Influence of the hole depth on plasma characteristics in radio frequency hollow cathode discharge

In order to increase the plasma density in radio-frequency (RF) hollow cathode discharge(HCD), we studied the influence of hole depth on RFHCD in Ar gas through experiments and numerical simulations. In the experiments, we measured the electron density of RFHCD using Langmuir probe, and compared the electron densities of different hole depths. We obtained the spatial-distribution of plasma density and ionization rate along with various hole depths using 2-D fluid model to simulate the RFHCD. The numerical results show that increasing the hole depth can enlarge high ionization region and increase plasma density in RF HCD, which is in accordance with the experimental results. Moreover, when the ratio of hole depth to hole diameter is higher than 3, the plasma density will reach its saturation value.