Meezan Nathan B, Cappelli Mark A
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-3032, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Sep;66(3 Pt 2B):036401. doi: 10.1103/PhysRevE.66.036401. Epub 2002 Sep 11.
Coaxial Hall discharges (also known as Hall thrusters, stationary plasma thrusters, and closed-drift accelerators) are cross-field plasma sources under development for space propulsion applications. The importance of the electron-wall interaction to the Hall discharge operation is studied the through analysis of experimental data and simulation of the electron energy distribution function (EEDF) inside the discharge channel. Experimental time-average plasma property data from a laboratory Hall discharge are used to calculate the electron conductivity and to estimate the rate of wall-loss collisions. The electron Boltzmann equation is then solved in the local field limit, using the experimental results as inputs. The equation takes into account ionization and wall collisions, including secondary electrons produced at the wall. Local electron balances are used to calculate the sheath potential at the insulator walls. Results show an EEDF depleted at high energy due to electron loss to the walls. The calculated EEDFs agree well with experimental electron temperature data when the experimentally determined effective collision frequency is used for electron momentum transport. The electron wall-loss and wall-return frequencies are extremely low compared to those predicted by a Maxwellian of equal average energy. The very low frequency of wall collisions suggests that secondary electrons do not contribute to cross-field transport. This conclusion holds despite significant experimental uncertainty.
同轴霍尔放电（也称为霍尔推进器、静止等离子体推进器和封闭漂移加速器）是正在开发用于空间推进应用的交叉场等离子体源。通过对实验数据的分析以及对放电通道内电子能量分布函数（EEDF）的模拟，研究了电子与壁面相互作用对霍尔放电运行的重要性。利用实验室霍尔放电的实验时间平均等离子体特性数据来计算电子电导率，并估计壁面损失碰撞率。然后在局部场极限下求解电子玻尔兹曼方程，将实验结果作为输入。该方程考虑了电离和壁面碰撞，包括壁面产生的二次电子。利用局部电子平衡来计算绝缘壁面处的鞘层电位。结果表明，由于电子向壁面的损失，EEDF在高能处出现耗尽。当将实验确定的有效碰撞频率用于电子动量传输时，计算得到的EEDF与实验电子温度数据吻合良好。与具有相同平均能量的麦克斯韦分布所预测的频率相比，电子壁面损失频率和壁面返回频率极低。壁面碰撞频率极低表明二次电子对交叉场传输没有贡献。尽管存在显著的实验不确定性，但这一结论仍然成立。
