Ignition and extinction phenomena in helium micro hollow cathode discharges

Abstract

International audienceMicro hollow cathode discharges (MHCD) were produced using 250 lm thick dielectric layer of alumina sandwiched between two nickel electrodes of 8 lm 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 ls long current peak as high as 24mA 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 ls relative to the current oscillations. Metastable atoms thus cannot be at the origin of the generation of the observed instabilities

Study on the characteristics of helium plasma jet by pulsed micro-hollow cathode discharge

“…And the stable discharge states can be kept until the falling edge of the voltage waveform. The waveforms are similar to the results in reference [28]. The discharge has undergone a pre-breakdown zone (from the rising edge of the voltage to the beginning of the current), transition zone (from the beginning of current to current reaching maximum) and stable discharge regime (after the current stabilizes).…”

On the difference between breakdown and quench voltages of argon plasma and its relation to 4p–4s atomic state transitions

“…The modified paschen curve replaces the left upturn of the pure Paschen curve with a plateau and a decline to zero [25,26]. Nevertheless, both traditional and modified Paschen curves are derived based on 1-D geometries and are confirmed experimentally to be accurate for electrodes much larger than the gap size [27][28][29][30][31][32][33][34][35]. However, in a practical microplasma device, the size of the electrodes has to be comparable to the gap size to retain all of the device dimensions in the sub-millimeter range [36,37].…”