Shunjiro Ikezawa

Observation of Electron Plasma Waves in Plasma of Two-Temperature Electrons

Propagation of electron plasma waves in a large and unmagnetized plasma containing two Maxwellian distributions of electrons is studied experimentally. Two kinds of plasma sources which supply electrons of different temperature are used. The temperature ratio is about 3 and the density ratio of hot to cool electrons is varied from 0 to 0.5. A small contamination of hot electrons enhances the Landau damping of the principal mode known as the Bohm-Gross mode. When the density of hot electrons is larger than about 0.2, two modes are observed. The results agree with theoretical dispersion relations when excitation efficiencies of the modes are considered.

Control of the Two-Electron-Temperature Plasma Parameter in a DP Device

A two-electron-temperature plasma is observed in a double-plasma device when the space potential approaches the potential of the cathode filaments. The densities of the hot and cold electrons (Neh and Nec) are controlled by the target discharge current It and target filament current IFt. When It increases, Neh increases. When IFt increases, Nec increases. The ratio of the density of the hot to the cold electronsm, N (=Neh/Nec), can be controlled: when It increases, N increases from 0.8 up to 5.0, and when IFt increases, N decreases from 1.1 to 0.25. The hot and cold electron temperatures Th and Tc are kept almost constant at 3.5~6.0 eV and 1.0 eV, respectively.

Production of High-Density Plasmas in Electron-Beam-Excited Plasma Device

We tried to enlarge the diameter of high-density beam plasmas in an electron-beam-excited plasma (EBEP) device. In order to enlarge the beam plasma, we made a cusp configuration at the end of the ion source region in the EBEP device. Also, a surface confined ring with permanent magnets called «surmac» was mounted on the cusp center to make the plasma profiles flat. It was found that high electron density (7×10 11 cm -3 ) and uniformity (ΔN e /N e <4% OVER 6 CMO) COULD BE OBTAINED AT LOW PRESSURE (7×10 -4 Torr)

Electron Plasma Waves in a Two-Temperature Plasma

Dispersion relations of electron waves of small amplitude in a plasma of two-temperature electrons are studied theoretically. Addition of small amount of hot electrons to the plasma increases the damping of electron plasma wave. For the temperature ratio of six, when the density of hot electrons exceeds about four percents, the wave separates into two modes. One is the plasma wave of cool electrons when \(\omega{\gtrsim}\omega_{\text{p}}\) and merges in one of higher-order modes when ω<ω p . The other mode which is cut off at ω=ω p also merges in higher-order modes when ω≫ω p . The non-dispersive mode when ω<ω p has much larger damping rate than the similar mode in the plasma of Maxwellian and water-bag electrons.

Effective collision frequency in the presence of an ion sound wave parametrically excited in Tonks‐Dattner resonance

Effective collision frequency enhanced by an ion sound wave parametrically excited in Tonks‐Dattner (T‐D) resonance is evaluated from the Q value and the damping rate of a surface wave propagating along the axial direction as a test wave, which are observed in a mercury vapor discharge. The ion sound wave is produced by a three‐wave process of the parametric excitation where the incident electromagnetic wave decays into two electrostatic waves, an ion sound wave, and a T‐D resonance. The effective collision frequencies thus obtained as a function of the absorbed pumping power are nearly in agreement with those based on the perturbed orbit theory proposed by Weinstock et al. The ion density fluctuation level estimated from Dawson’s formula is found to be lower than that obtained in other turbulent experiments.

Experimental observation of the radial pattern of an ion sound wave parametrically excited in Tonks‐Dattner resonance

The radial pattern of an ion sound wave in a mercury discharge tube where the ion sound wave is parametrically excited in Tonks‐Dattner resonance is observed. The frequency of the HF (high‐frequency) wave is chosen to be about one order lower than that in Sterns experiment so that the diameter of the tube can be large, by which means the detailed radial pattern of the wave can be obtained. The result qualitatively agrees with the theory predicted by Rosa and Allen‐that is, it does not show the standing‐wave pattern.

RF Confinement of a Plasma by Two Cylindrical Electrodes

Electron contribution in the RF confinement of a mirror plasma by two cylindrical electrodes is reported. It is effective at a frequency corresponding to a parallel resonance including the electrode and the plasma. The plasma is sufficiently confined by a voltage of 40 volts, peak to peak, externaly applied to the plasma with an electron density n e ∼10 10 cm -3 and an electron temperature T e ∼20 eV. The plugging force for the confinement is caused by the electric field E z parallel to the mirror axis, which produces the ponderomotive potential in electrons, and ions are confined by the ambipolar electric field. The measured distribution of the space potentials can explain well that the plasma is confined by RF field between two cylindrical electrodes.

Germination and Growth of a Vegetable Exposed to Very Severe Environmental Conditions Experimentally Induced by High Voltage

Ultra-high-voltage (UHV) transmission power lines are required in order to reduce transmission energy losses, and to transfer more power across long distances. However, the ecological and biological influence of UHV lines has not been documented well. Possible influences of UHV lines are: electro-magnetic field, ozone, NOx, and ion shower. The purpose of this study was to obtain information on the germination and growth of Raphanus sativus L.cv. Kaiware-daikon exposed to an experimental environment in which all the above influences at very severe intensity levels were working simultaneously. Several environmental conditions severer than those predicted for future UHV lines were set up, using a high voltage at 60 Hz. The germination and growth of this plant were suppressed under the experimental conditions used, the suppression being greater the severer the conditions. When the electric field is strong, corona discharge occurs at the tip of the plant.

Estimation of frequency shift of an ion sound wave parametrically excited in Tonks‐Dattner resonance

It is shown that the frequency shift of the excited ion sound wave in Tonks‐Dattner resonance is due to the nonlinear phenomenon represented by the frequency‐mismatched factor of the nearly free resonance parametric theory derived by Nishikawa. It is also shown that the increase of the electron temperature is negligibly small so that the effect of the increase of the electron temperature on the shift can be neglected.

Breakdown in Vacuum by a Microwave Field Superposed with d.c. Voltage

The microwave breakdown and its suppression by superposing d.c. voltage was investigated at the frequency of 2.45 GHz with regard to the high power microwave techniques for heating fusion plasmas. An increase of about 60% in r.f. breakdown voltage was realized by superposing d.c. voltage of 1000 volts in the cavity, whose height was 2 cm, at the pressure of 1×10-4 Torr.