Zgadzaj Rafal, Silva T, Khudyakov V K, Sosedkin A, Allen J, Gessner S, Li Zhengyan, Litos M, Vieira J, Lotov K V, Hogan M J, Yakimenko V, Downer M C
University of Texas at Austin, 1 University Station C1600, Austin, TX, 78712-1081, USA.
GoLP/Instituto de Plasmas e Fusão Nuclear-Laboratório Associado, Insituto Superior Técnico, Lisboa, Portugal.
Nat Commun. 2020 Sep 21;11(1):4753. doi: 10.1038/s41467-020-18490-w.
Metre-scale plasma wakefield accelerators have imparted energy gain approaching 10 gigaelectronvolts to single nano-Coulomb electron bunches. To reach useful average currents, however, the enormous energy density that the driver deposits into the wake must be removed efficiently between shots. Yet mechanisms by which wakes dissipate their energy into surrounding plasma remain poorly understood. Here, we report picosecond-time-resolved, grazing-angle optical shadowgraphic measurements and large-scale particle-in-cell simulations of ion channels emerging from broken wakes that electron bunches from the SLAC linac generate in tenuous lithium plasma. Measurements show the channel boundary expands radially at 1 million metres-per-second for over a nanosecond. Simulations show that ions and electrons that the original wake propels outward, carrying 90 percent of its energy, drive this expansion by impact-ionizing surrounding neutral lithium. The results provide a basis for understanding global thermodynamics of multi-GeV plasma accelerators, which underlie their viability for applications demanding high average beam current.
米级等离子体尾场加速器已使单个纳库仑电子束的能量增益接近10吉电子伏特。然而，为了达到有用的平均电流，必须在两次脉冲之间有效地去除驱动源沉积到尾场中的巨大能量密度。然而，尾场将能量耗散到周围等离子体中的机制仍知之甚少。在此，我们报告了皮秒时间分辨、掠射角光学阴影成像测量以及大规模粒子模拟，这些模拟针对的是从破碎尾场中出现的离子通道，这些尾场是由SLAC直线加速器的电子束在稀薄锂等离子体中产生的。测量结果表明，通道边界以每秒100万米的速度径向扩展超过一纳秒。模拟结果表明，原始尾场向外推动的离子和电子携带了其90%的能量，通过碰撞电离周围的中性锂来驱动这种扩展。这些结果为理解多GeV等离子体加速器的整体热力学提供了基础，而这是其在需要高平均束流的应用中具备可行性的基础。
