Experimental investigation on thermal instability in high current-carrying glow plasmas at high pressure

In this paper, the thermal instability of uniform large-volume DC glow plasma at high pressure is investigated by using discharge pulse modulation and two-color laser interferometry. It is found that the number density of neutral particles changes periodically with the pulse modulation. The number density of neutral particles decreases with time during the power-on duration, which is related to the thermal instability developed in the radial non-uniform temperature field, while the backflow of neutral particles during the power-off duration terminates the development of thermal instability. The alternation of these two processes gives rise to the periodic change in the number density of neutral particles. As the average discharge current continues to increase, it is found that there appears an abnormal fluctuation in the number density of neutral particles with time during the power-on duration. It is believed that this fluctuation is related to the thermal instability depending on the enhanced axial temperature gradient. Both axial and radial temperature gradients have an impact on the development of thermal instability, but the thermal instability dependent on the axial temperature field occurs only at a large axial temperature gradient.