Equivalent Circuits of Unipolar Pulsed Plasma System for Electrical and Optical Signal Analysis

Matching of pulse plasma generators to various gas discharges for surface treatment of materials depends on plasma processing equipment. In order to investigate the influence of pulse plasma generator and gas discharge parameters on electrical signal waveforms during the process of unipolar pulse plasma nitriding, equivalent electrical circuit was introduced. The influence of parasitic inductance of interconnection lines and vacuum chamber physical properties was also included in the given equivalent circuit. Gas discharge characteristics at different process parameters were investigated. It was found that the gas discharge and pulse plasma generator properties, as well as the electrical characteristics of interconnecting lines determined the system electrical signal response. From the analysis of optical signals emitted by the gas discharge it was found that the optical signal response might be represented by a typical RC integrator circuit response with the time constant higher than that of the equivalent electrical circuit of generator load. The conclusion was drawn that the process of charge particles generation is followed by the process of active species generation responsible for thermo-chemical processes on the cathode surface. Thus, the increase of the pulse plasma frequency is limited by the thermo-chemical process efficiency, and not only by the generator switching characteristics or by gas discharge electrical properties.