Control of the thermionic vacuum arc plasma

The aim of this paper is to investigate the properties of thermionic vacuum arc (TVA) plasma and to optimize the discharge parameters in order to obtain plasma with high energetic ions and high ionization degree. Using emissive probe technique, the spatial plasma potential distribution has been measured. Experimental results show that the spatial distribution of plasma potential strongly depends on operation parameters (arc current/voltage, filament temperature, relative position and geometry of the electrodes and anode material) and its value is directly related to the voltage arc drop. In order to evaluate the plasma ionization degree, we have analyzed the equivalent electric circuit of the discharge during arc operation. The total anode discharge current is the sum of thermoelectric current flowing from filament and the current flowing from anode to the vessel walls. The value of the current intensity, which flows to the vessel, is directly proportional with the arc voltage and it is a measure of the plasma ionization degree. The deposition rate is related to the power input and was estimated using a Quartz Crystal Microbalance.