Broadband beam applications of plasma wakefield accelerators

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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].