Reduction of interstitial impurities such as nitrogen (N) and oxygen (O) improves the mechanical properties of V-4Cr-4Ti alloys. Yttrium (Y) addition effectively reduces O content by Y₂O₃ slag-out on the melting ingot surface. The effects of Y addition on mechanical properties were investigated for V-4Cr-4Ti with N ranging from 0.009 to 0.29 mass% and O ranging from 0.009 to 0.36 mass%. The increase in yield stress (YS) and ultimate tensile stress (UTS) for vanadium alloys was saturated above 0.1 mass% in O content, because Ti precipitates increased with increasing O content regardless of Y addition. Y addition had little effect on YS and UTS of V-4Cr-4Ti alloys at room temperature (RT). However, Y addition improved impact properties of alloys highly doped with O. Y addition did not suppress hardening due to O doping but did increase deformation for crack initiation.

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We have examined ponderomotive acceleration/ion cyclotron resonance (PA/ICR) of argon ions by performing test particle simulations. The PA gives rise to the pure parallel acceleration of ions, while the ICR causes the perpendicular ion heating followed by the energy conversion from the perpendicular to the parallel direction in the presence of a divergent background magnetic field. The energy gain by the PA/ICR is classified in terms of the adiabatic parameter, Λ = L_BΩ₀/v_0||, where L_B is the axial divergent scale length of the background magnetic field, Ω₀ is the ion gyrofrequency at the resonance, and v_0|| is the initial ion drift velocity along the axial magnetic field. For Λ < 100, the energy gain, Δε, due to the PA/ICR increases as Λ increases. For Λ > 100, Δε saturates since the increased axial velocity of the ion via the PA reduces the transit time to cross the acceleration region. When the externally applied rf electric field intensity is increased to 1000 V/m, we find a maximal 60% increase in the energy gain for the PA/ICR scheme compared with the energy gain by the ICR only. We have applied the PA/ICR scheme to the next-generation electric thruster, and have estimated the thrust including ion wall-loss and ion-neutral collisions.

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High-power electromagnetic waves propagating in a negative-permeability space were investigated theoretically and experimentally, and they generated overdense plasmas successfully. Theoretical analysis predicted that high-density plasmas with negative permittivity can form via saddle-node bifurcations within an adequate electric field. To confirm theoretical predictions, using metamaterials with negative permeability achieved by magnetic resonances, we injected microwaves with several hundreds of watt into a waveguide filled with a low-pressure discharge gas. Langmuir probe measurement revealed that a generated plasma is well beyond the cutoff density for the wave frequency of 2.45 GHz, and indicated transition between positive-permittivity (low-electron-density) and negative-permittivity (overdense) states.

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Pure lithium ion (Li⁺) and electron (e⁻) plasmas are not only produced separately but also trapped simultaneously in a Malmberg-penning trap called BX-U. No extreme degradation of confinement times or disruptive instabilities are so far observed even for the case of simultaneous confinement of both Li⁺ and e⁻ plasmas.

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The theory of magnetosonic waves perpendicular to a magnetic field in a two-ion-species plasma is extended to include finite temperature effects based on the three-fluid model with finite ion and electron pressures. First, the condition for the dispersion relation of the low-frequency mode, the lower branch of magnetosonic waves, to be approximated as a form of weak dispersion is presented. Next, by virtue of this, it is shown that the KdV equation for the low-frequency mode is valid for amplitude ε < ε_max, where the upper limit of the amplitude ε_max is given as a function of the ratio of the kinetic to magnetic energies, the density ratio, and the cyclotron frequency ratio of two ion species. The finite-temperature effects on linear and nonlinear high-frequency modes and on heavy-ion acceleration by the high-frequency-mode pulse are also discussed.

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We develop a collisional radiative (CR) model of high-Z multiple charge ions based on computational atomic data. We use an algorithm to determine a set of atomic energy levels in the model with significant population in the plasmas and contribute to the dielectronic recombination (DR) processes. The model is validated through participation to the non-LTE kinetics workshops. At the nLTE workshop, an alternative method for the analysis of the spectrum from plasmas based on genetic algorithm (GA) is also discussed. An application of the present model to calculate the ion abundance and radiative power loss of Gd and Nd plasmas is also shown.

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Validation of modeling in meso-scale structure formation is undergoing by using multi-channel probe measurements and advanced analyzing techniques such as bispectrum. Study of meso-scale structures including streamers is important for understanding anomalous transports in magnetized plasmas. A streamer structure and its mediator mode were observed in the Large Mirror Device-Upgrade linear plasma. The mediator mode nonlinearly coupled with many other drift wave modes and generated a streamer structure by phase locking. The radial biphase profiles indicating the phase locking showed the radial elongation of the streamer structure. Modes having similar characteristics to the mediator were also found in a theoretical work based on the Hasegawa-Mima model and a numerical simulation code.

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The inductive method for measuring the critical current density j_C and detecting the crack in a high-temperature superconducting (HTS) film have been investigated numerically. To this end, a numerical code has been developed for analyzing the shielding current density in the film with a crack. The results of computations show that the accuracy of the inductive method is degraded remarkably due to the crack. Specifically, it is found that, if the orthographic projection of the coil overlaps with the crack, the value of measured j_C decreases. This is mainly because the spatial distribution of the shielding current density becomes asymmetry. In conclusion, the crack size and position can be accurately detected by measuring the j_C-distribution in the HTS film.

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An analysis method of tokamak plasma equilibrium by a relaxation method with specified magnetic axis and null points (two magnetic separatrix points) is developed. The six degrees of freedom due to designated positions of the magnetic axis and null points is possible by using six poloidal field coil currents. Stable steady state tokamak plasma equilibria are calculated along with the MHD (magnetohydrodynamic) potential energy. Assuming an RF heating plasma, the plasma generates a plasma current which partially or fully cancels the magnetic field from the poloidal field coils. For low-temperature plasmas, the plasma current distribution is centrally peaked; for high-temperature plasmas, the plasma current has a hole. A centrally peaked current distribution in a low-temperature plasma is evolved into a current distribution with a hole by increasing the plasma pressure by heating. These calculations show that, under sufficient heating, the pressure driven current in tokamak plasmas form a current hole which minimizes the MHD potential energy.

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Secondary electron emission (SEE) from a spherical metallic dust particle by electron incidence was analyzed according to the OML (Orbit Motion Limited) model. As the observed dust speed in fusion plasmas (<100 m/s) is much slower than electron thermal speed, its effect to the SEE current is negligibly small. It is clarified that there is a window of electron temperature, where the ratio of the SEE current to the absorbed electron current exceeds unity; for graphite 80 eV < T_e < 326 eV and the maximum of the ratio ∼1.10 at T_e ∼ 165 eV, for tungsten 32 eV < T_e, the maximum ∼2.47 at T_e ∼358 eV. These excesses come from the inverse proportion of the incident angle to the dust particle.

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A magnetosonic shock wave propagating obliquely to an external magnetic field can trap and accelerate electrons to ultrarelativistic energies. These electrons can excite electromagnetic fluctuations along the shock front. The effects of the electromagnetic fluctuations on electron motion are investigated by two-dimensional electromagnetic particle simulations and test particle calculations in which equation of motion of electrons in the electromagnetic fields averaged along the shock front is computed. Comparisons of the two results verify that the electromagnetic fluctuations along the shock front can cause detrapping of energetic electrons from the main pulse and their subsequent acceleration to higher energies. It is also demonstrated that as the external magnetic field strengthens, the electromagnetic fluctuations along the shock front grow to larger amplitudes, and the detrapping and subsequent acceleration of electrons enhance.

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Energy distribution of a pure electron plasma column rotating around the axis of a cylindrical vessel due to an E × B flow in a Malmberg–Penning trap is investigated. An abrupt relaxation of the energy distribution was observed in an electron string trapped for a few microseconds after injection from an electron emitter. The macroscopic E × B drift rotation of the electron column is mainly dominated by the microscopic axial energy distribution which determines the effective position of reflection at the end of the trap, that is, a radial electric field acting on the particles from an external trap potential.

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Microwave power at 14 GHz frequency coupled to a magnetic field aligned parallel to the beam extraction axis successfully excited a plasma in a compact negative hydrogen (H⁻) ion source. A volume of low electron temperature plasma was formed based on the idea of “tent filter” magnetic field geometry by placing the extraction aperture at a recess made inside of a magnetic material. The amount of H⁻ current increased by enlarging a volume of low electron temperature plasma, which seemed consistent with the two step model of H⁻ production via vibrational excitation of hydrogen molecules. The depth of the recess was made shallower expecting the H⁻current with the magnitude halfway between the one without the volume of low electron temperature plasma and the one with the volume. The result has indicated the expected correlation between the size of the volume and the H⁻ current at low H₂ pressure. Meanwhile, the beam current density has abruptly increased as the microwave discharge power was raised above 60 W, indicating a change of discharge mode around that input power.

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The three-dimensional analysis of electromagnetic wave propagation using meshless time domain method is numerically investigated. The basic concept of the Meshless Time Domain Method (MTDM) is same as Finite Differential Time Domain (FDTD) method. In the discretizing process of the space, the shape function of Radial Point Interpolation Method (RPIM) is adopted. Thus, MTDM can be applied to the problem in the complex shaped domain easily. The result of computation show that the value of the damping rate decrease as the frequency increases. Moreover, the value of the damping rate depend on the shape of waveguide.

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Higher order mode radiations of oversized K-band backward wave oscillator (BWO) are examined experimentally. By injecting an annular beam in the weakly relativistic region less than 100 kV, a beam mode with harmonic number n = 1 excites BWO radiations based on the TM₀₁ surface wave. The same beam mode excites higher order modes leading to radiations in the U- and E-bands. The power levels of the higher order modes are hundreds of times smaller than that of BWO due to the surface wave. For a beam mode with n = 2, higher order mode radiations are in the F- and D-bands, up to about 100 GHz, which is about four times higher than the frequency of the TM₀₁ surface wave. The power level of higher order mode radiation by the n = 2 beam mode decreases by a factor of hundreds from that of the n = 1 beam mode.

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In order to expand the applied range of the heavy ion beam probe measurement on LHD, it is important to increase the probing beam current. A method of increasing the current is the improvement of charge exchange efficiency of a gas cell. The experiments were carried out on a tandem accelerator at Kobe University, 5SDH-2, because various conditions of experiments can be selected for gas species, gas pressure, and ion energy. Charge fractions of negative ion, neutral atom and the positive ions were measured by a micro channel plate or Faraday cup. Dependence of the fractions of Au⁻, Au⁰, Au⁺ and Au²⁺ on gas thickness was measured. Results were compared with prior calculations, and a solution of rate equations. The cross sections for ionizing and electron capture were calculated, and some cross sections were obtained from experiments. The dependence of charge fractions for Au⁰, Au⁺ and Au²⁺ on the gas thickness was well presented.

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The modified accuracy assurance scheme for the Binary Interaction Approximation (BIA) to N-body problems is proposed. The present error-tolerance-adjusting scheme, implemented into the BIA introduced in this study significantly reduces the CPU times and numerical errors in invariants of the motion compared to the previous one.

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Charge transfer cross sections of ⁷Li⁺ ions in collisions with H₂, HD, and D₂ molecules have been measured in the energy range from 1.4 to 4.0 keV using the growth rate method. Significant differences in the charge transfer cross sections between collisions of ⁷Li⁺ ions with H₂ and HD, and with H₂ and D₂ molecules, the socalled target isotope effect, are observed at collision energies from 1.4 to 2.4 keV. The observed charge transfer cross section ratios of σ (HD)/σ (H₂) and σ (D₂)/σ (H₂) are found to be approximately 0.7 at 1.4 keV. They are gradually increasing, and finally approaching unity at energies above 2.4 keV.

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To investigate a condition of the numerical stability of an electromagnetic wave propagation simulation using the meshless time-domain method (MTDM), a 1-dimensional (1D) TM mode discretized by the MTDM has been analyzed theoretically. Under some assumptions, the Courant condition for the 1D MTDM has been derived. The Courant condition does not depend on the radial basis functions required to generate shape functions of the MTDM. In addition, the Courant condition for the 1D MTDM is equivalent to that for the finite-difference time-domain method. Based on the result for the 1D case, the Courant condition for the 2-dimensional (2D) MTDM is predicted. Furthermore, for the case where the predicted Courant condition is satisfied, the numerical stability of 2D MTDM has been investigated numerically.

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Fast magnetic reconnection mechanism triggered by current sheet ejection is studied in plasma merging laboratory experiment with a strong guide field. The current sheet is hardly compressed in the presence of the guide field and slow steady reconnection evolves in the early phase. It then transits to impulsively fast magnetic reconnection when the current sheet is ejected from the X point region. Behavior of the current sheet is investigated in detail by comparison with the fast reconnection case provided by anomalous resistivity.

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A nonlinear simulation of resistive drift wave turbulence in a cylindrical plasma is carried out. Long time evolution of turbulence with formation of a zonal flow is obtained for more than 1000 times of the typical drift wave period, which is sufficient for statistical analyses. Dynamical particle and momentum balance for the formation of the mean reveals that the radial turbulent fluxes are dominant contributors for the evolution of fluctuations. The particle flux is found to precede the momentum flux for 0.4 times of the typical drift wave period with large temporal variance. The analyses of the time series data of 3-D fields give the understanding of the dynamical structural formation mechanism.

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Pictures of plasmas and deposits in a discharge chamber taken by varying shutter speeds have been integrated into high dynamic range (HDR) images. The HDR images of a graphite target surface of a compact planar magnetron (CPM) discharge device have clearly indicated the erosion pattern of the target, which are correlated to the light intensity distribution of plasma during operation. Based upon the HDR image technique coupled to colorimetry, a formation history of dust-like deposits inside of the CPM chamber has been recorded. The obtained HDR images have shown how the patterns of deposits changed in accordance with discharge duration. Results show that deposition takes place near the evacuation ports during the early stage of the plasma discharge. Discoloration of the plasma-facing-walls indicating erosion and redeposition eventually spreads at the periphery after several hours of operation.

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Solar wind is the outflow of hot coronal plasma. Magnetohydrodynamical (MHD) wave and turbulence play an essential role in driving solar wind as well as stellar winds from solar-type stars. The sun, and in general,low-mass stars possess surface convective zones. Various modes of waves are excited from the stellar surfaces due to the convective motions, and these waves dissipate through various nonlinear processes such as turbulent cascade and the generation of compressive waves. As a result, the kinetic energy of the surface convection in the interior is transported to the upper atmosphere, which drives the wind. In this paper, we discuss these consecutive processes from both theoretical and observational viewpoints, and review our recent results of MHD simulations.

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Radial profile of floating potential inside the current sheet was measured for the purpose of investigating the two-fluid (Hall) effect during magnetic reconnection in the UTST merging experiment. During magnetic reconnection, the floating potential drop was formed spontaneously inside the current sheet, forming a steep electric potential gradient on its both downstream areas. Magnetic probe array measurement indicates that this potential drop appears spontaneously when the reconnection rate rapidly increase due to change in current sheet structure. The IDS probe measurement observed outflow almost equal to poloidal Alfvén speed in radial direction from the X-point, where steep gradient of floating potential is formed. This fact suggests that ion acceleration/heating is caused by the steep potential gradient formed in the downstream by magnetized electrons.

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We analyzed energy transfer processes induced by triad mode interactions in homogeneous, isotropic turbulence in magnetohydrodynamic (MHD) and Hall magnetohydrodynamic (HMHD) media. In particular, we analyzed the Fourier spectra of the energy transfers using geometric-series shell-partitioning methods, analogous to dyadic wavelet analysis. Snapshot datasets were collected once the MHD and HMHD turbulences had sufficiently developed. Graphs of all energy spectra were well collapsed after the normalization using the dissipation rates and the diffusion coefficients, i.e. they showed good self-similarity. Despite such self-similarity of energy spectra, the transfer due to mode interactions between the fluid advection and Hall term was reduced over time, while those due to the Lorentz force and induction remained rather stationary in regions of higher wave number.

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We have solved the two-dimensional time-dependent Schrödinger equation for a single particle in the presence of a non-uniform magnetic field for initial speed of 8 - 100 m/s, mass of the particle at 1 - 10 m_p, where m_p is the mass of a proton. Magnetic field at the origin of 5 - 10 T, charge of 1 - 4 e, where e is the charge of the particle and gradient scale length of 2.610 × 10⁻⁵ - 5.219 m. Previously, we found out that the variance, or the uncertainty, in position can be expressed as dσ²_r /dt = 4.3ħv₀/qB₀L_B, where m is the mass of the particle, q is the charge, v₀ is the initial speed of the corresponding classical particle, B₀ is the magnetic field at the origin and L_B is the gradient scale length of the magnetic field. In this research, it was numerically found that the variance, or the uncertainty, in total momentum can be expressed as dσ²_P/dt = 0.57ħqB₀v₀/L_B. In this expression, we found out that mass, m does not affect both our newly developed expression for uncertainty in position and total momentum.

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The single- and multiple-charge-transfer cross sections for ¹²C²⁺ and ¹³C³⁺ ions have been measured in collisions with CO and CO₂ molecules in the energy range of 0.35 to 3.0 keV per initial charge number based on the initial growth rate method. Most of the present single- and multiple-charge-transfer cross sections show weak energy dependence over the observed collision energy range. For CO₂ molecules, the present data smoothly join with the previously measured data in the energy range greater than 10 keV. The cross sections for total charge transfer, which are summations of single- and multiple-charge-transfer cross sections, are compared with a simple over-barrier model and available scaling laws.

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Magnetic energy injection through pull magnetic reconnection has been studied in the University of Tokyo Spherical Tokamak (UTST) using external poloidal field coils. Under constant plasma inflow, the magnetic energy of the produced ST increases as the guide field B_t is increased from zero to the optimized value B_t0, while it decreases after B_t exceeds B_t0. The pull reconnection process was often accompanied by the formation of plasmoids around the X-point. The reconnection rate was found to change with time, depending on the formation of plasmoids and the magnetic energy injection. Plamoids enhance the reconnection rate.

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To maintain load balance among processes in parallel calculation, we introduced a dynamic load balancing technique called Dynamic Domain Decomposition (DDD) into our newly developed multi-scale Particle-In-Cell (PIC) simulation code in which Adaptive Mesh Refinement (AMR) is incorporated. To evaluate the effectiveness of DDD, we performed test simulations with a model in which four particle clusters are non-uniformly distributed with different velocities. We confirmed that load imbalance among processes caused by non-uniform plasma distribution was successfully resolved by DDD and the computational time becomes almost half of that for simulation of the same model without using DDD.

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Interactions of exploding and surrounding plasmas are studied with two-dimensional (2D) electromagnetic particle simulations, for a case in which the initial velocity of the exploding plasma is perpendicular to an external magnetic field. It is confirmed that essentially the same phenomena (the penetration of exploding ions, the formation of a strong magnetic-field pulse, and the generation of forward and reverse shock waves) as in the previous one-dimensional (1D) simulations occurred in the 2D simulation. Further, modified two-stream instabilities excited by relative cross-field motion between ions and electrons are investigated with attention to their effects on the 2D structure of the strong magnetic-field pulse and on ion reflection by the pulse.

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A notch filter for the rejection of stray light from gigahertz range heating sources was developed to protect a vulnerable microwave plasma diagnostic system. As one of the applications, we consider the installation of the notch filter into the receiver of a collective Thomson scattering diagnostic in the Large Helical Device. Experimental observations indicate that two types of notch filters are required for main and spurious mode rejection; they have very narrow, steep shapes to avoid disturbing the diagnostic signal. On the basis of numerically simulated results, notch filters were fabricated, and their performance was evaluated. An attenuation level of 35 dB at 74.746 GHz with a 3 dB bandwidth of 0.49 GHz is achieved by two pairs of resonator cavities. This attenuation is acceptable in our study.

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Magnetic configurations of LHD experiment are analyzed based on the Fourier modes of the plasma boundary shapes. It was found that a small number of Fourier modes is sufficient to determine the confinement characteristics of different configurations with the magnetic axis shift of LHD. A new configuration is proposed with adifferent combination of Fourier modes, which has good particle orbits and a favorable property of high beta equilibrium. This solution has a smaller Shafranov shift than the inward-shifted configuration of LHD.

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One of the simplest self-consistent models of a plasma is single-fluid magnetohydrodynamic (MHD) equilibrium with no bulk fluid flow under axisymmetry. However, both fluid flow and non-axisymmetric effects can significantly impact plasma equilibrium and confinement properties: in particular, fluid flow can produce profile pedestals, and non-axisymmetric effects can produce islands and stochastic regions. There exist a number of computational codes which are capable of calculating equilibria with arbitrary flow or with non-axisymmetric effects. Previously, a concept for a code to calculate MHD equilibria with flow in non-axisymmetric systems was presented, called the KITES (Kyoto ITerative Equilibrium Solver) code [D. Raburn and A. Fukuyama, Plasma Fusion Res. 7, 240318 (2012)]. Since then, many of the computational modules for the KITES code have been completed, and the work-in-progress KITES code has been used to calculate non-axisymmetric force-free equilibria [D. Raburn and A. Fukuyama, Proceedings of the 9th EPS Conference on Plasma Physics, Stockholm, Sweden (2012)]. Additional computational modules are required to allow the KITES code to calculate equilibria with pressure and flow. Here, the authors report on the approaches used in developing these modules and provide a sample calculation with pressure.

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The InfraRed imaging Video Bolometer (IRVB) measures the radiation from the plasma in two dimensions, giving an image of the plasma radiation power loss. Using a geometry matrix calculated from a model of the LHD first wall, the IRVB sightline geometry and a three dimensional (3D) plasma grid, a synthetic instrument is developed using the 3D carbon impurity radiation results of the EMC3-EIRENE edge impurity transport code as an input. The output of the synthetic instrument are images of the plasma radiation at the IRVB foil due to the EMC3-EIRENE code, which are qualitatively compared with preliminary experimental images from the IRVB. Such a comparison for detached discharges in LHD in which an externally induced m/n = 1/1 magnetic island is applied shows that when the magnetic island is moved 36 degrees toroidally the enhanced radiation in the x-points of the magnetic island also moves as predicted by the EMC3-EIRENE code.

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Deposition/erosion measurements by means of a Quartz Micro Balance (QMB) located below the Load Bearing Septum Replacement Plate in the private flux region of the inner divertor of JET (with full carbon wall) revealed net deposition with the inner strike point located on the vertical tile and net erosion with the inner strike point on the horizontal tile [H.G. Esser et al., J. Nucl. Mater. 390–391, 148 (2009)]. ERO calculations show about 3.5 times larger flux entering the QMB aperture when the inner strike point is located on the vertical plate compared to the case when strike point is on the horizontal plate – thus indicating similar behavior. Using these fluxes from ERO as input, detailed modeling of erosion/deposition at the QMB itself considering the realistic geometry of the QMB housing has been performed with the 3D-GAPS code. The QMB measurements can be reproduced with combined ERO/3D-GAPS modeling if erosion due to deuterium atoms within the QMB housing is taken into account.

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Impurity behaviors in LHD are studied by a Tracer-encapsulated Solid Pellet (TESPEL) injection. By containing multiple tracers in a TESPEL, the different tracer species have been compared simultaneously under the same plasma condition. The density disturbance on the bulk plasma by TESPEL is typically less than 10 %. The amount of the tracer particles deposited locally inside a plasma is about a few 10¹⁷ particles which is smaller than that of the bulk plasma by a factor of three orders of magnitude. Triple tracers, V, Mn and Co are used, because the charges of nuclei of intrinsic impurities, Cr and Fe are in between those of the tracers. The impurity confinement behavior depends substantially on the electron density. In case of the density higher than n_e = 5×10¹⁹ m⁻³, the tracer impurity in the plasma core was kept for a long time, while it decays in order of 500 ms in the medium density case. Such temporal behavior is compared with a STRAHL simulation code assuming diffusion coefficient and convection. The general behavior fits well with the emissivity value integrated along the sight line.

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Terahertz wave diagnostics have been developed for current and future high-temperature and high-density fusion plasma measurements. Since the combined system of a reflectometer and a delayometer requires a wide-band frequency source for the density profile measurements, a terahertz pulse is a possible candidate. A test system using terahertz time-domain spectroscopy has been constructed to develop the diagnostics. The system utilizes a femtosecond fiber laser as a pumping source and a bow-tie-type photoconductive antenna as a THz wave emitter. An output THz pulse with a frequency of up to 2 THz has been obtained. Some investigations involving measurement of the refractive index of a test material are performed, and the transmission dispersion effects of an optical fiber are determined.

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Using a laboratory-scale plasma device, plasma-driven and gas-driven permeation of hydrogen through a ferritic steel alloy: F82H has been investigated under some of the DEMO-relevant conditions. The steady state plasma-driven permeation flux has been found to be strongly affected by the variation in upstream surface morphology resulted from plasma bombardment. The activation energy of permeability for gas-driven permeation has been estimated to be ∼0.5 eV, which is close to the result of plasma-driven permeation. Gas-driven permeation can occur in the opposite direction of plasma-driven permeation, which then results in an increase in first wall recycling.

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The technology for OPERA experiments in neutrino physics was applied to neutral-beam-heated deuterium discharges of NSTX in order to measure d-d neutron emission profile. The diagnostic system consisted of nuclear emulsions named OPERA films and the automatic track scanning system S-UTS developed in Nagoya University. A neutron collimator having three channels was temporarily built for this purpose. The nuclear emulsion indicated peaked neutron emission profiles at the plasma center in NSTX as expected.

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To establish a method for suppressing the spurious radiation that interferes with collective Thomson scattering measurements with less degradation of the main mode output power, the frequency evolution, and the output power of the megawatt 77-GHz gyrotron were measured during operation under optimized parameters. According to a mode competition calculation, the main mode output power may be increased by setting a lower gyrotron anode voltage at a higher magnetic field strength in the gyrotron resonator. Although the output power increased from 300 kW to 530 kW without any spurious radiation when the optimized operational parameters were used, the output power was about 50% of that at a lower magnetic field strength, and thus the output pulse width was limited to 60 ms. When an approach using the optimized operational parameters and a PIN switch was applied, the output power increased to 800 kW without any harmful spurious radiation effect and the pulse width was expanded to 2 s.

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High harmonic electron cyclotron resonance heating (ECH) can extend the plasma heating region to higher density and higher β compared to the normal heating scenario. In this study, the heating characteristics of the second-harmonic ordinary (O2) and third-harmonic extraordinary (X3) modes and the possible extension of heating regime are experimentally confirmed. At the same time, a comparative study using ray-tracing calculation was performed in the realistic three-dimensional configuration of the Large Helical Device. The O2 mode heating showed a 40% absorption rate even above the X2 mode cut-off density. The X3 mode heating using powerful 77 GHz gyrotrons demonstrated an increase of about 40% in the central electron temperature in the plasmas at β-value of about 1%. These results were quantitatively explained to some extent by ray-tracing calculations.

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In order to study migration of sputtered materials and profiles of their re-deposition in the Large Helical Device (LHD), material probes fixed with Si specimens were installed on the private region of the torus outer first-wall in all toroidal sections (10 sections) in the experimental campaign in 2011. The material probes fixed with the Si specimens were exposed to various wall conditionings such as glow discharges cleanings (GDCs), boronization, Ti sublimation and main plasma discharges. After the campaign, the specimens surfaces were investigated with visual observation, Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). A type of visual deposition (band) pattern has been observed on the probes at almost all toroidal sections of LHD. The analysis of these patterns on the material probes informs the source and direction of material migration inside the LHD vacuum vessel. The observation and result of the experiment have been presented in this paper.

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Micro-meter size carbon dusts have been formed in a 70 mm diameter, 370 mm long plasma container after running a 16 hour steady state Ar discharge. The formed carbon dusts have been observed by a scanning electron microscope (SEM) to identify their surface structures. The observed images have indicated that dusts with both flake and cauliflower structures were present on the surfaces of sample collectors. Carbon dusts with the flake structures exhibited smoother surfaces than dusts with cauliflower structures. Dust samples were also collected from arc spot parts of the carbon electrode surfaces by placing carbon compound adhesive tapes. Micro-meter size dusts were found collected on the surface of the tapes, indicating formation of dusts during arc discharges.

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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 the plug region (P-ECH) produces the electron flow with high energy along the magnetic filed line. From the power scaling of confining potential and electron flux in GAMMA 10, the higher ECH power generates the higher confinement potential and the higher electron flux. The peak heat-flux of more than 10 MW/m² has been obtained during the ECH injection within the available power of ECH. This value almost corresponds to the steady-state heat load of the divertor plate of ITER. However, we need substantial upgrade of the heating power to approach the ITER level ELM energy density. For this purpose, MW power gyrotrons at 28 GHz have been started and the development is undergoing efficiently in the ECH system upgrade program with the collaboration of Japan Atomic Energy Agency (JAEA).

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Space-resolved vacuum ultraviolet (VUV) spectroscopy using a 3 m normal incidence spectrometer has been developed in the large helical device (LHD) to study plasma transport in the ergodic layer by measuring the spatial profile of VUV lines from impurities emitted in the wavelength range of 300-3200 Å. Characteristics of the diagnostics system such as line dispersion, observable region and spatial resolution were evaluated. CIV spectra of 1548.20×2 Å were measured clearly. Intensity and ion temperature profiles were obtained simultaneously using CIV emissions in high-density discharges. Dependencies of the CIV intensity profiles on the electron density and magnetic configurations were observed.

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A new diagnostic for LHD is presented, which utilizes active charge-exchange signals from Hydrogen (main ions) and Helium (impurity ions) to derive the radial ion-temperature and ion-velocity profiles as well as the H/He ratio profile. In a sensitivity study, different models for profile fitting and measurement uncertainties are compared, which leads to first results. This covers fitting with one Gauss function and two Gauss functions as well as the inclusion of read-out noise and photon noise. Full error propagation from the measured spectra to the resulting profiles is provided by utilizing Bayesian statistics in combination with a weighted least-squares fit and boundary conditions. Reliable and accurate results were achieved for the ion-temperature profiles, which are in good agreement with the well-proven Carbon diagnostic. Concerning the quality of the velocity profiles, no statement could be made. The H/He ratio measurements in contrary lead to accurate results. Calibration with the H/He ratio of passive emission near the plasma edge just before the end of the discharge allows calculating absolute values for Helium and Hydrogen density profiles.

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A particle image velocimetry technique based on orthogonal dynamic programming is developed to measure the time resolved flow field of the fluctuating structures at the plasma edge and scrape off layer. This non-intrusive technique can provide two dimensional velocity fields at high spatial and temporal resolution from a fast framing image sequence and hence can provide better insights in plasma flow as compared to conventional probe measurements. Applicability of the technique is tested with simulated image pairs. Finally, it is applied to tangential fast visible images of QUEST as a test case to estimate the scrape off layer flow in Ohmic and ECRH driven plasma discharges.

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A new fast-ion diagnostic based on the spectroscopy of the Doppler shifted Balmer-alpha line of Deuterium is considered for JT-60SA. Two sight lines, one tangential and the other perpendicular, are examined as candidates. It was found that the tangential one has better sensitivity than the perpendicular one. A trial of the FIDA measurement was performed on JT-60U. Signals due to the tangential-NB injection were obtained. It was found that about the one third of the signal would be due to the active FIDA signal, which was produced by fast-ions and a probe beam, while the remainder would be due to passive signal. The results indicate the FIDA measurement on JT-60SA would be possible with proper background measurements.

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A decrease in the electron density is observed during high-power heating, particularly in electron cyclotron resonance heating (ECRH). One possible mechanism is the increase in the number of trapped particles, which can enhance the radial particle flux, because ECRH accelerates electrons in a direction perpendicular to the magnetic field lines. To observe the effects of the production of trapped particles, high-power (1 MW) ECRH was applied at the ripple bottom of the magnetic field strength, where trapped particles are readily produced. A rapid local outward flux of electrons was first observed near the heating position shortly after ECRH injection. The outward flux is proportional to the electron density in the density range of 0.4 × 10¹⁹ to 0.8 × 10¹⁹ m⁻³. The inward electron flux was subsequently enhanced in the core region.

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A new laser timing controller for the high time-resolution Nd:YAG Thomson scattering system with two Nd:YAG lasers has been developed to study improved confinement physics in Heliotron J. A PIC-based timing controller synchronizes the timings of laser oscillations with plasma discharges and enables the measurement of plasma profiles with a precision of <1 μs. The timing controller is used for the “soft start” of the system, which protects the optical components against initial unstable laser oscillations. The timing controller is designed to precisely control the delay time of the laser pulse from one laser to another, and to investigate the profile change of electron temperature and density within a short time span (>80 ns), which is crucial for transport physics studies including spontaneous transitions.

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