The Effect of Discharge Mode on Ion Energy and Plasma Potential in the Plume Plasma Region

The ion energy angle distribution and its relationship to plasma parameters for spot and plume modes are elucidated for a LaB6 hollow cathode with a radiative heater. Measurements were conducted using a retarding potential analyzer (RPA) and a single Langmuir probe. The ion energy distribution function (IEDF) characteristics showed different tendencies in the current density and mass flow-rate dependence under different plasma modes. The IEDF peak potential for the spot mode varied from 16 to 23V with increasing current density, and the IEDF peak potential for the plume mode varied from 16 to 32V with decreasing mass flow rate. Considering angle dependency of ion energy, when the observation angle was changed from the radial direction to the axial direction, the IEDF peak potential increased from 29 to 40V for the plume mode (10 A, 10 sccm) and increased slightly from 16 to 18V for the spot mode (20 A, 30 sccm). The probe measurement analysis revealed that the IEDF peak energies are the same as, or exceed, the plasma potential and have a qualitative correlation with the electron temperature spatial distribution.