基于气体放电等离子体射流源的模拟离子引出实验平台物理特性

离子引出过程是原子蒸气激光同位素分离中非常重要的物理过程之一,而其中关键的等离子体参数(等离子体初始密度和电子温度等)均会对离子引出特性产生影响.基于千赫兹电源驱动的氩气高压交流放电等离子体射流源,建立了离子引出模拟实验平台-2015 (IEX-2015),开发了用于诊断氩等离子体参数的"碰撞-辐射"模型,对等离子体射流区的电子温度和电子数密度等关键参数进行了测量.结果表明,电源输入功率和驱动频率以及工作气体流量均会对等离子体射流区的电子温度和数密度产生影响;在真空腔压强为10~(-2)Pa量级下,射流区电子数密度和电子温度的可调参数范围分别为10~9—10~(11)cm~(-3)和1.7—2.8 e V,这与实际离子引出过程中的等离子体参数范围相近.在此基础上,开展了不同引出电压、极板间距和电子数密度条件下初步的离子引出实验,所得到的离子引出电流变化规律亦与实际原子蒸气激光同位素分离中的离子引出特性定性一致.上述研究结果验证了在IEX-2015上开展离子引出模拟实验的可行性,为后续深入开展离子引出特性的实验研究准备了良好的条件.

Physical characteristics of ion extraction simulation system based on gas discharge plasma jet

In an atomic vapor laser isotope separation process, the required isotope atoms are ionized selectively by a pulsed laser with a specific narrow line width, and then the produced isotope ions are extracted to the collected plates under an externally applied electromagnetic field. In the whole ion separation process, the ion extraction sub-process is one of the most important physical processes. Previous studies have shown that the key parameters of the laser-induced plasma, e.g., the initial electron number density and temperature, have a significant influence on the ion extraction features. In an actual isotope separation process, a specifically designed laser is necessary to produce the required isotope ions, which, however, leads the whole facility to have a very complicated structure, high capital cost, and especially, very narrow window of the key plasma parameters. These will, to some extent, limit a more in-depth investigation of the influences of the key plasma parameters on the ion extraction characteristics. In this paper, an ion extraction platform (ion extraction simulation experimental platform-2015, IEX-2015) is developed on the basis of a gas discharge plasma jet driven by a kilo-hertz high-voltage power supply. And an argon plasma “collisional-radiative” model is established to measure the electron temperature and number density in the plasma jet region. The experimental results show that the power input and driving frequency of the power supply and the argon mass flow rate can all affect the electron temperature and electron number density. The measured variation ranges of the electron number density and temperature are 10⁹-10¹¹ cm^-3 and 1.7-2.8 eV, respectively, under a chamber pressure on the order of 10^-2 Pa, which are close to the parameter levels in the actual ion extraction process. Subsequently, the preliminary ion extraction experiments are conducted under different extraction conditions including different externally applied voltages, different electrode distances and different plasma densities. The experimental results are also qualitatively consistent with those in an actual ion extraction process. The preceding preliminary experimental results show that it is feasible to conduct the ion extraction simulation study on IEX-2015. This is very helpful for systematically studying the ion extraction characteristics under different operating conditions in our future research.