A team from Oxford has had a breakthrough in improving the repetition rate and efficiency of laser-driven plasma accelerators. These accelerators could revolutionise many areas of science and technology as they can accelerate particles to high energies in one-thousandth of the length of conventional machines. However, a major roadblock to realising their many applications is the fact that the high-energy short-pulse lasers used are inefficient and have very low (few hertz) pulse repetition rates.
A team from Oxford led by Emeritus Professor Roman Walczak has now shown how this could be overcome by using long (few picosecond) pulses from recently developed efficient high-repetition-rate lasers. The idea is based on the use of a short, low-energy ‘seed’ pulse to drive a low-energy plasma wave, that modulates the spectrum of a trailing long, high-energy ‘drive’ pulse. The spectrally-modulated drive pulse is then converted to a train of short pulses by reflecting it from a dispersive mirror. This train is used to resonantly drive a large-energy plasma wave which accelerates electrons in an analogy to a surfer gaining energy surfing down a large wave created by a series of wind blows. Numerical simulations of the entire concept show that existing laser systems could be used to drive efficient, kilohertz-repetition-rate plasma accelerators with beam energies comparable to those used in today’s large-scale synchrotrons and free-electron lasers.
‘Our findings come in the same year that the first lasing of a free-electron laser driven by an electron beam from a laser-driven plasma accelerator was demonstrated,’ adds Professor Walczak. ‘The significance of the concept developed by our team lies in opening a path for plasma accelerators to approach parameters, quality and stability of conventional RF accelerators; this would make devices such as free-electron lasers smaller, cheaper and therefore more accessible.’
Gev-scale accelerators driven by plasma-modulated pulses from kilohertz lasers, Jakobsson et al, Physical Review Letters, October 2021