Supervisor:       Professor Zulfikar Najmudin

Type:                   Experimental (will include simulation work)

Funding:             JAI studentship

This Ph.D. projects aims to conduct an examination of the potential of Laser Wakefield Acceleration (LWFA) as a novel and efficient method for generating high-quality electron beams for Free Electron Laser (FEL) applications.

Wakefield accelerators driven by intense lasers are now used to routinely generate multi-GeV electron beams in our experiments [1]. The generated beams already have a number of applications including in the generation of intense sources of x-rays [2]. However, the electron beams that are currently produced tend to have high charge but in large energy spread. Though these are then useful for generating incoherent sources of radiation, they cannot yet be used to drive a free-electron laser. A free electron laser is the latest generation of x-ray source which uses the coherent interaction between a radiation field and the electrons generating it to produce coherent radiation – a beam driven laser [3]. At high enough electron energy the output of these new laser sources can be in the x-ray regime. But FEL’s need really high quality drivers, such as those only found in the preeminent high-energy physics labs. A major breakthrough in the use of FEL’s could arise if they could be driven by much smaller and potentially more widespread accelerators such as LWFA’s. However for this to be possible, the quality of output of LWFAs has to increase significantly.

In this project, we will study ways of making the beams produced from LWFA suitable to drive FELs. In particular, the beams should have low energy spread and have a brightness such that the FEL enters the exponential growth phase of the FEL instability. The study will involve theoretical analyses, advanced numerical simulations, and experimental validations to verify that the production of such beams is possible.

[1] Kneip, S., Nagel, S., Martins, S., Mangles, S., Bellei, C., Chekhlov, O., Clarke, R., Delerue, N., Divall, E., Doucas, G., Ertel, K., Fiuza, F., Fonseca, R., Foster, P., Hawkes, S., Hooker, C., Krushelnick, K., Mori, W., Palmer, C., … Najmudin, Z. (2009). Near-GeV Acceleration of Electrons by a Nonlinear Plasma Wave Driven by a Self-Guided Laser Pulse. Physical Review Letters, 103(3), 035002. https://doi.org/10.1103/PhysRevLett.103.035002

[2] Kneip, S., McGuffey, C., Martins, J. L., Martins, S. F., Bellei, C., Chvykov, V., Dollar, F., Fonseca, R., Huntington, C., Kalintchenko, G., Maksimchuk,  a., Mangles, S. P. D., Matsuoka, T., Nagel, S. R., Palmer, C. a. J., Schreiber, J., Phuoc, K. T., Thomas,  a. G. R., Yanovsky, V., … Najmudin, Z. (2010). Bright spatially coherent synchrotron X-rays from a table-top source. Nature Physics, 6(12), 980–983. https://doi.org/10.1038/NPHYS1789

[3] McNeil, B. (2009). Free electron lasers: First light from hard X-ray laser. Nature Photonics. http://www.nature.com/nphoton/journal/v3/n7/full/nphoton.2009.110.html

A fully funded-PhD studentship position has become available in the Blackett Laboratory at Imperial College to work on the AWAKE project at CERN.

 Supervisor: Prof Zulfikar Najmudin

Plasma-based accelerators can sustain acceleration gradients orders of magnitude higher than conventional devices, thereby enabling more compact accelerators to be developed. Plasma wakefield acceleration (PWFA) driven by high energy proton beams is one of the most promising schemes for electron acceleration to 100 GeV or TeV energies, as required for particle physics applications and next-generation colliders [1]. This is being investigated by the AWAKE project at CERN, which uses 450 MeV proton beams from the Super Proton Synchrotron (SPS) to drive a wakefield in a 10 m plasma cell. This experiment has so far demonstrated wakefield growth [2] and electron acceleration by 2 GeV [3].

In order to reach the higher energies needed for a particle collider, a discharge plasma source (DPS) that can be scaled up to ~100 m is being developed in collaboration between CERN, Imperial College and IST, Lisbon. The versatility of the DPS has been demonstrated using a 10 m source at CERN, including its scalability and use of different mass ions as the plasma source. The 1 m DPS that we have at Imperial will enable the outstanding measurements and improvements of uniformity and reproducibility to be made.

This project aims to develop suitable methods to measure, control and optimise a DPS for use in PWFA. This includes designing and implementing improvements to the DPS electronics, developing longitudinal and transverse diagnostics to determine the uniformity of the plasma and modelling the interaction between the SPS proton bunch and the DPS to determine optimal plasma profiles. The project will be based at Imperial with opportunities to travel to CERN to implement the findings. This PhD is suitable for Physics or Engineering students, but funding is only available for UK applicants. All applications should be received by the 16^th August.

[1] Caldwell, A., Lotov, K., Pukhov, A. et al. Proton-driven plasma-wakefield acceleration. Nature Phys 5, 363–367 (2009). https://doi.org/10.1038/nphys1248

[2] Turner, M. et al. (AWAKE Collabortion). Experimental observation of plasma wakefield growth driven by the seeded self-modulation of a proton bunch. Phys. Rev. Lett. 122, 054801 (2019). https://doi.org/10.1103/PhysRevLett.122.054801

[3] Adli, E., Ahuja, A., Apsimon, O. et al. Acceleration of electrons in the plasma wakefield of a proton bunch. Nature 561, 363–367 (2018). https://doi.org/10.1038/s41586-018-0485-4

Keywords: Physics, Electrical Engineering, Engineering, Optical Physics, Accelerators

Supervisor:        Professor Stuart Mangles

Funding:              Pending

This project will explore the use of laser wakefield accelerator beams in experiments to study QED physics. Colliding high energy electron beams from a LWFA with a high intensity laser pulse allows us to study QED physics in strong fields (eg non-linear Compton Scattering, Radiation Reaction, and non-linear Breit-Wheeler pair production). LWFAs can also be used to produce bright gamma beams using bremsstrahlung converters. Colliding these with dense X-ray fields (produced by a laser plasma interaction or a X-ray free electron laser) allows us to study the two photon Breit Wheeler process and light-by-light scattering. 

Supervisor:               Professor Zulfikar Najmudin

Type:                           Experimental (will include simulation work)

Funding:                     JAI studentship       

This project aims to investigate the phenomenon of Radiation Pressure Acceleration (RPA) as a promising mechanism for generating high-energy particle beams. In RPA, the radiation pressure from intense laser beams to accelerate charged particles to high speeds [1]. But for the radiation pressure to be able to accelerate the material to high energies, its inertia must be low. This can be achieved in one of two ways, either making targets of very thin (few nanometre) size or using targets of low density [2]. In either case, the target must stay at high enough density for long enough, that the laser cannot penetrate. This means making targets of suitable uniformity that they do not become susceptible to instabilities that can grow from any non-uniformities [3].

The project will hence not only study laser physics at the highest intensities, where the interaction is extremely relativistic, but also involve a good understanding of making and manipulating targetry so that it can minimise unwanted destruction of the targets.

The outcomes of this research can have a major in high-energy physics, medical science, and nuclear physics technology.

[1] Robinson, A. P. L., Zepf, M., Kar, S., Evans, R. G., & Bellei, C. (2008). Radiation pressure acceleration of thin foils with circularly polarized laser pulses. New Journal of Physics, 10(1), 013021. https://doi.org/10.1088/1367-2630/10/1/013021

[2] Palmer, C., Dover, N., Pogorelsky, I., Babzien, M., Dudnikova, G., Ispiriyan, M., Polyanskiy, M., Schreiber, J., Shkolnikov, P., Yakimenko, V., & Najmudin, Z. (2011). Monoenergetic Proton Beams Accelerated by a Radiation Pressure Driven Shock. Physical Review Letters, 106(1), 014801. https://doi.org/10.1103/PhysRevLett.106.014801

[3] Palmer, C., Schreiber, J., Nagel, S., Dover, N., Bellei, C., Beg, F., Bott, S., Clarke, R., Dangor, a., Hassan, S., Hilz, P., Jung, D., Kneip, S., Mangles, S., Lancaster, K., Rehman, a., Robinson, A., Spindloe, C., Szerypo, J., … Najmudin, Z. (2012). Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser. Physical Review Letters, 108(22), 225002. https://doi.org/10.1103/PhysRevLett.108.225002