Abstract

We present an experimental comparison of parallel plate and hollow cathode microplasma structures, operated at high pressure with narrow anode–cathode gaps. A moveable anode arrangement with ±12 µm spatial resolution was used to vary the electrode separation to cover the pd range between 0.01 and 4 Torr cm for both structures. The hollow cathode discharge was operated with pressure–diameter ( pD ) product values between 1.8 and 7.2 Torr cm and an aspect ratio of ~5. Analysis of V – I characteristics shows j / p 2 and j 2 p scaling for low and high current modes, respectively. Electron temperature estimates between 2 and 3 eV were obtained by solving a numerical collisional–radiative model based on transitions from 4p argon levels. The hollow cathode sheath thickness for both ionizing and non-ionizing sheath conditions was determined analytically and the diffusion equation was solved numerically to estimate the plasma density profile for the ionizing sheath case.