Equilibrium states of anodic double layers
Equilibrium states of anodic double layers
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阳极双层的平衡状态
DOI：
10.1088/0963-0252/18/3/035002
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
N. Hershkowitz
中科院分区：
文献类型：
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作者：
S. Baalrud;B. Longmier;N. Hershkowitz
本文用静电探针对浸没在部分电离等离子体中的正偏压盘形电极附近形成的阳极双层的平衡状态进行了实验研究。当从电极到等离子体的电位降小于临界值Δ c时，观察到阳极辉光，其中双层电位降在电极表面的几毫米内。对于较大的偏置，阳极点形成在双层电位降距离电极几厘米处，并且中间区域是比本体等离子体更明亮的等离子体。建立了一个理论模型，该模型预测Δ c = 1/P + C，其中P为中性压力，C为常数，并预测电极处电流-电压特性的滞后;实验观察到这两种效应。该模型还提供了与测量结果一致的电极和双层电位降之间的距离的估计。在小电极附近，观察到阳极点是“火球”，形状是球形的。在更大的电极附近发现了“火棒”，它们具有圆柱形形状。结果表明，由于火棒的有效电子收集面积比火球小，因此需要使用火棒来实现全局电流平衡。实验还证实，全球非双极流（Baalrud S D等2007年物理等离子体14 042109）伴随着消防杆。在这种情况下，所有的电子都通过Firerod到电极，而所有的正离子都丢失到其他等离子体边界。
Equilibrium states of anodic double layers that form near a positively biased disk-shaped electrode immersed in a partially ionized plasma are studied experimentally using electrostatic probes. When the potential drop from the electrode to the plasma is less than a critical value, Δϕc, an anode glow is observed where a double layer potential drop is within a few millimeters of the electrode surface. For larger biases an anode spot forms where the double layer potential drop is centimeters from the electrode and the intervening region is a plasma more luminous than the bulk plasma. A theoretical model is developed which predicts that Δϕc ∝ 1/P + C, where P is the neutral pressure and C is a constant, and it predicts hysteresis in the current–voltage characteristic at the electrode; both effects are observed experimentally. The model also provides an estimate for the distance between the electrode and double layer potential drop that agrees with the measurements. Near small electrodes, anode spots are observed to be ‘fireballs,’ which are spherical in shape. Near larger electrodes ‘firerods’ are found instead, which have a cylindrical shape. It is shown that firerods are required by global current balance because they have a smaller effective electron collecting area than fireballs. Experiments also confirm that global nonambipolar flow (Baalrud S D et al 2007 Phys. Plasmas 14 042109) accompanies firerods. In this case all electrons are lost through the firerod to the electrode, while all positive ions are lost to the other plasma boundaries.