大功率热平衡感应耦合等离子体数值模拟及实验研究

Numerical simulation and experimental study of high-power thermal equilibrium inductively coupled plasma

感应耦合等离子体发生器是"临近空间高速目标等离子体电磁科学实验研究装置"的核心部件之一,常用于模拟高焓高速等离子体鞘套环境,为了研究大功率射频中压下感应耦合等离子体发生器的放电特性,采用数值模拟和实验相结合的方法研究其内部的传热与流动特性.本文基于局域热力学平衡条件,通过湍流场-电磁场-温度场的多场耦合开展了功率为100—400 kW的大尺寸射频中压感应耦合等离子体的数值模拟,并通过光强与光谱实验验证.结果表明:大功率等离子体发生器中的电磁场分布类似于中小型功率等离子体发生器;放电能量耗散主要发生在感应线圈所在的区域;石英管内壁温度在线圈所在处比其他区域较高,等离子体呈环状高温结构;等离子体受温差效应与电磁泵效应影响使得入口处产生回流涡.同时开展相应条件下的放电实验发现氩气放电的轴向图像呈边缘高亮与中心暗的环状结构,并通过光谱诊断系统测量氩等离子体的发射光谱,得到发生器电子温度的空间分布, COMSOL仿真温度结果与放电图像光强、光谱测得电子温度较为符合,验证了采用热力学平衡态条件进行数值模拟结果的有效性.本文数值模拟的结果可用于感应耦合等离子体发生器的优化设计及耐温评估.

Inductively coupled plasma generator is one of the core components of the near-space high-speed target plasma electromagnetic scientific experimental research device,which is often used to simulate high enthalpy and high speed plasma sheath environment.In order to study the discharge characteristics of inductively coupled plasma generator under high power,radio frequency and medium pressure,the numerical simulation and experiment are combined to study its internal heat transfer and flow characteristics in this paper.Based on the local thermodynamic equilibrium conditions,the numerical simulation of large-scale radio frequency and medium pressure inductively coupled plasma with a power of 100–400 kW is carried out through the multi-field coupling of flow,electromagnetic and temperature field,and verified by light intensity and spectrum experiment.The results show that the electromagnetic field distribution in the high-power thermal balance inductively coupled plasma generator is similar to that of the small-and medium-sized power plasma generator.The discharge energy dissipation occurs mainly in the area where the induction coil is located.The temperature of the inner wall of the quartz tube is higher at the coil location than in other areas,and the plasma has a ringshaped high-temperature structure.The outer wall of the quartz tube is set to be the boundary condition of heat flux for simulating the temperature change of the quartz tube under cold blowing.This setting is in coincidence with factual situations.The wall temperature of the quartz tube at the entrance and at the induction coil section are found to be relatively high.When the large-size inductively coupled plasma generator works,an obvious return vortex is generated at the entrance due to the temperature difference and the electromagnetic pumping effect,and the exit velocity increases slightly with the increase of power.At the same time,the discharge experiment under the corresponding conditions shows that there is found a ring structure with bright edges and dark centers in the axial image of the argon discharge.Moreover,the emission spectrum of argon plasma is measured through the spectrum diagnosis system and the spatial distribution of the generator electron temperature is obtained.The light intensity of the discharge image and the electron temperature measured by the spectrum are found to be in comparative coincidence with the COMSOL simulation temperature result,demonstrating the validity of the numerical simulation results under thermodynamic equilibrium conditions.The numerical simulation results in this paper are also applicable to the optimization design and temperature resistance evaluation of the inductively coupled plasma generator.