Femtosecond-micrometer spatiotemporal alignment of particle and laser beams

阿拉斯泰尔·纳特将开发一种新颖的多功能方法，用于粒子和激光束的时空对准和同步。基本原理是由我们的战略合作伙伴之一斯坦福大学SLAC国家加速器实验室的先进加速器实验测试设施（FACET）的E210合作获得的多年实验活动的关键结果。该项目将由我们在德国亥姆霍兹德累斯顿-罗森多夫研究所（HZDR）的合作伙伴共同资助。HZDR不仅同意直接共同资助这个博士项目，而且还将为新兴的合作提供大量资源，在他们的PW级激光系统上使用光束时间，每年约10周，并且可能会额外投资于重要的SCAPA光束时间（SCAPA 350 TW激光器的每日费用为3300英镑）。该学生将在斯特拉斯克莱德，但也将被放置在HZDR延长时间，符合斯特拉斯克莱德CDT的国际方面对等离子体粒子和光源http://ppals.phys.strath.ac.uk/。强激光和电子束的协调相互作用发挥着越来越重要的作用，例如用于各种泵浦-探测实验和超快和超小物体的成像。这需要精确的技术来测量和控制相互作用的时间和空间重叠。我们已经发现了一个基本的效果，它允许等离子体光子同步和强烈的激光和电子束的飞秒和微米精度在一个单一的强大的设备对准。激光产生的冷等离子体灯丝在不同程度上拾取瞬态电子束的电场，种子等离子体电子被这种耦合加热并执行复杂的振荡，这些振荡延伸到环境气体中。在这里，它们的非相对论能量正好可以通过碰撞电离产生大量的额外等离子体。这就像一个“放大镜”，将特定的飞秒-微米相互作用特征转化为可见的等离子体复合/去激发光，这是在微秒-毫米scales.We观察到的基本效果，已经证明了结合时空同步和对准的SLAC斯坦福大学20 GeV的电子束与聚焦钛：蓝宝石激光飞秒-微米精度。这种方法使先进的诊断，这将大大改善广泛的泵浦探测实验，并允许实现先进的时空分辨实验，这是迄今为止不可行的。这些现象也揭示了以前隐藏的碰撞电离的重要性，例如在先进的等离子体加速器实验中。支持粒子在细胞中的模拟揭示了在广泛的时间和长度尺度上迷人的动态：电子束的初始fs尺度反冲通过等离子体密度波和ps尺度上相应的GV/m尺度场沿着细种子丝沿着传播，然后在ns-us时间尺度上发生碰撞电离和复合过程。在斯坦福大学，我们一直在使用这种效应的基本版本，使用在常规线性加速器中产生的电子束。阿拉斯泰尔的博士工作将进一步发展这种时空对准的方法，以便当斯坦福大学的后续等离子体韦克菲尔德加速器设施FACET-II将于2019年上线进行用户辅助调试时，它将以先进的形式提供。然而，该效应具有更广泛的适用性，并且可以用于在诸如SCAPA或HZDR的激光等离子体加速器设施中实现先进的等离子体韦克菲尔德加速。为此，电子束不是由传统的加速器产生，而是由激光等离子体加速器产生。

Alastair Nutter will be developing a novel versatile method for spatiotemporal alignment and synchronization of particle and laser beams. The underlying principle was discovered as a key result of a multi-year experimental campaign obtained by the E210 collaboration at the Facility for Advanced Accelerator Experimental Tests (FACET) at the SLAC National Accelerator Laboratory at Stanford, one of our strategic partners. The project will be done co-funded by our partner at Helmholtz-Institute Dresden-Rossendorf (HZDR) in Germany. HZDR did not only agree to co-fund this PhD project directly, but will also be providing substantial resources into the burgeoning collaboration in terms of using beamtime at their PW-class laser system to the tune of ~10 weeks per year, and may be additionally investing into significant SCAPA beamtime (daily fees for the 350 TW laser at SCAPA are £ 3300). The student will be based at Strathclyde, but will also be placed at HZDR for extended times, in line with the international aspect of the Strathclyde CDT on Plasma-based Particle and Light Sources http://ppals.phys.strath.ac.uk/ . The coordinated interaction of intense laser and electron beams plays an ever-increasing role, for example for various pump-probe experiments and imaging of the ultrafast and ultrasmall. This requires precise techniques to measure and control temporal and spatial overlap of the interaction. We have discovered a fundamental effect which permits plasma-photonic synchronization and alignment of intense laser and electron beams with femtosecond and micrometer precision in a single robust apparatus. A laser-generated cold plasma filament picks up the electric field of a transient electron beam to varying degree, seed plasma electrons are heated by this coupling and perform complex oscillations which extend into ambient gas. Here, their non-relativistic energies are just right to generate substantial amount of additional plasma via impact ionization. This acts as a 'magnifying glass', transforming the specific femtosecond-micrometer interaction signature into visible plasma recombination / de-excitation light, which is observable on microsecond-millimeter scales.We have already exploited this basic effect to demonstrate combined spatiotemporal synchronization and alignment of the SLAC Stanford 20 GeV electron beam with a focused Ti:Sapphire laser with femtosecond-micrometer accuracy. This approach enables advanced diagnostics which will improve a wide range of pump-probe experiments substantially, and allows to realise advanced spatiotemporally resolved experiments which are hitherto not feasible. The phenomena also shed light on the previously hidden importance of impact ionization for instance in advanced plasma accelerator experiments. Supporting particle-in-cell simulations reveal fascinating dynamics over a wide range of time and length scales: The initial fs-scale kick by the electron beam is spread along the thin seed filament by plasma density waves and corresponding GV/m scale fields on the ps-scale, and impact ionization and recombination processes then take place on the ns-us time scale.In Stanford, we have been using a basic version of this effect, using an electron beam generated in a conventional linear accelerator. Alastair's PhD work will develop this method of spatiotemporal alignment further, such that it will be available in advanced shape when FACET-II, the follow-up plasma wakefield accelerator facility in Stanford will come online in 2019 for user-assisted commissioning. However, the effect has even wider applicability and can be used to enable advanced plasma wakefield acceleration at laser-plasma accelerator facilities such as SCAPA or HZDR. For this, the electron beam is generated not by a conventional accelerator, but by a laser-plasma-accelerator.