Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas
Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas
复制标题
DIII-D 和 JT-60U 等离子体中高电子离子温度比下的磁剪切效应对等离子体输运和湍流的影响
DOI：
10.1088/1741-4326/aa611e
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发表时间：
2017
期刊：
影响因子：
3.3
通讯作者：
W. M. Solomon
中科院分区：
文献类型：
--
作者：
M. Yoshida;G. R. McKee;M. Murakami;B. A. Grierson;M. Nakata;E. M. Davis;A. Marinoni;M. Ono;T. L. Rhodes;C. Sung;L. Schmitz;C. C. Petty9;J.R. Ferron;F. Turco;A. M. Garofalo;C. T. Holcomb;C. M. Collins;W. M. Solomon
负磁剪切已经在DIII-D和JT-60 U中得到证实，以减轻通常随着电子与离子温度比（Te/Ti）的增加而观察到的约束退化。在最近的实验中，在DIII-D负中心磁剪切（NCS）放电，在内部传输势垒周围的最小安全系数（q min）的半径形成的热输运几乎保持不变，并适度增加的区域以外的q min相比，正剪切（PS）的情况下，当Te/Ti增加约0.8至1.1，通过电子回旋加热（ECH）。NCS延伸到q min之外的区域中的益处可以通过NCS等离子体中相对于PS等离子体在等离子体半径上的较低磁剪切来解释。在DIII-D和JT-60 U中，通常观察到NCS等离子体在高Te/Ti下的约束退化减少。NCS和PS等离子体之间的不同的传输响应的机制进行了评估的波动测量和Gyrokinetic模拟在DIII-D方面，NCS给出了一个较小的上升，在低波数宽带湍流波动的增加Te/Ti相比，PS的情况下。这是一致的陀螺动力学模拟，这表明一个较小的上升，在NCS等离子体中的离子温度梯度模式的生长速率，随着T e/T i的增加。回旋动力学模拟也表明，与ECH应用的电子模式的稳定性的变化，符合较高的波数波动测量，虽然需要更详细的模拟给出定量解释的实验观察。控制q-分布和磁剪切将允许在未来的机器与占主导地位的电子加热约束改善。
Negative magnetic shear has been demonstrated in DIII-D and JT-60U to mitigate the confinement degradation typically observed with increasing the electron to ion temperature ratio (T e/T i). In recent experiments in DIII-D negative central magnetic shear (NCS) discharges, the thermal transport in the internal transport barrier formed around the radius of the minimum safety factor (q min) remained almost constant and modestly increased in the region outside of q min compared to the positive shear (PS) case, when T e/T i increased from about 0.8 to 1.1 through electron cyclotron heating (ECH). The benefit of NCS extending into the region outside of q min can be explained by the lower magnetic shear in the NCS plasma over the plasma radius relative to the PS plasma. Reduced confinement degradation at high T e/T i with NCS plasmas was commonly observed in DIII-D and JT-60U. The mechanism of the different transport responses between the NCS and PS plasmas has been assessed in terms of fluctuation measurements and gyrokinetic simulations in DIII-D; NCS gave a smaller rise in the low-wavenumber broadband turbulent fluctuations with the increase in T e/T i compared with the PS case. This is consistent with gyrokinetic simulations, which show a smaller rise in the growth rates of the ion temperature gradient mode in the NCS plasmas, with increasing T e/T i. Gyrokinetic simulations also showed a change in the stability of the electron modes with ECH applied, consistent with higher-wavenumber fluctuation measurements, although more detailed simulations are needed to give a quantitative explanation for the experimental observations. Control of q-profile and magnetic shear will allow confinement improvement in future machines with dominant electron heating.