Picosecond laser-driven proton acceleration study of SGⅡ-U device based on charged particle activation method

The laser-driven proton acceleration experiment is carried out on the SGⅡ-U device based on charged particle activation method, and the target parameters are optimized. The charged particle method is used to measure the maximum cutoff energy of proton, angular profile, total yield and conversion efficiency of laser energy to proton energy for different copper film thickness under the same laser condition. It is found that the optimal copper film thickness for the SGⅡ-U picoseond laser-driven proton experiment is 10 μm, the highest proton energy obtained is about 40 MeV, and the total yield of protons (>4 MeV) is about 4×1012, the conversion efficiency of laser energy to proton energy is about 2%. Thicker or thinner copper film can reduce the maximum cut-off energy of accelerated proton; when the target thickness is reduced to 1 μm, the pre-pulse of the laser begins to have a significant effect on the target normal sheath acceleration (TNSA) proton, proton energy drops sharply, the proton beam porfile exhibits a hollow structure; when the target thickness is increased to 35 μm, although the energy of the proton is reduced, the proton beam spot is more uniform. According to our experimental results, when using SGⅡ-U picosecond laser to generate protons as a backlight diagnostics, a thicker Cu film can be selected which can supply more uniform proton beams. When the target is too thin, the TNSA proton itself has a modulation structure which will cause interference to yield the photographic results; when the protons generated by the SGⅡ-U picosecond are used to generate neutron source, the higher proton energy and yield are required, and 10 μm Cu film is suitable. The further enhancing the TNSA accelerated proton energy and quantity of the SGⅡ-U picosecond laser requires the further improving of the laser contrast.