双线模型磁X点附近的等离子体动力学：理论与模拟
Plasma dynamics near the magnetic X-point of the two-wire model: Theory and Simulation
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中文总结 AI 辅助
该研究以双线模型为对象，通过理论分析和模拟，揭示了无碰撞与碰撞区域内磁X点附近等离子体的粒子迁移机制及密度平台形成规律，建立了相关基础认识。
中文摘要 AI 辅助
双线模型（TWM）是由两根平行载流导线产生的磁位形，其中心包含一个X点和一条分界面。由于TWM的磁场由闭式解析表达式描述且不含引导场，它为研究真实磁零点如何塑造等离子体动力学提供了易处理的场景。本研究探讨两个互补区域：无碰撞带电粒子动力学和碰撞低温等离子体输运。在无碰撞区域，拉格朗日分析确定了两个粒子运动不变量：总动能和基场线值，后者由守恒的轴向正则动量导出。无碰撞试验粒子模拟显示，当粒子穿越零点附近的大梯度区域时，磁矩会发生偏移。这些偏移使粒子能够迁移，即围绕一条基场线的一个分支回旋的粒子跳至X点另一侧对应分支的现象。推导了迁移的阈值能量，并建立了迁移约束时间的经验表达式。在碰撞区域，在保形场对齐坐标系中开发了低温等离子体的简化漂移-扩散模型，它们预测在强磁化区域分界面附近会形成密度平台。进行了自洽粒子模拟（PIC）以验证预测的密度平台。这两项互补研究为无碰撞和碰撞区域中真实磁零点附近的等离子体动力学建立了基础认识。
英文摘要
The two-wire model (TWM) is a magnetic configuration generated by two parallel current-carrying wires, and it contains an X-point at its center and a separatrix. Since the TWM magnetic field is described by a closed-form analytic expression and contains no guide field, it offers a tractable setting for studying how a true magnetic null shapes plasma dynamics. This work investigates two complementary regimes: collisionless charged particle dynamics and collisional low temperature plasma transport. In the collisionless regime, a Lagrangian analysis identifies two particle motion invariants: the total kinetic energy and the base field line value, which is derived from the conserved axial canonical momentum. Collisionless test particle simulations show that the magnetic moment undergoes shifts when the particle traverses the large gradient region near the null. These shifts enable particles to migrate, the phenomenon in which a particle gyrating about one branch of a base field line jumps to the corresponding branch on the other side of the X-point. A threshold energy for migration is derived, and an empirical expression for the migration confinement time is formulated. In the collisional regime, reduced drift-diffusion models for low temperature plasmas are developed in a conformal field-aligned coordinate system, and they predict density plateau formation near the separatrix in the strongly magnetized regime. Self-consistent particle-in-cell simulations are performed to verify the predicted density plateau. The two complementary studies establish a fundamental understanding of plasma dynamics near a true magnetic null for both the collisionless and collisional regimes.
