Impact of a pulsed supersonic deuterium gas jet on the ELM behaviour in ASDEX Upgrade
Impact of a pulsed supersonic deuterium gas jet on the ELM behaviour in ASDEX Upgrade
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DOI：
10.1088/0741-3335/47/9/009
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发表时间：
2005-09
影响因子：
2.2
通讯作者：
P. Lang;J. Neuhauser;J. Bucalossi;A. Chankin;D. Coster;R. Drube;R. Dux;G. Haas;L. Horton
中科院分区：
文献类型：
--
作者：
P. Lang;J. Neuhauser;J. Bucalossi;A. Chankin;D. Coster;R. Drube;R. Dux;G. Haas;L. Horton
在ASDEX升级中研究了通过间歇气体注入在H模式等离子体中起搏I型边缘局域模（ELM）的可能性，作为一种可能的替代方案，并与ELM控制弹丸进行比较。使用拉瓦尔喷嘴型分子氘喷射器，以2.2 km s-1的超音速流速提供1.7 ms长的射流，每个脉冲高达约1020 D。该注射器的重复频率为2 Hz，快速上升时间为1.25 µs，与典型的ELM上升时间相当，似乎非常适合单ELM触发测试。当应用于具有40-60 Hz的中等I型ELM频率的H模式放电时，与使用弹丸的经验相反，不能实现即时（<0.5 ms）ELM触发。然而，有明确的证据表明，气体脉冲振幅与气体脉冲和下一个ELM之间的时间间隔呈负相关的形式存在延迟效应。明显缺乏即时ELM触发似乎是由于气体射流的自阻塞的分界线附近的高密度等离子体层的一个非常快速的形成，而延迟效应可能只是由射流诱导的轴对称边缘轮廓修改，类似于延迟ELM级联后观察到的即时ELM在大颗粒注入的情况下。所观察到的延迟触发效应可能仍然适用于未来机器中的ELM控制，但在提高的脉冲频率下的相关高气体燃料可能使其在整体等离子体性能方面没有吸引力。
The possibility for pacing of type-I edge localized modes (ELMs) in H-mode plasmas by intermittent gas injection was investigated in ASDEX Upgrade as a possible alternative to, and in comparison with, ELM control by pellets. A Laval nozzle type molecular deuterium injector was used, delivering 1.7 ms long jets with up to about 1020D per pulse at a supersonic flow velocity of 2.2 km s−1. With a repetition rate of 2 Hz and a fast rise time of ≈25 µs, comparable to typical ELM rise times, the injector seemed to be well-suited for single ELM trigger tests. When applied to H-mode discharges with a moderate type-I ELM frequency of 40–60 Hz, no prompt (<0.5 ms) ELM triggering could be achieved, in contrast to the experience with pellets. There was, however, clear evidence for a delayed effect in the form of an inverse correlation of the gas pulse amplitude with the time interval between the gas pulse and the next ELM. The apparent lack of prompt ELM triggering seems to be due to a self-blocking of the gas jet by an extremely fast formation of a high density plasma layer in the separatrix vicinity, while the delayed effect may be simply caused by the jet-induced axisymmetric edge profile modification, similar to the delayed ELM cascade observed after a prompt ELM in case of large pellet injection. The delayed trigger effect observed might still be useful for ELM control in future machines, but the related high gas fuelling at elevated pulse frequency could make it unattractive in view of overall plasma performance.