Theoretical and Experimental Studies on Ionisation Properties for Plasma Accelerators

Plasma-based wakefield acceleration is a promising approach in shrinking the size and cost of future particle accelerators and free-electron lasers. In the FLASHForward project a wakefield accelerator will be driven by an electron bunch from the FLASH accelerator while a multi-TW short pulse laser will pre-ionise a hydrogen gas target to form a plasma. Disentangling the processes of ionisation and wakefield driving enables improved control over the plasma density profiles and therefore over the structure of the wakefields crucially effecting the quality of the accelerated beams. To work out the electron density distribution in the target, we compute the ionisation rates of hydrogen molecules in strong laser fields. To be able to benchmark the predicted behaviour experimentally we also take into account the temporal and spatial laser-intensity profile evolution. The here developed understanding of the underlying processes of plasma generation ultimately allows for tailoring of the focusing geometry and laser-power-profile evolution to achieve desired plasma properties. As a proof of concept, we aim to realise plasmas with tailored shapes experimentally early 2016

Investigation of advanced electron bunch generation and diagnostics in the BOND laboratory at DESY

Laser driven plasma wakefield accelerators have been explored as a potential compact, reproducible source of relativistic electron bunches, utilising an electric field of many GV/m. Control over injection of electrons into the wakefield is of crucial importance in producing stable, mono-energetic electron bunches. Density tailoring of the target, to control the acceleration process, can also be used to improve the quality of the bunch. By using gas jets to provide tailored targets it is possible to provide good access for plasma diagnostics while also producing sharp density gradients for density down-ramp injection. OpenFOAM hydrodynamic simulations were used to investigate the possibility of producing tailored density targets in a supersonic gas jet. Particle-in-cell simulations of the resulting density profiles modelled the effect of the tailored density on the properties of the accelerated electron bunch. Here, we present the simulation results together with preliminary experimental measurements of electron and x-ray properties from LPWA experiments using gas jet targets and a 25 TW, 25 fs Ti:Sa laser system at DESY

Future-oriented wakefield-accelerator research and development at FLASH

FLASHForward is a beam-driven plasma wakefield acceleration facility,currently under construction at DESY (Hamburg, Germany),aiming at the stable generation of electron beams of several \si{\GeV} with small energy spread and emittance.High-quality 1 GeV-class electron beams from the free-electron laser FLASH will act as the wake driver.The setup will allow studies on external injection as well as on various internal injection techniques, such as density-downramp or ionisation injection.With a triangular-shaped drive beam electron energies of up to 5 GeV from a few centimeters of plasma can be anticipated.Particle-In-Cell simulations are used to assess the feasibility of each technique and to predict properties of the accelerated electron bunches.In this contribution the physics case and the current status of FLASHForward will be reviewed.Concepts of the main components - the extraction beamline from the FLASH linac, the target area, the plasma cell and the post-plasma beam transport and diagnostics - will be described