Study on the elucidation of appearance and growth mechanism of magnetic islands and their active control in torus plasmas

研究了新古典主义撕裂模(NTM)开始和演化过程中的磁岛结构。NTM岛被发现是由一次与另一次不稳定有关的小坍塌触发的，除了开始时没有检测到不稳定。结果表明，有坍塌触发的NTM的归一化β值大于无触发的NTM的归一化β值，且前者的模式位置的压力梯度更陡峭。等离子体自转突然减慢的磁岛宽度大于减小磁岛宽度后等离子体开始自转时的磁岛宽度。这表明模式锁定和解锁的孤岛宽度中存在滞后。磁岛主动控制装置--双频回旋管的研制取得了进展，实现其标称值具有良好的前景。

Structure of magnetic islands associated with neoclassical tearing modes (NTMs) during their onset and evolution has been investigated. The NTM islands were found to be triggered by a small collapse associated with another instability, in addition to onset without detectable instabilities. It was found that the value of the normalized beta for the collapse-triggered NTM is larger than that for the trigger-less NTM, and that the pressure gradient at the mode location is steeper for the former case. The magnetic island width at which the plasma rotation suddenly slows down is larger than that at the plasma starts to rotate after the island width is decreased. This indicates that there is a hysteresis in the island width for mode locking and unlocking. The development of a device for active control of magnetic islands, a dual-frequency gyrotron, has made progressed, and a good prospect has been obtained toward the achievement of its nominal values.