A novel experimental method is proposed for observing plasma dynamics subjected to magnetic fields based on a newly developed cylindrical theta-pinch device. By measuring simultaneously the temporal profiles of multiple parameters including the drive current, luminosity, plasma density, and plasma temperature, it provides a basis for observing the plasma dynamics of the theta pinch, such as shock transport and magnetohydrodynamic instability. We show that the plasma evolution can be distinguished as three phases. First, in the radial implosion phase, the trajectories of the current sheath and shock wave are ascertained by combining experimental data with a snowplow model (Lee model) in a self-consistent way. Second, in the axial flow phase, we demonstrate that m = 0 (sausage) instability associated with the plasma axial flow suppresses the plasma end-loss. Third, in the newly observed anomalous heating phase, the lower-hybrid-drift instability may develop near the current sheath, which induces anomalous resistivity and enhanced plasma heating. The present experimental data and novel method offer better understanding of plasma dynamics in the presence of magnetic fields, thereby providing important support for relevant research in magneto-inertial fusion.

在PVT法生长AlN晶体的过程中, 很难保持理想的热力学平衡状态, 不可避免地会产生晶体缺陷。高温退火技术对提高晶体完整性十分有效，受到了广泛关注。本工作在N₂气氛环境下对PVT法生长的AlN晶片进行高温退火研究。为了评价退火前后AlN晶体的质量和结构变化情况, 进行了高分辨率X射线衍射(HRXRD)和拉曼光谱分析。通过室温光致发光(PL)和吸收光谱对AlN晶体的光学性质以及与杂质相关的带隙变化情况进行了表征。在1400~1800 ℃退火后, AlN晶体质量显著提高。1400 ℃退火后, (10-12)晶面的X射线摇摆曲线的半峰宽(FWHM)从104.04 arcsec减小到79.92 arcsec。随着退火温度升高, 吸收性能明显增强, 带隙增大, 说明高温退火处理有利于提高AlN晶体的质量。二次离子质谱(SIMS)结果表明, 退火过程降低了C杂质, 增加了AlN晶体的带隙, 这与光吸收结果一致。