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首页> 外文期刊>Plasma physics and controlled fusion >Studies of turbulence and transport in Alcator C-Mod ohmic plasmas with phase contrast imaging and comparisons with gyrokinetic simulations
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Studies of turbulence and transport in Alcator C-Mod ohmic plasmas with phase contrast imaging and comparisons with gyrokinetic simulations

机译：相衬成像技术研究Alcator C-Mod欧姆等离子体中的湍流和输运，并与运动学仿真进行比较

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摘要

Recent advances in gyrokinetic simulation have allowed for quantitative predictions of core turbulence and associated transport. However, numerical codes must be tested against experimental results in both turbulence and transport. In this paper, we present recent results from ohmic plasmas in the Alcator C-Mod tokamak using phase contrast imaging (PCI) diagnostic, which is capable of measuring density fluctuations with wave numbers up to 55 cm(-1). The experiments were carried out over the range of densities covering the 'neo-Alcator' (linear confinement time scaling with density, electron transport dominates) to the 'saturated ohmic' regime. We have also simulated these plasmas with the gyrokinetic code GYRO and compared numerical predictions with experimentally measured turbulence through a synthetic PCI diagnostic method. The key role played by the ion temperature gradient (ITG) turbulence has been verified, including measurements of turbulent wave propagation in the ion diamagnetic direction. It is found that the intensity of density fluctuations increases with density, in agreement between simulation and experiments. The absolute fluctuation intensity agrees with the simulation within experimental error (+/- 60%). In the saturated ohmic regime, the simulated ion and electron thermal diffusivities also agree with experiments after varying the ion temperature gradient within experimental uncertainty. However, in the linear ohmic regime, GYRO does not agree well with experiments, showing significantly larger ion thermal transport and smaller electron thermal transport. Our study shows that although the short wavelength turbulence in the electron temperature gradient (ETG) range is unstable in the linear ohmic regime, the nonlinear simulation with k(theta)rho(s) up to 4 does not raise the electron thermal diffusivity to the experimental level, where k(theta) is the poloidal wavenumber and rho(s) is the ion-sound Larmor radius. At the present time, it is not known whether even shorter wavelength turbulence would account for the measured electron transport.
机译：陀螺动力学模拟的最新进展已使岩心湍流和相关运输的定量预测成为可能。但是，必须针对湍流和运输中的实验结果测试数字代码。在本文中，我们使用相衬成像（PCI）诊断技术，从Alcator C-Mod托卡马克中的欧姆等离子体中获得了最新结果，该技术能够测量波数高达55 cm（-1）的密度波动。在覆盖“新Alcator”（密度的线性限制时间缩放，电子传输占主导）的密度范围至“饱和欧姆”状态下进行了实验。我们还用陀螺动力学代码GYRO模拟了这些血浆，并通过合成PCI诊断方法将数值预测与通过实验测得的湍流进行了比较。离子温度梯度（ITG）湍流所起的关键作用已得到验证，包括在离子反磁性方向上湍流传播的测量。结果发现，密度波动的强度随密度的增加而增加，这与模拟和实验一致。绝对波动强度与模拟在实验误差范围内（+/- 60％）一致。在饱和欧姆状态下，在实验不确定性范围内改变离子温度梯度后，模拟的离子和电子的热扩散率也与实验一致。但是，在线性欧姆状态下，GYRO与实验不太吻合，显示出明显更大的离子热传递和更小的电子热传递。我们的研究表明，尽管在线性欧姆状态下，电子温度梯度（ETG）范围内的短波长湍流不稳定，但k [rho]（s）高达4的非线性模拟并没有提高电子的热扩散系数。实验水平，其中k（theta）是极谱波数，rho（s）是离子声拉莫尔半径。目前，还不知道更短的波长湍流是否会解释所测量的电子传输。

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