Optimisation of Plasma Accelerators

The last fifty years have seen the development of accelerators, allowing physicists to probe the fundamental structure of reality. The culmination of this effort has been the Large Hadron Collider at CERN: a 27 kilometre long accelerator whose aim is to discover new particles - as it has done with the Higgs Boson - and investigate new phenomena such as the theory of supersymmetry. Continuing to use conventional techniques in acceleration suggests that the next step would be a linear electron-positron collider 30-50km long which would require a huge investment. My DPhil project will look at an alternative to this; the pursuit of an ultra-compact plasma based technology allowing the accelerator to be an order of magnitude shorter in length, and thus significantly less expensive.
The concept is to impact a high energy proton beam, like those produced at CERN, into plasma. The negatively charged electrons in the plasma are violently displaced from their equilibrium position by the proton beam but the positive ions in the plasma, being much heavier, remain relatively unmoved. These positive ions attract the displaced electrons back to their original position, creating a high gradient electric wakefield and a subsequent oscillatory motion in the plasma electrons. Experiments impacting a laser or electron beam onto a plasma have already been conducted and have observed accelerating gradients up to 1000 times greater than in conventional accelerators. As proton beams are the highest energy beams currently available, it is anticipated that the electric fields they create could accelerate electrons in the wakefield up to teraelectron-volts (TeV) . It is also hoped that this plasma accelerator will be able to reach the TeV regime in a single stage and within a few kilometres of acceleration.
The UK has seven groups in collaboration preparing for this test experiment in CERN. The main focus of Mr Savin's DPhil will be to design the diagnostic tools which will measure the amplitude, spatial size, and evolution of the wakefield. He will also be analysing the energy and spatial profile of the electron beam after it has been accelerated in the plasma. Initially Mr Savin's DPhil will start exploring the interaction of petawatt laser pulses with cluster targets to determine whether improvements observed scale with increased energy and pulse duration up to ten terawatts.