CERN Accelerating science

  Development and Testing of Crab Cavities for High Intensity Colliders
  by Peter McIntosh (STFC)


Fig 1: CLIC ‘Undamped’ Crab Cavity Fabricated.Image credit: Shakespeare Engineering Ltd (UK)

Fig 2: LHC 4-rod Crab Cavity Fabricated. Image credit: Niowave Inc (USA)

The development of innovative crab cavity solutions for high intensity particle colliders is part of both the FP7 EUCARD and HiLumi framework programmes.

The activity has been led by Lancaster University and STFC in the UK, in direct collaboration with CERN. For LHC, a compact Superconducting RF (SRF) solution at 400 MHz, capable of fitting into the confined space available at the LHC interaction regions is proposed. A compact TEM type deflecting structure has been manufactured at Niowave from bulk Niobium, which has been tested in SM18 at CERN, reaching a surface magnetic field of 33 mT (limited by a serious LHe leak). This represents the world's first high field test of a compact SRF deflector and the cavity is currently undergoing additional BCP processing in order to reach the LHC design gradient of 6 MV/m (Bpk~70 mT).

For CLIC, a high gradient 12 GHz, normal-conducting travelling-wave structure, with a high group-velocity to minimise the effects of beam loading, has been developed. Two ‘undamped’ structures have been fabricated, one in the UK by Shakespeare Engineering Ltd and the other at CERN. Systematic high gradient tests are planned at SLAC and CERN, to study breakdown differences between deflecting and accelerating structures. A third ‘damped’ cavity is currently being developed to allow verification of the operational performance. A high phase stability control system, which will keep the phase from a klystron stable over long distances, is also in development to meet the stringent CLIC phase stability tolerances.