Book Description

ABS>It is possible to generate plasma by passing a discharge between electrodes arranged such that the current is forced to flow across an initial strong magnetic field. The magnetic induction due to the discharge causes a bending of the original field. If the discharge is operated with a lowimpedance current source, electric breakdown starts in a limited region near the current- input connections and propagates as a well-defined front in the manner of a hydromagnetic shock wave. Such a shock is usually compressive, i.e. the sudden increase in temperature and ionization is usually accompanied by an abrupt onset of both transverse and longitudinal components of plasma flow. Consequently the front must be followed by a rarefaction wave in which the longitudinal flow is brought to rest. This phenomenon is analyzed as a one-dimensional single-fluid hydromagnetic problem, neglecting dissipation behind the wave. The assumptions are made of zero conductivity in front and thermodynamic equilibrium behind the wave. In the limit of essentially complete ionization behind the front, the problem can be solved analytically if the transverse magnetic field there remains small compared with the longitudinal field. In this case, the front velocity, plasma temperature and density, and the electric field behind the wave, as well as the structure of the rarefaction wave, can be ex pressed as simple functions of the initial magnetic field, the discharge current, the ionization energy, snd the initial gas density. Over a certain range of operating conditions, the electric field is relatively independent of the driving current and is primarily determined by the ionization energy per unit mass of the gas. Conditions are derived for noncompressive waves, hence also for production of uniform plasma. (auth).