Shingo Imazu

An experimental investigation of nonequilibrium effects in wall-confined argon plasma arcs

Deals with thermal equilibrium between the particles in argon plasma arcs. The current limit for LTE is experimentally defined as a function of the pressures. Plasma parameters were spectroscopically determined. In particular, the electron temperature and heavy particle temperature were measured. The electron temperature was determined from an absolute continuum strength. Two temperatures were obtained for the heavy particles, one of which was determined from the Doppler component of the Halpha line when argon gas seeded with hydrogen was used. The second was obtained through a kinetic formula using the measured density and temperature of the electron. The results show that the electrons did not equilibrate with the heavy particles at low currents and pressures. The limit value of the current for LTE increased with decreasing gas pressure. It is shown, furthermore, that the measured field strength of the arc was remarkably lower than those calculated at currents less than the above limits.

Collision frequencies between charged and neutral particles in a magnetic field

It is shown theoretically how much the magnetic field influences the collision frequencies between charged and neutral particles. The magnetic field B for the usual field strength does not affect the collision cross section. However, the respective charged particles gyrate around the field lines, and then the relative velocity between charged and neutral particles changes with B. Consequently, it is shown that, when the mean free path λ is large compared with 2πrL, the velocity component contribution to the collision is the velocity component due to the motion along the field axis and not that due to the gyration. Here, rL is a Larmor radius.

Nuclear Reaction Rates between Charged Particles at High Energies in a Magnetic Field

The effect of a magnetic field on the nuclear reaction rates between heavy charged particles in a fully ionized gas is theoretically investigated. The physics of the collision occurring between a pair of colliding charged particles is clarified by tracing the trajectories of the particles in the magnetic field. First, an expression of the relative velocity between the colliding particles is obtained, and then the equation of the collision frequency for the nuclear reaction is derived. Consequently it is indicated that the nuclear reaction rate in the presence of the magnetic field may be less than that in the absence of the magnetic field.

Effect of the Magnetic Field on the Collision Frequencies between Charged and Neutral Particles

The purpose of this paper is to show theoretically how much the magnetic field influences the collision frequencies between charged and neutral particles. First, the flow of charged particles crossing the cross section during time t is obtained, and then the collision frequency, F , in the magnetic field, B , is determined. Consequently, when 2π r L is small compared with the mean free path λ, it is shown that the contribution of the velocity component to the collision frequency is the velocity component due to the motion along the field axis and not that due to the gyration. Here, r L is the Larmor radius. When the velocity distribution function is isotropic, numerical results show that F in the magnetic field such that 2π r L ≪λ is half of that for B =0.

Bremsstrahlung Rates in Fully Ionized Gases in a Magnetic Field

The bremsstrahlung rates in fully ionized gases in a magnetic field are theoretically investigated. Here it is assumed that the charged particles have the Maxwell velocity distributions, and that an external electric field does not exists. In the theoretical treatment, the followings are considered: When the Larmor radius is larger than the radius of the collisional cross section due to the bremsstrahlung, the radiation of energy during a short time at an instant of the collision is not affected by the magnetic field. However, according to the gyration, the relative velocity between an electron and a colliding ion during the free path is affected by the magnetic field strength. Numerical calculations show that the bremsstrahlung rate in the presence of the magnetic field is smaller than that in the absence of the magnetic field.

Time lag of line‐intensity jump in decaying argon‐arc plasma

Time lag of the line‐intensity jump in a decaying argon arc was experimentally investigated. Especially, the time of intensity peaks during the intensity jump was measured in a wall‐stablized argon arc after the current interruption. The measurements were made for seven spectral lines of ArI. The result showed that the peak time changed depending on the ionization energy of the excited level. Namely, the peak time increased with increasing the ionization energy of the level. The peak time at lower levels involved additional delay to that predicted by the equilibrium theory. It was also shown that the amplitude of the jump at these lower levels did not reflect the accurate gas temperature.

Effect of helical instability on the internal magnetic field in a magnetized positive column

The effect of the helical instability on the internal magnetic field in the positive column, is investigated theoretically under the assumptions that the densities of electrons and ions are perturbed independently and that the perturbed densities have finite amplitudes. The internal magnetic field is found as a function of the amplitude of the superimposed helix for the helical instability (m=1) and the phase shift δm between the perturbed densities of electrons and ions. The theoretical results are compared with experimental data and found to be in fair agreement with experimental values. It is concluded that the direction of the internal magnetic field produced by the helical instability is parallel to that of the applied magnetic field.

Influence of Radial Diffusion Loss of Electrons on Ionization Waves Produced by Spatial Resonance

The spatial resonance which produces non-hydrodynamic ionization waves is investigated theoretically, with the radial potential distribution of (r)=w(r/R)l and the radial diffusion loss of electrons being taken into account. It is found that the radial diffusion loss of electrons disturbs the spatial resonance. Since the radial diffusion loss is suppressed markedly by increasing the axial magnetic field, spatial resonance is likely to occur in the magnetic field if the energy loss due to elastic collisions is small. Other effects of the axial magnetic field on facilitating or suppressing the spatial resonance are also disscussed.