JAI science: XBox at CERN

Third year John Adams PhD student Jan Paszkiewicz has spent the last two years at CERN, working on vital RF technology for future accelerators using high gradient X-band test stands. Here Jan explains how these test stands work and why they're so important:

The high gradient X-band test stands at CERN, XBox-1, 2 and 3, comprise a state-of-the-art experimental facility for research and development for the Compact Linear Collider (CLIC) project, a proposed electron-positron collider to expand the frontiers of particle physics. CLIC will be an 11 km long machine with a centre-of-mass energy of 380 GeV, upgradeable to 3 TeV at a final length of 50 km. Beyond CLIC, the XBoxes also aid in the development of high-gradient technology in other applications such as X-ray Free-Electron Lasers (XFELs) and medical linacs and the design of high-efficiency and high frequency klystrons.

In CLIC’s later stages of implementation, a very high accelerating gradient of 100 MV/m will have to be maintained within its normal-conducting RF accelerating structures – an unprecedented value for any operational machine. Achieving such gradients presents a number of challenges, including generating sufficient RF power (up to 55 MW over a 200 ns long pulse) and keeping the incidences of electrical breakdowns on the copper surface of the structures to an acceptably low rate.

The XBoxes allow the testing of prototype accelerating structures at and beyond their nominal power levels, facilitating the comparison of different designs and manufacturing techniques. The facility is also equipped with diagnostic equipment such as fast radiation detectors and an electron spectrometer, which aid in the study of the physics of vacuum breakdowns.