Recent one-dimensional simulations of planar sheaths with strong electron emission have shown that trapping of charge-exchange ions causes transitions from space-charge limited (SCL) to inverse sheaths. However, multidimensional emitting sheath phenomena with collisions remained unexplored, due in part to high computational cost. We developed a novel continuum kinetic code to study the sheath physics, current flow and potential distributions in two-dimensional unmagnetized configurations with emitting surfaces. For small negatively biased thermionic cathodes in a plasma, the cathode sheath can exist in an equilibrium SCL state. The SCL sheath carries an immense density of trapped ions, neutralized by thermoelectrons, within the potential well of the virtual cathode. For further increases of emitted flux, the trapped ion cloud expands in space. The trapped ion space charge causes an increase of thermionic current far beyond the saturation limit predicted by conventional collisionless SCL sheath models without ion trapping. For sufficiently strong emission, the trapped ion cloud consumes the entire 2D plasma domain, forming a mode with globally confined ions and an inverse sheath at the cathode. In situations where the emitted flux is fixed and the bias is swept (e.g. emissive probe), the trapped ions cause a large thermionic current to escape for all biases below the plasma potential. Strong suppression of the thermionic emission, required for the probe to float, only occurs when the probe is above the plasma potential.

最近的具有强电子发射的平面鞘层的一维模拟显示，捕获电荷交换离子会导致从空间电荷受限（SCL）到逆鞘层的跃迁。然而，由于部分高昂的计算成本，带有碰撞的多维发射鞘现象仍未得到开发。我们开发了一种新颖的连续动力学代码，以研究带有发射表面的二维非磁化结构中的鞘层物理，电流和势分布。对于等离子体中的小的负偏压热电子阴极，阴极护套可以平衡SCL状态存在。SCL护套在虚拟阴极的势阱内载有巨大密度的被热电子中和的捕获离子。为了进一步增加发射通量，被困的离子云在空间中扩展。捕获的离子空间电荷会导致热离子电流的增加，远远超过传统的无碰撞SCL护套模型在没有离子捕获的情况下预测的饱和极限。为了获得足够强的发射，被捕获的离子云会消耗整个2D等离子体域，从而形成一种模式，该模式具有全局约束的离子和位于阴极的逆鞘。在固定的发射通量且扫过偏压的情况下（例如，发射探针），对于低于等离子体电势的所有偏压，被捕获的离子都会导致较大的热电子电流逸出。仅当探针高于等离子体电势时，才发生探针浮动所需的热离子发射的强抑制。