Modeling of diode configuration glow discharge impedance connected to pulse power supply

The voltage and current waveforms of the nitrogen and nitrogen/hydrogen glow discharges used for plasma nitriding were recorded and analyzed concerning the discharge instabilities, glow-to-arc transition, hollow cathode effect and the influence of surface treatment process parameters. It was found that the shape of voltage and current contains the information on normal glow, hollow cathode discharge and arcing. We also performed the recording of dynamic parameters and static voltage–current characteristic was also recorded in order to model generator and chamber and use it for future process control. The gas discharge could be modeled as a parallel connection of a resistor and a capacitor, where one could determine actual values of the parameters depending on the type of the chamber, shape and size of the cathode. The influence of the glow spreading time over the cathode surface on the pulse plasma nitriding process was investigated by surface treatment of 1-m long cylinders in cold-wall vacuum chamber. The non-homogeneity of the discharge current density results in different diffusion zone depths at the bottom and the top of the cylinders. Thus, the use of bipolar pulse plasma and auxiliary high voltage pulses is recommended for surface treatment of very long workpieces in cold wall vessels.