Abstract: There are mainly two discharge modes in hollow cathodes，namely the spot mode and the plume mode.In order to study the transition mechanisms of the two modes，a hybrid model of the PIC（particle in cell）/PCD（plasma and chemical dynamics）was established.This model can solve the plasma parameter distribution in the hollow cathodes，and the heat radiation process can be solved by the radiation transportation coefficient.The solution can be converged after several iterations of the flow-heat coupling calculation.To verify the accuracy of the numerical model，the comparison of the calculation and test results of the 5 measurements on the cathode surface was conducted by a discharge test，and the relative error was less than 5%.Meanwhile，the comparison of the calculated color patterns and the photographs of the cathode plume showed that the numerical model could qualitatively capture the transition of the discharge mode.Based on those，the plasma parameters of the hollow cathode were solved with the PIC/PCD model under the condition of different gas flow rates and different orifice diameters.The mechanisms of the transition mode of the spot-plume discharge were obtained by analyzing the rules of the anode voltage and the plume pattern.This paper can provide the theoretical support for the cathode optimization design.

Key words:  , hollow cathode；discharge mode；PIC/PCD；plume pattern；optimization design