While plasma often behaves diamagnetically, we demonstrate that the laser irradiation of a thin opaque target with an embedded target-transverse seed magnetic field $B_\mathrm{seed}$ can trigger the generation of an order-of-magnitude stronger magnetic field with opposite sign at the target surface. Strong surface field generation occurs when the laser pulse is relativistically intense and results from the currents associated with the cyclotron rotation of laser-heated electrons transiting through the target and the compensating current of cold electrons. We derive a predictive scaling for this surface field generation, $B_\mathrm{gen} \sim - 2 \pi B_\mathrm{seed} \Delta x/\lambda_0$, where $\Delta x$ is the target thickness and $\lambda_0$ is the laser wavelength, and conduct 1D and 2D particle-in-cell simulations to confirm its applicability over a wide range of conditions. We additionally demonstrate that both the seed and surface-generated magnetic fields can have a strong impact on application-relevant plasma dynamics, for example substantially altering the overall expansion and ion acceleration from a $\mu$m-thick laser-irradiated target with a kilotesla-level seed magnetic field.

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相对论短脉冲激光-等离子体与外加种子磁场相互作用中产生的强表面磁场

虽然等离子体通常表现出抗磁性，但我们证明了具有嵌入目标横向种子磁场 $B_\mathrm{seed}$ 的薄不透明目标的激光照射可以触发产生一个数量级更强的磁场，具有相反的方向。在目标表面上签名。当激光脉冲相对强并且由与穿过目标的激光加热电子的回旋加速器旋转相关的电流和冷电子的补偿电流产生时，就会产生强表面场。我们推导出此表面场生成的预测比例，$B_\mathrm{gen} \sim - 2 \pi B_\mathrm{seed} \Delta x/\lambda_0$，其中 $\Delta x$ 是目标厚度，$ λ_0$ 是激光波长，并进行一维和二维细胞内粒子模拟，以确认其在各种条件下的适用性。我们还证明，种子和表面生成的磁场都可以对与应用相关的等离子体动力学产生强烈影响，例如显着改变 $\mu$m 厚的激光照射目标的整体膨胀和离子加速千特斯拉级种子磁场。