Model with anomalous diffusion and friction for a vacuum-arc plasma jet in a straight magnetic filter

F MINOTTI; L GIULIANI; D GRONDONA; H.DELLA TORRE; H KELLY

IEEE TRANSACTIONS ON PLASMA SCIENCE

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Lugar: New York; Año: 2011 vol. 39 p. 2014 - 2021

0093-3813

Abstract—A model is developed to describe the plasma jetgenerated in a vacuum arc, which enters and flows inside a straightmagnetic filter with a realistic magnetic field configuration. Consideringa low-density collisionless plasma projection of the electronmomentum equation along the magnetic field lines and theassumption of quasi-neutrality allows one to relate the plasmadensity to the electrostatic potential. The system of equations isclosed using the ion mass conservation and ion momentum equations.The model is compared to measurements on the plasma jetgenerated in a pulsed copper vacuum arc with an annular anode,moving along a straight magnetic filter. Probe measurements ofthe ion saturation current and of the floating potential at differentaxial and radial positions along the filter, and for different magneticfield values, are used in the comparison with the modelresults. It is found that anomalous diffusion is needed to fit theexperimental measurements. Moreover, a novel anomalous frictioneffect for ion motion across magnetic lines has to be invokedin order to prevent strong radial oscillations triggered by the fastmagnetic focusing of the plasma at the filter entrance and obtainrealistic results. A simple model is presented to account for both ofthese effects, based on the assumption of a high level of fluctuationsin the plasma.