脉冲驱动等离子体流中三维碰撞磁化弓形激波的结构
The structure of 3D collisional magnetized bow shocks in pulsed-power-driven plasma flow
摘要：
我们调查三维弓形冲击高度碰撞磁化铝等离子体中，在烧蚀阶段产生的爆炸线阵列的MAGPIE设施（1.4 MA，240 ns）。从金属丝阵列烧蚀等离子体产生径向发散的超音速（$M_S \sim 7$）、具有冻结磁通量（$R_M \gg 1$）的超阿尔文（$M_A > 1$）磁化流。这些气流与放置在气流中的感应探头碰撞，感应探头既作为产生磁化弓形激波的障碍物，又作为平流磁场的诊断。沿两条正交视线的激光干涉法被用来测量线积分电子密度。由于等离子体的电阻扩散长度与探针的尺寸相当，磁场从激波前沿的离子流体中扩散出来，产生流体动力激波，其结构由音速马赫数决定，而不是流的磁声马赫数。使用电阻性磁流体动力学（MHD）代码MIGON进行的3D模拟证实了这一点，但低估了在实验弓形激波形状中观察到的各向异性，这表明非MHD机制可能对修改激波结构很重要。
英文摘要：
We investigate 3D bow shocks in a highly collisional magnetized aluminum plasma, generated during the ablation phase of an exploding wire array on the MAGPIE facility (1.4 MA, 240 ns). Ablation of plasma from the wire array generates radially diverging, supersonic ($M_S \sim 7$), super-Alfvénic ($M_A > 1$) magnetized flows with frozen-in magnetic flux ($R_M \gg 1$). These flows collide with an inductive probe placed in the flow, which serves both as the obstacle that generates the magnetized bow shock, and as a diagnostic of the advected magnetic field. Laser interferometry along two orthogonal lines of sight is used to measure the line-integrated electron density. A detached bow shock forms ahead of the probe, with a larger opening angle in the plane parallel to the magnetic field than in the plane normal to it. Since the resistive diffusion length of the plasma is comparable to the probe size, the magnetic field decouples from the ion fluid at the shock front and generates a hydrodynamic shock, whose structure is determined by the sonic Mach number, rather than the magnetosonic Mach number of the flow. 3D simulations performed using the resistive magnetohydrodynamic (MHD) code GORGON confirm this picture, but under-predict the anisotropy observed in the shape of the experimental bow shock, suggesting that non-MHD mechanisms may be important for modifying the shock structure.
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