Extreme beam control

27 April 2018

An Oxford team has succeeded in stabilising the arrival time of a ‘relativistic’ beam of electrons, travelling at almost the speed of light, to 50 femtoseconds. This overcomes one of the major challenges facing the proposed Compact Linear Collider (CLIC).

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Researchers in the Department of Physics are partners on the Compact Linear Collider (CLIC) study, an international collaboration working on a concept for a machine to collide electrons and positrons (antielectrons) head-on at energies up to several Teraelectronvolts (TeV). This energy range is similar to the Large Hadron Collider’s, but by using electrons and their antiparticles rather than protons, physicists will gain a different perspective on the underlying physics.

Next-generation subatomic particle accelerators such as CLIC will require exquisite control of the particle beams in both space and time. Since the beams travel at almost the speed of light, controlling them requires advanced feedback systems based on novel, extremely fast electronic devices. The Oxford Physics Feedback On Nanosecond Timescales (FONT) Group has risen to the challenge, as reported in their paper published recently in Physical Review – Accelerators and Beams.

The team built a sophisticated ‘feed-forward’ system for measuring the incoming arrival times of a sequence of electron bunches moving at almost the speed of light. The system, deployed at a beamline at CERN, calculated these times relative to the desired clock time and provided a correction signal to a ‘kicker’. The kicker deflected ‘early’ bunches onto longer paths, and ‘late’ bunches onto shorter paths, through a magnetic chicane. These corrections ensured that the outgoing bunches were synchronised to the correct clock time to within 50 femtoseconds, as measured by special beam ‘phase monitors’.

The team, led by Professor Philip Burrows, Associate Director of the John Adams Institute for Accelerator Science, is based in Oxford Particle Physics. The project, with outstanding technical contributions from Colin Perry and Glenn Christian, provided the basis of the doctoral thesis of Jack Roberts, and was performed in collaboration with colleagues from CERN.

Professor Burrows said: ‘Synchronising the beam arrival at the Compact Linear Collider (CLIC), a possible successor to the Large Hadron Collider at CERN, is required at the 50-femtosecond level. We are proud to have shown that this can be done and that one of the major challenges to realising CLIC has now been overcome. Other types of electron accelerator also require beam synchronisation at this level and our technique has potential applications to future free-electron lasers.’