二次电子发射对稳态等离子体推进器加速通道鞘层的影响

稳态等离子体推进器(Stationary Plasma Thruster,SPT)工作时产生的高密度等离子体遇到其加速通道陶瓷器壁时,在陶瓷器壁与等离子体之间形成鞘层。离子会在鞘层电场作用下到达SPT加速通道器壁表面进而复合,而等离子体中的电子由于具有高能可跃过鞘层电场轰击器壁表面,从而产生二次电子发射效应。从器壁表面发射出的二次电子由于受到鞘层电场的排斥,导致其向等离子体源区移动,进而影响等离子体鞘层的特性。建立了考虑二次电子发射效应的无碰撞等离子体鞘层的一维流体模型,研究了二次电子发射对SPT加速通道鞘层特性的影响。计算结果显示,随二次电子发射系数增加,鞘层电势、离子密度、电子密度和二次电子密度增加,而离子速度降低,鞘层中离子密度始终大于电子密度。鞘层中二次电子绝大多数集中在器壁附近,随二次电子穿越鞘层厚度的增加,二次电子密度快速下降。

Effects of secondary electron emission on the sheath of stationary plasma thruster near the acceleration channel

When the high-density plasma produced as the stationary plasma thruster(abbreviation SPT) works meets the wall of acceleration channel,sheath forms between the wall and plasma.Ions could reach the surface of the channel in the sheath electric field,and they would be compounded at the surface,while electrons in the plasma could impact the surface of the channel due to its high energy,resulting the secondary electron emission effects.Secondary electrons would move towards the plasma source region because of the sheath electric field,which could lead to the variation of the plasma sheath characteristics.One-dimensional collisionless fluid model was built to study the effects of secondary electron emission on the sheath of SPT near the acceleration channel.Calculation results show that with the secondary electron emission coefficient increases,the sheath potential,ion density,electron density and secondary electron density increase,while the ion velocity decreases.The ion density in the sheath is always greater than the electron density.The secondary electrons are mostly concentrated in the zone near the wall.With the secondary electron traversing the sheath thickness increases,the secondary electron density decreases rapidly.