arXiv 1508.059712015-08physics.plasm-ph

电子预加热：正边界对等离子体的巨大影响

Electron Preheaths: The Outsized Influence of Positive Boundaries on Plasmas

Benjamin T. Yee, Brett Scheiner, Scott D. Baalrud, Edward V. Barnat, Matthew M. Hopkins

摘要：

电子鞘在物体表面附近形成，比等离子体电势偏置得更正，例如在朗缪尔探针迹线的电子饱和区域中。通常，电子鞘层的形成要求电子收集面积比离子收集面积足够小（$\sqrt{2.3m_e/M}$倍）。它们通常被认为是收集随机热电子流的局部现象，但不会干扰等离子体。在这里，使用实验嵌入在墙上的电极，粒子在细胞模拟和理论，它表明，在低温等离子体条件下（$T_e \gg T_i$）电子鞘是远离本地。相反，长的预鞘区（超过70 $λ_D$）延伸到等离子体中，在那里电子经由压力梯度被加速到超过鞘边缘处的电子热速度的流速。这种快速流动被发现激发不稳定性，导致鞘边缘附近的强烈波动。

英文摘要：

Electron sheaths form near the surface of objects biased more positive than the plasma potential, such as in the electron saturation region of a Langmuir probe trace. Generally, the formation of electron sheaths requires that the electron-collecting area be sufficiently smaller ($\sqrt{2.3m_e/M}$ times) than the ion-collecting area. They are commonly thought to be local phenomena that collect the random thermal electron current, but do not otherwise perturb a plasma. Here, using experiments on an electrode embedded in a wall, particle-in-cell simulations and theory, it is shown that under low temperature plasma conditions ($T_e \gg T_i$) electron sheaths are far from local. Instead, a long presheath region (in excess of 70 $λ_D$) extends into the plasma where electrons are accelerated via a pressure gradient to a flow speed exceeding the electron thermal speed at the sheath edge. This fast flow is found to excite instabilities, causing strong fluctuations near the sheath edge.

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