Plasma discharges are sustained in the focus of a continuous, high-power microwave beam. The experimental design minimizes interactions between the chamber walls and both the microwave beam and the resulting discharges so as to approximate free-space conditions. Discharges were generated by a multikilowatt, 4.7-GHz CW microwave beam at pressures ranging from 100 to 200 mtorr. The CW source enabled the evolution of the plasma-beam system to be observed over time scales ranging from seconds to hours. A variety of discharge behaviors are observed depending on the conditions (power, pressure, and gas composition) within the chamber. The observed discharges can be classified into three discharge modes: unstable, stable, and quasi-stable. Here, we present observations and a preliminary analysis of the various discharge modes observed in the experiment.

中文翻译：

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在聚焦微波束中维持的等离子体中观察到的放电模式

等离子放电在连续的高功率微波束的聚焦下持续进行。实验设计最大限度地减少了室壁与微波束和由此产生的放电之间的相互作用，以接近自由空间条件。放电由多千瓦、4.7 GHz CW 微波束在 100 至 200 毫托的压力范围内产生。CW 源能够在几秒到几小时的时间尺度上观察到等离子束系统的演变。根据腔室内的条件（功率、压力和气体成分）观察到各种放电行为。观察到的放电可分为三种放电模式：不稳定、稳定和准稳定。在这里，我们对实验中观察到的各种放电模式进行了观察和初步分析。