THz pulse acceleration of electron beams

There is growing interest in the use of lasers to reduce the scale of today's particle accelerators with the ultimate dream of producing compact laboratory-sized machines for versatile x-ray sources and medical treatment. One of the first steps towards this goal is the demonstration of laser-based schemes for the acceleration of relativistic electron beams. Laser-based ultrafast terahertz radiation sources offer a promising route towards this electron bunch acceleration. Such terahertz sources have already demonstrated electric field strengths in excess of 100 MV/m and benefit from providing inherent synchronization between laser and particle beams. A key challenge in using terahertz radiation for particle acceleration is in obtaining the sub-luminal phase velocities required to match the velocity of the particle beam. This has been demonstrated using a terahertz waveguide with non-relativistic electrons, achieving an acceleration of 7 keV over 3 mm. Such structures suffer however from high dispersion which limits the maximum interaction range. We have recently demonstrated a travelling-source and free space propagation approach to overcoming the sub-luminal propagation limit.
The objective of these studentships will be to build upon this work and demonstrate the first relativistic acceleration of an electron beam using the 5-50 MeV beams provided by the VELA/CLARA accelerator at STFC Daresbury Laboratory. This will be achieved by developing laser-driven terahertz sources with multi-MV/m field strengths, and exploring the interaction of the THz pulse with the electron beam, the physics of beam loading and depletion in a single THz cycle and the subsequent beam dynamics of the accelerated beam. By combining high field terahertz source development with new THz-electron beam interaction simulations we seek to develop an idealised interaction scheme and breakthrough the 100 MV/m accelerating gradient limit of conventional radio-frequency accelerating cavities.
The project will build upon the experimental work and provide the necessary theoretical and simulation framework for understanding and mitigating beam loading and THz depletion in acceleration schemes. This will include developing novel PIC code simulations that model the physics of beam depletion for single cycle broadband THz fields.