The subatmospheric CO2 microwave plasma is known to contract to a narrow filament with rising pressure as result of a mode transition. This changing state of contraction is investigated in relation to its dielectric properties, in order to directly relate the discharge parameters to the discharge radius. The electron density and gas temperature are measured, respectively, by 168 GHz microwave interferometry and Doppler broadening of the 777 nm oxygen emission lines. The plasma is operated in steady state with 1400 W at 2.45 GHz, between 100 mbar and 400 mbar. Electron density values in the central region range from 1018 to 1020 m−3 between the discharge modes, while the gas temperature increases from 3000 K to 6500 K, in good agreement with previously reported values. Based on the dielectric properties of the discharge in relation to the plasma radius, it is found that the discharge column constitutes a radius of a single skin depth. Implications of these insights on the conditions of previously reported CO2 dissociation experiments are discussed.

中文翻译：

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基于趋肤深度限制收缩现象的 CO ₂微波等离子体表征

众所周知，由于模式转换，负压 CO2 微波等离子体会随着压力升高而收缩成细丝。为了将放电参数与放电半径直接联系起来，研究了这种收缩状态的变化与其介电特性的关系。电子密度和气体温度分别通过 168 GHz 微波干涉测量和 777 nm 氧发射线的多普勒展宽测量。等离子体在 100 毫巴和 400 毫巴之间以 1400 W 和 2.45 GHz 的稳态运行。放电模式之间中心区域的电子密度值范围为 1018 到 1020 m-3，而气体温度从 3000 K 增加到 6500 K，与先前报告的值非常一致。基于与等离子体半径相关的放电的介电特性，发现放电柱构成单个趋肤深度的半径。讨论了这些见解对先前报告的 CO2 解离实验条件的影响。