Mode Structure of a Transparent Cathode Discharge

In this paper, we characterize a Transparent Cathode Discharge (TCD), a type of Inertial Electrostatic Confinement (IEC) plasma, operated in helium and argon in the pressure range of 1-100 Pa. The discharge was investigated using a combination of electrical and optical diagnostic techniques. The imaging of the discharge indicated distinct operating regimes related to the background gas pressure, with each mode being characterized by different patterns of optical emission. The spectroscopic analysis of the optical emission showed that this mode structure represented an electron-driven discharge at higher pressures, and a discharge sustained by the activity of energetic heavy particles at lower pressures. The high-pressure discharge is shown to be assisted by the hollow cathode effect toward its low-pressure limit, and the visible color of emission from the discharge in helium is found to provide a convenient diagnosis of active species. The identification of a stable discharge mode in which energetic heavy particles are responsible for collisional processes has the potential to lead to new industrial applications based on this novel heavy particle-driven reactive plasma source.