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/p2 and j2p 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.
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