A laser-driven accelerator generates protons with tens of MeV in energy by a compact, strong, and transient accelerating electric field produced as a result of laser–plasma interactions at relativistic intensities. In previous studies, two- and three-dimensional particle-in-cell simulations revealed that the application of a kT-level axial magnetic field results in an enhancement of proton acceleration via the target normal sheath acceleration mechanism due to reduced lateral electron divergence and improved electron heating efficiency. An experimental investigation of this scheme on the GEKKO-XII and the LFEX facilities found that the number and maximum energy of the accelerated protons decreased with increasing the temporal delay between the pulse driving the external magnetic-field and the pulse accelerating the protons, contrary to the theoretical and numerical expectations. We identify sources responsible for the degradation of the proton beam performance and we propose an alternative experimental setup to mitigate the degradation in future experiments.

激光驱动的加速器通过相对论强度下的激光-等离子体相互作用产生的紧凑，强而瞬变的加速电场，产生具有数十MeV能量的质子。在先前的研究中，二维和三维胞内粒子模拟显示，kT级轴向磁场的应用由于减少了侧向电子发散并改善了目标法向鞘层加速机制，从而提高了质子加速。电子加热效率。在GEKKO-XII和LFEX设施上对该方案进行的实验研究发现，加速质子的数量和最大能量随着驱动外部磁场的脉冲与质子加速脉冲之间的时间延迟的增加而降低，与理论和数值预期相反。我们确定了导致质子束性能下降的原因，并提出了另一种实验装置来减轻未来实验中的退化。