Kazushige Ishii

Optical escape factors and population densities for TPD-plasma

Abstract Optical escape factors and recalculated population densities are presented in connection with a remark by Hegde and Ghosh. It is shown that the optical escape factors given by these authors are too small for the experimental conditions used and, contrary to their results, the population densities for levels with principal quantum numbers larger than 4 of He(II) may be described by the optically-thin assumption.

A dc high‐current low‐energy electron beam gun

A dc high‐current and low‐energy electron beam gun has been developed. The maximum electron beam current is 63 A for an accelerating energy of 140 eV. The maximum ratio of the beam current to the discharge current is 78%. The ion current, which is extracted from the helium plasma produced by the electron beam, is 12.3 A. This value corresponds to the current density of about 7 A/cm2, which is the highest value among the ion sources in steady operation. The electron density of the plasma is estimated from the ion saturation current to be about 4.6×1013 cm−3, which corresponds to the degree of ionization of 21%. This gun will open the way for many electron beam applications.

Spectroscopic observation of a quasi-steady-state plasma in contact with a neutral gas☆

Abstract Very intense spectral lines of He + were observed when a He plasma was brought into contact with a He gas. The population densities of the excited levels of He + ions were found to be much larger than the values expected in the steady state for the given electron temperature and density. The contact mechanism and a method of determining the electron temperature and the electron and ion densities are discussed for the quasi-steady state.

Experiment on a large-diameter plasma-filled backward-wave oscillator

Abstract A large-diameter plasma-filled backward-wave oscillator (BWO) is investigated experimentally. The parameters of slow wave structure are chosen so that the oscillation frequency is about 20 GHz at 60 keV beam energy. Plasma is produced by the beam and has favorable effects for beam propagation and Cerenkov oscillations. The output power of the BWO with plasma is observed to be three to six times that of vacuum BWO. The power level is several kilowatts and the efficiency is about 0.01%. For Cerenkov oscillations of a large-diameter BWO, the beam energy mainly determines the starting conditions for oscillation. The output power is strongly enhanced when the guiding magnetic field approaches the fundamental electron cyclotron resonance. This mechanism is closely related to the anomalous Doppler cyclotron resonance. The maximum power of 480 kW with an efficiency of 5% is achieved even for a relatively low beam energy of 60 keV.

Measurement of Localized Electrostatic Oscillations Excited by Low-Power Microwaves in a Plasma Waveguide

Localized electron plasma oscillations excited at the resonant surface by low-power microwaves incident obliquely on an inhomogeneous unmagnetized plasma in a cylindrical waveguide are measured by a receiving antenna. The disturbance by the antenna on the electrostatic fields is significantly reduced in our condition with a steep density gradient and large angles of incidence. As a result, patterns of large and broad resonance field including phase information are observed. The peak values of the resonantly excited field are compared with numerical analyses.

Population Genetical Mechanism of Molecular Evolution

The neutralist-selectionist controversy persists with respect to the population genetical mechanism of molecular evolution. In this paper, we first show how we can explain, from a selectionist perspective, the fact that molecular evolution rates are smaller than total mutation rates. Next, using a statistical analysis of electrophoretic data on local differentiation, we show that, in most cases, stochastic selection is more responsible for local differentiation than is random drift.

Possible Existence of a Transient Superfluid Plasma in Liquid Helium II

A new and novel possibility for producing a transient superfluid plasma state in liquid helium II is proposed. Below 0.4 K, a superfluid plasma is analogous to a weakly ionized plasma in familiar gaseous discharge from the standpoint of equivalent momentum relaxation collision frequency between ions and neutral atoms or excitons, even though plasma parameters are quite different from each other. A preliminary experiment to create plasmas with very slow decay times in liquid helium is presented.

Development of Hydrogen Ion Source with a Sheet Plasma

A large-current hydrogen ion source has been developed by using a sheet plasma. The cathode of the discharge tube developed by the authors was lanthanum hexaboride (so called LaB6), which provided a stable plasma current of up to 30 A. The sheet plasma was formed by applying a pair of flat permanent magnets to a discharge plasma column. The electron density and the electron temperature in the sheet plasma were measured by a probe method. It was observed that the values of the electron temperature and the electron density distributed uniformly along the width direction and those values were about 3.8 eV and 1×1010 cm-3, respectively. On the other hand, the half width of the sheet plasma was about 14 mm in the thickness direction. It was clear that the arc current and the gas evacuation capability were important factors used to obtain the high density sheet plasma.