Ignition and extinction phenomena in helium micro hollow cathode discharges

摘要

Micro hollow cathode discharges (MHCD) were produced using 250 m thickdielectric layer of alumina sandwiched between two nickel electrodes of 8 mthickness. A through cavity at the center of the chip was formed by laserdrilling technique. MHCD with a diameter of few hundreds of micrometers allowedus to generate direct current discharges in helium at up to atmosphericpressure. A slowly varying ramped voltage generator was used to study theignition and the extinction periods of the microdischarges. The analysis wasperformed by using electrical characterisation of the V-I behaviour and themeasurement of He*(3S1) metastable atoms density by tunable diode laserspectroscopy. At the ignition of the microdischarges, 2 s long current peak ashigh as 24 mA was observed, sometimes followed by low amplitude dampedoscillations. At helium pressure above 400 Torr, an oscillatory behaviour ofthe discharge current was observed just before the extinction of themicrodischarges. The same type of instability in the extinction period at highpressure also appeared on the density of He*(3S1) metastable atoms, but delayedby a few s relative to the current oscillations. Metastable atoms thus cannotbe at the origin of the generation of the observed instabilities.