The effect of strong electron emission from material surfaces has been proposed to form an “inverse sheath”: a region with a positive potential relative to the near-wall plasma which prevents the flow of ions to the wall [M. D. Campanell, “Negative plasma potential relative to electron-emitting surfaces,” Phys. Rev. E. 88, 033103 (2013); M. D. Campanell and M. V. Umansky, “Strongly emitting surfaces unable to float below plasma potential,” Phys. Rev. Lett. 116, 1–5 (2016); M. D. Campanell and G. R. Johnson, “Thermionic cooling of the target plasma to a sub-ev temperature,” Phys. Rev. Lett. 122, 1–5 (2019)]. We assess the viability of this regime in a tokamak device using the 2D edge plasma transport code UEDGE [T. Rognlien et al., “A fully implicit, time dependent 2-D fluid code for modeling tokamak edge plasmas,” J. Nucl. Mater. 196–198, 347–351 (1992)]. Since the UEDGE code does not consider the sheath region directly, we apply boundary conditions at the divertor targets which emulate the physics of both “standard” and “inverse” sheath regimes [R. Masline et al., “Influence of the inverse sheath on divertor plasma performance in tokamak edge plasma simulations,” Contrib. Plasma Phys. 60, e201900097 (2020)]. Using these boundary conditions, we perform scoping studies to assess plasma parameters near the target by varying the density at the core-edge interface. We observe a smooth transition in the resultant profiles of plasma parameters for the standard sheath, and a bifurcation across the simulation set for plasmas with an inverse sheath. The cause of this bifurcation is assessed by performing the parameter scan both with and without impurity radiation; we observe that the bifurcation persists in both cases, indicating that this bifurcation is caused by plasma recombination.

中文翻译：

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具有反向鞘层的偏滤器等离子体的模拟

已经提出材料表面的强电子发射效应形成“反向鞘”：相对于近壁等离子体具有正电位的区域，可防止离子流向壁 [MD Campanell，“负等离子体电位相对于电子发射表面，“Phys. 修订版 E. 88, 033103 (2013)；MD Campanell 和 MV Umansky，“无法漂浮在等离子体电位以下的强发射表面”，Phys. 牧师莱特。116, 1-5 (2016); MD Campanell 和 GR Johnson，“目标等离子体的热离子冷却至亚 ev 温度”，Phys. 牧师莱特。122, 1–5 (2019)]。我们使用二维边缘等离子体传输代码 UEDGE [T. Rognlien 等人，“用于模拟托卡马克边缘等离子体的完全隐式、时间相关的二维流体代码，”J. Nucl。母校。196-198，347–351 (1992)]。由于 UEDGE 代码不直接考虑鞘区，我们在偏滤器目标处应用边界条件，模拟“标准”和“逆”鞘区 [R. Masline 等人，“在托卡马克边缘等离子体模拟中反向鞘层对偏滤器等离子体性能的影响”，Contrib。等离子体物理。60, e201900097 (2020)]。使用这些边界条件，我们进行范围界定研究，通过改变核心边缘界面的密度来评估目标附近的等离子体参数。我们观察到标准鞘层的等离子体参数的合成曲线的平滑过渡，以及具有反向鞘层的等离子体在模拟集上的分叉。这种分叉的原因是通过在有和没有杂质辐射的情况下进行参数扫描来评估的；