Deng Z G, Zhang Z M, Zhang B, He S K, Teng J, Hong W, Dong K G, Wu Y C, Zhu B, Gu Y Q
Research Center of Laser Fusion, China Academy of Engineering Physics, P.O. Box 919-986, Mianyang 621900, People's Republic of China.
IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China.
Phys Rev E. 2017 Feb;95(2-1):023206. doi: 10.1103/PhysRevE.95.023206. Epub 2017 Feb 14.
Electrons can be efficiently injected into a plasma wave by colliding two counterpropagating laser pulses in a laser wakefield acceleration. However, the generation of a high-quality electron beam with a large charge is difficult in the traditional on-axis colliding scheme due to the growth of the electron beam duration coming from the increase of the beam charge. To solve this problem, we propose an off-axis colliding scheme, in which the collision point is away from the axis of the driver pulse. We show that the electrons injected from the off-axis region are highly concentered on the tail of the bubble even for a large trapped charge, thus feeling almost the same accelerating field. As a result, quasimonoenergetic electron beams with a large charge can be produced. The validity of this scheme is confirmed by both the particle-in-cell simulations and the Hamiltonian model. Furthermore, it is shown that a Laguerre-Gauss (LG) laser can be adopted as the injection pulse to realize the off-axis colliding injection in three dimensions symmetrically, which may be useful in simplifying the technical layout of the real experiment setup.
在激光尾场加速中，通过使两个反向传播的激光脉冲碰撞，电子能够被高效地注入到等离子体波中。然而，在传统的同轴碰撞方案中，由于电子束电荷量增加导致电子束持续时间增长，很难产生具有大电荷量的高质量电子束。为了解决这个问题，我们提出了一种离轴碰撞方案，其中碰撞点远离驱动脉冲的轴。我们表明，即使对于大的俘获电荷量，从离轴区域注入的电子也高度集中在气泡的尾部，因此几乎感受到相同的加速场。结果，可以产生具有大电荷量的准单能电子束。该方案的有效性通过粒子模拟和哈密顿模型得到了证实。此外，研究表明，可以采用拉盖尔 - 高斯（LG）激光作为注入脉冲，以在三维空间中对称地实现离轴碰撞注入，这可能有助于简化实际实验装置的技术布局。
