VACUUM-ARC PLASMA-JET PROPAGATION IN A TOROIDAL DUCT

A two fluid magneto-hydrodynamic theory of vacuum are plasma jet propa gation in a magnetized toroidal duct is developed. The physical mechan isms 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 trans port 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 (1+phi/phi(0))(-1) where phi (0) is a characteristic angular distance, for the case when ions are m agnetized, and exponentially when the ions are not magnetized. Numeric al calculations show that the decrease of plasma density leads to a lo ngitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a current loop which is cl osed 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. (C) 1996 American Institute of Physics.