EXL-50 ECW等离子体边缘正浮置电位与等离子体电流之间强相关性的观测
Observation of a strong correlation between the positive floating potential near the edge and plasma current on EXL-50 ECW plasma
摘要：
在具有弱外部垂直场（Bv）的EXL-50球形环上使用了ECW等离子体中没有中心螺线管的完全非感应等离子体电流启动。一般情况下，通过梯度Bt离开血管壁的电子数大于离子数，并且在等离子体中建立正电势。利用边界附近的朗缪尔探针研究了悬浮电位与等离子体电流的关系。结果表明，悬浮电位为正（约200 V），与等离子体电流有很强的相关性。在开放磁场中，等离子体电流由处于优先约束的高能电子驱动，等离子体电流和电势与总电子密度近似正相关。形成闭合磁通面后，等离子体电流主要由ECW驱动电流组成，电势与等离子体电流呈负相关。通过主动调节Bv，证明了正电压与Bv和等离子体电流（Ip）近似负相关。考虑到边界附近等离子体温度相当低（~eV），边界附近的正电压是由高能电子损失引起的。因此，边界势的测量对于研究高能电子约束性能、无感等离子体电流启动和电流驱动具有重要意义。
英文摘要：
Fully non-inductive plasma current start-up without the central solenoid in ECW plasma was used on EXL-50 Spherical Torus with a weak external vertical field (Bv). Generally, the number of electrons leaving to the vessel wall by the gradient Bt is larger than ions, and the positive potential was built up in plasma. The relationship between floating potential and the plasma current was studied using the Langmuir probes near the boundary. The results show that the floating potential is positive (about 200V) and has a strong correlation with plasma current. In open magnetic field, the plasma current is driven by the high energy electrons in preferential confinement, the plasma current and potential approximately positively correlated with total electron density. After forming the closed flux surface, the plasma current consists mainly of the ECW driven current, and potential is negatively correlated with plasma current. By actively adjusting the Bv, it demonstrated that the positive voltage is approximately inversely correlated with the Bv and plasma current (Ip). Considering that the plasma temperature near the boundary is quite low (~eV), the positive voltage near the boundary caused by the high-energy electron loss. Therefore, the measurements of the boundary potential are important for the study of high-energy electron confinement performance, noninductive plasma current start-up and current driven.
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