A magnetosonic shock wave propagating obliquely to an external magnetic field can trap and accelerate electrons to ultrarelativistic energies when v_sh is close to ccosθ, where v_sh is the propagation speed of the shock wave, c is the light speed, and θ is the propagation angle of the shock wave. Because of instabilities driven by the trapped electrons, some electrons can be detrapped from the main pulse retaining their high energies and can then be further accelerated to higher energies as a result of their gyromotions. The dependence of electron motions on the parameters v_sh and θ is investigated by two-dimensional electromagnetic particle simulations with full ion and electron dynamics. If θ is fixed, electron energies become maximum when v_sh is slightly smaller than ccosθ. If the value of v_sh/(ccosθ) is fixed, the maximum energy of electrons tends to increase with decreasing θfor the range v_sh/(ccosθ) < 1. The number of electrons that are detrapped to the upstream region and suffer the subsequent acceleration is also examined.

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We have numerically solved the two-dimensional time-dependent Schödinger equation for a magnetized proton in the presence of a uniform electric field and a nonuniform magnetic field with a gradient scale length of L_B. It is shown that the particle mass and the electric field do not affect the time rate of variance change at which variance increases with time, and their characteristic times are of the order of L_B/v₀ sec with v₀ being the initial particle speed.

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Shock formation due to interactions between exploding and surrounding plasmas and evolution of modified two-stream instabilities are studied using two-dimensional (2D) electromagnetic particle simulations. After the exploding ions penetrate the surrounding plasma, a strong magnetic-field pulse forms near the front of the exploding plasma. Because of modified two-stream instabilities, electromagnetic fluctuations grow to large amplitudes in this pulse. At Ω_it ≃ 1, where Ω_i is the ion cyclotron frequency, the pulse starts to reflect ions and to split into two pulses, which then develop into forward and reverse shock waves. For various values of the initial exploding plasma velocity and of the angle between the velocity and external magnetic field, 2D simulations are performed. The parametric dependence of the properties of the generated pulses and of magnetic fluctuations is discussed.

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A collapse of the X-point occurs above a critical island width, Δ'w_c , in the resistive tearing mode for large instability parameter, Δ', leading to current sheet formation [N.F. Loureiro et al. Phys. Rev. Lett. 95, 235003 (2005)]. In this study, we analyze this problem by including viscosity effects on the onset of the X-point collapse and the explosive nonlinear growth dynamics of the reconnected flux. While explosive growth seems to be independent of viscosity in the magnetic Prandtl number regime Pr < 1, a transition behavior is revealed at Pr ≈ 1 for the viscosity dependence of Δ'w_c , for the X-point collapse as well as the linear tearing instability. A secondary instability analysis, which included quasi-linear modifications of the equilibrium current profile due to the zonal current, shows that current peaking is plausibly responsible for the onset of the X-point collapse and the explosive growth of reconnected flux, which leads to the current sheet formation.

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The eXtended Boundary Node Method (X-BNM) with the periodic Radial Point Interpolation Method (RPIM) shape function is proposed and its performance is investigated numerically. The results of computations show that the accuracy of the X-BNM with the periodic RPIM shape function is almost equal to that with the Moving Least-Squares (MLS) shape function. In addition, the speed of the X-BNM with the periodic RPIM shape function is extremely faster than that with the MLS shape function. Therefore, the periodic RPIM shape function is useful for improving the performance of the X-BNM.

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Electron energy distribution measurement with oscillating plasma potential compensation was performed in the radio-frequency plasma device, DT-ALPHA. Electrons near the plasma production region are confirmed to have Maxwellian distribution. The radial profile of the electron energy distribution in the high neutral pressure region, which is maintained by secondary helium gas puffing, was also investigated. Whereas the electrons still have Maxwellian distribution, the electron temperature in the outer region of the plasma column is lower compared with the inner region. This indicates that the volumetric recombination is enhanced at the periphery of the gas target experiment in the DT-ALPHA device.

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The micellar shape transition in amphiphilic solutions is studied by coarse-grained molecular dynamics simulations of rigid amphiphilic molecules with explicit solvent molecules. Our simulations show that the dominant micellar shape changes from disc to cylinder, and then to sphere as the hydrophilic interaction increases. We find that, as the hydrophilic interaction increases, the potential energy decreases monotonically even during the micellar shape transition, whereas the slope of the potential energy decreases in a stepwise manner in relation to the micellar shape transition. We also ascertained that there exists a wide coexistence region in the intensity of the hydrophilic interaction between a cylinder and a sphere, whereas the coexistence region between a cylinder and a disc is very narrow.

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As the capability of a supercomputer is improved, the sizes of simulation and its output data also become larger and larger. Visualization is usually carried out on a researcher’s PC with interactive visualization software after performing the computer simulation. However, the data size is becoming too large to do it currently. A promising answer is in-situ visualization. For this case a simulation code is coupled with the visualization code and visualization is performed with the simulation on the same supercomputer. We developed an in-situ visualization tool for particle-in-cell (PIC) simulation and it is provided as a Fortran’s module. We coupled it with a PIC simulation code and tested the coupled code on Plasma Simulator supercomputer, and ensured that it works.

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A dense plasma focus device can produce dense and high energy plasma in a short time. Recently, it has been proposed that the device could be applied to fusion for clean energy production (focus fusion). In order to understand the behavior of the plasma current filaments in the device, two-dimensional, relativistic, fully electromagnetic, particle-in-cell simulations were performed. Sixteen plasma current filaments were initially located on the edge of a circle in our model. They begin to interact with each other while pinching, and then coalesce in the vicinity of the center of system. In the pinch phase (during the coalescence), there appears dense plasma, whose maximum number density is 10 times larger than the initial value. The ions are accelerated, but the rate of the number of them is somewhat small. After that, the current becomes unstable and jumps out from the center. These results are useful for understanding the coalescence process of current filaments.

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Using a dissipation-scale adaptive, wavelet-like shell decomposition method and normalization by dissipation-scale characteristics, we found a novel sustaining behavior of self-similarity in the quadratic energy transfer process in freely decaying, fully developed, homogeneous and isotropic turbulences of an incompressible Hall magnetohydrodynamic medium. The process is associated with the relative reduction of nonlinear energy transfer in the dissipation range, which was reported in our previous study [K. Araki and H. Miura, Plasma Fusion Res. 8, 2401137 (2013)]. Gradual reductions in energy transfers by fluid advection and the Hall-term effect are compensated by enhancement of energy transfers due to mutual interactions between velocity and magnetic fields, i.e. between the Lorentz force effect and magnetic induction. This sustaining behavior suggests that coupling between velocity and magnetic fields may be crucial, even when linear dispersive waves aroused by a uniform background magnetic field are absent.

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The two-dimentional meshless time-domain method (2D-MTDM) was used to simulate the electromagnetic wave propagation phenomena in complex-shaped waveguides considering the influence of metals and to numerically investigate the relation of the dispersion medium with the attenuation rate. The simulation results suggest that the waveguide with grooves is strongly affected by the frequency of the propagating wave than the waveguide without grooves because the wave propagating in the waveguide with the grooves penetrates deep into the metal compared with the waveguide without grooves. The transmission loss for the curved waveguide is greater than that for the straight waveguide.

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We propose a TOKI (Time Order, Kinetic, and Irreversible) compression method for recording smooth trajectories of particles from PIC (electromagnetic particle-in-cell) simulations. In a TOKI compression, instead of storing entire time sequences of particle positions, we store particle trajectories in terms of coefficients of approximating polynomials. In the current implementation, these coefficients are determined either by the least-squares method or by the Chebyshev approximation formula to obtain quasi-minimax polynomials. In this paper, we present the technique of TOKI compression and compare it with other lossy compression schemes, such as XTC. Comparisons are made using data from a PIC simulation for 150,000 electrons and 150,000 ions. For smooth trajectories, the compression ratio by TOKI is better than that by the XTC format. However, for ballistic trajectories, the compression ratio by TOKI is not good because of the significant overhead in storing raw values of trajectories. We also found that the compression efficiency for ion trajectories is better than that for electron trajectories. This is attributed to different characteristic time scales of motions due to the difference in mass. We expect that the behavior of the compression ratio in TOKI can be used to characterize motions of plasma particles.

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To speed up electromagnetic wave propagation simulations using the meshless time-domain method (MTDM) in complex shaped domains, this paper presents a strategy for embedding the modified radial point interpolation method (MRPIM)-based shape functions to MTDM, while maintaining the stability of the simulations. Numerical experiments show that, by using the strategy with appropriate parameters, the stability of the simulations using MTDM with MRPIM-based shape functions (MRPIM-MTDM) is considerably improved. In addition, the approach of the amplification/damping rate to convergence in MRPIM-MTDM is almost the same as that in the conventional MTDM. Furthermore, the total computation time of MRPIM-MTDM is less than that of the conventional MTDM.

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We calculated the binding and migration energies of mono-vacancies and di-vacancies in tungsten material using density functional theory. Mono-vacancies diffuse in the [111] direction easier than in the [001] direction. The migration energies of mono-vacancies and di-vacancies are almost the same; moreover, the migration of mono-vacancies and di-vacancies is nearly similar. The di-vacancy binding energies are almost zero or negative. The interactions between two vacancies in tungsten material are repulsive from the second to the fifth nearest neighbors. The vacancies are difficult to aggregate because di-vacancies are less stable than mono-vacancies.

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Single and multiple charge transfer cross sections for Ne^q+ (q = 2 - 6) ions were measured in collisions with Ne, Ar, Kr, and Xe atoms at 2q keV. Quintuple charge transfer cross sections σ_6,1 were derived for the Ne⁶⁺ + Ne, Ar, and Xe collisions. In Ne atoms, the double, triple, and quadruple charge transfer of Ne²⁺, Ne³⁺, and Ne⁴⁺ ions, respectively, represent so-called symmetric resonant charge transfer processes. The present data for these collisions are in good accordance with the previous data. The scaling properties of the total, single, and multiple charge transfer cross sections were examined, and it was found that the double, triple, and quadruple charge transfer cross sections can be scaled using the second, third, and fourth ionization potentials, respectively.

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We have developed a simulation code based on the percolation model to understand the stochastic behavior of discharge, which is observed in natural phenomena such as lightning as well as experimental discharges used for light sources and environmental technologies. We have developed a model of ionization and attachment to determine the distribution of ionized region in the gas, and carried out calculation of spatial and temporal evolution of discharge in SF₆. In addition, we discuss computational algorithms used to analyze the structure of the ionized region and its statistics in the plasma. The work presented in this article will also be useful for analyzing properties of the plasmas with spatially non-uniform structure.

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The inductive method for measuring the critical current density in a high-temperature superconducting (HTS) film has been reproduced numerically. To this end, a numerical code has been developed for analyzing the time evolution of a shielding current density in an HTS film containing a crack. The of computational results show that the accuracy of the inductive method monotonously increases with the height of the coil. In addition, the accuracy is slightly improved by changing the inner radius of the coil, and there exists the optimum inner radius. Although the accuracy is degraded due to the crack, this result means that the inductive method can be applied to the crack detection. Consequently, the crack located near the film edge cannot be detected with high accuracy because the crack is treated the same as the film edge.

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The finite difference time domain method (FDTDM) is a robust numerical scheme for time-dependent electromagnetic wave propagation phenomena that uses orthogonal meshes, like staggered meshes, also known as Yee lattices. However, treating complex shaped domains is challenging for the FDTDM. Meshless methods, in contrast, do not require meshes for a geometrical structure. The meshless time domain method (MTDM), based on the radial point interpolation method, can be used for numerical simulations in computational electromagnetics. In MTDM, shape functions have to be generated before the time-dependent calculation, and the computational cost involved can be very large. We herein propose a new method for reducing the computational cost of generating shape functions and we confirm the effectiveness of the proposed method by numerical experiments.

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An integrated transport analysis suite, TASK3D-a, has been developed with the emphasis on establishing close-link with the LHD experiment database. The suite makes possible energy transport analyses for huge cases, from which the systematic understandings can be elucidated. A statistical approach for implementing large-scale simulation results into the integrated modelling has been tested. The importance of strengthening trilateral links among experiments, large-scale simulations, and integrated numerical modelling tools such as TASK3D, is crucial for promoting systematic understandings, performing validations, and then increasing the predictive capabilities.

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The concept of digital correlation electron cyclotron emission (ECE) measurement is proposed for studying of the mesoscale phenomena. The recent progress in fast sampling and computing enables the acquisition of waveforms of intermediate frequency (IF) in the range of several gigahertz. Correlation analysis using an IF digitizing technique can be helpful for analyzing mesoscale phenomena. This paper discusses the concept and characteristics of the IF digitizing technique for correlation analysis, and presents an example of IF waveform acquisition of ECE.

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The physical confinement properties of stellarators are analyzed for the neo-classical transport and the magnetic well. Three typical concepts of stellarators (LHD, Wendelstein 7-X and TJ-II) are compared in terms of the helical movement of cross sections of the last closed magnetic surface. It is shown that this geometric element strongly determines the confinement properties of both non-planar axis and planar axis stellarators.

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The InfraRed imaging Video Bolometer (IRVB) is a powerful diagnostic to measure a plasma radiation profile especially for three-dimensional measurements. An IRVB mainly consists of a pinhole camera section and an IR camera section. The plasma radiation profile is projected on a thin metal foil through an aperture in the pinhole camera resulting in a two-dimensional temperature distribution. Then, the distribution is observed from the back side by an IR camera as an IR image. Since the image contains the effects of heat diffusion, a calibration of the heat characteristics of the foil is needed to obtain the radiation profile by solving the two-dimensional heat diffusion equation. Some deposition was observed on the foil in the Large Helical Device (LHD) plasma experiment. The effect of this on the heat characteristics of the foil should be studied although it can be compensated for by the calibration. Currently four IRVBs are operating in LHD to investigate the radiation collapse and plasma detachment phenomena. The sensitivities of IRVBs at the 6.5-L and 10-O ports were improved from the experimental campaign in FY 2013 by replacing the IR cameras of these ports. The sensitivity at the 6.5-U port was also improved by applying the periscope system.

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One of the purposes of the UTST device is to demonstrate of magnetic reconnection heating using external coils to conduct field line merging. In order to measure the ion heating, a Doppler spectroscopy system was developed. By increasing the reconnection magnetic field to 17 mT from 4 mT after the UTST upgrade, the ion heating was observed for the first time in the UTST reconnection experiments. The ion temperature increased to 50 eV from 15 eV due to reconnection during the plasma merging.

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RF magnetic probes can be used to measure not only the wavevector, but also the polarization of waves in plasmas. A 5-channel RF magnetic probe (5ch-RFMP) was installed in the TST-2 spherical tokamak and the waves were studied in detail during lower hybrid wave injection experiments. From the polarization measurements, the poloidal RF magnetic field is found to be dominant. In addition to polarization, components of k perpendicular to the major radial direction were obtained from phase differences among the five channels. The radial wavenumber was obtained by scanning the radial position of the 5ch-RFMP on a shot by shot basis. The measured wavevector and polarization in the plasma edge region were consistent with those calculated from the wave equation for the slow wave branch. While the waves with small and large k_∥ were excited by the antenna, only the small k_∥ component was measured by the 5ch-RFMP; this suggests that the waves with larger k_∥ were absorbed by the plasma.

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A multichannel far-infrared (FIR) laser interferometer is being developed for the helical-axis heliotron device Heliotron J with asymmetrical poloidal cross-section to study high-density plasma. Due to the shape of the cross-section, a new density reconstruction method based on the regularization technique was investigated for obtaining the electron density profile from the line-integrated density. For this purpose, the regularization parameter was optimized and determined by the generalized cross-validation (GCV) function and singular value decomposition (SVD). The reconstruction results show that the reconstructed profiles can be improved by carefully considering the beam position arrangement. The optimum beam arrangement is discussed in detail.

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Electrode biasing experiments were carried out in the Tohoku University Heliac (TU-Heliac) to investigate the role of ion viscosity maxima in the L-H transition. To investigate the relation between ion viscosity and poloidal Mach number, the driving force of the poloidal rotation and poloidal rotation velocity must be normalized by the ion temperature T_i and ion pressure P_i. Doppler spectroscopy was used to directly measure the ion temperature and the poloidal rotation velocity. Therefore, the dependence of the ion temperature and poloidal rotation velocity on the electrode current was obtained. The relation between the normalized driving force of the poloidal rotation and the poloidal Mach number M_p was non-linear. Bifurcation phenomena in the poloidal rotation appeared at M_p ∼−3. These results qualitatively agreed with the neoclassical theory.

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To improve capability of tokamak plasma equilibrium control in TOKASTAR-2, a pair of pulsed vertical field coils (PVF coils) was installed in 2012. Optimization of PVF coil current waveform was made with re-calculation using TOSCA code in varying the conditions of tokamak discharge. Then, simulation of the electric circuit of PVF coil system with LTspice code was done to find the optimum capacitance and charging voltage of capacitor for PVF coils consistent to the optimal current waveform. Eventually capacitor parameters for PVF coils to be used as base for experiment were obtained.

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High energy particles’ behavior including fusion born alpha particles in an ITER like tokamak in the presence of background driftwave turbulence is investigated by an orbit following calculation. The background turbulence is given by the toroidal driftwave eigenmode combined with a random number generator. The transport level is reduced as the particle energy increase; the widths of the guiding center islands produced by the passing particles are inverse proportional to the square root of parallel velocities. On the other hand, the trapped particles are sensitive to E ×B drift at the banana tips whose radial displacement is larger for lower energy particles. Coulomb collisional effects are incorporated which modifies the transport process of the trapped high energy particles whose radial excursion resides in limited radial domains without collisions.

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An effect of nuclear plus interference (NI) scattering on D(d,n)³He, T(d,n)⁴He and ³He(d,p)⁴He reaction rate coefficients in ³He-containing deuterium plasma is evaluated on the basis of the Boltzmann-Fokker-Planck (BFP) analysis model. An energetic ³He beam and/or externally-fueled low-energy ³He enhance the ³He(d,p)⁴He reaction rate from the value for Maxwellian plasma, and increase energetic proton production rate. The energetic protons create the knock-on tail via NI scattering on the fuel-ion velocity distribution functions. It is shown that a recognizable change in the rate coefficients of fusion reactions due to the knock-on tail formation appears.

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Detached (from the divertors) plasma regime is a very important operational phase for future fusion device operation and is sustained in the Large Helical Device (LHD) by applying an m/n = 1/1 resonant magnetic perturbation (RMP). The radiation from the plasma is found to be localized near the X-point of this RMP during plasma detachment which is confirmed both by the EMC3-EIRENE edge impurity transport code and experiments. This agreement motivates the establishment of a comparison between the results from the transport model and InfraRed imaging Video Bolometer (IRVB) experiments. A synthetic instrument has been developed which can simulate the radiation by tracing the sight lines through the three dimensional carbon impurity radiation results of the EMC3-EIRENE, giving a synthetic image. These synthetic images can be compared with the IRVB image obtained experimentally. Such a comparison is attempted here for two IRVBs installed on LHD for the data from the 2012 and 2013 experimental campaigns. The comparison reveals a fair amount of qualitative agreement but quantitative disagreement among both the approaches. Probable causes for the disagreement are discussed and corrective measures are suggested.

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A local current diagnostic using a small Rogowski coil was developed in the TST-2 spherical tokamak device (R = 0.38 m, a = 0.25 m, B_t = 0.3 T, I_p = 0.1 MA). A Rogowski coil is a cost effective tool for local current diagnostic that can detect the current signal directly. A new small Rogowski coil (outer diameter = 20 mm, inner diameter = 12 mm, number of turns = 360) with small sensitivity to external magnetic fields, such as B_t and B_p, was developed and successfully installed in the TST-2. The measured local current at the edge just inside the last closed flux surface for ohmic heating was about 15 A.

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In present day devices, the external kink ideal MHD instability establishes hard operational boundaries for both the tokamak and the Reversed Field Pinch (RFP) configurations. An interesting feature of it is that its growth rate critically depends on the device passive boundary characteristics and this can slow it down to time scales accessible to modern real time feedback control systems, normally using external active coils as actuators. 3D passive structures and external fields play a key role in determining physics and control of this instability. This is in particular true for equilibria with multimodal unstable RWM spectra where modes can couple to specific 3D features of passive and active magnetic boundary. In the paper we will present recent data and simulations from RFX-mod, a medium size (R = 2 m, a = 0.459 m) device able to confine RFP and tokamak plasmas with currents up to 2 MA and 120 kA, respectively. Successful quantitative modeling of multimodal RWM control experiments performed using different actuator configurations will be presented and commented.

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The effect of the electron temperature T_e on the plasma current decay after the mini-collapse was investigated for the disruption in JT-60U owing to a massive neon gas puff by using the disruption simulation code DINA. During the current quench in JT-60U, the fast electron temperature decrease is followed by a transient plasma current increase. This is called “mini-collapse”, typically occurring when the plasma current decreases to 80 - 90 % of its value at the flattop phase. The plasma evolution after the mini-collapse was investigated using the DINA code for three assumed T_e profiles: flat, broad, and peaked profiles. The time evolution of the plasma current, plasma center position, plasma cross section, and vacuum vessel current were not found to be sensitive to the T_e profile after the mini-collapse. The plasma current after mini-collapse decreased owing to the plasma resistance, although it was previously found that the plasma current decrease during the initial phase of current quench was owing to the time derivative of the plasma inductance [Y. Shibara et al., Nucl. Fusion 50, 025065 (2010)].

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In this paper, results of spectral measurement in the end-cell of the GAMMA 10/PDX are described. A spectral measurement system consisting of two spectrometers was developed in order to measure the detailed radiation behavior in D-module. Firstly, angular dependence of the V-shaped target plate on the spatial distribution of the Hα radiance was investigated. It is found that the spectral distribution in Hα intensity along the axial direction is affected by the angle of the target plate. Next, in the experiment with H₂ and Ar gas injection, primary 17 line spectra of Ar I were identified and the radiation loss from Ar neutrals was also evaluated from intensity of spectra. A correlation between the power of radiation loss and the electron temperature in D-module are recognized. The correlation between radiation power and electron temperature is also discussed from the view point of radiation cooling.

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High β_p (εβ_p ∼ 1) equilibria obtained in a ECW heated Ohmic plasma is investigated using a simple analytic solution of Grad-Shafranov equation. The formation of a natural inboard poloidal null associated with high β_p is explained consistently by high diamagnetism and negative triangularity. As β_p is increased, the poloidal null point penetrates further into the vacuum vessel, which is qualitatively explained by the analytic model. Transition from inboard (high field side) limiter bound to the natural divertor configuration is associated with a reduction of the edge safety factor without appreciable enhancement of MHD activities. Such a scenario is also addressed successfully with the model.

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In this study, using a scintillator-based lost fast-ion probe, we have measured fast-ion losses in the Large Helical Device, in which the losses were caused by externally applied static magnetic perturbations (MPs) having small amplitudes. Energy and pitch-angle resolved measurements reveal that the effects of MPs on fast-ion losses occur in both high and low pitch-angle regions. A Lorentz orbit-following calculation indicates that static MPs can change the orbits of fast ions, which can enhance the transport/loss of fast ions.

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Development of high power gyrotrons and electron cyclotron heating (ECH) systems for the power modulation experiments in GAMMA 10 have been started in order to generate and control the high heat flux and to make the ELM (edge localized mode) like intermittent heat load pattern for divertor simulation studies. ECH for potential formation at plug region (P-ECH) produces electron flow with high energy along the magnetic filed line. By modulating the ECH power, we can obtain arbitrary pulse heat load patterns. By changing the on/off timing, we can simulate the ELM intermittent heat pulses. The heat flux factor increases almost linearly with ECH power. An intense axial electron flow with energy from hundreds of eV to a few keV generated by fundamental P-ECH is observed. When ECH is turned off, a short burst appears in the end loss ion current due to the axial drain of the confined plasma.

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In the GAMMA 10/PDX tandem mirror device at the University of Tsukuba, divertor simulation experiments were conducted for realizing detached plasma. A divertor simulation experimental module (D-module), in which a V-shaped target is mounted, was installed in the west end-cell of GAMMA 10/PDX. The spatial distribution of the heat flux was measured with calorimeters on the V-shaped target under target angle conditions of 30^◦, 45^◦ and 60^◦. The spatial distribution depends on the structure of magnetic field in the end-cell. The heat flux depended on the gas species and the amount of gas injection was also investigated. With increasing Ar gas pressure, the ion flux decreased by approximately a factor of four, whereas the heat flux decreased by three fifths.

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Microwave imaging reflectometry (MIR) and electron cyclotron emission imaging (ECEI) systems have been developed on the HL-2A tokamak to visualize the density and temperature fluctuations. The MIR system is comprised of a quasi-optical system, a four frequency microwave source and receiver system that generate 8(poloidal) × 4(radial) × 2(toroidal) = 64 channel images of density fluctuations. The ECEI system is comprised of a quasi-optical system, a front-end 24 channel heterodyne imaging array with a tunable RF from 75 to 110 GHz,and a set of back-end ECEI electronics that together generate 24(poloidal) × 8(radial) = 192 channel images of the 2D temperature fluctuations. Characteristics of both systems are presented. Simulations and laboratory tests of both optical systems have been conducted. The test results are in good agreement with simulations.

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In experiments on electron cyclotron resonance (ECR) heating of plasma at the second harmonic of the electron gyrofrequency in the L-2M stellarator, the effect of partial reflection of high-power gyrotron radiation from the ECR heating region located in the center of the plasma column have been revealed. The reflection coefficient is found to be on the order of 10⁻³. The coefficient of reflection of an extraordinary wave from the second-harmonic ECR region is calculated in the one-dimensional full-wave model. The calculated and measured values of the reflection coefficient are found to coincide in the order of magnitude.

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The life time of trapped ion granulations (trapped ions correlated by resonance) in sheared flows is calculated. The dynamics of trapped ion granulations, in the presence of sheared flows, is formulated in terms of two point correlation function of phase space density fluctuations. The evolution equation is closed by a simplified closure calculation of the triplet term. Based on the closed equation, the life time of the relative dispersion of trapped ion granulations is calculated. The result shows that i.) a relevant time scale enters via a hybrid of decorrelation and shearing, (Δω_cv'_y²)^1/3 and ii.) small scale singularities in the absence of collisional dissipation enters through logarithmic divergence.

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Operation and exploitation of present and future Tokamak reactors require advanced scenario modeling in order to optimize engineering parameters in the design phase as well as physics performance during the exploitation phase. The simulation of Tokamak scenarios involves simultaneous modeling of different regions of the reactor, characterized by different physics and symmetries, in order to predict quantities such as particle and energy confinement, fusion yield, power deposited on wall, wall load from fast particles. JINTRAC is a system of 25 interfaced Tokamak-physics codes for the integrated simulation of all phases of a Tokamak scenario. JINTRAC predictions reflect the physics and assumptions implemented in each module and extensive comparison with experimental data is needed to allow validation of the models and improvement of Tokamak-physics understanding.

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To study toroidal rotation shear effect on Resistive Wall Mode (RWM) stability, kinetic RWM formulation is extended to include general equilibrium rotation. By starting from the guiding-center Lagrangian with sheared rotation, an energy functional of kinetic resonance is generalized. Based on the generalized energy functional, a new dispersion relation is derived in the large aspect ratio limit. Numerical analysis of the new dispersion relation indicates that the rotation shear can reduce the growth rates of the RWMs.

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The simulation study of nonlocal transport for peripheral density source is performed using the 4-field reduced MHD model. A spherical density source is applied in the plasma edge, after saturation of the resistive ballooning turbulence is attained. After a while, the source is switched off. It is found that the nonlocal transport appears at the location far from the edge source, which induces not only (0,0) and (±1,0) modes but also finite n modes, where (m, n) indicates the set of poloidal mode number m and the toroidal mode number n. These modes interact with each other by the nonlinear and/or toroidal couplings. After switching-on the source, the formation of the spiral structure with poloidal rotation is observed, which yields a connection between core and edge regions. The simulation result indicates that 2D transport plays an essential role to the transient plasma response.

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A magnetohydrodynamic equilibrium control simulator (MECS) has been developed to study the techniques of plasma equilibrium control in JT-60SA. The new modules of the plasma shape reconstruction, power supply, and simulated poloidal field coils are incorporated into MECS to simulate plasma equilibrium control considering the power supply capability and the influence of the identification error between the actual and reconstructed plasma boundary, just as in a real plasma experiment. The MECS uses the Cauchy condition surface (CCS) method for plasma shape reconstruction. Plasma equilibrium control is demonstrated during the heating phase along with the CCS method and power supply capability.

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The sawtooth oscillation is one of the important instabilities driven by the plasma current in tokamak plasma. The sawtooth period is a key parameter that characterizes the effect of the sawtooth oscillation on the plasma behavior. For prediction of sawteeth in burning plasma, the sawtooth model in the 1.5-dimensional transport code TOTAL has been extended to include the effects of fast particles and the magnetic shear. By using the newly implemented model, we simulated sawteeth in the presence of the alpha particles as the fast ion in ITER. It is found that the sawtooth periods in DT plasma are longer than those in DD plasma. In DT plasma, the sawtooth period doesn’t change monotonically but has a peak as a function of the average central ion temperature or the RF heating power. This is because the mechanisms of triggering sawteeth are different in the low RF heating power region and in the high RF heating power region.

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Magnetohydrodynamic (MHD) instabilities driven by energetic alpha particles and beam deuterium particles are investigated for ITER operation scenarios using a hybrid simulation code for energetic particles interacting with an MHD fluid. The particle simulation method with finite Larmor radius effects is applied to both alpha and beam deuterium particles. For the steady-state scenario with 9 MA plasma current, beta-induced Alfvén eigenmodes (BAE modes) with low toroidal mode number (n = 3, 5) were found to become dominant in the nonlinear phase although many toroidal Alfvén eigenmodes (TAE modes) with n ∼ 15 are most unstable in the linear phase. The redistribution of energetic particles with δβ_α ∼ δβ_beam ∼ 0.07%, which respectively correspond to 6% and 8% of the central values, occurs in the nonlinear phase. When the toroidal mode number of the fluctuations is restricted to n ≤ 8, the redistribution is substantially reduced, thus, suggesting that the resonance overlap between the n ∼ 15 TAE and low-n BAE modes enhances the energetic particle transport in the run with full toroidal mode numbers. For the ITER scenario with 15 MA plasma current, an MHD instability with n = 3 that peaks around the q = 1(q is the safety factor) magnetic surfaces is driven by bulk plasma current and bulk pressure, and results in significant redistribution of alpha particles with δβ_α ∼ 0.3%. For the equilibrium profile with the safety factor profile uniformly raised by 0.1 to remove the q = 1 surfaces, only a benign MHD instability occurs and the energetic particle transport is negligible.

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Huge power handling in the SOL/divertor region is one of the crucial issues for a tokamak fusion reactor. Divertor design study of a DEMO reactor with fusion power of 3 GW and ITER size plasma has progressed using the integrated divertor code SONIC. Recently, to improve conversion of the solution for the DEMO divertor plasma simulation, SONIC code has been improved. The calculation time is significantly reduced by (i) the backflow model for the simplified impurity exhaust process and (ii) optimization on HELIOS at BA-IFERC. In the SONIC simulation, the partial detached divertor plasma was obtained by the Ar impurity seeding. Although the plasma heat load at the outer target was reduced by the partial detachment, the contribution of the impurity radiation and the surface recombination of the fuel ions to the target heat load became large. As a result, the peak of the total target heat load was estimated to be 16 MW/m². In order to reduce the total heat load, control of the impurity radiation profile by kind of seeding impurity species and the divertor geometry has been studied. They can decrease the target heat load, but the peak heat load is still larger than the heat removal capability of the present divertor target concept. Further design study including change of the machine specifications is necessary.

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An energetic particle Landau-fluid closure model (TAEFL) is applied to a case where both RSAE (Reversed Shear Alfvén Eigenmode) and TAE (Toroidal Alfvén Eigenmode) modes are destabilized by beam ions. The nonlinear evolution of the coupled modes are followed for about 10⁴ Alfvén times under the simplifying assumptions that a density source is present that exactly balances the quasi-linear fast ion profile changes driven by the instabilities. Saturation is achieved via self-regulation/organization through zonal flows and currents. A quasi-stationary nonlinear state persists, which is characterized by repetitive predator-prey phenomena. As the mode grows, it drives zonal flows/currents, these quench its amplitude until the linear mode structure sets in again and grows, driving further zonal flows/currents, etc. This capability of following nonlinear fast ion-driven instabilities over longer time intervals (achieved here by using a higher order time-stepping method) is an important requirement for future integrated models of burning plasmas.

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We studied the optimization of the magnetic configuration for the LHD-type fusion energy reactor (FFHR). We propose thin and flat helical coil systems, which are partitioned to three blocks with independent current value control, to satisfy the following requirements: (1) sufficient blanket space and large plasma volume under the helical coils with appropriate major radius and (2) divertor legs with little disorder that turn to the back of the helical coils. The cross-section of the plasma boundary changes from elliptical to racetrack-type. By extending the coil height, the coil current density of the central block for helical coil is observed to decrease gradually.

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