• X.H. Yang, C.L. Tian, Y. Yin, T.P. Yu
  National University of Defense Technology, Changsha, Hunan
• Y.Q. Gu
  Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang
• S. Kawata, Y.Y. Ma
  Center for Optical Research and Education, Utsunomiya University, Utsunomiya
• F.Q. Shao
  National University of Defense Technology, Graduate School, Changsha
• H. Xu
  National University of Defense Technology, Parallel and Distributed Processing, Changsha
• M.Y. Yu
  Ruhr-Universität Bochum, Bochum

We have proposed a scheme for the generation of collimated proton beams from the interaction of an ultra-intense laser pulse with a rear hole target, which is studied by a 2.5D particle-in-cell (PIC) code PLASIM. When an ultraintense short laser pulse irradiates on such a target, the hot electrons will expand fast into the hole from the inner surfaces of the hole, and strong longitudinal sheath electric field and transverse electric field are produced. However, the plasma in the corners expand slower and be compressed strongly, and then a strong plasma jet is sprayed out from the corner with very high speed, which is just like what happened in armor piercing bullet due to the cumulative energy effect. The two jets extend into the hole and focus along the axis of the hole. At last, a high quality collimated proton beam can be obtained near the end of the hole along the propagation axis. It's found that the beam can propagate over a much longer distance without divergence. The effect of the hole diameter on the collimated proton beam is also investigated. Such target may serve as an important source for collimated proton beam in practical applications.

• Y.Y. Ma, S. Kawata, K. Takahashi
  Center for Optical Research and Education, Utsunomiya University, Utsunomiya
• Y.Q. Gu, Y.Y. Ma
  Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang
• F.Q. Shao
  National University of Defense Technology, Graduate School, Changsha
• Z.M. Sheng
  Shanghai Jiao Tong University, Shanghai
• Y. Yin, T.P. Yu, D. F. Zhou
  National University of Defense Technology, Changsha, Hunan
• M.Y. Yu
  Ruhr-Universität Bochum, Bochum
• H.B. Zhuo
  National University of Defense Technology, Parallel and Distributed Processing, Changsha

Energetic protons of tens MeV or more produced by intense lasers have been observed in recent experiments and numerical simulations. Meanwhile, significant efforts have been made to improve the proton beam quality *,**,***. For most applications, it is important to improve the quality of the proton beam both during the production and during the propagation. Some schemes are proposed to improve the quality of the proton beam both during the production form the laser plasma interaction and during the propagation. The physics is investigated by 2D3V and 3D particle-in-cell codes PLASIM and PLASIM3D. In this paper, we propose to use an umbrella-like target to accelerate, and collimate protons. It is found that high intensity collimated MeV-proton beams can be produced ****. We also propose a scheme to generate quasi-monoenergetic proton beam from the interactions of an ultra-intense laser pulse and a thin tailored hole target. Particle simulation shows that a monoenergetic proton beam is generated from the hole. The propagation of a proton beam both in vacuum and in a plasma is also studied. Compared with the propagation in vacuum, the proton beam quality can be improved obviously.

* T. Toncian, et al. Science 312, 410(2006).
** B. M. Hegelich, et al. Nature 439, 441(2006).
*** H. Schwoerer, et al. Nature 439, 445(2006).
**** Y. Y. Ma et al., Phys Plasmas 16, 34502(2009).

• I. Jovanovic, Y. Yin
  Purdue University, West Lafayette, Indiana
• S. Boucher, R. Tikhoplav
  RadiaBeam, Marina del Rey
• G. Travish
  UCLA, Los Angeles, California

One approach for detecting special nuclear material (SNM) at a distance is to use highly penetrating gamma-rays (>6 MeV) to produce photofission. We are investigating inverse gamma-ray sources (IGS), based on inverse Compton scattering (ICS) of a laser pulse on a relativistic electron bunch. Nearly monochromatic gamma rays with high brightness, very small source size and divergence can be produced in IGS. For the interaction drive laser recirculation it is necessary to meet the repetition rate requirements. Three implementations of laser recirculation are proposed for the interaction drive laser, which can significantly reduce the requirements on the interaction drive laser average power. It is found that the recently demonstrated recirculation injection by nonlinear gating (RING) technique offers unique advantages for beam recirculation in IGS.