Simulations of radiatively cooled magnetic reconnection driven by pulsed power
Simulations of radiatively cooled magnetic reconnection driven by pulsed power
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DOI：
10.1017/s0022377824000448
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发表时间：
2024-01
影响因子：
2.5
通讯作者：
R. Datta;Aidan Crilly;J. Chittenden;Simran Chowdhry;K. Chandler;N. Chaturvedi;C. Myers;Will Fox
中科院分区：
文献类型：
--
作者：
R. Datta;Aidan Crilly;J. Chittenden;Simran Chowdhry;K. Chandler;N. Chaturvedi;C. Myers;Will Fox
磁场重联是天体物理环境中的一个重要过程，因为它会重新配置磁场拓扑结构，并将磁能转换为热能和动能。在极端的天体物理系统中，如黑洞日冕和脉冲星磁层，辐射冷却通过辐射内部能量来改变能量分配，这可能导致重连层的辐射坍缩。在本文中，我们进行了二维和三维模拟模型的MARZ（磁重联Z）实验，这是为了访问冷却率在实验室必要的调查在以前未探索的辐射冷却制度的重联。这些模拟是在Eulerian双温电阻磁流体动力学代码Eulerian two-temperature resistant magnetohydrodynamic code中进行的，该代码模拟了实验几何形状，该实验几何形状包括在Z机器（Sandia National Laboratories）上由20 MA电流驱动的两个爆炸线阵列。辐射损失的实现使用非本地的热力学平衡表使用原子代码Spk计算，我们探测辐射输运的影响，通过实现本地辐射损失模型和$P_{1/3}$多群辐射输运。负载产生高度碰撞，超Alfvénic（Alfvén马赫数$M_A \约1.5$），超音速（音速马赫数$M_S \约4-5$）强烈驱动等离子体流，产生细长的重连层（纵横比$L/\delta \约100$，Lundquist数$S_L \约400$）。当辐射损失超过欧姆加热和压缩加热的速率时，重联层会发生辐射坍缩（冷却速率/流体动力传输速率= $\tau _{\text {cool}}^{-1}/\tau _{H}^{-1}\approximately 100$）;这会产生一个冷的强压缩电流片，导致加速的重联速率，与理论预测一致。最后，电流片对等离子体团不稳定性也是不稳定的，但是磁岛在从层中喷射出来之前被强烈的辐射冷却所熄灭。
Magnetic reconnection is an important process in astrophysical environments, as it reconfigures magnetic field topology and converts magnetic energy into thermal and kinetic energy. In extreme astrophysical systems, such as black hole coronae and pulsar magnetospheres, radiative cooling modifies the energy partition by radiating away internal energy, which can lead to the radiative collapse of the reconnection layer. In this paper, we perform two- and three-dimensional simulations to model the MARZ (Magnetic Reconnection on Z) experiments, which are designed to access cooling rates in the laboratory necessary to investigate reconnection in a previously unexplored radiatively cooled regime. These simulations are performed in GORGON, an Eulerian two-temperature resistive magnetohydrodynamic code, which models the experimental geometry comprising two exploding wire arrays driven by 20 MA of current on the Z machine (Sandia National Laboratories). Radiative losses are implemented using non-local thermodynamic equilibrium tables computed using the atomic code Spk, and we probe the effects of radiation transport by implementing both a local radiation loss model and $P_{1/3}$ multi-group radiation transport. The load produces highly collisional, super-Alfvénic (Alfvén Mach number $M_A \approx 1.5$), supersonic (Sonic Mach number $M_S \approx 4-5$) strongly driven plasma flows which generate an elongated reconnection layer (Aspect Ratio $L/\delta \approx 100$, Lundquist number $S_L \approx 400$). The reconnection layer undergoes radiative collapse when the radiative losses exceed the rates of ohmic and compressional heating (cooling rate/hydrodynamic transit rate = $\tau _{\text {cool}}^{-1}/\tau _{H}^{-1}\approx 100$); this generates a cold strongly compressed current sheet, leading to an accelerated reconnection rate, consistent with theoretical predictions. Finally, the current sheet is also unstable to the plasmoid instability, but the magnetic islands are extinguished by strong radiative cooling before ejection from the layer.