Using a local gyrokinetic code to study global ion temperature gradient modes in tokamaks
Using a local gyrokinetic code to study global ion temperature gradient modes in tokamaks
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DOI：
10.1088/0741-3335/57/6/065004
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发表时间：
2015-02
影响因子：
2.2
通讯作者：
P. Abdoul;D. Dickinson;C. Roach;H. Wilson
中科院分区：
文献类型：
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作者：
P. Abdoul;D. Dickinson;C. Roach;H. Wilson
本文采用一种新的技术，将局部回旋动力学程序GS 2的结果与解析理论相结合，重建了托卡马克等离子体中线性离子温度梯度（ITG）模的整体本征模结构。对径向通量面x和气球状相位角p的范围进行局部回转运动计算，以绘制出单个环形模式数n的局部复模式频率Ω0（x，p）= ω0（x，p）+ iγ0（x，p）。泰勒展开Ω0在x = 0的参考表面，并采用傅立叶气球表示导致二阶ODE的振幅包络，A（p），它描述了如何结合本地的结果，以形成全球模式。平衡分布影响Ω0（x，p）的变化，从而影响全局模结构。这里提出的模拟是基于一个全球性的扩展的旋风基地的情况下，并采用循环米勒平衡模型。在a/LT和a/Ln的径向变化曲线的平衡中，在x = 0处达到峰值，并且所有其他平衡曲线保持恒定，包括ηi = Ln/LT，发现Ω0（x，p）有一个稳定点。重建的全局模位于托卡马克的外侧中平面，全局增长率为γ <$Max[γ0]。包括径向变化的其他平衡配置文件，如安全系数和磁剪切，导致一个模式，峰值远离外侧中平面，全球增长率降低。最后，还通过引入多普勒频移ω0→ω0−nΩφ′ x？>研究了环形流剪切的影响，式中，Ω是平衡环向流，撇表示径向导数。平衡剖面的变化在全球增长率谱中引入了关于Ωφ′？>符号的不对称性，使得在非零剪切的情况下实现最大生长速率，这与最近的全球回转动力学计算一致。
In this paper the global eigenmode structures of linear ion temperature gradient (ITG) modes in tokamak plasmas are obtained using a novel technique which combines results from the local gyrokinetic code GS2 with analytical theory to reconstruct global properties. Local gyrokinetic calculations are performed for a range of radial flux surfaces, x, and ballooning phase angles, p, to map out the local complex mode frequency, Ω0(x, p) = ω0(x, p) + iγ0(x, p) for a single toroidal mode number, n. Taylor expanding Ω0 about a reference surface at x = 0, and employing the Fourier-ballooning representation leads to a second order ODE for the amplitude envelope, A(p), which describes how the local results are combined to form the global mode. The equilibrium profiles impact on the variation of Ω0(x, p) and hence influence the global mode structure. The simulations presented here are based upon a global extension to the CYCLONE base case and employ the circular Miller equilibrium model. In an equilibrium with radially varying profiles of a/LT and a/Ln, peaked at x = 0, and with all other equilibrium profiles held constant, including ηi = Ln/LT, Ω0(x, p) is found to have a stationary point. The reconstructed global mode sits at the outboard mid-plane of the tokamak, with global growth rate, γ ∼ Max[γ0]. Including the radial variation of other equilibrium profiles like safety factor and magnetic shear, leads to a mode that peaks away from the outboard mid-plane, with a reduced global growth rate. Finally, the influence of toroidal flow shear has also been investigated through the introduction of a Doppler shift, ω0→ω0−nΩφ′ x?>, where Ωϕ is the equilibrium toroidal flow, and a prime denotes the radial derivative. The equilibrium profile variations introduce an asymmetry into the global growth rate spectrum with respect to the sign of Ωφ′?>, such that the maximum growth rate is achieved with non-zero shearing, consistent with recent global gyrokinetic calculations.