Development of high-power radio-frequency components for electron-beam feedback and control systems.

Ultra low-emittance electron beams are required for the next generation of electron-positron colliders (eg. CLIC) and X-ray light sources (eg. NLS). The tolerances on the beam size, orbit and stability are two to three orders of magnitude greater than at current facilities. For example, at CLIC the beams will be roughly 1 nanometre high and they must be stabilised at the sub nanometre level at the interaction point in order to achieve the high luminosity required for Higgs boson and supersymmetry physics. Similar demands must be met to achieve peak brilliance at X-ray free electron laser (XFEL) light sources. Because of the bunch structure of such accelerators a feedback system for beam orbit stabilisation must operate on the 1-100 nanosecond timescale, which is extremely challenging. The Feedback on Nanosecond Timescales (FONT) project has been supported (by PPARC and STFC) to develop low-latency feedback prototypes for this purpose. The prototypes have been tested in beamlines at SLAC and KEK and feedback latencies as low as 23ns and 132ns have been demonstrated with all-analogue, and digital, systems respectively. We now propose to extend this technology to the development of a feed-forward system for correction of longitudinal phase instabilities in the CLIC drive beam. Such instabilities present a potential 'show-stopper' for the CLIC approach of decelerating a low-energy, high-current drive beam to provide high-gradient acceleration to a high-energy, low-current main beam. Therefore, development of an appropriate correction system has been assigned a high priority in the CLIC R&D programme for the next 5 years, leading towards a technical design report in 2016. CERN is explicitly supporting the FONT group at the John Adams Institute (JAI)/ Oxford to work on this system as a key part of the UK/CERN R&D programme on CLIC. Conceptually many of the CLIC feed-forward system demands are similar to those of the FONT feedback prototypes: low latency, high bandwidth and high drive power over short timescales (hundreds of ns). However, the design parameters call for a dynamic range of +-375 urad kick to the 2.5 GeV drive beam, with 10ns bandwidth, and a pulse length of 240ns. This presents a major challenge for the drive amplifier system. The current CLIC drive beam feed-forward system outline design (subject to revision) will require around 800 amplifiers, with a total peak power of 200 MW, and an estimated system cost of around £60M. This presents a considerable opportunity for an industrial company to participate in the advanced engineering required for design for manufacture, and the resulting business. The student will work with the JAI/Oxford FONT group to develop radio frequency (RF) components for the feed-forward system. We propose to design and fabricate prototype amplifier components. Initial component design will be done in JAI/Oxford. Production design and fabrication will be done by TMD. Prototypes will be bench tested in Oxford, and shipped to CERN for installation in the CTF3 beamline for subsequent operations with the electron beam. The student will work with groups that have international profiles in this area. The JAI/Oxford group has developed RF devices for the FONT system tests at SLAC and KEK. These are world-leading low-latency beam feedback systems. TMD has world-class manufacturing capability in high-power RF devices and considerable experience with particle physics accelerator projects. The project team has a demonstrated track record in this area: JAI/Oxford and TMD collaborated between 2004 and 2008 (via a CASE studentship project) on the high-power drive amplifier for the FONT4 feedback system at KEK. The team will provide many opportunities, options and flexibility to pursue development of the hardware and general training in RF design. This is an extremely exciting and challenging project that is vital for the future development of high-current drive-beam accelerators.