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Discharge homogeneity is one of the dominant factors affecting cathode lifetime. In this work, the arc ablation behavior of a zirconium cathode is investigated in air and argon atmospheres. Homogeneous discharge processes are observed in air, while poor discharge homogeneity with scattered cathode spots is found in argon. The homogeneous discharge process is related to the layered structure at the discharge center. The surface zirconium oxide layer stabilizes the arc foot and reduces the effective work function. A dual-phase layer underneath, consisting of zirconium oxides and zirconium, enables the transition from the zirconium matrix to the surface oxide layer. The sustainable discharge behaviors are realized by the balance in the cathode, which is created by the ablation of surface zirconium oxides and the oxidization of zirconium in the dual-phase layer.

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An adaptive method based on dynamic programming is proposed to identify the spectral band for non-continuous measurement of surface temperature of heatshield materials when Fourier transform infrared (FTIR) spectrometer is used to collect the radiation spectrum in the dynamic heating environment of a high-frequency plasma wind tunnel. First, the radiation spectrum is converted to a time series. Then, high-frequency parts of the measurement spectral signal are obtained by multi-resolution analysis of one-dimensional discrete wavelet and then the suitable spectral band required by a non-contact temperature measurement is adaptively identified based on dynamic programming. Eventually, surface temperature and its corresponding emissivity can be determined. Results of the experiment conducted on a benchmark material (graphite) in the dynamic heating environment of high frequency plasma wind tunnel show the proposed method to be practical.