PhD Vacancies in the QUASAR Group

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The QUASAR Group is pleased to announce several open PhD positions for start in October 2015 or sooner. Projects are outlined below and further information can be obtained by contacting Prof. Carsten Welsch. Applications including a statement of interest, CV, academic background and two letters of reference should be submitted by 06 March 2015.

Novel optical diagnostics for present and future accelerators

You would be joining the QUASAR Group in Liverpool University’s physics department, based at the Cockcroft Institute, and carry out beyond state‐of‐the‐art research into advanced beam diagnostics methods to monitor charged particle beams. While this work targets on-campus facilities initially, the impact of the project is expected to be global since these monitors will benefit a very wide range of accelerators used in research, industry and medicine. You would be joining an established team of leading experts in this multi‐disciplinary field and collaboration with partners from across Europe will be possible.

Your project will consist of the development of two different diagnostics: Firstly, you would experimentally validate a new method to determine the rms emittance of beams with significant space charge. This method, if successful, will provide the accelerator community a new, easily implemented, accurate means to measure emittance of low to moderate energy (15-500 MeV) electron beams. Secondly, you would develop a new method that can measure any bunch length, is simple to implement, capable of single‐shot measurements and is useful over very wide range of beam energies. The technique employs the angular distribution of CDR produced as the bunch passes through a simple aperture, e.g. a slit. The method will be validated and optimized in the project.


Characterisation of the longitudinal and transverse energy distribution of electrons emitted from photocathodes using TESS and the VELA/CLARA accelerator

Knowledge of photocathode emission properties is essential to the accelerator community to drive forward the increases in electron beam brightness necessary to maximise exploitation of current and planned FEL facilities. This research project will focus on measuring the transverse and longitudinal energy distribution curves for photoelectrons emitted from a variety of metal and semiconductor photocathode sources, with the intention of identifying the optimum photocathode materials and preparation techniques to achieve minimum energy spread.

The work will be conducted in two parts:
Offline work using the Transverse Energy Spread Spectrometer constructed by ASTeC (and possibly other experimental systems in the vacuum laboratory) to characterise photocathode emission properties
Online work using with the cathode under test installed in the VELA/CLARA electron injector, and measurements of transverse and longitudinal emittance made using the machine diagnostics
You would work with ASTeC’s Accelerator Physics group and would be supervised by Dr Tim Noakes and Dr Lee Jones, as well as Prof Carsten Welsch from the QUASAR Group.


Investigations into Laser-electron beam Interaction in a Storage Ring

The energy modulation of 2.75 GeV electrons by high electric field femtosecond laser pulses is used at the SOLEIL storage ring for the purpose of producing photon pulses in the range of 100 fs with moderated flux. Radiation with this duration can then be extracted at two different beamlines for time resolved electron spectroscopy (TEMPO) and for diffraction in the sub-picosecond time scale (CRISTAL).
The TEMPO beam line will use a helical undulator covering a photon energy range from 200 eV to 1,000 eV and the CRISTAL beam line will use an in-vacuum undulator for emission in the 4 – 30 keV energy range. In addition, bending magnet radiation in the THz-regime is used for longitudinal slicing diagnostics and monitoring of slicing efficiency. Commissioning of the laser-electron interaction process has recently started and detailed studies are now required to further optimize the process and a joint Liverpool-SOLEIL PhD student shall carry out research and development into a number of key areas, including:

• Investigations into various laser and electron beam parameters and how they affect the light characteristics;
• Studies into the transverse and longitudinal distribution of the electron beam after the interaction;
• Optimization of the interaction using the THz signal as a diagnostics tool;
• Optimization of the photon flux on the two beamlines CRISTAL and TEMPO, especially for the case of a circularly polarized beam at 200 eV;
• Studies into micro bunching formation;
• Studies into halo effects and background signals created by halo radiation;
• Investigations into novel filling patterns compatible with multi-bunch operation mode.

In addition to these broad experimental studies which are closely linked to current work at both SOLEIL and in the QUASAR Group, there will be opportunities to study the possibility to obtain such short pulses also on other beamlines. This includes investigations into photon pulses separation schemes.
Practical arrangements: You would spend most of their first year at the Cockcroft Institute where you will be familiarized with the storage ring lattice, simulation codes, beam dynamics and beam diagnostics. This would include advanced diagnostics studies. You would also follow the in-house PGR lecture program. Year 2 and year 3 would be spent at SOLEIL for the above-mentioned experimental studies with shorter visits to CI. The final year would be spent at CI for data analysis and thesis writing. In case you are already in possession of your degree, opportunities exist to start the project earlier than October 2015 – this would allow for additional beam diagnostics studies during the first year.