Striations in moderate pressure dc driven nitrogen glow discharge
Striations in moderate pressure dc driven nitrogen glow discharge
复制标题
DOI：
10.1088/1361-6463/ac33da
复制
发表时间：
2021-10
期刊：
影响因子：
--
通讯作者：
M. Tahiyat;J. Stephens;V. Kolobov;T. Farouk
中科院分区：
文献类型：
--
作者：
M. Tahiyat;J. Stephens;V. Kolobov;T. Farouk
血浆分层研究已经有一个多世纪了。尽管有许多关于这一主题的实验研究报告，但这一现象的理论分析和数值模拟大多局限于稀有气体。在这项工作中，采用具有电子和振动激发分子详细动力学的一维流体模型，模拟了在半径0.55 cm的15.5 cm长管内氮气中压（即几个Torrs）直流放电。该模型还考虑了双极性扩散，以解释离子和电子向壁面的径向损失。提出的模型预测了在一定放电电流范围内氮中的自激立纹。评估了从局部两项和多项玻尔兹曼方程解中得到的电子传递参数和反应速率对预测的影响。深入的动力学分析表明，这些条纹是由电离反应和振动反应相互作用引起的电子温度波动引起的。此外，发现与较低能级相关的振动激发分子对氮等离子体分层和条纹模式有强烈影响。电离过程和电子能量传递之间的平衡允许形成观察到的固定条纹。模拟的放电电流密度范围为~ 0.018 ~ 0.080 mA cm−2，工作压力为0.7 Torr。参数化研究表明，随着放电电流的增大，条纹长度减小。将模型的预测结果与实验测量结果进行了比较，发现结果非常吻合。
Plasma stratification has been studied for more than a century. Despite the many experimental studies reported on this topic, theoretical analyses and numerical modeling of this phenomenon have been mostly limited to rare gases. In this work, a one-dimensional fluid model with detailed kinetics of electrons and vibrationally excited molecules is employed to simulate moderate-pressure (i.e. a few Torrs) dc discharge in nitrogen in a 15.5 cm long tube of radius 0.55 cm. The model also considers ambipolar diffusion to account for the radial loss of ions and electrons to the wall. The proposed model predicts self-excited standing striations in nitrogen for a range of discharge currents. The impact of electron transport parameters and reaction rates obtained from a solution of local two-term and a multi-term Boltzmann equation on the predictions are assessed. In-depth kinetic analysis indicates that the striations result from the undulations in electron temperature caused due to the interaction between ionization and vibrational reactions. Furthermore, the vibrationally excited molecules associated with the lower energy levels are found to influence nitrogen plasma stratification and the striation pattern strongly. A balance between ionization processes and electron energy transport allows the formation of the observed standing striations. Simulations were conducted for a range of discharge current densities from ∼0.018 to 0.080 mA cm−2, for an operating pressure of 0.7 Torr. Parametric studies show that the striation length decreases with increasing discharge current. The predictions from the model are compared against experimental measurements and are found to agree favorably.