壁面二次电子发射对霍尔推力器放电通道绝缘壁面双鞘特性的影响

为进一步揭示霍尔推力器放电通道绝缘壁面鞘层的特性, 利用考虑了壁面二次电子分布函数的一维稳态流体鞘层模型, 研究了壁面二次电子发射对近壁双鞘特性的影响. 分析结果表明, 由于壁面发射的二次电子对近壁鞘层中的电子密度有增加作用, 存在一个临界二次电子发射系数σ_dc使得: 当σ≤σ_dc时, 鞘层为单层的正离子鞘结构; 当σ>σ_dc时, 鞘层表现为双层的正离子鞘和电子鞘相连结构, 连接点对应于垂直于壁面方向上电势分布的拐点. 然而, 当σ进一步增大到0.999时, 鞘层转变为三层的正离子鞘-电子鞘-正离子鞘交替结构. 数值结果表明: 随着σ的增加, 电子鞘与离子鞘的连接点向远离壁面的方向移动, 电子鞘的厚度逐渐增加; 随着壁面出射电子能量系数a的增加, 近壁区鞘层的厚度也逐渐增加. 关键词： 霍尔推力器 双鞘 壁面二次电子发射

Effect of wall secondary electron emission on the characteristics of double sheath near the dielectric wall in Hall thruster

To further reveal the characteristics of sheath near the dielectric wall in Hall thruster discharge channel, a one-dimensional fluid sheath model combined with the velocity distribution function of electron emitted from wall is used to study the influence of secondary electron emission yield (SEEy) σ on the characteristics of double sheath near wall. Analytic results show that because of the contribution of secondary electron flux to the density of sheath electron, the sheath presents single-layer positive ion sheath formation when σ is lower than a critical SEEy σ_dc, and also presents double-layers formation that joins with positive ion sheath and electron sheath when σ>σ_dc. However, when σ further increases to 0.999, the sheath presents the formation of three-layers that are alternated by positive ion sheath, electron sheath and positive ion sheath. Numerical results also indicate that with the increase of σ, the joining point between positive ion sheath and electron sheath moves away from wall, and the thickness of electron sheath increases obviously.