Self-pulsing microplasma at medium pressure range in argon

A microplasma is generated in the microhole (200–400 µm diameter) of a metal–dielectric–metal sandwich (microhollow cathode type) at medium pressure (50–100 Torr) in pure argon. At low discharge current ( I < 0.1 mA), the plasma is stable and confined inside the hole. At higher current ( I > 0.8 mA), the plasma is also stable and expands on the cathode backside region. For intermediate current, the plasma is self-pulsed at a frequency ranging from a few tens to a few hundreds of kilohertz depending on the averaged discharge current and scales as a linear function of the product pD (pressure × hole diameter).