The physical mechanisms determining the diffusive and non-diffusive terms of particle, momentum and heat transports are described. The non-diffusive term in particle transport, which causes inward pinch or outward flux, is driven by the temperature gradient and the magnetic field curvature. The non-diffusive term in the momentum transport, which drives spontaneous toroidal rotation, is found to depend on the electric field and ion temperature gradient in the plasma. In heat transport, no clear non-diffusive term is observed. The temperature and temperature gradient dependences of the diffusive terms are discussed.

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We consider a sheath region bounded by a corrugated surface of material conductor and a flat boundary held to a constant voltage bias. The real profile of the film deposited from plasma on a limiter in a fusion device was used in numerical solving of the Poisson's equation to find a profile of electrostatic potential. The rough surface influences the equipotential lines over the surface. We characterized a shape of equipotential lines by a fractal dimension. The long-range correlation in the potential field is imposed by the non-trivial fractal structure of the surface. Dust particles bounced in such irregular potential field can accelerate due to the Fermi acceleration.

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Backscattered X-ray intensity was measured coincidently with a CPA laser-produced X-ray pulse. Results show that the coincident measurement is useful in reducing the effect of natural radiation. Even for signals at the photon counting level, we can distinguish the scattering materials and their thickness from the difference in backscattered X-ray counts. These results suggest that the backscattered X-ray can be used for imaging any distant object.

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A fast camera clearly detected a simple helical structure in the visible-light emission region in the reversed field pinch (RFP) configuration. The observed structure is consistent with magnetic field structures deduced from magnetic measurements with the help of equilibrium reconstruction. The observed simple structure is probably an indication of the internally resonant kink mode structure in a low aspect ratio RFP configuration.

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The effect of gas flow on the characteristics of a microgap discharge was investigated experimentally. In a gap length of 0.7 mm, the spatial structure and spectrum of light emitted from the discharges in helium gas were observed to be changed with the gas flow velocity. The transition of the discharge from a transversally uniform structure to a silent discharge structure in a high flow velocity region is found to be caused by air contamination in the gas flow channel. The edge effect on the transition is confirmed from the light emission pattern of the discharge.

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Reflectometry is expected to be come one of the key diagnostic tools for measuring density profiles in large fusion devices. It provides good spatial and temporal resolutions, while requires only a single viewing chord and minimal vacuum access, in contrast to interferometry and Thomson scattering. We applied an ultrashort-pulse reflectometer (USPR) to Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS), and a signal record analysis (SRA) method was used as a reconstruction method. Here, we report a simulation study of USPR conducted using a finite-difference time domain (FDTD) method to confirm the effectiveness of the SRA reconstruction method.

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Two dimensional electron density profile measurement has been performed in the spherical tokamak CPD (Compact PWI experimental Device) using Li sheet beam imaging technique. The topological change from the open magnetic field line configuration to the closed one is visualized by this technique. The plasma current can be driven by RF waves itself in a weak mirror configuration and a clear change is observed in plasma boundary as well as magnetic field topology associated with the transition of the current from low (∼1 kA) to high (∼3 kA) value.

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The effect of the spectrum of the radial wave number of zonal flows on zonal flow generation is theoretically investigated using the Hasegawa-Mima turbulence model by representing the spectrum by means of two monochromatic waves. Based on this method, we explored a ten-wave coupling model of modulational instability. We found that the zonal flow generation is qualitatively different in cases with and without such a spectral effect, exhibiting the enhancement of the growth rate. This originates from the coupling property of the new zonal flow eigenmode equation system. We refer to this state as a coupled zonal flows eigenmode, which leads to a spatial modulation of zonal flows affected by the turbulence structure.

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Structural bifurcation of microwave-sustained jet discharge at atmospheric gas pressure was found to produce a stable helium plasma jet, which may open the possibility of a new type of high-flux test plasma beam for plasma-wall interactions in fusion devices. The fundamental discharge properties are presented including hysteresis characteristics, imaging of discharge emissive structure, and stable ignition parameter area.

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An electric field measurement system in the Electron Cyclotron Range of Frequency (ECRF) has been developed for the direct detection of mode-converted Electron Bernstein Waves (EBWs), where a low-power ECRF wave (1-2.1 GHz, 10 W) is injected into overdense plasmas (typical peak density is 7 × 10¹⁶ m^-3 ), and the ECRF electric field is directly measured using a small monopole antenna (an element size of 5 mm) inserted into the confined plasma. A density gradient is an important parameter for mode conversion to EBW. In the internal coil device, Mini-RT, a steep density gradient (e.g., L_n ∼ 5 cm) is available at the plasma surface. We have detected short-wavelength waves with refractive indices of ∼10 or more around the electron cyclotron harmonic resonance layers, and confirmed a phase reversal of an ECRF electric field at the same locations. Since the EBW is a backward wave with a short wavelength, experimental results suggest the direct measurement of the mode-converted EBW in plasma.

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High-power gyrotrons are required for electron cyclotron heating/current drive in high-performance plasma experiments. In Japan Atomic Energy Agency, the operation conditions of the JT-60U gyrotron, which was originally designed as a 1-MW gyrotron, were optimized in order to achieve high-power and long-pulse operation with some modifications of the gyrotron components. As a result, the output power level of 1.5 MW for 1 s was successfully achieved.

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The paper presents the development of sinusoidally grooved polarizers for electron cyclotron resonance heating (ECRH) systems in the HL-2A tokamak. The polarizer groove shape was designed according to a sinusoidal function with a groove period p = 0.48λ and depth d = 0.5λ. Here, λ is the wavelength, whose value is 4.41 mm. The low-power test results of the polarizer performance are in agreement with a numerical calculation based on the integral method developed in vector theories of diffraction gratings. High-power experiments reveal that 340 kW high-power EC waves can be transmitted through the corrugated waveguide line with the polarizer assembled in a miter bend at atmospheric pressure. With the polarizer, ECRH/electron cyclotron current drive (ECCD) experiments in the extraordinary mode have been successful in a HL-2A tokamak.

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Proton acceleration experiments using an intense ultraviolet laser were conducted for the first time. The laser system produced pulses having energies of up to 750 mJ at a wavelength of 248 nm with a temporal duration of 400 fs. Thin copper foils of 4 μm were used as targets, and the maximum intensity on the target was 1.3 × 10¹⁸ W/cm². The highest energy of protons was 700 keV, which was observed when the laser beam was ppolarized and was incident on the target at an angle of 30°C . Fast electrons were generated by vacuum heating or resonance absorption because of the polarization dependence. These protons were accelerated in the target normal direction, which is suggestive of the target normal sheath acceleration mechanism (TNSA).

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Experiments on erosion and dust formation on graphite materials have been performed using high power induction plasmas containing high atomic hydrogen flux (∼10²⁴ m^-2 s^-1 ). Chemical sputtering by atomic hydrogen irradiation with an incident energy below 1 eV eroded the graphite targets significantly, and the sputtering yield was roughly estimated to be 0.002-0.005, which is as high as that obtained by ion beam experiments. The transport of the released hydrocarbon along the gas flow results in carbon dust formation on the eroded graphite target and also on the silicon and graphite targets located at the remote position. The dust structure strongly depends on the target surface temperature, and the graphite dust turns into diamond crystals when the surface temperature rises to 1100 K.

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A compact Nd:YAG laser Thomson scattering system was constructed and applied to the TST-2 spherical tokamak in order to measure the electron temperature and the electron density. A large solid angle (∼35 msr) was achieved by use of a compact Newtonian mirror system for the collection optics. Absolute calibration was performed by Rayleigh scattering. An electron temperature increase from 140 eV to 210 eV was observed upon injection of 200 kW of RF power.

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Quasi-periodic growth of a single core-resonant instability has been observed in a low-aspect ratio (low-A) reversed field pinch experiment in RELAX. In round-topped current discharges, the innermost core resonant m = 1/n = 4 mode grows with suppression of the neighboring m = 1/n = 5, 6 modes. The resultant toroidal mode spectrum of the m = 1 modes is similar to that of the quasi-single helicity (QSH) state with higher amplitudes. These phenomena are discussed along with the low-A characteristic of RELAX, indicating simpler MHD mode dynamics and easier access to the QSH state.

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In the Large Helical Device, coherent fluctuations related to energetic-ion-driven magneto-hydrodynamic (MHD) instabilities such as Alfvén eigenmodes (AEs) were detected for the first time using an Hα detector array having high-frequency response up to 200 kHz. Correlation analysis between detector and magnetic probe signals has enabled us to successfully extract coherent fluctuations in the AE frequency range. The radial profile of the excess of the coherence from the background value (Δγ) has a clear peak around the predicted toroidal Alfvén eigenmode (TAE) gap.

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Alternating magnetic perturbations, generated by external electrodes, are applied to a neutral-beam-heated plasma in the Compact Helical System, to excite stable Alfvén eigenmodes (AEs). Resonant peaks in the frequency range of the toroidal Alfvén eigenmode (TAE) have been observed in a transfer function defined by the ratio between the magnetic probe signal and the alternating electrode current. The resonant frequency f_o agrees well with that of the TAE gap located near the plasma edge, where the strength of energetic ion drive of AEs will be sufficiently low. The damping rates γ derived from the width of the resonant peak are fairly large, i.e., γ/(2π f_o) ∼ 20%.

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Nonlinear simulation of plasma blob propagation in the tokamak scrape-off layer is reported. Three types of model equations are introduced and the simulation results are compared. It is found that in the parameter regime where the interchange instability appears during the propagation process, the theoretical model of propagation velocity determined by the initial blob size provides a good approximation of the simulation results. In the regime where the Kelvin-Helmholtz instability appears, however, the blob velocity saturates at a lower value.

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In the TST-2 spherical tokamak, a non-inductive start-up plasma produced by electron cyclotron heating (ECH) at 2.45 GHz (3-5 kW) is sustained by RF wave heating at 21 MHz (10-24 kW). A current jump, which occurs at a certain time when only ECH is used, can be induced earlier by the RF heating, and a constant plasma current is sustained even after the ECH power is turned off. The plasma current is sustained in both hydrogen and deuterium plasmas, as long as the RF power exceeds a threshold level, which is lower for deuterium plasma. The maximum sustainment time by the the RF power alone was 40 ms, limited by the RF pulse length. According to CCD camera images of the total plasma light, the major radii are almost the same, but the RF-sustained plasma has a more peaked profile, compared with the distribution of an ECH-sustained plasma.

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In this study, scientific visualization by the CAVE virtual reality (VR) system is applied to the analysis of magnetic reconnection simulation data for the first time. The magnetic field streamline, the isosurface of density profile, the contour of temperature profile, the arrow of flow velocity, and other variables are displayed in VR space. The trajectories of particles under the electromagnetic field obtained by simulation are also traced simultaneously. We can clearly see the relationship between complex three-dimensional structures of magnetic fields, distribution of particle temperature, particle trajectories, and other variables in VR space.

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Optical emission spectra in the wavelength range of molecular hydrogen were observed in both ionizing and recombining plasma modes of hydrogen discharges. The optical emission spectrum from the ionizing plasma was dominated by the Fulcher-α system (a³Σ_g⁺ - d³Π_u^-) of molecular hydrogen. On the other hand, the optical emission spectrum from the recombining plasma was composed of many lines, and was completely different from the spectrum of the ionizing plasma. The many peaks observed from the recombining plasma were assigned to the X²Π - A²Σ⁺ transition of OH. The OH(A²Σ⁺) is thought to originate from the chemical etching of a glass discharge tube by atomic hydrogen. This is analogous to the interaction between a detached divertor plasma and a graphite plate, and a possible process for the enhancement of OH(A²Σ⁺) density in a recombining plasma is discussed with this analogy in mind.

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Nonlinear energy transfer of the drift-wave spectrum is investigated experimentally in a cylindrical laboratory plasma. Using the Hasegawa-Mima equation, the nonlinear transfer function of electrostatic potential energy in frequency space is estimated by bispectral analysis. The transfer function derived from the drift-wave spectrum indicates a forward cascading of energy transfer from fundamental to higher harmonic modes.

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Discriminating acquisition of 15-MeV protons is possible in LHD D-³He experiments (D⁺ beam to ³He plasma), due to the nonaxisymmetric structure of the magnetic field and the ultra-high energy of the fusion products. The collisionless orbits of D-³He fusion products are studied numerically in the standard magnetic field configuration of LHD. Three sets of fusion product acquisition systems are installed in LHD and numerical computations show the possibility of discriminating between fusion products and plasma particles. The acquisition rate of 15-MeV protons is expected to be in the range of 12 ∼ 28 %.

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To increase the acceleration rate for producing highly energetic protons, a scheme using a cone-shaped target with a coated proton layer is proposed and demonstrated by 2D particle-in-cell (PIC) simulation. The simulation results show that because the laser light and electrons are guided along the cone wall, the energy and density of hot electrons are enhanced in the cone target. Thus, the amplitude of the sheath field on the target's rear surface is enhanced, since it is proportional to the hot electrons' temperature and the logarithm of their density. Therefore, protons are accelerated strongly by this sheath field.

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Ablation of a solid hydrogen pellet in hot plasmas of Large Helical Device (LHD) has been studied. A position sensitive detector (PSD) diagnostics has been newly installed to measure the trajectory of ablating pellets. 2-D diagnostics enables the measurement with high time (1 MHz) and spatial resolutions (80 μm). A 3-D pellet trajectory can be described by a combination of 2-D images and information of initial pellet direction and velocity. A deflection of the pellet trajectory in the neutral beam injection (NBI) heated plasmas of LHD has been observed. Means of improving the measurement accuracy of this system are also discussed.

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The effects of a supersonic plasma flow on emissive Langmuir probes were experimentally investigated using a Pockels electric field sensor. When the flow velocity exceeded the ion sound speed, the probe characteristics were modified, and the emissive probe overestimated the plasma potential. The modification of probe characteristics is explained by the formation of a humped potential profile, caused by a shock in the supersonic plasma flow.

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We discuss a simulation framework, called Equation-Free Projective Integration (EFPI), which can perform macro-simulations while still taking the effects of micro-scale physics into account. In particular, we propose a primal-EFPI scheme to simulate the ion sound wave paradigm, which includes nonlinear wave steepening and kinetic effects in a plasma.

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Experiments were performed to study non-inductive current generation by electron cyclotron heating (ECH) in the TST-2 spherical tokamak. A magnetron (2.45 GHz/5 kW) and a horn antenna were used to inject either the O- or X-mode. The maximum plasma current does not depend on the injected wave polarization; however, it has a weak dependence on the vertical field configuration and is proportional to the vertical field. The initial current ramp-up rate depends on various operational parameters. The ramp-up rate increases with the injected EC wave power, and decreases with the filling pressure, resonance position (i.e., the toroidal field strength), and vertical field strength. It also depends on the magnetic field configuration. Conversely, the ramp-up rate does not depend on wave polarization, suggesting that multiple pass absorption of the EC wave is important.

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Johnsen-Rahbek electrostatic chuck (ESC) for holding a silicon wafer in semiconductor processing is investigated in inductively coupled plasma (ICP). Bi-layer model of the ESC consisting of a thick bulk layer and a thin interface layer is proposed. The resistance of each layer is obtained by measuring the ESC voltage-current (V-I) characteristic with and without the wafer in ICP, along with the voltage effectively applied to the interface layer. Surface charges stored in the interface layer capacitance are found by the time-integration of current in a turn-on phase of a ramped voltage. On the other hand, the chuck holding force is in situ obtained in a turn-off phase of slowly ramped voltage, from the critical conditions of helium gas pressurization for wafer de-chuck. The electrostatic force predicted on a basis of equivalent circuit in the bi-layer model coincides with the mechanical force obtained in the wafer de-touch experiments.

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Red-fluorine-atom (Red-F^* ) laser oscillation (λ = 630-780 nm) and strong fluorescence of VUV-F₂ emission (λ = 157 nm) are observed in a lamp-like discharge in a longitudinal discharge excitation tube. The laser tube consists of a 30 cm long Pyrex glass pipe with an inner diameter of 2 mm, and a step-up transformer coupled directly to the discharge tube without a high-voltage switch. Excitation is produced by wall-coupled discharge. The laser pulse width is 6.1 ns at 100 Torr (13.3 kPa, with an F₂ concentration of 5 %) when a slow-rising voltage pulse of -40 kV (rise time: 253 ns) is applied. VUV-F₂ emission of a 24.5 ns (FWHM) pulse width was generated simultaneously with the red-F^* laser.

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A new matching scheme for linear magnetohydrodynamic (MHD) stability analysis is proposed in a form offering tractable numerical implementation. This scheme divides the plasma region into outer regions and inner layers, as in the conventional matching method. However, the outer regions do not contain any rational surface at their terminal points; an inner layer contains a rational surface as an interior point. The Newcomb equation is therefore regular in the outer regions. The MHD equation employed in the layers is solved as an evolution equation in time, and the full implicit scheme is used to yield an inhomogeneous differential equation for space coordinates. The matching conditions are derived from the condition that the radial component of the solution in the layer is smoothly connected to those in the outer regions at the terminal points. The proposed scheme is applied to the linear ideal MHD equation in a cylindrical configuration, and is proved to be effective from the viewpoint of a numerical scheme.

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Zonal flow type oscillation, which is driven by a small modulation of the electron cyclotron resonance (ECR) power in a low-frequency band (< 0.1 kHz), and its impact on drift wave turbulence are observed in linear cylindrical ECR plasmas by simultaneous spatiotemporal measurements with a multi-ring probe array. It is found that a potential low-frequency (< 0.1 kHz) oscillation can have a zonal flow type structure. Bicoherence analysis reveals that this zonal flow type oscillation has a nonlinear interaction with the drift mode. These results indicate that an electric field with zonal flow, which is excited externally, can modulate the drift mode amplitude, similar to spontaneous zonal flow.

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Comparative study on Coulomb type and Johnsen-Rahbek type of electrostatic chuck used for holding a silicon wafer in plasma processing is presented. The remarkable differences between the two types are found in dechuck operation where a high voltage applied to the chuck electrode is turned off to release the wafer from the chuck stage. In case of the Coulomb type, an instantaneous large short-circuit current flows exponentially decreasing with a short time constant (τ = 0.14 ms). In case of the J-R type, a non-exponentially decaying small current is sustained for much longer time (∼1000 ms), thus giving rise to the considerable delay of wafer dechuck. The mechanism of such decay is explained by a microscopic bi-layer model where the interfacial layer is divided into three distinct regions having their own capacitance and surface resistance.

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We have measured fast magnetic fluctuations (> 10 kHz) using a complex edge probe in the edge region of TPE-RX reversed-field pinch plasma. We observed that the frequency of magnetic fluctuation at the peak power in the frequency spectrum varies with time, and this frequency variation is determined by the values of pinch and reversed parameters, although the amplitude of the fast magnetic fluctuations are almost independent of those parameter values.

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The effects of neutral particle density on equilibrium of field-reversed configuration (FRC) plasmas sustained by rotating magnetic fields (RMF) were investigated in the FRC Injection Experiment apparatus. Two different gas feeding methods were used to realize different neutral particle density conditions. The experimental results show that a higher current drive efficiency with full penetration of the RMF was achieved in the lower neutral particle density case. On the other hand, the plasma current in a higher neutral particle density case flowed in a narrower region near the geometric axis than in a lower neutral particle density case. The FRC equilibrium with higher neutral particle density resulted in lower current drive efficiency, possibly due to the shorter penetration length of the RMF. No significant ion spin-up was observed in the present conditions.

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In order to estimate the electromagnetic force acting on vessel components during tokamak disruptions, an accurate prediction of the plasma current decay time is necessary. We have verified a current decay model based on a simple series circuit with a plasma resistance and an inductance. The circuit is employed for establishment of a plasma current decay time database using disruptive discharges in a small tokamak HYBTOK-II. An increase in the decay rate of the plasma current during the current quench phase was observed in experiments associated with an increase in the plasma resistance. This experimental result is consistent with the prediction of the model.

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The poloidal eigenmode of the geodesic acoustic mode (GAM) is analyzed in the case of high aspect ratio circular plasmas, and an analytic representation for poloidal eigenfunction is derived. The m = ±1 and m = ±2 (m is the poloidal number) components of eigenfunction show up-down antisymmetry and up-down symmetry, respectively, in a torus. The mixing of the up-down symmetric and antisymmetric components becomes significant, when the ion gyroradius is large or when electron temperature is higher than ion temperature.

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A new method is proposed to measure the magnetic field direction in hot plasmas using helium (He) neutral beam injection. The injected He beam is ionized by collisions with field electrons, and the ionized He beam atoms emit line radiation during their gyromotion with their rotational axis in the direction of the magnetic field. The direction of that axis can be determined locally from the Doppler width of the line radiation in the region along the beam path. The current intensity and energy of the injected He beam necessary to obtain reasonable intensity of line radiation from He⁺ ions are estimated. This estimation includes the effect of ionization from the metastable state of the He beam atoms and takes the 468.6 nm line radiation from He⁺ ions as an example. It is shown that the radiation intensity and line broadening width obtained using a He neutral beam with energy of 1 keV and current of 10 mA - 100 mA are sufficient for spectral measurement in typical reversed field pinches. It is also shown that the beam with energy of 10 keV and current of 0.1 - 1 A is sufficient in medium sized tokamaks.

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High-energy particles in a finite beta plasma of the Large Helical Device (LHD) are numerically traced in a real coordinate system. We investigate particle orbits by changing the beta value and/or the magnetic field strength. No significant difference is found in the particle orbit classifications between the vacuum magnetic field and the finite beta plasma cases. The deviation of a banana orbit from the flux surfaces strongly depends on the beta value, although the deviation of the orbit of a passing particle is independent of the beta value. In addition, the deviation of the orbit of the passing particle, rather than that of the banana-orbit particles, depends on the magnetic field strength. We also examine the effect of re-entering particles, which repeatedly pass in and out of the last closed flux surface, in the finite beta plasma of the LHD. It is found that the number of re-entering particles in the finite beta plasma is larger than that in the vacuum magnetic field. As a result, the role of reentering particles in the finite beta plasma of the LHD is more important than that in the vacuum magnetic field, and the effect of the charge-exchange reaction on particle confinement in the finite beta plasma is large.

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The manufacturing process of creep specimens and an irradiation technique in a liquid metal environment for in-pile and creep measurements of irradiated samples are established for highly purified V-4Cr-4Ti, NIFS-HEAT alloys. Irradiation experiments with sodium-enclosed irradiation capsules in JOYO and lithiumenclosed irradiation capsules in HFIR-17J were conducted using pressurized creep tubes. From thermal creep experiments, the activation energy of creep deformation using pressurized creep tubes was determined to be 210 kJ/mol·K, the creep stress factor was 4.9 for an 800°C creep test, and its mechanism was determined to be a climb-assisted glide of dislocation motion. It was found that the creep strain rate exhibited a linear relationship with effective stress up to 150 MPa from 425 to 600°C under JOYO and HFIR irradiation. The activation energy of irradiation creep was estimated to be 46 kJ/mol·K. No significant difference in irradiation creep behavior between the liquid sodium and liquid lithium environments was observed. A set of essential physical data of irradiation creep properties was obtained for V-4Cr-4Ti alloys.

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A new application using an electric impulse signal has been developed for electron density profile measurements in the Large Helical Device (LHD). Using an impulse waveform voltage, which has broadband frequency components, we constructed an ultrashort pulsed radar reflectometer with 28 channels in X-, Ka-, and U-band frequency components. The effect of the bandwidth of an inline band-pass filter was investigated, and was optimized. For a multiple-channel and multiple-frequency band system, a new switching technique and multiplexer were developed. Using the Abel inversion method, the reconstructed electron density profile was obtained from the delay time as a function of the probing frequency. Good agreement with other diagnostics was obtained.

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To distinguish between the beta effect and configuration effect due to an increment in beta on the gradual degradation of the global confinement property in high-beta plasmas on the Large Helical Device (LHD), the local transport characteristics in the high-beta plasmas are studied by considering the change in the major radius of the magnetic flux surface with the beta value. First, the influence of the change in the magnetic configuration on the local transport is studied in low-beta plasmas, and it is confirmed that the dependence of the local transport properties on the magnetic configuration is almost the same as that proposed in the ISS04 scaling in the entire plasma region. Next, the dependence of the local transport characteristics in high-beta plasmas on the major radial position of a geometric center of the magnetic flux surface is studied in comparison with that in low-beta plasmas. The dependence of the local transport in the peripheral region is correlated more with beta itself than the magnetic configuration effect, whereas the core transport appears to be correlated more with the configuration effect.

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Optical emission spectroscopy was used for examining the temporal variations in the spatial distributions of the blackbody temperature and electron density of plasmas produced by laser ablation of a BN target in ambient nitrogen gas. The blackbody temperature was estimated by fitting the continuum component in the optical emission spectrum using the Planck's law of radiation, and the electron density was evaluated from the Stark broadening of a line emission of a B atom. The blackbody temperature was evaluated to be close to 10⁴ K and the electron density was on the order of 10¹⁷- 10¹⁸ cm^-3, immediately after the irradiation of the laser pulse on the target. The dynamics of the blackbody temperature and the electron density were understood by considering plasma expansion and the confinement effect of ambient gas.

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A heavy ion beam probe (HIBP) using a 3 MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. It is calibrated and can be used to measure the electrostatic potential profiles in LHD plasmas. The radial electric field (E_r) obtained from the potential profiles measured using the HIBP agrees with that measured by charge exchange spectroscopy (CXS). E_r predicted by the neoclassical theory is also compared to that measured using the HIBP, and is in good agreement with the experimental results in the core region.

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An assessment of in-vessel metallic mirror materials for the transmission of the laser beam used in the ITER edge Thomson scattering diagnostics is reported. The transient temperature increase due to the laser pulse irradiation on the laser transmission mirror is calculated by a one-dimensional heat conduction equation. Candidate mirror materials are discussed based on a comparison between the numerical calculation and current data relevant to the laser-induced damage threshold (LIDT). Gold, silver, and copper are considered promising because of its high reflectivity. The LIDT is evaluated considering multi-pulse effects and used to determine the necessary size for the laser transmission mirror for the ITER edge Thomson scattering diagnostics.

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Reduced single-fluid and two-fluid equations for axisymmetric toroidal equilibria of high-beta plasmas with flow are derived by using asymptotic expansions in terms of the inverse aspect ratio. Two different orderings for the flow velocity, comparable to the poloidal Alfvén velocity and comparable to the poloidal sound velocity, are considered. For a poloidal-Alfvénic flow, the two-fluid equilibrium equations with hot ion effects are shown to have a singularity that is shifted by the gyroviscous cancellation from the Alfvén singularity found in singlefluid magnetohydrodynamics (MHD) when the poloidal flow velocity equals the poloidal Alfvén velocity. For a poloidal-sonic flow, a reduced single-fluid model is used to derive a set of equilibrium equations that includes higher-order terms. The singularity at a poloidal flow velocity equal to the poloidal sound velocity is recovered in the higher order equations.

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We investigate ion energy spectra of a droplet target composed of different ion species, which is assumed to be heated by ultrashort laser pulse. The dynamics is studied with three-dimensional particle-in-cell simulation. It is found that the maximum ion energy E_i,max of the ion species with a charge a state Z has proportionality, E_i,max ∝ Z² , when multi-species ions exist in large quantities simultaneously. This is a crucial new result different from the scaling E_i,max ∝ Z, where the fraction of such contaminating ions is small compared with that of the background ions. We discuss this present numerical result by comparing with a self-similar solution, which takes a full account of the charge separation effect.

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Normalized bootstrap current coefficients are calculated for Large Helical Device (LHD, Japan) plasma configurations with different magnetic axis positions using the VENUS+δf code [Fusion Sci. Technol. 50, 440 (2006)]. The dependences on the different collisionality regimes (over the full experimental range of LHD plasma discharges) and the plasma radii are presented. The comparison of the VENUS+δf, SPBSC and DKES codes results is shown. The approach to the LHD experimental results is discussed. The bootstrap current effect on the iota = 1 islands is considered.

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In this study, a computational method of the kinetic model of carbon tetrafluoride (CF₄) in wet argon gas under electron beam irradiation was developed. Using this method, the mechanism of decomposition and the optimum concentration of H₂O during decomposition of CF₄ was determined. It was found that 99% of 1000 ppm of CF₄ of in atmospheric-pressure argon gas decomposed at an input energy density of 1 J/cm³ .

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