Magnetised plasma turbulence can have a multiscale character: instabilities driven by mean temperature gradients drive turbulence at the disparate scales of the ion and the electron gyroradii. Simulations of multiscale turbulence, using equations valid in the limit of infinite scale separation, reveal novel cross-scale interaction mechanisms in these plasmas. In the case that both long-wavelength (ion-gyroradius-scale) and short-wavelength (electron-gyroradius-scale) linear instabilities are driven far from marginal stability, we show that the short-wavelength instabilities are suppressed by interactions with long-wavelength turbulence. Two novel effects contributed to the suppression: parallel-to-the-field-line shearing by the long-wavelength ${{\boldsymbol {E}} \times \boldsymbol {B}}$ flows, and the modification of the background density gradient by the piece of the long-wavelength electron adiabatic response with parallel-to-the-field-line variation. In contrast, simulations of multiscale turbulence where instabilities at both scales are driven near marginal stability demonstrate that when the long-wavelength turbulence is sufficiently collisional and zonally dominated the effect of cross-scale interaction can be parameterised solely in terms of the local modifications to the mean density and temperature gradients. We discuss physical arguments that qualitatively explain how a change in equilibrium drive leads to the observed transition in the impact of the cross-scale interactions.

中文翻译：

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通过长波长 E × B 流中的平行场剪切稳定短波长不稳定性

磁化等离子体湍流可以具有多尺度特征：由平均温度梯度驱动的不稳定性在离子和电子回转半径的不同尺度上驱动湍流。多尺度湍流的模拟，使用在无限尺度分离极限有效的方程，揭示了这些等离子体中新的跨尺度相互作用机制。在长波长（离子-陀螺半径）和短波长（电子-陀螺半径）线性不稳定性远离边际稳定性驱动的情况下，我们表明短波长不稳定性通过与长波的相互作用得到抑制。波长湍流。两种新的效应有助于抑制：长波长的平行于场线的剪切 ${{\boldsymbol {E}} \times \boldsymbol {B}}$ 流动，以及通过平行于场线变化的长波长电子绝热响应片段修改背景密度梯度。相比之下，多尺度湍流的模拟，其中两个尺度的不稳定性被驱动接近边际稳定性，表明当长波长湍流具有足够的碰撞性并在区域上占主导地位时，跨尺度相互作用的影响可以仅根据对平均密度和温度梯度。我们讨论了物理论点，这些论点定性地解释了平衡驱动的变化如何导致观察到的跨尺度相互作用影响的转变。