Broadband beam applications of plasma wakefield accelerators

激光等离子体加速器可以在厘米尺度的距离上产生具有相对论能量和大电流的电子束，这要归功于等离子体可以承受的巨大电场——这是等离子体加速器与传统粒子加速器相比的主要吸引力，后者要大几个数量级。等离子体加速器产生的光束的能量传播本质上是广泛的。虽然通常不可取，但在一些独特的应用程序中，该特性是一种资产。事实上，用等离子体加速器产生宽带光束比产生单能量光束更容易——因此宽带光束有更高的TRL。应在这项工作中开发从这种宽带波束中获益的应用。其中一个应用是在实验室中再现空间辐射。太空辐射是宽带的，对电子设备和宇航员都是危险的。用等离子体加速器精确再现空间辐射为先进的辐射硬度测试开辟了一条道路。类似的宽带、低能量光束可以用于表面癌症治疗。这个相关的应用是由Strathclyde[2]与工业界合作获得专利的。辐射的宽带特性允许深度剂量沉积剖面，可以针对表面肿瘤进行定制，从而消除传统加速器对周围健康组织的辐射。要研究的第三个应用是在数百兆电子伏特数量级的较高能量下使用相对宽带的电子束。这种光束是混合等离子体尾流场加速器[3]的理想驱动器，这种方法有望允许等离子体尾流场加速器的能量和亮度转换器，因此，当与等离子体光电阴极[4]耦合时，可以实现比最先进的光束亮100,000倍的光束。在欧洲合作中，这是一个实验上非常成功的推动力[5,6]。就在最近，一篇关于该主题的突破性论文被《自然通讯》接受，该论文由Strathclyde和HZDR之前的一名联合博士生作为第一作者之一b[6]获得。这项研究的博士生也将由HZDR共同资助，并将研究上述三种宽带电子束的应用。该项目的另一个合作伙伴将是斯坦福大学，我们将在那里在FACET-II上提供经批准的E-310等离子体光电阴极实验，同时也将在斯特拉斯克莱德的SCAPA和HZDR的DRACO激光等离子体设施上进行开发和测试。等离子体光电阴极的发展及其应用前景是由ERC NeXource资助的。该学生将探索等离子体加速器运行的基础激光等离子体物理学，目标是稳定的宽带光束及其应用。SCAPA的内部能力将被利用来解决这些问题，辅以HZDR的DRACO设施的实验，该设施的规模与SCAPA相似。与HZDR的合作有着良好的记录，包括联合发表的高水平论文[5,6]。此外，HZDR还与工业合作伙伴OncoRay共同活跃于医学癌症治疗领域，并对空间辐射复制有浓厚兴趣。因此，他们是这个学生的理想合作伙伴。该项目的主要目标是将上述三个应用推力的TRL至少提高一个点。这将包括SCAPA的建模和实验活动，包括英国Cockcroft研究所和ERC NeXource项目合作采购的新型kHz激光器和光束线，DRACo和斯坦福大学的光束线。该学生将被安置在Strathclyde博士培训中心PPALS[8]，与之前的学生一样，包括Strathclyde- hzdr联合博士生，他是[8]的第一作者之一。

Laser-plasma accelerators can generate electron beams with relativistic energies and large current on centimetre-scale distance, thanks to the huge electric fields a plasma can sustain - the chief attraction of plasma accelerators compared to conventional particle accelerators that are orders of magnitude larger. The energy spread of beams from plasma accelerators inherently tends to be broad. While generally not desirable, there are unique applications for which this feature is an asset. In fact, producing broadband beams with plasma accelerators is easier than to produce monoenergetic beams - broadband beams therefore have higher TRL. Applications that profit from such broadband beams shall be developed in this work. One application is the reproduction of space radiation in the laboratory [1]. Space radiation is broadband, and a danger to electronics and astronauts onboard. Exact reproduction of space radiation with plasma accelerators opens up a path to advanced radiation hardness testing. Similar broadband, low energy beams can be used for surficial cancer therapy. This related application is patented by Strathclyde [2] in collaboration with industry. The broadband character of the radiation allows a depth-dose deposition profile that can be tailored to surface tumours, thus eliminating irradiation of surrounding healthy tissue as would occur with conventional accelerators. The third application to be investigated is using relatively broadband electron beams at higher energies of the order of hundreds of MeV. Such beams are ideal drivers for hybrid plasma wakefield accelerators [3], an approach that promises to allow plasma wakefield accelerator energy and brightness converters and therefore beams 100,000 x brighter than state-of-the-art to be realized when coupled with plasma photocathodes [4]. This is now an experimentally very successful thrust in a European collaboration [5,6]. Just recently, a breakthrough publication on this topic was accepted in Nature Communications, obtained by a previous joint PhD student between Strathclyde and HZDR as one of the first authors [6]. The PhD student for the proposed work likewise would be co-funded by HZDR and would be working on the above three applications of broadband electron beams. Another partner in this project will be Stanford University, where we will deliver the approved E-310 experiment on the plasma photocathode at FACET-II, which in parallel is also to be developed and tested at Strathclyde's SCAPA and HZDR's DRACO laser-plasma facilities. The plasma photocathode development and its prospects for applications are co-funded by the ERC NeXource grant [7]. The studentship will explore fundamental laser-plasma-physics underlying the operation of plasma accelerators aiming at stable, broadband beams and its applications. SCAPA's in-house capabilities will be exploited to address these questions, complemented by experiments at HZDR's DRACO facility, which is of similar scale as SCAPA. A strong track record exists in collaboration with HZDR, including joint high-level papers such as [5,6]. In addition, HZDR is also active in medical cancer therapy jointly with their industrial partner OncoRay, and has strong interest in space radiation reproduction. They are therefore the ideal partner for this studentship. Main aims of the project are to increase the TRL of the above mentioned three application thrusts by at least one point. That will include modelling and experimental campaigns at SCAPA, including the new kHz laser and beamline procured as collaboration between the UK Cockcroft Institute and the ERC NeXource project, the beamlines at DRACo and at Stanford. The student will be embedded in the Strathclyde Centre for Doctoral Training PPALS [8], as previous students including the joint Strathclyde-HZDR PhD student who was one of the first authors of [6].