The irradiation of a target with high laser intensity can lead to self-generation of an intense magnetic field (B-field) on the target surface. It has therefore been suggested that the sheath-driven acceleration of high-energy protons would be significantly hampered by the magnetization effect of this self-generated B-field at high enough laser intensities. In this paper, particle-in-cell simulations are used to study this magnetization effect on sheath-driven proton acceleration. It is shown that the inhibitory effect of the B-field on ion acceleration is not as significant as previously thought. Moreover, it is shown that the magnetization effect plays a relatively limited role in high-energy proton acceleration, even at high laser intensities when the mutual coupling and competition between self-generated electric (E-) and B-fields are considered in a realistic sheath acceleration scenario. A theoretical model including the v × B force is presented and confirms that the rate of reduction in proton energy depends on the strength ratio between B- and E-fields rather than on the strength of the B-field alone, and that only a small percentage of the proton energy is affected by the self-generated B-field. Finally, it is shown that the degraded scaling of proton energy at high laser intensities can be explained by the decrease in acceleration time caused by the increased sheath fields at high laser intensities rather than by the magnetic inhibitory effect, because of the longer growth time scale of the latter. This understanding of the magnetization effect may pave the way to the generation of high-energy protons by sheath-driven acceleration at high laser intensities.

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高激光强度下磁抑制对离子加速作用的研究

用高激光强度照射目标会导致目标表面自产生强磁场（B 场）。因此，有人提出，在足够高的激光强度下，这种自生 B 场的磁化效应会显着阻碍高能质子的鞘驱动加速。在本文中，细胞内粒子模拟用于研究这种磁化对鞘驱动质子加速的影响。结果表明，B场对离子加速的抑制作用并不像以前认为的那么显着。此外，研究表明磁化效应在高能质子加速中的作用相对有限，即使在高激光强度下，当在实际鞘层加速场景中考虑自生电场 (E-) 和 B 场之间的相互耦合和竞争时。一个理论模型包括提供了 v × B力并证实质子能量的减少率取决于 B 场和 E 场之间的强度比，而不是仅取决于 B 场的强度，并且只有一小部分质子能量受自生 B 场的影响。最后，结果表明，在高激光强度下，质子能量缩放比例降低可以用高激光强度下鞘场增加引起的加速时间减少来解释，而不是磁抑制效应，因为生长时间尺度较长后者。这种对磁化效应的理解可能为在高激光强度下通过鞘驱动加速产生高能质子铺平道路。