Multi MeV protons, deuterons and carbon ions produced by the PALS laser system

Multi MeV ions and fusion neutrons were generated by focused radiation of the 3 TW Prague Asterix Laser System (PALS). The use of 8 μm Al foil as XUV filter positioned in front of an ion collector allowed measuring currents of 4-MeV protons emitted behind a thin target in the forward direction. The proton energy of 4 MeV generated by a PALS laser irradiance Iλ2~5×1016 W cm-2 μm2 on target is nominally reachable for picosecond lasers when they deliver the intensity Iλ2~3×1018 W cm-2 μm2. The enhanced maximum proton energy is favoured by a non-linear interaction of the laser beam with the pre-generated plasma. Nonlinear processes also cause enhancement in the yield of fusion neutrons per focused laser energy from the CD2 plasma. The obtained results show that an equivalent neutron yield was reached by ps- and sub-ps laser beams for Iλ2~1019 W cm-2 μm2. The hampering influence of the electromagnetic pulse generated within the interaction chamber on diagnostics signals was eliminated.

本数据集通过3太瓦（TW）布拉格星型激光系统（PALS）的聚焦辐射，生成了多兆电子伏特（MeV）离子与聚变中子。在离子收集器前端布设8μm厚铝箔作为极紫外滤光片（XUV filter），成功实现了对薄靶后方沿正向出射的4-MeV质子电流的测量。当靶面辐照度Iλ²约为5×10¹⁶ W·cm⁻²·μm²时，PALS激光可产生4 MeV的质子能量；而皮秒激光器在靶面辐照度Iλ²达到约3×10¹⁸ W·cm⁻²·μm²时，理论上也可实现该质子能量。激光束与预生成等离子体的非线性相互作用，有利于提升最大质子能量。非线性过程同时提升了CD₂等离子体中单位聚焦激光能量对应的聚变中子产额。实验结果表明，当靶面辐照度Iλ²约为10¹⁹ W·cm⁻²·μm²时，皮秒与亚皮秒激光束可获得等效的中子产额。本研究消除了相互作用腔室内产生的电磁脉冲对诊断信号的干扰影响。