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ECCD-induced sawtooth crashes at W7-X
Nuclear Fusion ( IF 3.3 ) Pub Date : 2020-09-22 , DOI: 10.1088/1741-4326/aba72b
M. Zanini 1 , H.P. Laqua 1 , H. Thomsen 1 , T. Stange 1 , C. Brandt 1 , H. Braune 1 , K.J. Brunner 1 , G. Fuchert 1 , M. Hirsch 1 , J. Knauer 1 , U. Hfel 1 , S. Marsen 1 , E. Pasch 1 , K. Rahbarnia 1 , J. Schilling 1 , Y. Turkin 1 , R.C. Wolf 1, 2 , A. Zocco 1
Affiliation  

The optimised superconducting stellarator W7-X generates its rotational transform by means of external coils, therefore no toroidal current is necessary for plasma confinement. Electron cyclotron current drive experiments were conducted for strikeline control and safe divertor operation. During current drive experiments periodic and repetitive crashes of the central electron temperature, similar to sawtooth crashes in tokamaks, were detected. Measurements from soft x-ray tomography and electron cyclotron emission show that the crashes are preceded by weak oscillating precursors and a displacement of the plasma core, consistent with a (m, n)=(1, 1) mode. The displacement occurs within 100μs, followed by expulsion and redistribution of the core into the external part of the plasma. Two types of crashes, with different frequencies and amplitudes are detected in the experimental program. For these non-stationary parameters a strong dependence on the toroidal current is found. A 1-D heuristic model for current diffusion is proposed as a first step to explain the characteristic crash time. Initial results show that the modelled current diffusion timescale is consistent with the initial crash frequency and that the toroidal current rise shifts the position where the instability is triggered, resulting in larger crash amplitudes.

中文翻译:

ECCD 引起的 W7-X 锯齿崩溃

优化的超导仿星器 W7-X 通过外部线圈产生旋转变换,因此等离子体约束不需要环形电流。电子回旋电流驱动实验进行了打击线控制和安全偏滤器操作。在电流驱动实验中,检测到中心电子温度的周期性和重复性碰撞,类似于托卡马克中的锯齿形碰撞。软 X 射线断层扫描和电子回旋加速器发射的测量表明,碰撞之前是弱振荡前体和等离子体核心的位移,与 (m, n)=(1, 1) 模式一致。位移发生在 100μs 内,随后核心被排出并重新分布到等离子体的外部。两种类型的崩溃,在实验程序中检测到不同的频率和幅度。对于这些非平稳参数,发现对环形电流有很强的依赖性。提出了电流扩散的一维启发式模型作为解释特征碰撞时间的第一步。初步结果表明,建模的电流扩散时间尺度与初始碰撞频率一致,环形电流上升移动了触发不稳定的位置,导致更大的碰撞幅度。
更新日期:2020-09-22
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