First demonstration of the use of crab cavities on hadron beams

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Intra-bunch motion from three different cases measured with the head-tail monitor (courtesy Phys Rev AB).

Particle colliders are important engines of discovery, and collisions between both protons and leptons have shone a light on the fundamental structure of our universe for decades. These colliders operate by the acceleration, subsequent manipulation and finally collision of charged particle beams. The beam manipulation at the interaction point (IP) of the beams is crucial to create optimal collision conditions and maximise the rate of collisions over several hours and in multiple IPs around the ring. Many future particle colliders will require so-called "beam crabbing" to recover geometric luminosity loss from the non-zero crossing angle at the IP.

A first demonstration experiment of crabbing with hadron beams was successfully carried out with high energy protons. This breakthrough result is fundamental to achieve the physics goals of the high luminosity LHC (HL-LHC) and the future circular collider (FCC). Several QUASARs have made important contributions to this study which has just been published in Physical Review Accelerators and Beams in open access format.

Their measurements show an expected peak luminosity gain (related to collision rate) of 65% for HL-LHC and even greater for the FCC. Novel beam physics experiments with proton beams in CERN’s Super Proton Synchrotron (SPS) were performed to demonstrate several critical aspects for the operation of crab cavities in the future HL-LHC including transparency with a pair of cavities, a full characterization of the cavity impedance with high beam currents, controlled emittance growth from crab cavity induced rf noise. 

The major accomplishments made in this operation of a crab cavity in a hadron beam are a stepping stone toward the successful use of crab cavities for future colliders as the HL-LHC and opens the door to an era of high luminosity hadron beam physics.


Further information:

R. Calaga, et al., “First demonstration of the use of crab cavities on hadron beams”, Phys. Rev. Accel. Beams 24, 062001 (2021)