托卡马克中低频芯部-边缘耦合的研究：III. 芯部局域MHD连续谱脉动与远距离受迫磁重联

中文摘要 AI 辅助

在托卡马克等离子体的MHD模拟中发现了慢磁声脉动（SMAPs），该等离子体中心附近的安全因子$q$平坦且略高于1（$q \gtrsim 1$）。SMAPs位于慢磁声连续谱$\omega_{\rm S} = k_\parallel c_{\rm S}$的中央平台区，其中$c_{\rm S}$是声速，$k_\parallel$是平行于磁场的波数。在我们的模型中，当离子粘性和热扩散系数足够低时，SMAPs存在。当电阻率足够高时，$q \sim 1$区域的压力梯度可以驱动它们不稳定。指数增长的SMAPs由磁面上的驻立慢波组成，这些波在径向上同步形成极向/环向模数$m/n=1/1$的准互换结构。在自由能耗尽后，中心$q\sim 1$区域的饱和准线性脉动（交替的$n=1$和$0$）与远处的$q\geq 2$有理面耦合，这些有理面经历“可逆”磁重联：随着磁岛以周期$2\pi/\omega_{\rm S}$涨落，其X点和O点交替出现。这些结果展示了MHD模型如何促进慢波、压力驱动的电阻互换和撕裂的非局域耦合。这激发了在动力学模型中的进一步研究，其中存在快速可逆重联的无碰撞机制，对平行动力学的适当处理将允许评估朗道阻尼的作用，以及$q\sim 1$区域中${\mathbf B}$场的弱遍历性是否允许波超过离子的平行流动以维持SMAPs背后的热失衡。同样值得关注的是更接近阿尔芬分支的脉动，满足$\omega \approx k_\parallel v_{\rm A}$，其中$v_{\rm A}$是阿尔芬速度，这些脉动不需要电阻率，且对热失衡的依赖性较小。

英文摘要

Slow magnetoacoustic pulsations (SMAPs) are found in MHD simulations of a tokamak plasma whose safety factor $q$ near the center is flat and slightly above unity ($q \gtrsim 1$). SMAPs are located on the central plateau of the slow magnetoacoustic continuum $ω_{\rm S} = k_\parallel c_{\rm S}$, where $c_{\rm S}$ is the speed of sound and $k_\parallel$ the wavenumber parallel to the magnetic field. In our model, SMAPs exist when the ion viscosity and thermal diffusivity are sufficiently low. They can be driven unstable by a pressure gradient in the $q \sim 1$ region when the electric resistivity is sufficiently high. Exponentially growing SMAPs consist of standing slow waves on magnetic surfaces that are radially synchronized into a quasi-interchange structure with poloidal/toroidal mode numbers $m/n=1/1$. After free energy depletion, saturated quasi-linear pulsations (alternating $n=1$ and $0$) in the central $q\sim 1$ region couple to distant $q\geq 2$ rational surfaces that undergo "reversible" magnetic reconnection: as the magnetic islands wax and wane with period $2π/ω_{\rm S}$, their X- and O-points alternate. These results show how the MHD model facilitates non-local coupling of slow waves, pressure-driven resistive interchange and tearing. This motivates further study in kinetic models, where collisionless mechanisms for fast reversible reconnection exist and proper treatment of parallel dynamics will allow to assess the role of Landau damping as well as the question whether the ${\mathbf B}$ field's weak ergodicity in the $q\sim 1$ region allows the waves to outpace the ion's parallel streaming to maintain the thermal misbalance underlying SMAPs. Also of interest are pulsations closer to the Alfvénic branch, satisfying $ω\approx k_\parallel v_{\rm A}$ with Alfvén speed $v_{\rm A}$, which require no resistivity and are less dependent on thermal misbalance.

发表机构

• National Institutes for Quantum Science and Technology (QST)（量子科学和技术研究院）
• KAIST（韩国科学技术院）
• Research Organization for Information Science and Technology (RIST)（信息技术科学研究机构）

机构由 AI 辅助整理，请以论文原文为准。

补充信息

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29 pages, 18 figures