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DPhil Delight!

A gentle August for the JAI was kicked into life last week as Oxford DPhil student Luke Dyks successfully defended his thesis. Luke joined the JAI in 2018 following an undergraduate degree at the University of Manchester and has spent the past few years working on the CLEAR user facility at CERN.


Luke Dyks with his external examiner Steinar Stapnes.

CLEAR, a rather swish acronym for the CERN Linear Accelerator for Research, is a small electron linac used to provide 200 MeV electron beams to a variety of users. Since beginning operation in 2017, the CLEAR team have worked with groups from a wide variety of institutes and fields, from the ESA to the University Hospital in Laussanne. Of particular interest presently is the ability to use CLEAR to provide beams to study Very-High Energy Electron radiotherapy, VHEE, at dose rates high enough to unlock the so-called FLASH effect.


An X-band accelerating cavity at CLEAR.

During the early part of his DPhil, Luke looked to improve the range of beam parameters available to users. His particular focus was to compress the length of the electron bunches in the linac, for the first time demonstrating compression to only a few hundred femtoseconds was possible. Demonstrating the compression of short bunches was desirable to several users and was a vital step in demonstrating that the CLEAR accelerator could be re-used as the injector for the eSPS at CERN.

One of Luke's uniform beam profiles.

Luke's other main research topic was using a simple photoinjector setup to produce beams with a uniform beam profile. Such uniform beam profiles would be very desirable for future VHEE facilities as well as general irradiation facilities due to their uniform dose distribution. Luke's method of producing uniform beam profiles is distinct to the typical optimisation undertaken on photoinjectors, namely to minimise the beam emittance. Instead, Luke allowed non-linear space-charge forces to distort the beam towards a uniform beam profile, optimising the machine setup for this uniformity, ignoring the emittance entirely. By simulating a simple, compact accelerator following the photoinjector, Luke was able to demonstrate that such uniform beams could be accelerated to useful energies, high enough for use in a VHEE facility.

Following his successful defence, Luke is beginning a Senior Fellowship at CERN. For his fellowship, Luke has joined the experimental areas group at CERN, working with experimental users to provide particle beams suited to their needs.