Formation and Sustainment of Spherical Tokamak by Electron Cyclotron Heating

在晚期装置上进行了单独电子回旋加热而不进行欧姆加热的球形托卡马克等离子体的启动和形成实验，得到了以下结果：[1]在2.45 GHz，5kW的微波功率下，产生了高达3kA的等离子体电流，并维持了1s。磁性测量表明，形成了闭合的磁通面。电子密度大于等离子体截止密度，表明发生了电子伯恩斯坦波(EBW)加热。[2]要形成封闭的磁通面，(1)气压为2-4×10~(-3)pA，(2)真空垂直磁场的n指数大于0.18。[3]根据静电探针测量的电子密度和温度分布，研究了封闭磁通面形成前的电流驱动机制。[4]注入2 GHz/0.1s、50kW的微波脉冲，并在形成封闭磁通面后增加垂直磁场，可使等离子体电流增加到5kA。为了维持MHD平衡，必须控制垂直场的强度。在放电过程中进行额外的气体膨胀，使电子束的密度增加到截止密度的6倍以上。[5]我们找到了在任意密度梯度和注入角度下，使电子束的模式转换效率最大化的入射电磁波的偏振计算方法，并编制了计算程序。得到的新结果是，即使在先前理论预测转换效率较低的情况下，通过优化偏振也可以获得90%以上的模式转换效率。

Experiments on start-up and formation of spherical tokamak plasmas were carried out on the LATE device by electron cyclotron heating alone without Ohmic heating, and following results were obtained.[1] A plasma current UP to 3 kA was generated and maintained for 1 sec by injecting a 2.45 GHz, 5 kW microwave power. Magnetic measurement showed that closed flux surfaces were formed. The electron density was more than the plasma cutoff density, suggesting that electron Bernstein wave (EBW) heating occurred.[2] In order to form closed flux surfaces, it was necessary that (1) the gas pressure was 2 - 4 x 10^<-3> Pa, and that (2) the n index of the vacuum vertical magnetic field was more than 0.18.[3] The mechanism of current drive before formation of closed flux surfaces were investigated on the basis of electron density and temperature profiles measured by electrostatic probes. Th estimated value of driven current was in fairly good agreement with the observed value.[4] By injecting 2GHz/0.1s, 50 kW microwave pulse and increasing the vertical magnetic field after formation of closed flux surfaces, the plasma current increased up to 5 kA. The strength of the vertical field had to be controlled to maintain the MHD equilibrium. Additional gas puffing during the discharge increased the density more than 6 times the cutoff density.[5] We found the method to calculate the polarization of incident electromagnetic waves which maximized the mode conversion efficiency to EBW for arbitrary density gradient and injection angle, and made the calculation code. The new result was obtained that the mode conversion efficiency more than 90 % can be obtained by optimizing the polarization even in the condition where previous theory predicted bad conversion efficiency.