Introduction

Our lead academics are all members of the John Adams Institute (JAI), working in Oxford's sub-departments of Particle Physics and in Atomic & Laser Physics. We collaborate closely with JAI at Imperial College and with groups in Maryland, Munich, and Berkeley. Our experiments are undertaken in our new high-power laser laboratories in Oxford, at facilities based at the Rutherford Appleton Laboratory (just outside Oxford), or with our collaborators in the USA and Europe.

Our work on laser-driven plasma accelerators is in four areas: (i) investigation of techniques for controlling the injection of electrons into the plasma wakefield; (ii) development of new techniques for driving plasma accelerators, such as multi-pulse laser wakefield acceleration; (iii) development of techniques for driving the intense driving laser pulse over 100s of mm; and (iv) development of applications of laser-driven plasma accelerators, particularly their application to the generation of x-rays. We pursue these goals by both experiment and numerical modelling.


 

Gemini experiment
Some members of the group, together with a team from University of Liverpool, in the target area of the Astra-Gemini laser at Rutherford Appleton Laboratory

Projects available to start in 2022

1. Controlled injection and acceleration in all-optical plasma channels 

Conventional electron-beam-driven light sources (i.e. synchrotrons and free-electron lasers) use electron bunches with energies of a few GeV. An Oxford-Berkeley collaboration were the first to generate electron beams with comparable energy from a laser-plasma accelerator. Reaching this energy requires that the driving laser pulse, which has an intensity of around 1018 W cm-2, is guided over several centimetres — well beyond the distance over which diffraction occurs.

The Oxford group has recently developed a new type of plasma channel generated by auxiliary laser pulses. Since they are free-standing, these channels are immune to laser damage, and hence they are very promising stages for future multi-GeV plasma accelerators operating at kilohertz pulse repetition rates.

In order to drive the most interesting (and challenging) applications — such as driving very compact free-electron lasers, or future particle colliders — the electron bunches generated by the plasma accelerator must be of very high quality. In other words, they must have low energy spread, be of small transverse size, and have a low transverse momentum. Further in order to reach very high bunch energies it may be necessary to couple two or more plasma accelerator stages together.

In this project we will bring these ideas together to investigate methods for controlling the injection of high-quality electron bunches into laser wakefields driven in all-optical plasma channels and transporting them between plasma accelerator stages. The project will involve experimental work in Oxford and at international high-power laser facilities, and numerical simulations using particle-in-cell codes and other numerical tools.

2. Multi-pulse laser wakefield accelerators

Most work to date on laser-driven plasma accelerators has been done with single driving pulses, which must have an energy of order 1 J and a duration shorter than the plasma period (around 100 fs). These demanding parameters can be generated by Ti:sapphire laser systems. However, Ti:sapphire lasers have very low efficiencies (< 0.1%) and (at these pulse energies) are limited to pulse repetition rates below 10 Hz.

Many potential applications of laser-plasma accelerators — such as light sources and future particle colliders — require operation at much higher pulse repetition rates (at least in the kilohertz range) and much higher ‘wall-plug’ efficiencies. New types of laser have recently become available which are very efficient, and which can provide joule-level pulses at pulse repetition rates in the kHz range. However, these pulses are too long (a few picoseconds) to drive a plasma wave directly.

We have recently proposed a new concept for spectral- and temporal-modulation of picosecond-duration pulses to convert a picosecond laser pulse into a train of short pulses spaced by the plasma frequency. This approach, combined with the all-optical plasma channels described above, appears to be a promising route to achieving multi-GeV, kHz repetition rate plasma accelerators.

In this project we will seek to demonstrate these ideas for the first time, by demonstrating the generation of pulse trains, their application to the excitation of laser wakefields, and acceleration of electrons in those wakefields. The project will involve experimental work in Oxford and at international high-power laser facilities, and numerical simulations using particle-in-cell codes and other numerical tools.

How to apply

Theoretical and experimental work on plasma accelerators in Oxford is undertaken by a collaboration of research groups in the sub-departments of Particle Physics (particularly within the John Adams Institute for Accelerator Science) and Atomic & Laser Physics. For this reason, applications to work in this area should be made to the sub-departments of Atomic & Laser physics AND to Particle Physics. Further information about research projects available in Atomic & Laser Physics and in the John Adams Institute is available on the ALP and JAI web pages.

Please note that applicants are considered several times per year in “gathered fields”; most applicants are considered in the January gathered field, so you apply for that deadline unless you are unable to do so.

Please be aware that much of the funding we have available to support graduate students is aimed at supporting UK and EU students. However, some scholarships are available for candidates from further afield. You can find details on the university's graduate admissions pages.

Questions about the procedure for applying for graduate work in laser-plasma accelerators at Oxford should be addressed to Sue Geddes.

Further reading

  1. O. Jakobsson, S. M. Hooker, and R. Walczak, "GeV-scale accelerators driven by plasma-modulated pulses from kilohertz lasers," https://arxiv.org/abs/2110.00417

  2. A. Picksley, A. Alejo, R. J. Shalloo, C. Arran, A. von Boetticher, L. Corner, J. A. Holloway, J. Jonnerby, O. Jakobsson, C. Thornton, R. Walczak, and S. M. Hooker, "Meter-scale conditioned hydrodynamic optical-field-ionized plasma channels," Phys. Rev. E 102, 053201 (2020). DOI: 10.1103/PhysRevE.102.053201

  3. A. Picksley, A. Alejo , J. Cowley, N. Bourgeois, L. Corner, L. Feder, J. Holloway, H. Jones, J. Jonnerby, H. M. Milchberg, L. R. Reid, A. J. Ross ,R. Walczak, and S. M. Hooker, "Guiding of high-intensity laser pulses in 100-mm-long hydrodynamic optical-field-ionized plasma channels," Phys. Rev. Accel. Beams 23 081303 (2020). DOI: 10.1103/PhysRevAccelBeams.23.081303

  4. R. J. Shalloo, C. Arran, A. Picksley, A. von Boetticher, L. Corner, J. Holloway, G. Hine, J. Jonnerby, H. M. Milchberg, C. Thornton, R. Walczak, and S. M. Hooker, "Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens," Phys. Rev. Accel. Beams 22 041302 (2019). DOI: 10.1103/PhysRevAccelBeams.22.041302

  5. R. J. Shalloo, C. Arran, L. Corner, J. Holloway, J. Jonnerby, R. Walczak, H. M. Milchberg, and S. M. Hooker, "Hydrodynamic optical-field-ionized plasma channels," Phys. Rev. E 97 053203 (2018). DOI: 10.1103/PhysRevE.97.053203
  6. J. Cowley, C. Thornton, C. Arran, R. J. Shalloo, L. Corner, G. Cheung, C. D. Gregory, S. P. D. Mangles, N. H. Matlis, D. R. Symes, R. Walczak, and S. M. Hooker, "Excitation and Control of Plasma Wakefields by Multiple Laser Pulses," Phys. Rev. Lett. 119 044802 (2017). DOI: 10.1103/PhysRevLett.119.044802
  7. S. M. Hooker, R. Bartolini, S. P. D. Mangles, A. Tünnermann, L. Corner, J. Limpert, A. Seryi, & R. Walczak, "Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources," J. Phys. B 47 234003 (2014). DOI: 10.1088/0953-4075/47/23/234003
  8. M. Heigoldt, A. Popp, K. Khrennikov, J. Wenz, S.W. Chou, S. Karsch, S. I. Bajlekov, S. M. Hooker, and B. Schmidt, "Temporal evolution of longitudinal bunch profile in a laser wakefield accelerator," Phys. Rev. Spec. Top. Accel. Beams18 121302 (2015). DOI: 10.1103/PhysRevSTAB.18.121302
  9. S. M. Hooker, "Developments in laser-driven plasma accelerators," Nature Photonics 775–782 (2013). DOI: 10.1038/nphoton.2013.234
  10. N. Bourgeois, J. Cowley and S. M. Hooker, "Two-Pulse Ionization Injection into Quasilinear Laser Wakefields," Phys. Rev. Lett. 111 155004 (2013). DOI: 10.1103/PhysRevLett.111.155004
  11. W. P. Leemans, S. M. Hooker et al., "GeV electron beams from a centimetre-scale accelerator," Nature Physics 696 (2006). DOI: 10.1038/nphys418
  12. M. Fuchs, F. Gruner, S. Karsch, S. M. Hooker et al., "Laser-driven soft-X-ray undulator source," Nature Physics 826 (2009). http://www.nature.com/nphys/journal/v5/n11/full/nphys1404.html