Stabilization of Neoclassical Tearing Mode by Electron Cyclotron Current Drive

电子回旋电流驱动新古典撕裂模式的稳定

• 批准号: 17560728
• 负责人: NAGASAKI Kazunobu
• 金额: $ 2.28万
• 依托单位: Kyoto University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2005
• 资助国家: 日本
• 起止时间: 2005 至 2007
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17560728/
• 关键词: neoclassical tearing mod; electron cyclotron current drive; tokamak

It is an important task to control MHD instabilities for keeping plasma beta high steadily. In particular, neoclassical tearing mode (NTM) is a critical instability which limits the maximum beta. Electron cyclotron current drive (ECCD) is considered attractive scheme to stabilize the NTM since it locally drives non-inductive current. In this research, we have conducted experiments stabilizing NTM of m=3/n=2 and m=2/n=1 modes and their simulation. Here m and n is the poloidal and toroidal mode numbers, respectively. The main purpose of the experiment is to stabilize the NTM for the maintenance of high beta plasmas. The current density profile around magnetic island is analyzed by using a slab model. As the EC driven current enters into the magnetic island at the O-point phase, the peak value of EC driven current density is lower than that at the outside of magnetic island. This is because the current is averaged along the magnetic surface in the magnetic island. The current density at the O-point is found to be the same as the birth current density when the center of the magnetic island coincides with the peak of driven current profile. This result suggests that the position of EC driven current should be carefully adjusted if the width of EC driven current profile is comparable with the magnetic island width. The experiment on reducing the EC injection power for the m/n=2/1 mode is also conducted. The experimental results reveal that the stabilizing effect is weaker with the decrease of EC power. The NTM is fully stabilized up to 0.3 MW, and the power threshold is between 0.3 MW and 0.5 MW. The width of current profile is also found to be important as well as the total EC driven current. The EC driven current density is almost the same as the bootstrap current density for both the fundamental O-mode and the second harmonic X-mode, and the stabilizing effect of the misalignment of EC driven current position is independent of the EC mode.

控制MHD不稳定性是维持等离子体高β稳定的重要任务。特别地，新古典撕裂模（NTM）是限制最大β的临界不稳定性。电子回旋电流驱动（ECCD）被认为是稳定NTM的有吸引力的方案，因为它局部驱动无感电流。在本研究中，我们进行了稳定的NTM的m=3/n=2和m=2/n=1模式的实验和模拟。这里m和n分别是极向和环向模数。实验的主要目的是稳定NTM，以维持高β等离子体。用平板模型分析了磁岛周围的电流密度分布。当EC驱动电流在O点阶段进入磁岛时，EC驱动电流密度的峰值低于磁岛外部的峰值。这是因为电流是沿磁岛中的磁表面沿着平均的。当磁岛中心与驱动电流峰值重合时，O点处的电流密度与出生电流密度相同。这一结果表明，如果EC驱动电流分布的宽度与磁岛宽度相当，则EC驱动电流的位置应仔细调整。对m/n=2/1模进行了降低EC注入功率的实验研究。实验结果表明，随着EC功率的减小，稳定效果减弱。NTM完全稳定，最高可达0.3 MW，功率阈值在0.3 MW和0.5 MW之间。电流分布的宽度也被发现是重要的，以及总EC驱动电流。对于基波O模和二次谐波X模，EC驱动电流密度与自举电流密度几乎相同，并且EC驱动电流位置不对准的稳定效果与EC模式无关。

项目成果

Experimental study of plasma breakdown by second harmonic electron cyclotron waves in Heliotron J

Heliotron J中二次谐波电子回旋波击穿等离子体的实验研究

• 发表时间: 2005
• 期刊: Nuclear Fusion 45
• 作者: K.Nagasaki;et al.
• 通讯作者: et al.

ECCD Experiments in Stellarator/Heliotron

仿星器/日光管中的 ECCD 实验

• 发表时间: 2008
• 作者: K. Nagasaki;et. al.
• 通讯作者: et. al.

Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D

• DOI: 10.1088/0029-5515/47/5/001
• 发表时间: 2007-05
• 期刊: Nuclear Fusion
• 影响因子: 3.3
• 作者: R. Prater;R. L. La Haye;T. Luce;C. Petty;E. Strait;J. Ferron;D. Humphreys;A. Isayama;J. Lohr-J

ECCD Experiments in the TJ-II Stellarator

TJ-II 仿星器中的 ECCD 实验

• 发表时间: 2008
• 期刊: Fusion Sci. and Tech. 53
• 作者: A. Fernandez;A. Cappa;F. Castejon;J. M. Fontdecaba;K. Nagasaki
• 通讯作者: K. Nagasaki

Change of Edge Plasma Distribution during a Discharge in Heliotron J

Heliotron J 放电期间边缘等离子体分布的变化

• 发表时间: 2007
• 期刊: Plasma Fusion Res. 2
• 作者: Tohru MIZUUCHI;et. al.,
• 通讯作者: et. al.,