PhD opportunities

Novel particle acceleration based on laser wakefield accelerators

Title 
Novel particle acceleration based on laser wakefield accelerators
Supervisor
Professor  Zulfikar Najmudin
 Type
 Experimental (may include simulational work)
 Description  

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. However, the beams produced are not yet of the quality required for the high energy physics applications.  This project will investigate novel techniques to improve the beam quality from laser wakefield accelerators including structuring of targets and staged acceleration. The work will be performed using the high-power lasers at the Rutherford-Appleton Laboratory as well as with the laser being developed in the basement of the Blackett Laboratory

Funding JAI studentship

Radiation pressure effects at the focus of intense lasers

Title 
Radiation pressure effects at the focus of intense lasers
Supervisor
Professor  Zulfikar Najmudin
 Type
 Experimental (may include simulational work)
 Description  

State-of-the-art lasers can now reach intensities well in excess of 1020 Wcm-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. This can manifest itself in a number of ways. It can drive a collisionless shocks which can be diagnosed by the ions it accelerates in its path. Alternatively, for sufficiently thin targets, the whole plasma can be propelled forward gaining momentum as it propagates. The result in both cases is the production of dense beams of energetic ions. These ions could have numerous applications, not least in next-generation particle accelerators. The project proposed here will investigate radiation pressure driven acceleration schemes through optimisation of targets and of the characteristics of the laser beam that drives them. The experiments will take place on the high intensity lasers at the Rutherford-Appleton Laboratory and the IR laser at the ATF Brookhaven National Laboratory. A near term goal is to produce protons with energies exceeding 100 MeV, which would be of interest for applications such as radiation treatment of tumours or for fast heating of fusion capsules.

Funding JAI studentship  

Using Laser Wakefield Accelerators Probing strong field QED

When charged particles accelerate they radiate, and so must lose energy and momentum. The force on a charged particle in an electromagnetic field, the Lorentz force does not include this “radiation reaction”.  Radiation reaction can be added ad hoc into classical electromagnetism, however as the force on the electrons increases it becomes necessary to include quantum effects. Various approaches to modelling this quantum radiation reaction have been proposed, but they are yet to be tested experimentally.

Quantum radiation reaction plays a role anywhere there are extreme electromagnetic fields, including the extreme magnetic fields of magnetars and spinning blackholes.  

In the lab one way to reach the quantum radiation reaction regime is to collide a high energy electron bunch with a high intensity laser as in the rest frame of the electron bunch the electric fields can approach the critical field of quantum electrodynamics. 

In 2018 our group published some of the first measurements of radiation reaction in the collision between a high intensity laser and a high energy electron beam, using a Laser Wakefield accelerator.  However, the measurement was not able to clearly discriminate between different models of quantum radiation reaction. We are actively pursuing further experiments in this area to make the first definitive measurement of quantum radiation reaction and are looking to recruit a PhD student in 2021 to join this program.

For further information please contact Dr Stuart Mangles.

Using Laser Wakefield Accelerators to Make Matter From Light

When two photons collide normally nothing happens, however if the photons have enough energy they can collide creating an electron-positron pair.  This process was first predicted by Breit and Wheeler in the 1930s, but has not been observed in the laboratory using real photons. This is because it is a major challenge to produce bright enough photon sources to make a sufficient number of positrons to be detected.  

The Breit Wheeler process is important in astrophysics - it prevents very high energy gamma rays travelling long distances across the universe and also leads to production of vast amounts matter in the accretion disks near black holes. 

We are developing  a new platform for making this observation for the  first time, based on the very bright photon sources that can be produced using laser-plasma interactions. By generating high-energy gamma rays using the electron beam from a Laser Wakefield accelerator and colliding them with the X rays generated by a rapidly heated plasma we expect to be able to produce up to 1 pair per shot. 

Our first run at the Gemini laser facility in 2018 successfully showed that the background levels are sufficiently low to make a measurement, and by making a number of improvements to the experiment we hope to be able to make a clear observation. We are looking to recruit a student in 2021 to develop the improvements necessary to make a clear observation of light turning into matter.   

 For more information contact Dr Stuart Mangles.

Using Laser Wakefield Accelerators to Probe Matter in Extreme Conditions

Much of the visible universe exists in extreme conditions, for example at high pressures and  temperatures inside stars and gas giant planets or in the presence of intense x-ray fluxes (eg the low density gas near black holes). Much of our understanding of these systems comes from detailed atomic physics calculations.  However testing these models experimentally is very challenging -- such extreme conditions can now be created in the lab but only for very short periods of time (~ 1ps).

One of the ideal ways to study these highly transient lab systems under extreme conditions is to use X-ray absorption spectroscopy, and the ideal X-ray source would have a broad spectrum (to allow absorption features to be observed) and femtosecond duration (to freeze the transient behaviour). Our group has pioneered the development of X-ray radiation from laser wakefield accelerators which uniquely has both these properties. 

We have recently developed an experimental platform for making X ray absorption measurements on the Gemini laser system (Kettle PRL 2019) and we are interested in recruiting students to start in 2021 who are interested in experimental or theoretical aspects of the study of matter in extreme conditions.

For more information please contact Stuart Mangles.