利用均匀密度等离子体通道加速质子的辐射压力增强方案

An enhanced radiation pressure acceleration scheme for accelerating protons using the uniform density plasma channel

提出了辐射压力加速与激光尾波场加速相结合的高能质子加速方案.该方案中在临界密度薄靶后端增加一个均匀密度等离子体通道获得了峰值能量为22.2 GeV、截止能量为36.4 GeV和电荷量为0.67 nC的高能质子束,与质子在纯辐射压力加速中相比,其高能质子的截止能量可以提升2个数量级.结果证实了通过在近临界密度薄靶后面连接一个均匀密度等离子体通道,等离子体通道中激光激发的尾波场可以捕获经辐射压力过程预加速的质子并维持长时间的加速,最终获得高能质子,本文还研究了不同均匀密度等离子体通道中质子的加速情况,发现密度越高,则被加速质子的峰值能量和截止能量越高,电荷量也越大.该组合加速方案对高能质子束的产生与应用具有一定的指导意义.

High-energy proton beams have broad application prospects in medical imaging,tumor therapy and nuclear fusion physics.Laser plasma acceleration is a new particle acceleration method with great potential because its acceleration gradient can reach 103-106 times that of traditional acceleration method,so it can theoretically accelerate electrons and ions to high energies in the scale of a few centimeters to a few meters.Radiation pressure acceleration(RPA)is considered to be the most promising mechanism of high energy proton acceleration in laser plasma acceleration,but the Rayleigh-Taylor instability(RTI)inherent in the process of radiation pressure acceleration will cause transverse density modulation on the target surface,resulting in the premature termination of the proton acceleration process and the failure to obtain high energy proton beams.In order to obtain high-energy proton beams,an acceleration scheme combining radiation pressure acceleration with laser wakefield is proposed.In this scheme,a high-energy proton beam with peak energy of 22.2 GeV,cut-off energy of 36.4 GeV and charge of 0.67 nC is obtained by adding a uniform density plasma channel at the back end of the thin target with critical density,the cut-off energy of the high energy proton can be increased by two orders of magnitude compared with the proton only in the radiation pressure acceleration process.The results confirm that in a uniform-density plasma channel connected behind a thin target,the laser wakefield can capture protons pre-accelerated by the radiation pressure process and maintain the acceleration for a long period of time,finally obtain high-energy protons.The acceleration of protons in plasma channels with different uniform densities is also investigated in this work,and it is found that the higher the density,the higher the peak energy,cut-off energy and charge of the accelerated protons are.The combined acceleration scheme is instructive for the generation and application of high-energy proton beams.