PhD opportunities

Discharge plasmas as a medium a collider based on wakefield accelerators

Supervisor:       Professor Zulfikar Najmudin

Type:                   Experimental (will include simulation work)

Funding:             JAI studentship

Wakefield accelerators use the immense fields produced in plasmas to accelerate particles to high energy. Energy gains > GeV are now routinely produced at laser facilities around the world over only centimetre distances [1]. However, the relatively low energy available in even the most powerful laser pulse is a limitation on the particle’s energy gain. By contrast the ion beams available at CERN have energy that exceeds 10’s of kJ (if not more). This means that instead of accelerating particles over centimetres, there is the potential to accelerate over tens if not hundreds of metres [2]. This would produce an accelerator relevant to high-energy physics experiments [3].

The AWAKE experiment at CERN has already produced exciting results using the SPS beam demonstrating 2 GeV energy gain of electrons in a 10m cell [4]. To overcome the fact that the SPS beam is too long to ideally drive a wakefield, a process called self-modulation has been used to produce beamlets within the SPS beam that are resonant with a wakefield [5]. This is initiated in a Rb cell by a laser that ionises the plasma as the proton beam is passing through it. However, the use of the ionising laser puts a limit on the acceleration length.

We have proposed (along with IST Lisbon) using a discharge plasma that would enable acceleration lengths well in excess of the 10m available now. But for controlled acceleration the plasma density must be controlled to better than 1%, and it may be further necessary to have ramps in plasma density to optimise the acceleration process. Hence, in this project, we will look to diagnose and model the generation of large scale (metre long) plasmas, using the prototype discharge we have here in the Blackett Lab. We will also model the interaction of the SPS proton beam with our accelerator stage. We will then look further to optimise the plasma profile to improve the acceleration. These investigations will be performed with a view to implementing both the discharge and the diagnostics on future runs of AWAKE at CERN.

[1] S. Kneip, et al, “Near-GeV Acceleration of Electrons by a Nonlinear Plasma Wave Driven by a Self-Guided Laser Pulse”, Phys. Rev. Lett. 103 035002 (2009)

[2] A. Caldwell, et al, “Proton-driven plasma-wakefield acceleration”, Nat. Phys. 5 (2009) 363–367.

[3] M. Wing, “Particle physics experiments based on the AWAKE acceleration scheme”, Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 377 (2019)

[4] E. Adli, et al, “Acceleration of electrons in the plasma wakefield of a proton bunch”, Nature. 561 363 (2018)

[5] M. Turner et al, “Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch”, Phys. Rev. Lett. 122 054801 (2019)

Imaging of shock compressed material for application in inertial confinement fusion

Supervisor:         Professor Zulfikar Najmudin
Type:                     Experimental (but will include simulation work)
Funding:               JAI studentship

The recent announcement of positive energy gain in an inertial confinement fusion has generated great excitement around the world [1] [2]. These results suggest that we are at the dawn of being able to control fusion in the laboratory, and potentially opening it up as a new source of (carbon-free) energy. These results were made possible by meticulous improvements in capsule design and better understanding of the power balance between laser beams to ensure more uniform irradiation of the capsule being compressed. However, the results to-date still suffer from shot-to-shot fluctuation (with only one shot showing positive energy gain so far?). Most of the difficulties in the compression have been a result of lower-than-expected velocities for the laser-driven shocks that initiate the compression, which has only been inferred from the poor neutron yields in previous shots. Being able to diagnose and characterise the shock formation and velocity would be a major step in better controlling the inertial confinement process [3].

We have been developing new x-ray imaging techniques for characterising dense matter interaction with high temporal and spatial resolutions. This source is based on synchrotron radiation from laser wakefield accelerators. The same large fields that make wakefield accelerators much more compact than conventional accelerators, also make them emit synchrotron radiation strongly. The source, with its small temporal and spatial emission size, and high photon energy (> 10 keV) is ideal for diagnosing dense dynamic systems [4]. We propose to use this imaging source to better understand the coupling of laser energy to a variety of targets in direct-laser driven targets as would be found in high-gain ICF designs. We will also study methods to improve laser-matter coupling which could drive the implosions much faster making the capsules potentially much easier to ignite.

[1] [Online].
[2] [Online].
[3] A. Do et al “Direct Measurement of Ice-Ablator Interface Motion for Instability Mitigation in Indirect Drive ICF Implosions, Phys. Rev. Lett. 129 215003 (2022)
[4]  J. C. Wood et al, "Ultrafast Imaging of Laser Driven Shock Waves using Betatron X-rays from a Laser Wakefield Accelerator," Scientific Reports, vol. 8, p. 11010, 2018.

Novel particle acceleration based on wakefield accelerators driven by shaped laser pulses

Supervisor:                  Professor Zulfikar Najmudin
Type:                            Experimental (but requires simulation / computation)
Funding:                       JAI studentship

Laser wakefield accelerators are being investigated for the next generation of particle accelerators. A high intensity laser pulse generates a large amplitude plasma wave, which can accelerate particles at a rate more than thousands of times faster than conventional accelerators. Acceleration of electrons sourced directly from the plasma is now well established with wakefield accelerators with acceleration to greater than GeV energies routinely performed in our experiments [1,2].

Early experiments suffered from lack of reproducibility and lack of control on the laser properties. However, a new generation of high-power laser sources are now being developed with greater control on the spatial and temporal characteristics of the pulses, and which operate at high repetition rates (10 Hz to kHz). These laser sources offer the ability to greater control on the accelerating process offering the ability to improve in real-time and to use machine learning techniques to implement optimisations [3]. In particular, shaping of the laser pulse on time scales shorter than 10 fs will offer the ability to enhance injection of plasma electrons and to match the acceleration length to the length over which the laser energy is spent.

The work will be performed using the high-power lasers at national and international facilities such as the SYLOS laser at ELI-ALPS, the ASTRA lasers at the Rutherford-Appleton Laboratory as well as with the laser being developed in the basement of the Blackett Laboratory.

[1] S.P.D. Mangles, et al, "Monoenergetic beams of relativistic electrons from intense laser-plasma interactions", Nature. 431 535–538 (2004)
[2] S. Kneip et al, “Near-GeV Acceleration of Electrons by a Nonlinear Plasma Wave Driven by a Self-Guided Laser Pulse”, Phys. Rev. Lett. 103  035002 (2009) 
[3] R.J. Shalloo, et al, “Automation and control of laser wakefield accelerators using Bayesian optimization”, Nat. Commun. 11 6355 (2020)


Radiation pressure acceleration of thin foils with intense lasers

Supervisor:               Professor Zulfikar Najmudin

Type:                           Experimental (will include simulation work)

Funding:                     JAI studentship       

State-of-the-art lasers can now reach intensities well in excess of 1024 Wm-2 at focus. When directed onto a target that is sufficiently dense that it can stop the laser beam, the intense radiation pressure can directly drive the critical density surface of the target. For sufficiently thin targets, the whole plasma can be propelled forward gaining momentum as it propagates driven by the radiation pressure, resulting in the production of a dense beam of energetic ions [1]. However previous results have demonstrated that imperfections in either the driver beam or the targets can lead to instabilities that terminate the acceleration [2]. The results can be further complicated by early heating of the target which causes it to expand to such a level that the density falls below the relativistically corrected critical density such that the laser propagates into the target at high intensity. Luckily though, we have recently found that this too can lead to efficient ion acceleration [3].  These ions could have numerous applications, not least as part of a next-generation particle accelerator for radiobiology and oncology [4].  This is motivated by recent discovery of the so-called ‘FLASH’ effect, showing improved healthy tissue sparing at ultrahigh dose rates, which is well suited to laser driven sources.

Recent advances in high-power lasers, which offer higher beam quality at much higher repetition rates (>10 Hz), will allow us to do real-time improvements in both targetry and laser beam shape to optimise the interaction, potentially using machine learning techniques. This will give the ability to accelerate high quality beams to much higher energies. Hence, this project aims to develop radiation pressure driven acceleration schemes through novel ultrathin targets and through better control of the drive laser properties.

The experiments will take place firstly on our in-house laser in Blackett but will then be migrated to higher power national facilities such as Gemini at the Rutherford-Appleton Laboratory and J-Karen at KPSI in Japan.

[1] A.P.L. Robinson, et al, “Radiation pressure acceleration of thin foils with circularly polarized laser pulses”, New J. Phys. 10 013021 (2008)

[2] C.A.J. Palmer et al, “Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser”, Phys. Rev. Lett. 108 225002 (2012)

[3] N. Dover et al, “Enhanced ion acceleration from transparency-driven foils demonstrated at two ultraintense laser facilities”, Light Sci. Appl. (2022). 

[4] G. Aymar et al., “LhARA: The Laser-hybrid Accelerator for Radiobiological Applications”, Front. Phys. 8, 567738 (2020)


Time Resolved X-Ray Spectroscopy using Laser Wakefield Accelerators

Time Resolved X-Ray Spectroscopy using Laser Wakefied Accelerators

Professor Stuart Mangles

Type: experimental with computional modelling 

Funding:  JAI and Science Technology and Facilities Council - STFC studentship

Description:  This PhD project will research the use of X-Rays produced by laser wakefield accelerators for ultrafast time-resolved absorption spectroscopy.

The project will develop X-Ray absorption methods for the UK's new EPAC laser facility and will provide insights into the potential of laser wakefield accelerators for a range of of applications, including time-resolved studies of dynamic processes in material systems, detection of ultrafast electronic dynamics, and matter in extreme conditions.