Centre for Plasma Physics, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, United Kingdom.
Phys Rev Lett. 2011 Jun 3;106(22):225003. doi: 10.1103/PhysRevLett.106.225003. Epub 2011 Jun 2.
By using a thick (250 μm) target with 350 μm radius of curvature, the intense proton beam driven by a petawatt laser is focused at a distance of ∼1 mm from the target for all detectable energies up to ∼25 MeV. The thickness of the foil facilitates beam focusing as it suppresses the dynamic evolution of the beam divergence caused by peaked electron flux distribution at the target rear side. In addition, reduction in inherent beam divergence due to the target thickness relaxes the curvature requirement for short-range focusing. Energy resolved mapping of the proton beam trajectories from mesh radiographs infers the focusing and the data agree with a simple geometrical modeling based on ballistic beam propagation.
通过使用具有 350μm 曲率半径的厚（250μm）靶，在距靶约 1mm 的距离内，所有可探测到的能量高达约 25MeV，都可以将由皮瓦特激光驱动的强质子束聚焦。箔片的厚度有助于聚焦光束，因为它抑制了由靶后侧面的峰电子通量分布引起的光束发散的动态演化。此外，由于靶厚度引起的固有光束发散的减小，放宽了对短程聚焦的曲率要求。从网格射线照相术中的质子束轨迹的能量分辨映射推断出聚焦，并且数据与基于弹道束传播的简单几何建模一致。
