LOW-VOLTAGE OHMIC AND ELECTRON-CYCLOTRON HEATING ASSISTED STARTUP IN DIII-D
LOW-VOLTAGE OHMIC AND ELECTRON-CYCLOTRON HEATING ASSISTED STARTUP IN DIII-D
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DOI：
10.1088/0029-5515/31/11/001
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发表时间：
1991-11-01
期刊：
影响因子：
3.3
通讯作者：
PRATER, R
中科院分区：
文献类型：
--
作者：
LLOYD, B;JACKSON, GL;PRATER, R
在大型托卡马克的低电压启动方案的发展有相当大的兴趣，因为它是建议，在ITER的电场，这将是用于电离和等离子体电流斜升将被限制到E小于或等于0.3 V/m的值。在DIII-D装置上进行了有无电子回旋预电离和预热的低电压启动研究。通过仔细注意误差场和预充压力，成功实现了欧姆启动，E约为0.25 V/m，而电子回旋加速器加热（ECH）辅助启动，E约为0.15 V/m。ECH辅助启动在如此低的电场下提高了可靠性，并允许在扩展的预充压力和误差磁场范围内运行。使用ECH，在E = 0.3 V/m时启动，B在大部分血管横截面上接近50 G。这样的误差场表示比在相同电场下实现欧姆启动的最高值增加超过两倍。在预充压力和/或误差磁场的极端值下的低电压欧姆启动期间，观察到过度的击穿延迟。实验数据与基于汤森雪崩理论的理论预测吻合得很好。ECH辅助启动始终迅速。在等离子体电流斜升期间ECH的主要效应是回路电压V（res）的电阻分量的减小。 对于低ECH功率（P（RF）约300-400 k（W）），实现了V（res）的显著降低（约30%），但P（RF）的进一步大幅增加仅导致V（res）的适度额外降低。 在这些实验中，在整个斜升阶段没有施加ECH，并且产生了小于或类似于10%的伏秒消耗降低，直到电流平顶（I（p）约为1 MA）。这些实验证实了ITER设计中规定的低电场是可以接受的，并证明了使用ECH辅助启动所带来的实质性好处。
There is considerable interest in the development of low voltage startup scenarios for large tokamaks since it is proposed that in ITER the electric field which will be applied for ionization and plasma current ramp-up will be limited to values of E less-than-or-equal-to 0.3 V/m. Studies of low voltage startup have been carried out in DIII-D with and without electron cyclotron preionization and preheating. Successful Ohmic startup has been achieved with E approximately 0.25 V/m by paying careful attention to error fields and prefill pressure, while electron cyclotron heating (ECH) assisted startup with E approximately 0.15 V/m has been demonstrated. ECH assisted startup gives improved reliability at such low electric fields and permits operation over an extended range of prefill pressures and error magnetic fields. Using ECH, startup at E = 0.3 V/m with \B perpendicular-to\ > 50 G over most of the vessel cross-section has been demonstrated. Such an error field represents an increase by more than a factor of two over the highest value for which Ohmic startup was achieved at the same electric field. During low voltage Ohmic startup with extreme values of prefill pressure and/or error magnetic fields, excessive breakdown delays are observed. The experimental data agree well with theoretical predictions based on the Townsend avalanche theory. ECH assisted startup is always prompt. The primary effect of ECH during the plasma current ramp-up is a decrease of the resistive component of the loop voltage V(res). A significant reduction (approximately 30%) in V(res) is achieved for low ECH powers (P(RF) approximately 300-400 k(W)), but a further large increase in P(RF) results in only a modest additional decrease in V(res). ECH was not applied over the whole ramp-up phase in these experiments and produced a reduction in volt-second consumption up to the current flat-top (I(p) approximately 1 MA) of less-than-or-similar-to 10%. These experiments confirm that the low electric fields specified in the ITER design are acceptable and demonstrate the substantial benefits which accrue from the use of ECH assisted startup.