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
