Investigation of electron heat pinch in ASDEX-Upgrade
Investigation of electron heat pinch in ASDEX-Upgrade
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DOI：
10.1088/0741-3335/48/3/004
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发表时间：
2006-03
影响因子：
2.2
通讯作者：
P. Mantica;F. Ryter;C. Capuano;H. Fahrbach;F. Leuterer;W. Suttrop;J. Weiland
中科院分区：
文献类型：
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作者：
P. Mantica;F. Ryter;C. Capuano;H. Fahrbach;F. Leuterer;W. Suttrop;J. Weiland
利用ASDEX-Upgrade实验研究了强离轴电子回旋加热（ECH）等离子体中电子热箍缩的存在。在低欧姆功率（<100 kW）的等离子体中，当ρdep = 0.65时，1.6 MW的ECH功率仍然会导致密度ne 0 = 2.7 × 1019 m−3时的峰值电子温度（Te）分布。四个回旋管中的两个被调制，以研究对流效应也在不同频率的Te瞬态响应。测量了调制幅度的特殊分布，在ρdep（0.3 < ρtor < 0.65）内的区域非常平坦，甚至在内侧远离ρdep的区域增加而不是减少。相反，相位分布规律地表明热波在远离ρdep的两个方向上的传播。功率平衡分析表明，在核心区域的热通量是非常接近于零，但不确定性不允许明确确定其符号。当ρdep内部的区域接近临界阈值并在其附近振荡时，使用经验模型模拟稳态和调制结果，该经验模型具有以临界梯度长度（LTe = −Te/Δ Te）行为为特征的扩散项和恒定的高斯形热夹点轮廓，可以很好地再现数据，并且在同一区域存在小对流项U 1-2 m s−1。在较高密度下，Te轮廓变得更平坦，振幅轮廓恢复到通常的形状，内部相对于外部ρdep具有更强的衰减。在这种情况下，不需要热箍缩，等离子体在ρdep内低于临界阈值。计算结果与理论预言的在R/LTe中由阈值调节的湍流和由小湍流产生的电子热箍缩项一致。然而，最初的尝试执行第一原理为基础的模拟使用准线性静电漂移波Weiland模型未能再现实验结果。
The existence of an electron heat pinch has been experimentally investigated in ASDEX-Upgrade in plasmas with strong off-axis electron cyclotron heating (ECH). Localization of 1.6 MW of ECH power at ρdep = 0.65 in plasmas with low Ohmic power (<100 kW) still resulted in peaked electron temperature (Te) profiles at densities ne0 ∼ 2.7 × 1019 m−3. Two out of four gyrotrons were modulated in order to study convective effects also on the Te transient response at different frequencies. Peculiar profiles of the modulation amplitude have been measured, very flat in the region just inside ρdep (0.3 < ρtor < 0.65) or even increasing rather than decreasing away from ρdep on the inner side. The phase profiles instead regularly indicate the propagation of the heat wave in both directions away from ρdep. Power balance analysis shows that the heat flux in the core region is very close to zero, but uncertainties do not allow a clear determination of its sign. Modelling steady-state and modulation results with an empirical model featuring a diffusive term characterized by a critical gradient length (LTe = −Te/∇Te) behaviour and a constant Gaussian shaped heat pinch profile allows good reproduction of the data when the region just inside ρdep is close to the critical threshold and oscillates around it, and a small convective term U ∼ 1–2 m s−1 is present in the same region. At higher density the Te profile becomes flatter and the amplitude profiles recover the usual shape with stronger decay inside with respect to outside ρdep. In this case no heat pinch is needed and the plasma goes below the critical threshold inside ρdep. The results are consistent with the theoretical prediction of a turbulence regulated by a threshold in R/LTe and a small turbulence generated electron heat pinch term. However initial attempts to perform first principle-based simulations using the quasi-linear electrostatic drift wave Weiland model have failed to reproduce the experimental results.