发表机构
Escola de Artes, Ciências e Humanidades, University of São Paulo（圣保罗大学艺术与人文学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究揭示有限法向磁场在撕裂时间尺度上演化电流片背景，通过阿尔文波前增宽中性层并削弱经典电阻撕裂，导致增长率显著下降，从而动力学抑制线性放大。
AI 中文摘要
经典电阻撕裂理论假设电流片平衡是预先给定的，但有限法向磁场可以在撕裂时间尺度上演化背景。对于初始半厚度为 $a$、渐近重连场大小为 $B_0$ 的横向压力平衡 Harris 剖面，并贯穿均匀 $B_n$（$\xi=B_n/B_0$），我们在理想磁流体力学中推导出精确演化：反向传播的阿尔文波前使中性层增宽，并在其侧翼产生具有剪切的中性层平行中心流。内层估计得出经典电阻平衡破坏的 $\xi_{\mathrm{crit}}\sim S^{-3/4}$，其中 $S$ 是基于 $a$ 的 Lundquist 数。数值冻结剖面计算显示，随着中性层扩展，中心电阻主导性丧失，撕裂增长率下降。在固定波数和主要多普勒频移传播下的本征函数比较支持法向场修正的经典撕裂延续。法向场不提供净扰动能量。随着电流片增宽，从重连场梯度提取的能量减弱。当中性层宽度接近初始片厚度时，速度梯度贡献变得相当，但并未逆转增长率的下降。对于 $S=10^6$、$\mathrm{Pr}_m=0$ 和 $\xi=10^{-4}$，最大增长率在中性层半宽度 $w\simeq1.59a$ 处从其初始值下降约十倍，此时增长和增宽时间变得相等。在此交叉点与 $w/a=2$ 之间，估计仅增加约 0.18 个上包络 e 折，此时增长率约为初始值的 25 分之一。这些结果支持在所采样的演化过程中进一步线性放大的动力学抑制，尽管瞬时谱仍不稳定。
英文摘要
Classical resistive tearing theory assumes a prescribed current-sheet equilibrium, but a finite normal magnetic field can evolve the background on the tearing timescale. For a transversely pressure-balanced Harris profile of initial half-thickness $a$ and asymptotic reconnecting-field magnitude $B_0$, threaded by uniform $B_n$ ($ξ=B_n/B_0$), we derive an exact evolution in ideal magnetohydrodynamics: counter-propagating Alfvenic fronts broaden the neutral layer and generate a central sheet-parallel flow with shear at its flanks. Inner-layer estimates recover $ξ_{\mathrm{crit}}\sim S^{-3/4}$ for breakdown of the classical resistive balance, where $S$ is the Lundquist number based on $a$. Numerical frozen-profile calculations show loss of central resistive dominance and decreasing tearing growth as the neutral layer expands. Eigenfunction comparisons at fixed wavenumber and predominantly Doppler-shifted propagation support a normal-field-modified continuation of classical tearing. The normal field supplies no net perturbation energy. Energy extraction from the reconnecting-field gradient weakens as the sheet broadens. The velocity-gradient contribution becomes comparable when the neutral-layer width approaches the initial sheet thickness, without reversing the decline in growth. For $S=10^6$, $\mathrm{Pr}_m=0$, and $ξ=10^{-4}$, the maximum growth rate falls by a factor of about ten from its initial value at neutral-layer half-width $w\simeq1.59a$, where the growth and broadening times become equal. Only about 0.18 additional upper-envelope e-folds are estimated between this crossing and $w/a=2$, where the growth rate is about 25 times smaller than its initial value. These results support dynamical suppression of further linear amplification over the sampled evolution, even though the instantaneous spectrum remains unstable.
Comments13 pages, 3 figures. Submitted to Physical Review E
