Vacuum arc plasma jet propagation in a toroidal duct

Abstract

A two fluid magneto-hydrodynamic theory of vacuum arc plasma jet propagation in a magnetized toroidal duct is developed. The physical mechanisms of jet transverse displacement and plasma losses are analyzed and the centrifugal force on the ions is shown to play the principle role in these processes. Optimal conditions for jet propagation occur when the centrifugal force is balanced by the electrical force on the ions. An analytical solution of the nonlinear problem of plasma beam transport through a toroidal duct is obtained for the two cases where ions are magnetized or not magnetized. The ion mass current decreases with the azimuthal distance along the torus as ͑1ϩ/ 0 ͒ Ϫ1 where 0 is a characteristic angular distance, for the case when ions are magnetized, and exponentially when the ions are not magnetized. Numerical calculations show that the decrease of plasma density leads to a longitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a current loop which is closed through the plasma and structures outside the torus. Moreover if there are optimal conditions for jet propagation at the torus entrance, they are approximately conserved along the length of the torus.

Shock front formation at vacuum arc anodes

“…These values correspond to Mach number Mϭ13, thus the vacuum arc plasma jet ͑VAPJ͒ is considerably supersonic. The hydrodynamic description of the VAPJ was discussed previously, [7][8][9] as was the necessity of shock front formation, in multicathode VAPJs, 10 in the interaction with an ambient gas, [11][12][13] and in the interelectrode gap. 14 The VAPJ interacts with an obstacle in several practical devices, e.g., in vacuum arc plasma coating apparatus and circuit breakers.…”

Presheath in Fully Ionized Collisional Plasma in a Magnetic Field

“…The self-consistent two-fluid model was applied to the plasma of the vacuum arc jet, characterized by a directed supersonic ion speed (1-2x10 4 m/s) parallel to the wall, electron temperature (T e ) about 3 eV and ion temperature about 1 eV. [2,[15][16][17]. Dependence of plasma density on the electric potential in the presheath is not assumed to be a Boltzmann distribution, and the dependence of the mean collision time τ on the plasma density is not neglected.…”

Motion of magnetized vacuum arc plasma beam in a quarter-torus

“…The magnetic field is strong enough so that both the electron and ion Larmor radii are smaller than the torus minor radius. Under these conditions electrons and ions drift across magnetic field to the filter walls with velocities [7,9] 9 where E and B are the electric and magnetic field vectors respectively, b=B/B, g=r(vil/r)2 is the centrifugal acceleration, r is the distance from the main axis of the torus, r is a position vector in the radial direction, Pa=nakTa is the partial pressure of the a component where (a =e) and (a =i ) represent the electrons and ions respectively, na , T, are the component densities and temperatures, -e is the electron charge, and Ze is the ion charge. Quasi-neutrality is satisfied by imposing Znj=ne=n.…”

“…The electron current depends on the longitudinal electrical conductivity of the plasma oI and is defined by Ohm's low for an in-homogeneous plasma [7,9]:…”

“…The purpose of this paper is to find an approximate analytical solution of magnetized plasma beam transport in a torus on the base of a self-consistent two fluid magneto-hydrodynamic model of plasma jet [7], to calculate the filter efficiency and to present a preliminary comparison of the theoretical results with experimental data. The model considered the influence of electromagnetic fields, collisions, pressure and centrifugal forces on charged particle motion.…”