Quantitative comparisons of electron-scale turbulence measurements in NSTX via synthetic diagnostics for high-k scattering.

Two synthetic diagnostics are implemented for the high-k scattering system in NSTX [D. R. Smith, E. Mazzucato, W. Lee, H. K. Park, C. W. Domier, and N. C. Luhmann Jr., Rev. Sci. Instrum., 79, 123501 (2008)] allowing direct comparisons between synthetic and experimentally detected frequency and wavenumber spectra of electron-scale turbulence fluctuations. Synthetic diagnostics were formulated in real-space and in wavenumber space, and were deployed to realistic electron-scale simulations carried out with the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186 (2003) 545]. A highly unstable ETG regime (electron temperature gradient mode) in a modest beta NSTX NBI-heated H-mode discharge was chosen for the analysis. Mapping the measured wavenumbers to field aligned coordinates showed that the high-k system is sensitive to fluctuations that are closer to the spectral peak in the density fluctuation wavenumber spectrum (streamers) than originally predicted. Analysis of synthetic spectra show that the frequency response of the detected fluctuations is dominated by Doppler shift and insensitive to the turbulence drive. The shape of the high-k density fluctuation wavenumber spectrum is sensitive to the ETG turbulence drive conditions, and can be reproduced in a sensitivity scan of the most pertinent turbulent drive terms in the simulation.针对国家球形环面实验装置（National Spherical Torus Experiment，NSTX）的高k散射系统，本文实现了两套合成诊断系统[D. R. Smith, E. Mazzucato, W. Lee, H. K. Park, C. W. Domier, 及N. C. Luhmann Jr., Rev. Sci. Instrum., 79, 123501 (2008)]，可实现合成诊断与实验探测到的电子尺度湍流涨落的频率谱和波数谱之间的直接对比。合成诊断系统分别在实空间与波数空间中构建，并应用于采用GYRO代码开展的真实电子尺度模拟[J. Candy和R. E. Waltz, J. Comput. Phys. 186 (2003) 545]。本分析选取了中等β值、经中性束注入（Neutral Beam Injection，NBI）加热的H模（H-mode）放电中的高不稳定电子温度梯度模（Electron Temperature Gradient mode，ETG）区间。将测量得到的波数映射至场对齐坐标系后发现，相较于最初的预测，该高k散射系统对更接近密度涨落波数谱（流注结构，streamers）谱峰的涨落更为敏感。对合成谱的分析表明，探测到的涨落的频率响应主要由多普勒频移主导，且对湍流驱动源不敏感。高k密度涨落波数谱的形状对ETG湍流驱动条件十分敏感，且可通过对模拟中最关键的湍流驱动项开展灵敏度扫描实现重现。