Abstract:
In this paper, the spatiotemporal dynamics of hollow cathode discharge in helium is simulated by using the fluid model. The spatiotemporal distribution of electrons density, metastable helium atoms density, potential, electric field, direct ionization rate and step-wise ionization are calculated. In particular, the effects of metastable atoms and step-wise ionization on the discharge are discussed. The results show that the discharge is divided into five different discharge modes with the increase of current. In the first stage, the discharge is Townsend discharge mode, the current rises very slowly, and the charged particle density, metastable atom density and radial electric field are very weak. In the second stage, the current increases rapidly, and the discharge mode changes from the Townsend discharge to the hollow cathode discharge. The charged particle density, metastable atom density and radial electric field increase rapidly. The third stage reaches the quasi steady state, and the discharge current increases slowly, resulting in an obvious cathode sheath structure; The fourth stage is the formation stage of the hollow cathode effect, and transits to the steady state. The fifth stage is the steady-state discharge stage. The results also show that the metastable helium atoms and the stepwise ionization are weak in the initial stage of the discharge, and in the initial three stages, the formation of new electrons are dominated by ground ionization. With the development of the discharge, the stepwise ionization caused by the metastable atoms gradually approaches and exceeds the ground ionization, and the contribution rate to the total ionization is getting higher and higher.