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中国物理学会期刊

氩气感应耦合等离子体非平衡特性分析

CSTR: 32037.14.aps.74.20251186

Non-equilibrium characteristics analysis of argon inductively coupled plasma

CSTR: 32037.14.aps.74.20251186
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  • 受制于感应耦合等离子体(ICP)发生器内极高温度、有限空间以及电磁场与化学反应的复杂耦合, 实验方法在揭示发生器内电磁场与流场的相互作用及放电特性方面存在较大局限, 数值模拟因而成为研究该类问题的重要手段. 本研究以氩气ICP为研究对象, 利用COMSOL在平衡态(LTE)与非平衡态(NLTE)假设下建立二维模型, 比较两者在温度场与能量耦合特性上的差异. 结果表明, 在千帕级压力下, LTE下温度峰值约8200 K, 高温区范围更大且集中于线圈区域. 而NLTE最高温度仅约5990 K, 且分布偏移至下游; 同时, 轴心区域以基态氩为主, 线圈附近激发态与离子分数升高, 表明能量沉积与粒子转化主要集中在趋肤层. 进一步分析不同压力下中心线分布发现, 随压力降低, 电子与气体温度差值增大, 体系热非平衡特征显著增强. 研究揭示了千帕级压力下ICP放电过程中的电磁-热-流动耦合机制及其非平衡特征. 结果表明, 在千帕级压力模拟中, NLTE模型能更准确地捕捉能量耦合与温度分布的关键特征, 为高焓风洞等应用中的ICP数值模拟提供了模型选择依据.

     

    Inductively coupled plasma (ICP) generators involve complex interactions between electromagnetic, thermal, and chemical processes, which makes direct diagnostics difficult. To clarify these coupling mechanisms, a two-dimensional axisymmetric model of an argon ICP torch operating at kilopascal pressure is developed using COMSOL Multiphysics under local thermodynamic equilibrium (LTE) and non-equilibrium (NLTE) assumptions. A two-dimensional axisymmetric magnetohydrodynamic (MHD) model is established, which combines electromagnetic induction, convective-radiative heat transfer, and a seven-reaction argon plasma chemistry mechanism. The LTE model assumes that the temperature of all species is uniform, while the NLTE model independently solves for the electron temperature (Te) and gas temperature (Tg), thereby accounting for incomplete energy exchange between electrons and heavy particles. At a discharge power of 1000 W and a working pressure of 10 kPa, the LTE model predicts a peak temperature of approximately 8200 K, concentrated around the induction coils. In contrast, the NLTE model yields a maximum gas temperature of about 5990 K, with the hot zone shifted downstream. The NLTE model reveals a clear two-temperature structure: Te peaks near the coil wall (~0.93 eV), while Tg reaches its maximum downstream, indicating a pronounced thermal non-equilibrium state where electrons are preferentially heated by the induced field. The calculated skin depth (~11.3 mm) coincides with the region of strongest electromagnetic energy deposition. Species analysis shows that the plasma core is dominated by ground-state argon (Ar) (>99%), while excited argon (Ar*) and argon ions (Ar+) increase notably near the coil region, confirming that excitation and ionization processes are localized within the skin layer. Furthermore, comparison between the 5 kPa and 10 kPa cases shows that as pressure decreases, the difference between Te and Tg increases, indicating enhanced thermal non-equilibrium due to reduced collisional coupling. Overall, the results highlight that LTE and NLTE assumptions lead to markedly different predictions of temperature and energy coupling at kilopascal pressures. The NLTE model more realistically captures delayed energy transfer and spatial temperature decoupling, offering new insights into the electromagnetic-thermal-flow interactions of ICP discharges and providing a modeling reference for designing ICP-based high-enthalpy plasma wind tunnel and realizing related aerospace applications.

     

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