Experimental study on nanosecond pulsed discharge mode transition in supersonic flow with needle-to-plate electrodes

Magnetohydrodynamics (MHD) provides a new solution for addressing the total temperature rise issue in hypersonic wind tunnels, in which generating a stable and uniform conductive fluid is the key challenge for practical application of this technology. Pulsed discharge technology can rapidly establish high voltage, enabling large-area breakdown and uniform ionization of the air gap, making it an effective approach for generating conductive fluids. However, under supersonic flow conditions, the appropriate discharge parameters remain unclear, which can easily lead to a transition to intense spark discharge, thereby affecting the ionization efficiency and system safety. In this study, experiments were conducted in a Mach 2 flow field using a needle-to-plate electrode configuration to systematically investigate the effects of pulse voltage, pulse frequency, and pulse waveform on discharge mode transition. The experimental results show that glow discharge is the ideal mode for generating a uniform conductive fluid as it enables effective energy injection while avoiding electrode ablation. Among the parameters, pulse voltage is the key factor influencing discharge mode transition; pulse frequency determines the strength of the “memory effect” between consecutive discharges; and pulse rise time and pulse width primarily govern the amount of deposited energy. Therefore, appropriate parameter settings are essential for achieving glow discharge and improving energy injection efficiency. This study provides an experimental basis and parameter guidance for designing discharge schemes in MHD acceleration wind tunnels under supersonic conditions.