Abstract:
Arc-heated plasma generates thermal arc by breakdown discharge between electrodes to heat cold test medium. The high-power arc heater is the most important ground test facility to evaluate thermal protection system for hypersonic vehicles. Based on the developed non-intrusive spectroscopic methods, a study was carried out for quantitative and qualitative research on the ignition characteristics of the arc plasma for a 10 MW high-power long-segmented arc heater in this paper. In situ measurements were conducted to obtain the spectrum of the plasma flow, and the gas temperature and copper concentration by electrode erosion were measured to analyze the flow characteristics. The results demonstrate that: at the beginning stage of arc ignition, pure argon is injected and the spectrum of the plasma flow is mainly composed of the isolated spectrum of argon atoms; at the transition stage, there exist continuous molecular spectrum of N
2 and N
2+ and atomic spectrum of Ar, N, O when test medium of air is added into the arc heater, with the decrease of plasma electron temperature; at the normal operation stage with pure air operation for the plasma, the spectrum consists of N
2 and N
2+ continuous molecular spectrum and N, O atomic spectrum. In the whole ignition process, electrode erosion is observed from obvious copper atomic lines in the measured spectrum. When the argon arc plasma is operated, the electron temperature is stabilized at 11 000 K±300 K, indicating steady ignition characteristics for the arc heater. Meanwhile, mole fraction of the copper concentration periodically changes between (1~25)×10
-6 during ignition, which shows the irregular electrode erosion owing to rotation of the arc root. This diagnostic method of emission spectroscopy developed in this paper provides a quantitative means for studying the characteristics of the vacuum argon ignition process, which can provide a direct quantitative basis for the development of vacuum- atmospheric pressure ignition for argon plasma and electrode optimization, and lay the foundation for the development of atmospheric pressure ignition for high-power segmented arc-heated test facility.