Remarkable effects of radially produced shear of electric fields dE_r⁄dr on both turbulent fluctuations and drift waves are experimentally demonstrated with improvement in plasma confinement for the first time in the tandem mirror GAMMA 10. These electric-shear effects are performed on the basis of a factor of two progress in ion-confining potential (φ_c) formation due to advanced electron-cyclotron-heating powers and vacuum conditions; the dependence of φ_c is consistent with our proposed physics scaling.

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Spherical torus plasma is started-up by electron cyclotron heating alone without Ohmic heating in the LATE (Low Aspect ratio Torus Experiment) device. By injecting a 2.45 GHz microwave pulse up to 10 kW for 4 seconds, a plasma current is initiated and ramped up to I_p≈4 kA by adjusting the external vertical field for the equilibrium of the plasma loop. Magnetic measurements show that the last closed flux surface has an aspect ratio of A˜1.4 and an elongation of κ˜1.3. The line-averaged electron density is 1.3×10¹¹ cm^-3 which is almost twice the plasma cutoff density, suggesting that electron cyclotron heating by mode-converted electron Bernstein waves may take place.

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In this paper we compare conventional and imaging reflectometry systems by means of numerical simulation. A corrugated wheel is used as an approximation of the reflections by real plasma fluctuations. Our simulations prove that in the case of conventional reflectometry the correlations between the phase fluctuations of the received signal and the shape of the wheel decrease with an increase in distance from the target to the antenna, while the two-lenses imaging system shows high correlations far from the target.

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Transverse particle distributions inside an intense ion beam in a final buncher of heavy ion fusion are discussed using particle simulations. In order to evaluate the uniformity of the particle distribution in one beam, evolutions of the nonlinear field energy factor in the buncher are investigated as a function of presumed initial particle distributions. The results indicate that regardless of the initial conditions, the beam particle distributions come close to a unified one in real space at the final stage.

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The dispersion relation of electromagnetic waves in one-dimensional plasma photonic crystals is studied. The plasma photonic crystal is a periodic array composed of alternating thin plasma and dielectric material. The dispersion relation is obtained by solving a Maxwell wave equation using a method analogous to Kronig-Penny’s problem in quantum mechanics, and it is found that the frequency gap and cut-off appear in the dispersion relation. The frequency gap is shown to become larger with the increase of the plasma density as well as plasma width.

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The band structure of the A²Δ→X²Π system of the CH radical, the method of hydrocarbon flux measurement, and the modeling of hydrocarbon elementary processes are described. Reviews of recent research achievements are also presented. At JT-60U divertor plates, the chemical sputtering yields of not only CH₄ but also C₂H_y have been measured with simultaneous observation of the CH and C₂ bands. In the MAP-II device in the University of Tokyo, hydrocarbon-enhanced molecular assisted recombination processes have been qualitatively proved by comparison of the measured and the modeled CH band intensity.

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We classify the incoherent laser Thomson scattering (LTS) diagnostics of plasmas for measurements of electron density n_e and temperature T_e (or more generally electron energy distribution functions;EEDFs) as having evolved from the first stage, in which a whole Thomson spectrum is obtained during a single laser pulse from plasmas having n_e above 10¹⁸ m^-3, through the second stage, in which data accumulation is prerequisite for n_e below 10¹⁸ m^-3, and to the third stage, in which measurements from a material surface as close as a few tens of μm is required. In this last case, a strong suppression of stray light in addition to the data accumulation is necessary, and this was first demonstrated for a PDP (plasma display panel)-like discharge in 2000. In order to further expand its applicable range, we have been pursuing a more systematic approach, taking into account factors such as laser propagation⁄profile control, further stray light suppression, and other aspects. In this review article, we describe these developments and discuss future plans.

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In this article, we deal with weakly ionized gas discharges as low temperature plasmas. First, the electron swarm theory is outlined in order to bring the electron behavior in such plasmas into relief, which highlights similarity law and hydrodynamic regime as a specific nature of electron avalanche in static electric fields. Next, a study of electron dynamics in a high frequency electric field ranging from 100 MHz to 1 GHz is presented to show a coupling analysis associated with Maxwell’s equations and the Langevin equation. With the help of a Monte Carlo simulation for electrons, this analysis enables us to estimate the depth of energy injection from the oscillating external field to plasma reactors. A simple self-consistent scheme to investigate the ignition process of the high frequency plasmas is also suggested.

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Kinetic computer plasma modeling occupies an intermediate position between the time consuming rigorous particle dynamic simulation and the fast but rather rough cold- or warm-plasma fluid models. The present paper reviews the kinetic modeling of microwave surface-wave discharges with accent on recent kinetic self-consistent models, where the external input parameters are reduced to the necessary minimum (frequency and intensity of the applied microwave field and pressure and geometry of the discharge vessel). The presentation is limited to low pressures, so that Boltzman equation is solved in non-local approximation and collisional electron heating is neglected. The numerical results reproduce correctly the bi-Maxwellian electron energy distribution functions observed experimentally.

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Plasma Immersion Ion Implantation (PIII) has been developed as a method for high-flux implantation and conformal implantation on a complex shaped target. In PIII, a negative pulsed high voltage is applied to the target immersed in low-pressure high-density plasma. Then an ion sheath is formed around the target and energetic ions are implanted on the target surface. By increasing the plasma density, conformal implantation is possible. However, this process can not be easily realized for a complex shaped target, for instance which has a trench or holes with high aspectratios. In order to find the best condition in the process, it is very important to know the sheath shape around the target and the energy and flux distributions of implanted ions at each surface point. Plasma behavior in the PIII process has been simulated using “PEGASUS”.

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Kinetic simulation is a good numerical method for investigating plasma characteristics and behavior in a collisional micro plasma display because the kinetic simulation code describes the motion of particles with relatively better accuracy than that of the fluid simulation code. Using two-dimensional kinetic simulation code, we calculated the ion incident angle and energy distributions on the dielectric surface of the cathode region in an alternating-current plasma display panel cell with variations in gas mixture, cell type, and pressure. The angle distribution of ions impinging on the cathode surface is one of the important factors for accurate experimental measurement of the secondary electron emission coefficient and for estimation of MgO sputtering. We also observed the striation phenomenon in a PDP cell and attempted to explain the striation mechanism based on the kinetic simulation results.

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The equation of radiation transport describes the emission and absorption of a spectral line in a plasma. An apparent decrease in the emission intensity is demonstrated for an optically thick line, which is confirmed with the Balmer−α line observed for hydrogen ice pellet injection into the LHD plasma. The effective decrease in the spontaneous transition probability is expressed in terms of an escape factor, and is incorporated into the collisional-radiative model for neutral helium. For the glow discharge plasma in the LHD, a substantial decrease in the effective A coefficient of the 1¹S−3¹P line results in an increase in the upper-level population, leading to a very strong emission of the 2¹S−3¹P line; this resolves the last puzzle in the observed spectra. An emission line intensity is proportional to the ionization flux or the recombination flux of the ion species concerned. From the measured line intensities of ionized and neutral helium in the decaying phase of the LHD plasma, densities of the ions, and thus the electron density are estimated, which are in accordance with the electron densities determined by the interferometer. Under the condition of fixed atom and ion densities, starting from a high electron temperature where the plasma is ionizing and an emission line is strong, with a decrease in temperature the line intensity decreases. It takes the minimum at a temperature of ionization balance, and then it increases again in a recombining plasma. This feature interprets various observations. The above conclusion is a substantial generalization of the conventional belief that an emission intensity takes its maximum at the temperature at which the atom and ion densities are approximately equal; this latter statement is valid only under the condition of an ionization balance plasma.

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The external and independent control of parallel and perpendicular flow shears in collisionless magnetized plasmas are realized using two newly-developed plasma sources. The ion flow velocity shears parallel to the magnetic-field lines are then observed to destabilize not only the D’Angelo mode but also the drift-wave instability depending on the sign of the parallel shear in the absence of field-aligned electron drift flow in laboratory experiments. On the other hand, perpendicular ion flow velocity shears are demonstrated to suppress the drift-wave and the ion-cyclotron instabilities, and furthermore, these suppressions are found to take place independently of the sign of the perpendicular shear.

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The existence of the London layer along the boundary of the stable plasma is studied by relations including London equation obtained by the variational calculation using a Lagrangian density of the two fluid model of the plasma. Most interesting result derived by this process is that the length of the Larmor radius of the electron is equal to the width of the London Layer when the beta value of the plasma is equal to 1. This is explained by a simple model for the diamagnetic flux produced by rotating electrons in the magnetic field. Furthermore, the same result is obtained by using the equilibrium condition of the plasma which satisfies all the conditions given by our calculation.

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