Cascaded target normal sheath acceleration

Abstract

A cascaded target normal sheath acceleration (TNSA) scheme is proposed to simultaneously increase energy and improve energy spread of a laser-produced mono-energetic proton beam. An optimum condition that uses the maximum sheath field to accelerate the center of the proton beam is theoretically found and verified by two-dimensional particle-in-cell simulations. An initial 10 MeV proton beam is accelerated to 21 MeV with energy spread decreased from 5% to 2% under the optimum condition during the process of the cascaded TNSA. The scheme opens a way to scale proton energy lineally with laser energy. V C 2013 AIP Publishing LLC.

Effective post-acceleration of ion bunches in foils irradiated by ultra-intense laser pulses

“…A similar modelling was reported in Ref. 7, where a situation of a bunch with very low density of n p % 0.01n cr and with energetic broadening of $2% was investigated. Results of our simulation of the proton bunch distribution function for two different densities are depicted in Fig.…”

“…which represents the condition that during the life time of the field, all protons of Gaussian distribution have propagated through the field. In the paper, 7 this condition was not mentioned, because there it was obviously assumed that it is automatically fulfilled for a mono-energetic proton distribution. The distribution function of protons has, in this case, the form of Eq.…”

Research Progress of Scheme of Target-Normal Sheath Acceleration Ion

“…透靶。Sentoku 等 [20] 研究了靶的厚度对离子加速的影响， 指出了对于较薄的靶， 电子可以通过再循环流通来提 [23] ， 利用这种方 Fig.9 Electron density distribution at 300 fs 混 合 加 速 方 案 的 提 出 ， 为 得 到 高 能 量 、 高 密 度 的 质 子 束 提 供 了 一 种 非 常 好 的 方 案 [17,25] 。 此 方 案 中 ， 首 先 利用 TNSA 机制得到高能质子束， 再将质子束引入到一个由强场螺线管、 永磁四极透镜及磁偶极子组成的后 续加速系统中， 在后续的加速系统中， 不仅可以继续提高质子束的能量， 而且可以使得质子束会聚。如图 10 Lund 等 [26] 提出了一种新的方案使得鞘层加速中的离子束准直性得到了较好的改善。其方法是在靶后 放置一个由多片相互分离的导电薄膜组成的 "透镜" ， 如图 11 所示， 这个结构不但可以很好地抑制库伦膨胀 带来的质子束的发散， 而且利用质子束自身产生的磁场可以对质子束进行很好的准直。Ni 等 [27] 对这种加速 方案也进行了详细的理论研究。 图 11 薄膜组 "透镜" 结构 在国内， 中国科学院上海光学精密机械研究所沈百飞小组一直致力于 TNSA 机制的研究， 2013 年， 王文 鹏等 [28] 提出了级联 TNSA 方案， 即在模拟中将已有的质子束再利用 TNSA 方案进行加速。如图 12 所示， 此方 案可以使质子束能量增加一倍， 而能散度却降低为原来的一半。此外， 王文鹏等 [29] 就激光预脉冲对质子加速 的影响也进行了讨论， 研究表明预脉冲过强会对靶造成破坏而影响质子的加速。…”

Cascaded radiation pressure acceleration

“…The cascaded acceleration scheme has already been realized in the conventional accelerator, 23 and there has also been some work on cascaded laser-driven electron acceleration 24,25 and the TNSA scheme in ion acceleration. 26 One of the interesting characteristics of the RPA scheme is that the strong charge separation field established by the light pressure can accelerate not only the ions in the foil itself but also the externally injected ions. When irradiated by a strong, circularly polarized laser pulse, the thin layer is quickly accelerated to quasi-light speed, and a strong charge separation field with high speed is generated.…”