PLASMA MOTION IN A FILTERED CATHODIC VACUUM-ARC

In this paper a model is proposed for the flow of a plasma originating from a cathodic vacuum arc into a curvilinear magnetic field. The model gives good agreement with measurements obtained from a filtered cathodic-arc thin film deposition system. The important parameters involved in the motion of a vacuum arc plasma beam through a magnetic filter are examined. The analysis is based on the use of the guiding center approximation to describe the motion of the charged particles produced in the plasma where the thermal energy is negligible compared to the mass flow energy. Electron-ion collision effects are included within the framework of the drift model. The prime motivation to include collision effects are two-fold: First, spectroscopic measurements on a carbon vacuum arc plasma show strong evidence for Stark-broadening effects. Secondly, the coupling effect between ions and electrons is seen through the Coulombic collisional interactions. We show that under the limiting condition of a collision frequency which is much higher than the cyclotron frequency of the electron, the motion of the plasma ions around the bend becomes independent of the magnetic field, with the number of ions traversing the filter significantly reduced. However, in the collisionless plasma case (cyclotron frequency higher than the collision frequency), the model predicts a square-law relationship between ion-saturation current and magnetic field, I(p) is-proportional-to B2.