AI 中文总结
该研究通过NSTX球形托卡马克的模拟，发现负密度梯度驱动的电子尺度湍流模式可解释数兆瓦实验功率，其特性有别于标准微撕裂模式，实验梯度或处于不同湍流状态的分岔点。
AI 中文摘要
NSTX球形托卡马克等离子体的回旋动理学模拟揭示了电子回旋半径尺度上的新型负密度梯度（NDG）漂移波，其驱动的湍流输运与实验能流相当。线性模拟表明，主导不稳定性是主要由负电子密度梯度驱动的捕获电子型电子尺度撕裂 parity 模式，定义为 $a/L_{ne} \equiv - a/n_e \\, (dn_e/dr) < 0$。尽管热输运主要由平行磁矢势扰动 $\delta A_{\parallel}$ 携带，其增长率却对平行磁扰动 $\delta B_{\parallel}$ 敏感，这使其区别于标准微撕裂模式（MTMs）。线性敏感性分析还显示，该模式在低碰撞率下最不稳定，与捕获电子特性一致。电子尺度及多尺度非线性模拟表明，这些模式可解释数兆瓦的实验功率，后者提示实验梯度可能处于不同湍流 regime 间的分岔点。
英文摘要
Gyrokinetic simulations of an NSTX spherical-tokamak plasma reveal novel negative-density-gradient (NDG) drift waves at electron-gyroradius-scale that drive turbulent transport comparable to the experimental power flow. Linear simulations indicate that the dominant instability is a trapped-electron electron-scale tearing-parity mode driven mainly by negative electron density gradient, $a/L_{ne} \equiv - a/n_e \, (dn_e/dr) < 0$. Although thermal transport is mainly carried by transverse magnetic, $δA_{\parallel}$, fluctuations, the growth rate is sensitive to compressional magnetic fluctuations, $δB_{\parallel}$, differentiating these from standard microtearing modes (MTMs). Linear sensitivity analysis also reveals that the modes are most unstable at lower collisionality, consistent with the trapped-electron character. Electron-scale and multi-scale nonlinear simulations show that these modes can account for several megawatts of experimental power, with the latter suggesting that experimental gradients may lie at a bifurcation between distinct turbulence regimes.
