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Implications of thermo-chemical instability on the contracted modes in CO2 microwave plasmas
Plasma Sources Science and Technology ( IF 3.3 ) Pub Date : 2020-02-06 , DOI: 10.1088/1361-6595/ab5eca
A J Wolf 1 , T W H Righart 1 , F J J Peeters 1 , W A Bongers 1 , M C M van de Sanden 1, 2
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Understanding and controlling contraction phenomena of plasmas in reactive flows is essential to optimize the discharge parameters for plasma processing applications such as fuel reforming and gas conversion. In this work, we describe the characteristic discharge modes in a CO2nmicrowave plasma and assess the impact of wave coupling and thermal reactivity on the contraction dynamics. The plasma shape and gas temperature are obtained from the emission profile and the Doppler broadening of the 777 nm O(5S ←n5P) oxygen triplet, respectively. Based on these observations, three distinct discharge modes are identified in the pressure range of 10 mbar to atmospheric pressure. We find that discharge contraction is suppressed by an absorption cut-off of the microwave field at the critical electron density, resulting in a homogeneous discharge mode below the critical transition pressure of 85 mbar. Further increase in the pressure leads to two contracted discharge modes, one emerging at a temperature of 3000 K to 4000 K and one at a temperature of 6000 K to 7000 K, which correspond to the thermal dissociation thresholds of CO2nand CO respectively. The transition dynamics are explained by a thermo-chemical instability, which arises from the coupling of the thermal-ionization instability to heat transfer resulting from thermally driven endothermic CO2ndissociation reactions. These results highlight the impact of thermal chemistry on the contraction dynamics of reactive molecular plasmas.

中文翻译:

热化学不稳定性对 CO 2微波等离子体收缩模式的影响

了解和控制反应流中等离子体的收缩现象对于优化等离子体处理应用(如燃料重整和气体转化)的放电参数至关重要。在这项工作中,我们描述了 CO2n 微波等离子体中的特征放电模式,并评估了波耦合和热反应性对收缩动力学的影响。等离子体形状和气体温度分别从 777 nm O(5S ←n5P) 氧三重态的发射剖面和多普勒展宽获得。根据这些观察,在 10 毫巴到大气压的压力范围内确定了三种不同的排放模式。我们发现,在临界电子密度下,微波场的吸收截止抑制了放电收缩,导致在低于 85 毫巴的临界转变压力下的均匀放电模式。压力的进一步增加导致两种收缩放电模式,一种在 3000 K 至 4000 K 的温度下出现,另一种在 6000 K 至 7000 K 的温度下出现,分别对应于 CO2n 和 CO 的热解离阈值。转变动力学由热化学不稳定性解释,这是由于热电离不稳定性与由热驱动的吸热 CO2n 离解反应引起的热传递的耦合引起的。这些结果突出了热化学对反应分子等离子体收缩动力学的影响。一种出现在 3000 K 到 4000 K 的温度下,一种出现在 6000 K 到 7000 K 的温度下,它们分别对应于 CO2n 和 CO 的热解离阈值。转变动力学由热化学不稳定性解释,这是由于热电离不稳定性与由热驱动的吸热 CO2n 离解反应引起的热传递的耦合引起的。这些结果突出了热化学对反应分子等离子体收缩动力学的影响。一种出现在 3000 K 到 4000 K 的温度下,一种出现在 6000 K 到 7000 K 的温度下,它们分别对应于 CO2n 和 CO 的热解离阈值。转变动力学由热化学不稳定性解释,这是由于热电离不稳定性与由热驱动的吸热 CO2n 离解反应引起的热传递的耦合引起的。这些结果突出了热化学对反应分子等离子体收缩动力学的影响。这是由于热电离不稳定性与由热驱动的吸热 CO2n 离解反应引起的热传递的耦合引起的。这些结果突出了热化学对反应分子等离子体收缩动力学的影响。这是由于热电离不稳定性与由热驱动的吸热 CO2n 离解反应引起的热传递的耦合引起的。这些结果突出了热化学对反应分子等离子体收缩动力学的影响。
更新日期:2020-02-06
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