Multi-pulse laser wakefield acceleration

Laser-driven plasma accelerators can already accelerate electrons (and, in principle, positrons) to multi-GeV energies in accelerator stages only a few centimetres long. However, several issues must be overcome before these systems can realize their enormous promise: (i) the shot-to-shot jitter of the bunch parameters is too high for many applications; (ii) the lasers used to drive the accelerator operate at only a few pulses per second, which is too low for applications such as driving compact light sources; and (iii) the driving lasers are very inefficient (below 0.1%), which will be an issue for long-term applications such as driving particle colliders. This project seeks to address the last two of these issues by using a train of low-energy laser pulses to drive the plasma wave, rather than a single high energy pulse. If the pulses in the train are spaced by the plasma period then the wakefields add coherently to produce a plasma wave with an amplitude which grows towards the back of the pulse train. This approach, known, as multi-pulse laser wakefield acceleration (MP-LWFA), allows novel lasers to be employed which cannot easily generate high energy pulses, but which can generate few-milijoule laser pulses at mulit-kilohertz pulse repetition rates, with high efficiency. The MP-LWFA approach therefore offers a route to achieving compact accelerators able to generate GeV-scale electron bunches at high repetition rates, and in turn a route to a new generation of compact light sources. This project will investigate, experimentally and theoretically, important aspects of the physics of MP-LWFAs, including: the extent to which ion motion limits the number of pulses which can be used; the effects of laser hosing; and experimental demonstration of acceleration in a MP-LWFA. This work will be undertaken in our labs in Oxford and at national laser facilities such as the Central Laser Facility at Rutherford Appleton Laboratory.The proposed research comes under EPSRC's Plasma and Lasers Research Area. The compact, MP-LWFA-driven X-ray sources we wish to develop would enable breakthroughs in the Medical Imaging, Catalysis, Photonic Materials and Metamaterials, Condensed Matter: Electronic Structure, and Chemical Reaction Dynamics and Mechanisms Research Areas and therefore contribute to the Healthcare Technologies, Manufacturing the Future, and Energy Challenge Themes as well as the Physical Sciences Capability Theme.