两种正离子的碰撞等离子体鞘层的离子特性

Characteristics of ions in a collisional plasma sheath with two species of positive ions

建立了包含两种正离子的碰撞等离子体鞘层的流体模型,通过四阶龙格-库塔法模拟了碰撞对含有两种正离子的等离子体鞘层中的离子密度和速度分布产生的影响。结果表明,对于两种正离子的等离子体来说,鞘层中无论哪种离子与中性粒子碰撞频率的增加,该种离子的密度和速度分布都将呈现波动变化,密度是先增加后降低,速度是先降低后增加;而另一种离子的密度和速度呈单调变化。鞘边正离子的含量越少,受自身与中性粒子的碰撞频率增加,鞘层中该种离子密度先增加后降低的变化位置就越远离等离子体的鞘层边界。同时发现该种离子密度分布受自身碰撞频率增加,降低的幅度变化非常小。另外发现电子碰撞器壁产生的二次电子发射系数对质量较轻的离子影响要大一些。

A fluid model is developed in a collisional plasma sheath including two species of positive ions. It is discussed that collisions which consist of ion-neutral collision and secondary electron emitted from the wall affect the density distribution and＇ velocity. Numerical results are obtained through a fourth-order-Rung-Kutta method. It is shown that by increasing the collision frequency of one of two ions with neutrals, the density distribution and velocity of this ion will take on the fluctuation in the sheath. The density increases, then decreases But the velocity is in verse. The other ion is completely monotone. It is discovered that the position where the density of the ion presents the transformation by the collision between this kind of positive ions and neutral particles in the sheath will be away from the sheath edge if the ion＇s density is less at the sheath edge. It is also found that the abatement of this ion density distribution is very small when the collision between the less ion and neutral particles increases. In addition, the coefficient of secondary electron emission affects the density distribution of the lighter ion species greatly in two different masses of positive ions.