produced by the nuclear fusion reactions) which can escape from a high-temperature plasma region. Investigation of fast fusion-produced protons from tokamak discharges is reported. New ion probes, which were developed by the NCBJ team, are also presented. For the first time there is given a detailed description of an ion pinhole camera, which enables irradiation of several nuclear track detectors during a single tokamak discharge, and a miniature Thomson-type mass-spectrometer, which can be used for ion measurements at plasma borders.

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Escande, D. F., F. Sattin, and P. Zanca. "Plasma-wall self-organization in magnetic fusion." Nuclear Fusion 62, no. 2 (December 16, 2021): 026001. http://dx.doi.org/10.1088/1741-4326/ac3c87.

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Abstract This paper introduces the concept of plasma-wall self-organization (PWSO) in magnetic fusion. The basic idea is the existence of a time delay in the feedback loop relating radiation and impurity production on divertor plates. Both a zero and a one-dimensional description of PWSO are provided. They lead to an iterative equation whose equilibrium fixed point is unstable above some threshold. This threshold corresponds to a radiative density limit, which can be reached for a ratio of total radiated power to total input power as low as 1/2. When detachment develops and physical sputtering dominates, this limit is progressively pushed to very high values if the radiation of non-plate impurities stays low. Therefore, PWSO comes with two basins for this organization: the usual one with a density limit, and a new one with density freedom, in particular for machines using high-Z materials. Two basins of attraction of PWSO are shown to exist for the tokamak during start-up, with a high density one leading to this freedom. This basin might be reached by a proper tailoring of ECRH assisted ohmic start-up in present middle-size tokamaks, mimicking present stellarator start-up. In view of the impressive tokamak DEMO wall load challenge, it is worth considering and checking this possibility, which comes with that of more margins for ITER and of smaller reactors.

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Nowak vel Nowakowski, P., D. Makowski, B. Jabłoński, P. Szajerski, Santosh P. Pandya, R. O’Connor, R. Tieulent, and R. Barnsley. "Evaluation of optical transmission across the ITER hard x-ray monitor system designed for the first plasma scenarios." Review of Scientific Instruments 93, no. 10 (October 1, 2022): 103512. http://dx.doi.org/10.1063/5.0101802.

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Hard x-ray (HXR) spectroscopy is applied for diagnostics of runaway electrons in nuclear fusion reactors. The scintillation counter is one of the most commonly used types of detectors for HXR spectroscopy. It consists of a detector that emits light when excited by HXR radiation (scintillator) directly coupled to a PMT (Photomultiplier Tube) that converts light pulses into an electrical signal. This type of detector is commonly used in existing tokamaks, such as Joint European Torus (JET), Experimental Advanced Superconducting Tokamak (EAST), Compact Assembly (COMPASS), and Axially Symmetric Divertor Experiment (ASDEX-U). In all these cases, the scintillator is directly coupled to the PMT to provide the best possible light transmission efficiency. The Hard X-ray Monitor (HXRM) is one among the first plasma diagnostic systems at ITER that provides information about the energy distribution of runaway electrons inside a tokamak by HXR spectroscopy. This system also uses a scintillator and a PMT as a detector. Due to the heavy shielding of the blanket modules, vacuum vessel, and port-plugs, it is not possible to assemble the scintillator outside the tokamak vacuum vessel. The PMT detector cannot be installed in the close vicinity of the tokamak due to either the significant magnetic field or temperature. A possible solution is to decouple the scintillator from the PMT and place the PMT inside the port-cell. Light pulses will be transmitted to the PMT via a 12 m long optical fiber bundle. Evaluation of the optical transmission was carried out to assess the performance of the HXR monitor and verify possible problems related to the PMT pulse discrimination under low light conditions.

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31

Mitrishkin, Yuri V., Pavel S. Korenev, Artem E. Konkov, Valerii I. Kruzhkov, and Nicolai E. Ovsiannikov. "New Identification Approach and Methods for Plasma Equilibrium Reconstruction in D-Shaped Tokamaks." Mathematics 10, no. 1 (December 23, 2021): 40. http://dx.doi.org/10.3390/math10010040.

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The paper deals with the identification of plasma equilibrium reconstruction in D-shaped tokamaks on the base of plasma external magnetic measurements. The methods of such identification are directed to increase their speed of response when plasma discharges are relatively short, like in the spherical Globus-M2 tokamak (Ioffe Inst., St. Petersburg, Russia). The new approach is first to apply to the plasma discharges data the off-line equilibrium reconstruction algorithm based on the Picard iterations, and obtain the gaps between the plasma boundary and the first wall, and the second is to apply new identification methods to the gap values, producing plasma shape models operating in real time. The inputs for on-line robust identification algorithms are the measurements of magnetic fluxes on magnetic loops, plasma current, and currents in the poloidal field coils measured by the Rogowski loops. The novel on-line high-performance identification algorithms are designed on the base of (i) full-order observer synthesized by linear matrix inequality (LMI) methodology, (ii) static matrix obtained by the least square technique, and (iii) deep neural network. The robust observer is constructed on the base of the LPV plant models which have the novelty that the state vector contains the gaps which are estimated by the observer, using input and output signals. The results of the simulation of the identification systems on the base of experimental data of the Globus-M2 tokamak are presented.

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Punjabi, Alkesh, Arun Verma, and Allen Boozer. "Tokamak divertor maps." Journal of Plasma Physics 52, no. 1 (August 1994): 91–111. http://dx.doi.org/10.1017/s0022377800017797.

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A mapping method is developed to investigate the problem of determination and control of heat-deposition patterns on the plates of a tokamak divertor. The deposition pattern is largely determined by the magnetic field lines, which are mathematically equivalent to the trajectories of a single-degree-of-freedom time-dependent Hamiltonian system. Maps are natural tools to study the generic features of such systems. The general theory of maps is presented, and methods for incorporating various features of the magnetic field and particle motion in divertor tokamaks are given. Features of the magnetic field include the profile of the rotational transform, single- versus double-null divertor, reverse map, the effects of naturally occurring low M and N, and externally imposed high-M, high-N perturbations. Particle motion includes radial diffusion, pitch angle and energy scattering, and the electric sheath at the plate. The method is illustrated by calculating the stochastic broadening in a single- null divertor tokamak. Maps provide an efficient, economic and elegant method to study the problem of motion of plasma particles in the stochastic scrape-off layer.

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33

Stangeby, P. C., E. A. Unterberg, J. W. Davis, T. Abrams, A. Bortolon, I. Bykov, D. Donovan, et al. "Developing solid-surface plasma facing components for pilot plants and reactors with replenishable wall claddings and continuous surface conditioning. Part B: required research in present tokamaks." Plasma Physics and Controlled Fusion 64, no. 5 (March 18, 2022): 055003. http://dx.doi.org/10.1088/1361-6587/ac55f8.

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Abstract The companion part A paper (Stangeby et al 2022) reports a number of independent estimates indicating that high-duty-cycle DT tokamaks starting with pilot plants will likely experience rates of net erosion and deposition of solid PFC, plasma facing component, material in the range of 103 to 104 kg yr−1, regardless of the material used. The subsequent redeposition of such large quantities of material has the potential for major interference with tokamak operation. Similar levels and issues will be involved if ∼continuous low-Z powder dropping is used for surface conditioning of DT tokamaks, independent of the material used for the PFC armor. In Stangeby et al (2022) (part A) it is proposed that for high-duty-cycle DT tokamaks, non-metallic low-Z refractory materials such as ceramics (graphite, SiC, etc) used as in situ replenishable, relatively thin—of order mm—claddings on a substrate which is resistant to neutron damage could provide a potential solution for protecting the main walls, while reducing the risk of degrading the confined plasma. Assessment of whether such an approach is viable will require information, much of which is not available today. Section 6 of part A identifies a partial list of major physics questions that will need to be answered in order to make an informed assessment. This part B report describes R&D needed to be done in present tokamaks in order to answer many of these questions. Most of the required R&D is to establish better understanding of low-Z slag generation and to identify means to safely manage it. Powder droppers provide a unique opportunity to carry out controlled studies on the management of low-Z slag in current tokamaks, independent of whether their protection tiles use low-Z or high-Z material.

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34

Zohm, Hartmut. "On the size of tokamak fusion power plants." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2141 (February 4, 2019): 20170437. http://dx.doi.org/10.1098/rsta.2017.0437.

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Figures of merit for future tokamak fusion power plants (FPPs) are presented. It is argued that extrapolation from present-day experiments to proposed FPPs must follow a consistent development path, demonstrating the largest required leaps in intermediate devices to allow safe extrapolation to an FPP. This concerns both plasma physics and technology. At constant plasma parameters, the figures of merit depend on both major radius R and magnetic field B . We propose to use the term ‘size’ for a combination of R and B to avoid ambiguities in scaling arguments. Two routes to FPPs are discussed: the more conventional one increasing R , based on the assumption that B is limited by present technology; and an alternative approach assuming the availability of new technology for superconducting coils, allowing higher B . It is shown that the latter will lead to more compact devices, and, assuming a criterion based on divertor impurity concentration, is in addition more favourable concerning the exhaust problem. However, in order to obtain attractive steady-state tokamak FPPs, the required plasma parameters still require considerable progress with respect to present experiments. A credible strategy to arrive at these must hence be shown for both paths. In addition, the high-field path needs a demonstration of the critical technology items early on. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

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Costley, A. E. "Towards a compact spherical tokamak fusion pilot plant." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2141 (February 4, 2019): 20170439. http://dx.doi.org/10.1098/rsta.2017.0439.

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The question of size of a tokamak fusion reactor is central to current fusion research especially with the large device, ITER, under construction and even larger DEMO reactors under initial engineering design. In this paper, the question of size is addressed initially from a physics perspective. It is shown that in addition to size, field and plasma shape are important too, and shape can be a significant factor. For a spherical tokamak (ST), the elongated shape leads to significant reductions in major radius and/or field for comparable fusion performance. Further, it is shown that when the density limit is taken into account, the relationship between fusion power and fusion gain is almost independent of size, implying that relatively small, high performance reactors should be possible. In order to realize a small, high performance fusion module based on the ST, feasible solutions to several key technical challenges must be developed. These are identified and possible design solutions outlined. The results of the physics, technical and engineering studies are integrated using the Tokamak Energy system code, and the results of a scoping study are reviewed. The results indicate that a relatively small ST using high temperature superconductor magnets should be feasible and may provide an alternative, possibly faster, ‘small modular’ route to fusion power. This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

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Yoo, Min-Gu, and Yong-Su Na. "Understanding the electromagnetic topology during the ohmic breakdown in tokamaks considering self-generated electric fields." Plasma Physics and Controlled Fusion 64, no. 5 (April 6, 2022): 054008. http://dx.doi.org/10.1088/1361-6587/ac5bb6.

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Abstract The physical mechanisms of the ohmic breakdown in a tokamak have been understood based on the classical Townsend avalanche theory. However, a new systematic theory (Yoo et al 2018 Nat. Commun. 9 3523) recently demonstrated that electron avalanches during the ohmic breakdown are completely different from the Townsend avalanche due to strong self-generated electric fields. In this study, we elucidate the multi-dimensional effects of the self-generated electric field on plasma dynamics during the ohmic breakdown. We also propose a novel electromagnetic topology analysis method that can easily predict the overall plasma behavior and where the main plasma is generated. The topology analysis method is validated by a state-of-art particle simulation for various magnetic configurations. New physical insights into the complex electromagnetic topology would facilitate designing more reliable and optimized ohmic breakdown scenarios in future tokamaks, such as ITER and beyond.

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Li, Yingying, Xianghui Yin, Bangxin Wang, Yi Zhang, Jia Fu, and Bo Lv. "Design of filter spectroscopy for the measurement of plasma ion temperature and rotation on the Experimental Advanced Superconducting Tokamak tokamak." Chinese Optics Letters 13, Suppl. (2015): S21202. http://dx.doi.org/10.3788/col201513.s21202.

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Dlougach, Eugenia, Mikhail Shlenskii, and Boris Kuteev. "Neutral Beams for Neutron Generation in Fusion Neutron Sources." Atoms 10, no. 4 (November 25, 2022): 143. http://dx.doi.org/10.3390/atoms10040143.

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Neutral beam injection is supposed to be the main source of high-energy particles, driving non-inductive current and generating primary neutrons in fusion neutron sources design based on tokamaks. Numerical simulation of high-energy particles’ thermalization in plasma and fusion neutron emission is calculated by novel dedicated software (NESTOR code). The neutral beam is reproduced statistically by up to 109 injected particles. The beam efficiency and contribution to primary neutron generation is shown to be dependent on the injection energy, input current, and plasma temperature profile. A beam-driven plasma operation scenario, specific for FNS design, enables the fusion rate and neutron generation in plasma volume to be controlled by the beam parameters; the resultant primary neutron yield can be efficiently boosted in plasma maintained at a relatively low temperature when compared to ‘pure’ fusion reactors. NESTOR results are applicable to high-precision nuclear and power balance estimations, neutron power loads distribution among tokamak components, tritium generation in hybrid reactors, and for many other tasks critical for FNS design.

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KOMOSHVILI, K., S. CUPERMAN, and C. BRUMA. "Plasma-turbulence suppression and transport-barrier formation by externally driven radiofrequency waves in spherical tokamaks." Journal of Plasma Physics 65, no. 3 (April 2001): 235–53. http://dx.doi.org/10.1017/s0022377801001015.

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Turbulent transport of heat and particles is the principle obstacle confronting controlled fusion today. We investigate quantitatively the suppression of turbulence and formation of transport barriers in spherical tokamaks by sheared electric fields generated by externally driven radiofrequency (RF) waves, in the frequency range ωA ∼ ω < ωci (where ωA and ωci are the Alfvén and ion cyclotron frequencies).This investigation consists of the solution of the full-wave equation for a spherical tokamak in the presence of externally driven fast waves and the evaluation of the power dissipation by the mode-converted Alfvén waves. This in turn provides a radial flow shear responsible for the suppression of plasma turbulence. Thus a strongly nonlinear equation for the radial sheared electric field is solved, and the turbulent transport suppression rate is evaluated and compared with the ion temperature gradient (ITG) instability increment.

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Razumova, Kseniya A. "Transport barrier formation in a tokamak plasma." Uspekhi Fizicheskih Nauk 171, no. 3 (2001): 329. http://dx.doi.org/10.3367/ufnr.0171.200103h.0329.

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LABIT, B., and M. OTTAVIANI. "Comparison between fluid electron-temperature-gradient driven simulations and Tore Supra experiments on electron heat transport." Journal of Plasma Physics 73, no. 2 (April 2007): 199–206. http://dx.doi.org/10.1017/s0022377806004466.

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Abstract.In recent years, much attention has been devoted to the electron-temperature-gradient (ETG) driven instability as a possible explanation for the high electron thermal conductivity found in most tokamaks. The present contribution assesses whether a specific three-dimensional fluid ETG model can reproduce the conductivity observed in the Tore Supra tokamak [Equipe Tore Supra (presented by R. Aymar) 1989 Plasma Physics and Controlled Nuclear Fusion Research (Proc. 12th Int. Conf., Nice, 1988, Vol. 1.) Vienna: IAEA, p. 9]. Although the model reproduces fairly well the observed critical gradient, a large discrepancy factor, of the order of 50, is found for the ratio between the experimental and the simulated conductivity. On the basis of this study, one must conclude that the electron heat transport cannot be explained only with a fluid ETG turbulence model.

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Мелузова, Д. С., П. Ю. Бабенко, А. Н. Зиновьев, and А. П. Шергин. "Моделирование ионного облучения кристаллических и аморфных мишеней --- материалов первой стенки токамака-реактора." Журнал технической физики 91, no. 12 (2021): 2038. http://dx.doi.org/10.21883/jtf.2021.12.51770.204-21.

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An overview of results concerning simulation of various processes which occur due to atomic bombardment of crystalline and amorphous solids is presented. With the use of original computational codes, the following data were obtained: reflection coefficients, projected energy losses and ranges of ions in solids, channeling data as well as sputtering yield and its dependence on incident angle of bombarding particles for Be-W and Ne-W combinations. Be, C and W targets were studied as these are among the plasma-facing materials in tokamaks, including ITER. The emphasis was made on atom-target combinations which lack reliable experimental data. Experimental data on other materials were used to verify calculations. A significant influence of the interaction potential used on the simulation results is shown. The reviewed results are tied by a common subject – a study of interaction of plasma ions and first-wall materials of a tokamak-reactor – and also by a common method of study – the use of an original computational code.

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Lewandowski, J. LV. "Radial structure of electron drift waves and anomalous transport in the edge plasma." Canadian Journal of Physics 77, no. 2 (June 1, 1999): 113–26. http://dx.doi.org/10.1139/p98-067.

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The radial structure of electron drift waves in a low-pressure tokamak plasma is presented. The ions are cold and an electrostatic approximation for the fluctuating potential is used. It is shown that the problem of the radial structure of drift waves in toroidal geometry is amenable to a two-step solution; in first approximation, the radial structure of the mode is neglected and the problem to be solved is the usual eigenmode equation along the (extended) poloidal angle; in second approximation, the mode amplitude is expanded in ascending powers of the parameter (k⊥Ln)-1/2 , where k⊥ is the magnitude of the lowest-order wavevector and Ln is the radial density scale length. It is shown that the radial structure of drift-type modes can depend strongly on the magnetic shear and the scalar magnetic curvature. Numerical calculations for plasma parameters relevant to the edge region of medium-size tokamaks are presented. PACS Nos.: 52.35Kt, 52.30Jb, and 52.35Ra

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Jardin, A., J. Bielecki, D. Mazon, J. Dankowski, K. Król, Y. Peysson, and M. Scholz. "Synthetic X-ray Tomography Diagnostics for Tokamak Plasmas." Journal of Fusion Energy 39, no. 5 (August 5, 2020): 240–50. http://dx.doi.org/10.1007/s10894-020-00250-9.

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AbstractTomography diagnostics represent an essential tool in tokamaks to infer the local plasma properties using line-integrated measurements from one or several cameras. In particular, soft X-rays (SXR) in the energy range 0.1–20 keV can provide valuable information on magnetohydrodynamic activity, magnetic equilibrium or impurity transport. Heavy impurities like tungsten (W) are a major source of concern due to significant radiation losses in the plasma core, thus they have to be kept under acceptable concentrations. Therefore, 2D SXR tomography diagnostics become crucial to estimate the W concentration profile in the plasma, quantify the W poloidal distribution and identify relevant impurity mitigation strategies. In this context, a synthetic diagnostic becomes a very valuable tool (1) to study the tomographic reconstruction capabilities, (2) to validate diagnostic design as well as (3) to assess the error propagation during the reconstruction process and impurity transport analysis. The goal of this contribution is to give some highlights on recent studies related to each of these three steps, for the development of SXR synthetic diagnostic tools in tokamak plasmas.

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Kurnaev, V. A., V. E. Nikolaeva, S. A. Krat, E. D. Vovchenko, A. V. Kaziev, A. S. Prishvitsyn, G. M. Vorob'ev, T. V. Stepanova, and D. S. Gvozdevskaya. "Systems of in situ diagnostics of plasma-surface interaction in MEPHIST-1 tokamak." Izvestiya vysshikh uchebnykh zavedenii. Fizika 64, no. 1 (2021): 118–24. http://dx.doi.org/10.17223/00213411/64/1/118.

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In the Institute for Laser and Plasma Technologies of NRNU MEPhI a compact spherical tokamak MEPhIST (MEPhI-Spherical Tokamak) for educational, demonstration and research purposes is under development and construction. The creation of plasma diagnostics systems involves several stages, determined by the successive complication of the plasma researchtasks, the upgrading of the device and the development of educational and methodological material for laboratory work to be put at the tokamak. Working out in situ methods of plasma-surface interaction analysis is one of the main scientific and technological goals of this tokamak. The complex of diagnostics described in the paper provides complementary information about the processes occurring at plasma with surface contact, is a set of very informative and well-tested diagnostic tools that allow students to obtain visual and reliable information about the processes occurring in the discharge chamber of the tokamak.

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Genco, Filippo, and Ahmed Hassanein. "Numerical simulations of laser ablated plumes using Particle-in-Cell (PIC) methods." Laser and Particle Beams 32, no. 2 (March 28, 2014): 305–10. http://dx.doi.org/10.1017/s0263034614000196.

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AbstractLaser ablation of graphite materials in the presence of an external magnetic field is studied with the use of the newly developed HEIGHTS-PIC particle-in-cell code and compared with both theoretical and experimental results. Carbon plumes behavior controlled by a strong magnetic field is of interest to evaluate the plume shielding effects to protect the original exposed target from further damage and erosion. Since intense power deposition on plasma facing components is expected during Tokamaks loss of plasma confinement events such as disruptions, vertical displacements event, runaway electrons, or during normal operating conditions such as edge-localized modes, it is critical to better understand the evolving target plasma behavior for more accurate prediction of the potential damage created by these high-energetic dumps which may not be easily mitigated without loss of structural and functional performance of the plasma facing components. Numerical experiments have been performed to provide benchmarking conditions for the HEIGHTS-PIC simulation package originally designed to evaluate the erosion of the Tokamak surfaces, splashing of the melted/ablated-vaporized material, and transport into the bulk plasma with consequent plasma contamination. Evolving target plasma temperature and density are calculated and compared with measured reported values available into literature for similar conditions and show good agreement with the HEIGHTS-PIC package predictions.

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Yuan, Fei Fei, Tao Xu, Tian Tian Qian, and Fan Zhang. "Research on Electromagnetic Engineering and Technology with Application of EFIT Code in J-TEXT Tokamak." Applied Mechanics and Materials 707 (December 2014): 364–67. http://dx.doi.org/10.4028/www.scientific.net/amm.707.364.

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The Grad-Shafranov equation is solved by EFIT code in J-TEXT tokamak. In this paper, it applies EFIT code to analyze the evolution of some plasma parameters during the discharge of J-TXET tokamak. Through plasmas balance calculation, the pressure of plasmas, internal magnetic surface and plasma current density profile are given. It provides important reference data for the operation and control of the J-TXET tokamak discharge.

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Zhu, Hongxuan, T. Stoltzfus-Dueck, R. Hager, S. Ku, and C. S. Chang. "Effects of collisional ion orbit loss on neoclassical tokamak radial electric fields." Nuclear Fusion 62, no. 6 (April 5, 2022): 066012. http://dx.doi.org/10.1088/1741-4326/ac5b8a.

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Abstract Ion orbit loss is considered important for generating the radially inward electric field E r in a tokamak edge plasma. In particular, this effect is emphasized in diverted tokamaks with a magnetic X point. In neoclassical equilibria, Coulomb collisions can scatter ions onto loss orbits and generate a radially outward current, which in steady state is balanced by the radially inward current from viscosity. To quantitatively measure this loss-orbit current in an edge pedestal, an ion-orbit-flux diagnostic has been implemented in the axisymmetric version of the gyrokinetic particle-in-cell code XGC. As the first application of this diagnostic, a neoclassical DIII-D H-mode plasma is studied using gyrokinetic ions and adiabatic electrons. The validity of the diagnostic is demonstrated by studying the collisional relaxation of E r in the core. After this demonstration, the loss-orbit current is numerically measured in the edge pedestal in quasisteady state. In this plasma, it is found that the radial electric force on ions from E r approximately balances the ion radial pressure gradient in the edge pedestal, with the radial force from the plasma flow term being a minor component. The effect of orbit loss on E r is found to be only mild.

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Medvedev, S. Yu, A. A. Martynov, V. K. Gusev, Yu V. Petrov, M. I. Patrov, A. Yu Tel'nova, A. A. Ivanov, and Yu Yu Poshekhonov. "COMPUTATIONS OF TOROIDAL ALFVÉN MODES IN SPHERICAL TOKAMAK GLOBUS-M PLASMAS." Problems of Atomic Science and Technology, Ser. Thermonuclear Fusion 41, no. 2 (2018): 95–104. http://dx.doi.org/10.21517/0202-3822-2018-41-2-95-104.

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Kumawat, Devilal, Kumudni Tahiliani, Suresh I, S. K. Pathak, Santosh P. Pandya, Sameer Kumar, Raju Daniel, et al. "First results of fast visible imaging diagnostic in Aditya-U tokamak." Review of Scientific Instruments 93, no. 11 (November 1, 2022): 113548. http://dx.doi.org/10.1063/5.0101795.

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A Fast Visible Imaging Diagnostic (FVID) system, measuring the visible light emission spectrum (400–1000 nm) from tokamak plasma, has been installed on the Aditya-U tokamak to monitor the two-dimensional dynamics of the poloidal cross section of the plasma. In this work, we present the design and installation of the FVID system on the Aditya-U tokamak. The evolution of plasma and plasma–wall interactions is described. The signature of the runaway electron beam in visible imaging and its correlation with other diagnostics is presented. The estimation of the electron cyclotron resonance layer position during pre-ionization is also discussed in this work.

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Journal articles on the topic 'Plasmi in tokamak'

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