Study of the transmission of a Vacuum- arc plasma jet in a straight magnetic filter

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

Congreso; ICPP International Congress on Plasma Physics LAWPP XIII LatinAmerican Workshop on Plasma Physics; 2010

An experimental study of the plasma jet generated in a pulsed copper vacuum arc with an annular anode and operated with a straight magnetic filter is presented. In this work, probe measurements of the ion saturation current and the plasma potential at different axial positions along the filter and for different magnetic field values are reported. In order to explain the experimental results, a model is developed to describe the plasma jet entering and flowing inside a straight magnetic filter, including realistic magnetic field line geometry, for a low density, collisionless plasma. Projection of the electron momentum equation along the magnetic field lines and the assumption of quasi-neutrality allow to relate the plasma density to the electrostatic potential, which, together with the ion mass and momentum equations, completely determine the state of the plasma. Further simplification is obtained by assuming consistent radial profiles for the different magnitudes, leaving only the axial dependency. The resulting set of ordinary differential equations can thus be easily solved using standard numerical techniques. It is found that in order to fit the experimental measurements anomalous diffusion coefficients need to be used; in particular, ambipolar diffusion with electron Bohm coefficient and ion-acoustic turbulent decay of radial oscillations.