Investigation on transient process of dense hydrogen microdischarge by dual-wavelength laser interferometry

Abstract

In this paper, the transient process of single-pulse hydrogen microdischarge with peak discharge current of 45 A at constant pressure of 1300 Pa is investigated by dual-wavelength laser interferometry. It is found that the phase shift signals related to electrons and excited H (n=2) atom appear almost simultaneously after breakdown, with a delay of 700 ns compared with the current signal. The velocity of the ionization wave is thus estimated to be on the order of 10^3 m/s. Subsequently, the current and phase signals increase rapidly, indicating that the energy deposited is applied to heat electron and gas, and strong molecular ionization and atomic excitation process occur in microdischarge. The phase signal for excited H (n=2) atoms shows the maximum value at t=7.84 μs and then decreases rapidly, while the current reaches the peak at t=10 μs. In the duration between these two peaks the electronic degrees of freedom continue to gain energy from the external field, but the energy transferred to the atomic degrees of freedom decreases. After t=10 μs, the current drops first rapidly, and then slowly decreases until the end of the discharge. In discharge attenuation process, the energy flowing into all degrees of freedom decreases. The phase-shift dispersion curve is obtained by changing laser frequency. Through the global optimized fitting of the phase shift curve, the average line-of-sight density of excited H (n=2) atoms is estimated to be 1.836×10^12 cm^-3 in microdischarge, and the corresponding broadening information is given.