Beam-driven Plasma Wakefield Acceleration

This project will involve carrying out theoretical, computational and experimental studies related to Beam Driven Plasma Wakefield acceleration, in particular using the plasma photocathode method for electron injection. The project in particular will focus on a potential plasma based laser-beam synchronisation diagnostic. All studies will involve close collaboration with the FLASHForward experiment based at DESY Hamburg.
Lewis Boulton's PhD work will aim at developing a novel, versatile and robust electron beam diagnostics method based on plasma afterglow. This research will be co-funded by DESY in Hamburg by the FLASHForward group, who also agreed to host Lewis for experimental campaigns. FLASHForward is an experiment for electron beam-driven plasma wakefield acceleration which is now a couple of years in the making, and will see first beamtime in 2019. The experiment uses the electron beam of the FLASH soft x-ray free-electron laser light source in order to drive a plasma wave. This approach is the 'sibling' of laser-driven plasma wakefield acceleration, a cornerstone at SCAPA, the Scottish Centre for the Application of Plasma-based Accelerators, which allows substantial synergies to be harnessed.
The plasma afterglow effect and the connected plasma torch injection effect has been observed for the first time within the E210: Trojan horse collaboration, led by B. Hidding at Stanford's SLAC FACET facility from 2013-2017. Here, the electron beam interacts with pre-generated plasma and depending of the mode of operation, either nearly non-intrusive interaction can be harnessed, or heavily perturbative interaction which includes the injection and generation of electrons with dramatically improved characteristics compared to the driver beam. In the non-intrusive mode of operation, the electron beam couples only very briefly with a tiny laser-generated plasma filament. Plasma filament electrons are then locally heated and leave a highly specific 'fingerprint', which can be detected in the most simple approach with a simple CCD operating with a bandpass filter for one of the plasma afterglow lines, for example ~589 nm for helium as a medium, as used in the past in Stanford by Hidding's research team. The Stanford measurement results are currently under review at Nature Physics. While this setup and measurement at Stanford simply integrated the total photon yield to retrieve a simple number, simulations indicate that there is huge benefit by resolving the afterglow signature spatially, spectrally and temporally resolved. Lewis shall develop this diagnostic by implementing these capabilities, for example by using optical spectrometers, streak cameras and high spatial resolution. This way, shot-to-shot variations of electron beam charge, size, duration and current but also as regards local plasma density can be resolved. By retrieving as much information from the localized interaction as possible, highly specific interaction fingerprints can be taken. Lewis will therefore also develop algorithms which will allow to retrieve interaction data unambiguously, which may require machine learning approaches.
If the interaction takes place in an underlying plasma medium, such as hydrogen, the localized laser-based helium ionization can lead to an all-optical version of plasma downramp injection, which is termed 'plasma torch' injection. First signatures of this effect have been seen in E210 in Stanford, but now the scheme shall be explored and exploited in detail at DESY in a complementary parameter range to SLAC. In his previous research at DESY, Hidding had invested ~100kEURO into future provision of femtosecond synchronization capability at FLASHForward, which shall now be exploited in the coming years.