A team, led by scientists at the University of Oxford, have published new research that highlights the potential for plasma accelerators to be driven by trains of low-energy pulses, generated by emerging laser technologies, at much higher pulse repetition rates than has been possible to date.
Laser-driven accelerators use an intense laser pulse to displace the electrons in a plasma (an ionised gas), leaving a trailing “plasma wake" behind. The immense electric field generated within the plasma wave, otherwise known as the wakefield, is approximately 1000 times stronger than that formed in a conventional accelerator and can be used to accelerate particles. Typically, one requires the driving laser energy to be delivered within a single oscillation of the plasma wave (around 100 fs); unfortunately, the short-pulse, high-energy lasers available today can only operate at a few pulses per second, which limits the repetition rate of laser-driven accelerators.
Using the Astra laser, a part of the Gemini facility at the CLF, Professor Simon Hooker and his team have demonstrated that plasma wakefields can be driven by a train of correctly spaced, low energy (10s mJ), short (~50 fs) laser pulses. This discovery could facilitate the use of emerging laser technologies which could deliver thousands of trains of this type per second, with high wall-plug efficiency, offering the prospect of plasma accelerators operating at multi-kilohertz repetition rates for various applications, including those in healthcare industry.
The paper , recently published in the journal Physical Review Letters, promotes the future development of an “energy-recovery" plasma accelerator, based on the principle that a trailing out-of-resonance laser pulse can damp the plasma wave. This could serve two purposes: (i) removal of wakefield unused for particle acceleration, which could damage the plasma cell; (ii) increasing the overall efficiency of the accelerator by re-using the recovered energy.
The research was supported by EPSRC ; the Helmholtz Association of German Research Centres; Air Force Office of Scientific Research, Air Force Material Command, USAF; and STFC. The full publication is available to view in PRL and is also highlighted on the APS Physics journal
For further information about the research, please contact Professor Simon Hooker (firstname.lastname@example.org)
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 J. Cowley , C. Thornton, C. Arran, R. Shalloo, L. Corner, G. Cheung, C. Gregory, S. Mangles, N. Matlis, D. Symes, R. Walczak and S. Hooker, "Excitation and Control of Plasma Wakefields by Multiple Laser Pulses," Phys. Rev. Lett, vol. 119, no. 4, p. 044802, Jul 2017.