Measurement of the Gas Flow Velocity in the Low Pressure Hollow Cathode Plasma Jet Sputtering System
Abstract
We present results from two mutualy independent measurements of flow velocity from the plasma jet nozzle outlet. Operation of the discharge in the pulse regime enables a simple use of the classical Langmuir probe for the flow velocity measurement.
Previous probe measurements showed that in the space below the nozzle there is almost no electric field which could accelerate the ions and so we can assume that the propagation of positive ions towards the negatively biased probe is driven just by mutual collisions and the diffusion process. As the second method the well known Pitot tube was used.
By this method we have experimentally proved that the flow velocity is almost not at all affected by the presence of plasma, i.e. it does not depend on the fact whether the discharge is on or off. Results of both metods are in a good correspondence.
It was documented that the discharge can be operated both as subsonic and as supersonic one. The appropriate dependences of the flow velocity on the distance from the cathode, on the pressure in the reactor chamber and on the input flow of the working gas were measured.