Ignition and extinction phenomena in helium micro hollow cathode discharges

TL;DR

This study investigates ignition and extinction phenomena in helium micro hollow cathode discharges using electrical and spectroscopic methods, revealing oscillatory behaviors and metastable atom dynamics at various pressures.

Contribution

It provides new insights into the temporal behavior and stability of microdischarges, especially regarding metastable atom roles and pressure-dependent oscillations.

Findings

Observed 2 s current peaks of up to 24 mA during ignition.

Detected oscillatory discharge behavior above 400 Torr pressure.

Metastable atom density oscillations lag behind current oscillations.

Abstract

Micro hollow cathode discharges (MHCD) were produced using 250 m thick dielectric layer of alumina sandwiched between two nickel electrodes of 8 m thickness. A through cavity at the center of the chip was formed by laser drilling technique. MHCD with a diameter of few hundreds of micrometers allowed us to generate direct current discharges in helium at up to atmospheric pressure. A slowly varying ramped voltage generator was used to study the ignition and the extinction periods of the microdischarges. The analysis was performed by using electrical characterisation of the V-I behaviour and the measurement of He*(3S1) metastable atoms density by tunable diode laser spectroscopy. At the ignition of the microdischarges, 2 s long current peak as high as 24 mA was observed, sometimes followed by low amplitude damped oscillations. At helium pressure above 400 Torr, an oscillatory behaviour of the discharge current was observed just before the extinction of the microdischarges. The same type of instability in the extinction period at high pressure also appeared on the density of He*(3S1) metastable atoms, but delayed by a few s relative to the current oscillations. Metastable atoms thus cannot be at the origin of the generation of the observed instabilities.