Yoshisuke Hatta

Enhanced heating of mirror-trapped ions under an instability around ion-cylotron frequency

Abstract The high-energy tail of the ion energy distribution is heated by an instability with broad-band frequency spectrum having a peak a little above the ion-cyclotron frequency. The tail heating of the ions is enhanced under a mirror configuration of the magnetic field.

Quiescent and turbulent plasmas under mirror-configurations of magnetic field

Particle reflection and trapping are investigated on plasma flows injected into mirror-configurations of magnetic field. Detailed measurements are made on a collisionless plasma whose ion energy distribution is controlled before entering into the mirror configuration, and the results are well explained by the orbit theory. When the plasma density is so high that the ion-ion collision mean free path is comparable to the mirror length, a clear plasma trapping due to the collisions is observed. An instability around the ion-cyclotron frequency is excited in order to trap a collisionless plasma, and enhanced tail heating of ion energy distribution is observed in addition to the trapping.

Instability of Three- or Four-Component (Electron, Ion and Beam) Plasma Systems

The instability of a beam-plasma system with no magnetic field is investigated mainly by means of the graphical analysis of the dispersion equation. Unstable regions are determined in detail in kinetic theory approach for three types of waves of electron beam-electron coupling, ion beam-electron (electron beam-ion) coupling and ion beam-ion coupling. The effect of the stationary electron appears in the region of the beam-ion coupling in a three-component plasma and in the region of all the waves except electron beam-electron coupling in a four-component plasma.

Low-Frequency Oscillations in a Weakly Ionized Plasma in Crossed Electric and Magnetic Fields

In a hot cathode discharge tube with a coaxial electrode configuration, low frequency oscillations (300 c/s to 30 kc/s) propagating in the direction of E × B 0 ( E and B 0 are a radial electric and an axial magnetic fields, respectively) are observed when B 0 exceeds a critical value correspounding to the condition ω c e τ e n ≈O(1) and the magnetic field has no effect on ions. The experimental results agree with the results of the analysis based on the two-fluid model in which the effect of the collisions between charged and neutral particles is taken into account. Oscillations are excited by an azimuthal relative velocity between electrons and ions. When the plasma is uniform, the waves are ion acoustic waves. When the plasma is non-uniform, the wave frequencies are determined by the drift velocity and the ratio of the electron to ion mobilities, if the collision frequency is higher than the oscillation frequency.

Synchronous quenching of drift-wave instability

Synchronous quenching of drift‐wave instability is investigated experimentally. The measurements show resonance phenomena similar to that of ion‐sound instability. The result is quantitatively compared with a phenomenological theory which includes a linear growth and a nonlinear saturation source term.

Drift motion of a plasma in a curved magnetic field

The drift motion of a collisionless plasma is measured in a curved magnetic field. A large drift is observed when the plasma is isolated from electric conductors. In a stationary state where the plasma is in contact with the conductors, the E*B drift is found to be very small, because a short-circuit path is formed through the conductors by the fast motion of electrons along the magnetic field.

Measurements of Growth and Damping Rate of Resistive Instability in Gaseous Plasma

Time rates of growing and damping of resistive instability in gaseous plasma in the crossed electric and magnetic fields are obtained experimentally. The discharge tube used has a coaxial cylindrical configuration with a grid, and works in the state of “anode glow mode”. The gas used is Ne, Ar and Hg. The damping rate is measured by means of an external excitation of damping waves by supplying a rectangular pulse to the grid. The growth rate is obtained by an observation of the transient of self-excitation of waves by abrupt change of the magnetic field strength beyond the critical field. Those experimental results are compared with those obtained theoretically using equations of three component fluid model.

The Deposition of Atoms Sputtered in an Abnormal Glow Discharge

Using an optical‐transmission method, the deposition of sputtered Ni atoms on a glass collector in an abnormal glow discharge is measured in Ar and Ar‐H2 mixture at 5 Torr. The distribution of atoms deposited on a glass collector is found to be determined by the diffusion process of sputtered atoms in the gases. The results show that the sputtering rate is proportional to the square of the current, and the sputtering rate of 100% Ar is about twice as large as that of 70% Ar‐30% H2 mixture.

LANGMUIR PROBE METHOD FOR A PLASMA HAVING SMALL AMPLITUDE OSCILLATIONS

Langmuir probe characteristics for a plasma having oscillations of space potential, electron density and electron temperature are discussed in detail. The method to derive amplitudes of oscillation as well as values of d.c. component of them in the case of the ideal plane probe are introduced. In order to get informations about oscillating components, “method of constant current probe” developed by Barnes and Eros is applied with some extention. The newly developed method to determine the amplitude of oscillation of the electron temperature seems to be useful because of its improved accuracy.

Moving Striations in Tapered Discharge Tubes

It is reported that the wavelength of moving striations is experimentally proportional to R n , where R is the tube radius and index n ranges from 1.5 to 2.0. Those measurements are done using tapered discharge tubes. A theory that can give a general explanation of the moving striations is introduced. The relation between the wavelength and the tube radius obtained from those theoretical considerations is in a good agreement with the experimental results.