We develop a three-dimensional electromagnetic PArticle Simulation code for investigating driven Magnetic reconnection in an Open system from the kinetic view-point (PASMO). In this paper, we advance a new model for the upstream and downstream boundaries. We succeed in achieving the frozen-in condition for both electrons and ions with high accuracy at the upstream boundary, while we can decrease unphysical noise at the downstream boundary. We compare the simulation results of long and short-simulation boxes to check whether the downstream boundary model fulfills its function. The results of the short-simulation box effectively mimic those of the long-simulation box. Using the new boundary model, we succeed in increasing the accuracy of simulation.

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Two-dimensional distributions of D_α, D_β, D_γ and D_δ are reconstructed from line-integral measurements. The two-dimensional emission ratio of D_δ to D_γ indicates that the volume recombination occurs throughout the inner divertor plasma. In particular, at an emission peak above the inner strike point, it is shown that the population density of high n levels (n = 4, 5 and 6) is determined by the electron-ion volume recombination with an electron temperature and density of 0.2-0.5 eV and 1 × 10²⁰ m^-3 , respectively, and that the population density of the n=3 level is not explained by the recombining plasma component with or without the ionizing plasma component.

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Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 × 10²¹ m^-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (R_ax), and the steepest profile is obtained at R_ax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 × 10¹⁹ m^-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around R_ax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor.

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The liquid-gas interfacial region, which is the boundary between plasmas and liquids, activates physical and chemical reactions, thus attracting much attention as a novel reactive field in nanobiomaterial creation. Owing to the unique properties of ionic liquids such as their extremely low vapor pressure and high heat capacity, we successfully created a reactive liquid-gas (ionic liquids-plasmas) interfacial field under a low gas pressure condition, in which the plasma ion behavior can be controlled. The effects of plasma ion irradiation on the liquid medium are for the first time revealed quantitatively. In connection with the plasma ion irradiation, the potential structure and optical emission properties of the liquid-gas interfacial plasma were investigated by changing the polarity of the electrode in the liquid to evaluate liquid-plasma interactions. These results may contribute to systematizing the field of liquid-gas interfacial plasma physics for certain applications. Furthermore, novel nanobiocomposite materials, such as DNA-encapsulated carbon nanotubes, were formed using liquid-phase plasma, and for the first time, modifications of the electrical properties of nanocarbons according to the types of encapsulated DNA were demonstrated.

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The spectral energy distributions of the magnetohydrodynamic (MHD) fluctuations of the solar wind turbulence are derived using the dimensional arguments a la Kolmogorov within the framework of the Hall magnetohydrodynamics. While the velocity and the magnetic field fluctuations are dynamically related, the density fluctuations could behave as a passive scalar and be simply convected by the velocity or the magnetic field fluctuations. The Hall effect removes the degeneracy of the ideal Alfvénic spectra of the velocity and the magnetic fluctuations, at spatial scales shorter than or equal to the ion- inertial scale, adding steeper branches to the ideal MHD spectra. Which spectrum would the density fluctuations, behaving as a passive scalar, follow in such a case? The answer leads to the interesting consequence that the electron density fluctuations should follow the magnetic spectra since the electrons are frozen to the magnetic field and the ion density fluctuations should follow the kinetic energy spectra as ions carry the inertia. Thus the electron and the ion density would have different spectra at spatial scales equal to and smaller than the ion-inertial scale. However this raises the issue of the quasineutrality that must be maintained at each scale within the Hall-MHD. One way to accommodate both the quasineutrality as well as the electron- magnetic freezing in the Hall MHD is to discard the passive nature of the density fluctuations; they must be dynamically active in the turbulence. The quasineutrality could also be restored by a third species of particles providing a stationary background.

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We present a statistical theory of intermittency in plasma turbulence based on short-lived coherent structures (instantons). In general, the probability density functions (PDFs) of the flux R are shown to have an exponential scaling P(R) ∝ exp (-cR^s ) in the tails. In ion-temperature-gradient turbulence, the exponent takes the value s = 3/2 for momentum flux and s = 3 for zonal flow formation. The value of s follows from the order of the highest nonlinear interaction term and the moments for which the PDFs are computed. The constant c depends on the spatial profile of the coherent structure and other physical parameters in the model. Our theory provides a powerful mechanism for ubiquitous exponential scalings of PDFs, often observed in various tokamaks. Implications of the results, in particular, on structure formation are further discussed.

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We collected dust particles ranging in size from 1 nm to 10 µm from the Large Helical Device employing two methods: an ex-situ filtered vacuum collection method and an in-situ dust collection method. The size distribution from 1 nm to 10 µm is well expressed by the Junge distribution. Dust particles are classified into three kinds: small spherical dust particles below 1 µm in size, agglomerates consisting of primary particles of 10 nm, and large dust particles above 1 µm in size and irregular in shape; this suggests three formation mechanisms of dust particles: chemical vapor deposition growth, agglomeration, and peeling from walls. In-situ collection shows that agglomeration between dust particles takes place in main discharges. The primary dust particles in agglomerates are around 10 nm in size, suggesting agglomeration between a negatively charged large agglomerate and a positively charged dust particle 10 nm in size. We have also confirmed the important fact that a large number of dust particles move during vacuum vent. Therefore, the in-situ dust collection method is needed to reveal the generation-time and -processes of dust particles and their deposition position during discharges.

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Effects of the stochasticity of magnetic field lines on transport properties are investigated. In a high-β LHD plasma, the structure of field lines in the peripheral region becomes stochastic by finite-β effects but the finite pressure gradient exists in that region. The radial diffusion coefficient and the Kolmogorov length of stochastic field lines are estimated. In the stochastic region, the radial diffusion of stochastic field lines becomes large and the Kolmogorov length becomes short due to increasing β. In that region, the radial heat transport becomes large due to the stochasticity of field lines.

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Electron cyclotron range of frequency system of the JT-60U finished operation at the end of August 2008, and improvements toward JT-60SA have been started. In the last two years stable gyrotron oscillation at an output power of 1.5 MW for 1 s was demonstrated, for the first time, using the 110 GHz gyrotron. It was verified that the heat load on the cavity was at an acceptable level with continuous oscillations at 1.5 MW. The absorption power of the collector was also at an acceptable level for the longer pulse oscillation of 5 s. A power modulation technique based on anode voltage modulation was also developed in order to study the effects of modulated Electron Cyclotron Current Drive (ECCD) on Neoclassical Tearing Mode (NTM) stabilization. Modulation frequencies of up to 7 kHz were achieved at output power of 0.8 MW exceeding the previous limit of 3 kHz. Modulated ECCD experiments in synchronization with the NTM were successfully performed with a modulation frequency of around 5 kHz. Development of an accurate synchronization system played an essential role in the experiments that needed a maintained phase between the magnetic probe signal and modulated ECCD in real time. The results provide significant information for further developments that will enhance the overall performance of ECRF systems in the near future.

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In order to discuss the feasibility of compact neutron sources for scientific, medical and industrial applications, the yield of laser-produced neutrons is scaled by the laser energy. The laser energy scaling law of the neutron yield is derived from the laser intensity scaling law for the energy and the number of laser produced ions. High-energy ions are generated by Coulomb explosion of clusters through intense femtosecond laser-cluster interactions. The reactions of D(D,n)He generating high yield even by relatively low deuterium energy and Li(p,n)Be generating relatively low energy neutrons are discussed. The neutron yield of D(D,n)He determines the potential for using compact neutron sources with the aid of modern laser technology. In addition, p(Li,n)Be shows much higher yield than Li(p,n)Be with the assumption of Coulomb explosion of a cluster with a diameter of 500 nm.

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We are developing a spectroscopic diagnostics system in ultraviolet and visible wavelength regions for monitoring ITER divertor plasmas. An equivalent-size prototype of the optical components for viewing upper port fanarray chords has been assembled as a system to measure spectral throughput, i.e., étendu. Collisional-radiative models for He_I and C_IV are used to estimate the emission line intensities of helium ash and carbon impurity ions in a divertor region of a burning plasma. The estimated line intensity of C_IV, λ772.6 nm, satisfies ITER requirements for the time resolution of measurement of T_i. A numerical simulation of the computerized tomographic technique for various pairs of viewing fan arrays has been applied to the divertor plasma region to reconstruct a two-dimensional distribution. The optimized pair of viewing fan arrays resolves a model distribution with a reasonable spatial resolution. We measure the reflectance of surfaces of carbon-fiber-composite and tungsten blocks, which make up the plasma-facing divertor target plates and the divertor dome. The reflectance of the surface of the tungsten divertor block is 23% at H_α (λ656.3 nm). A sandblast-processed tungsten surface effectively reduces direct reflectance; the resultant reflectance is less than 0.7%.

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A new technique for the direct measurement of electric field distribution along the plasma column in microwave jet discharges is developed and employed. The technique is based on a servomotor-controlled reciprocating antenna moving along the nozzle axis and plasma column. The measurement technique is applied to a rectangular waveguide-based 2.45 GHz argon and helium plasma jets generated by using the modified TIAGO nozzle at atmospheric pressure with a microwave power of less than 500 W. The measurement has been done with and without igniting the plasma jet in order to investigate the standing wave propagation along the nozzle axis and plasma column. It is observed that the electric field decay occurs slowly in space with plasma ignition than that of without plasma, which indicates the surface electromagnetic wave propagation along the plasma column in order to sustain the plasma jet. This study enables one to design, determine and optimize the size and structure of launcher nozzle, which plays an important role for the stable and efficient microwave plasma generators.

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We have carried out experiments to clarify the stabilizing effect of a plasma rotation on the resistive wall mode (RWM) that could limit the achievable-β_N in high-β_N plasmas above the no-wall ideal β_N-limit. On JT-60U plasma rotations are controlled using neutral beams with varying combinations of net torque input while keeping β_N constant. The RWM is destabilized as the plasma rotation is being reduced. Detailed measurements of the mode structure revealed that the RWM has a global structure that rotates with the order of the resistive wall time. In these experiments, it is found that the critical toroidal rotation speed for the RWM stabilization is less than 1% of the Alfvén speed. Moreover, the critical rotation does not strongly depend on β_N. The results suggest that high-β_N operation up to the ideal wall β_N-limit could be possible by suppressing the RWM with a slow plasma rotation in fusion reactors.

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An array of microplasmas with sizes ranging from a millimeter to a micrometer, has potential for novel and promising electromagnetic-wave media, especially when the wave frequency is below the electron plasma frequency. Photonic crystals or band-gap materials composed of microplasmas have unique properties arising from their loss term, and they can become band-pass filters instead of the band-stop filters usually observed in photonic crystals of dielectrics. Such behavior is well understood using the dispersion relation in a three-dimensional space of frequency and complex wavenumber with real and imaginary parts. Another functional array is a simple one-dimensional (1D) array; it can conduct microwaves for a wide frequency range below the electron plasma frequency. The propagating modes are similar to the coupling of localized surface plasmon polaritons observed along a metallic nanoparticle chain in the photon range; however a 1D microplasma array features differ from those of a metallic sphere array, leading to a dynamic wide-band waveguide.

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Strong electrostatic turbulence in magnetically confined plasmas is characterized by trapping or eddying of particle trajectories produced by the E × B stochastic drift. Trapping is shown to produce strong effects on test particles and on test modes by causing nonstandard trajectory statistics: non-Gaussian distribution, memory effects, and coherence. Trapped trajectories form quasi-coherent structure. Trajectory trapping has strong nonlinear effects on the test modes on turbulent plasmas. We determine the growth rate of drift modes as function of the statistical characteristics of the background turbulence. We show that trapping provides the physical mechanism for the inverse cascade observed in drift turbulence and for the zonal flow generation.

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The Ring Trap 1 (RT-1) device can confine a pure-electron plasma in the magnetospheric dipole field configuration [Z. Yoshida et al., Plasma Fusion Res. 1, 008 (2006); Y. Ogawa et al., Plasma Fusion Res. 4, 020 (2009); H. Saitoh et al., Plasma Fusion Res. 2, 045 (2007)]. While this system has proved long-term (typically about 400 s) stable confinement, the internal structure of the electron cloud has not been well understood. The spatial distribution of the charge density has been estimated using an array of wall probes. Multiple wall probes with current amplifiers and analog integration circuits were developed and used to estimate image charge profiles on the chamber walls. The electrons are trapped inside the separatrix during the injection phase. In the stable confinement phase, electrons shift toward the stronger magnetic field region and produce a rather peaked profile.

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