World’s first crabbing of a proton beam

Experts from across the Cockcroft Institute, working closely with colleagues at CERN, have contributed to a technology breakthrough that promises to revolutionise the world of high energy particle physics and is a crucial step along the path to the future development of the Large Hadron Collider and the further unlocking of the secrets of the universe.

The first prototype crab cavities being assembled during summer 2017 (Image: Julien Ordan/CERN)

The CI team has worked alongside experts from around the world to successfully test a new technology called ‘crab cavities’ and rotate a beam of protons for the first time. The test took place on 23 May 2018 using a beam from CERN’s Super Proton Synchrotron (SPS) accelerator and showed that bunches of protons can be tilted using these superconducting transverse radio-frequency cavities.

These cavities are a key component of the High-Luminosity Large Hadron Collider (HL-LHC), a major upgrade of the LHC.

The crab cavity technology revolutionises the world of high energy particle physics as the implementation of these cavities is critical to the delivery of the next level of energy and luminosity of the LHC, paving the way to increasing our understanding of exotic particles, such as the Higgs Boson. CI had a key role in the development and construction of this technology and in making HL-LHC a reality.

STFC’s Executive Director of Programmes Professor Grahame Blair said: “This is a fantastic result for CERN and for all the collaborators involved.  I am particularly happy that UK university teams, working with staff at STFC national laboratories and with the international community, have made such a key contribution. This demonstrates the value of our world class university-based programme in accelerator physics working alongside our detector and analysis teams in mapping out fully the structure of nature at the LHC energy scale; every bit of luminosity will count in this endeavour.”

The HL-LHC, which will be commissioned after 2025, will increase the luminosity of the LHC by a factor of five to ten. Luminosity is a crucial indicator of a collider’s performance: it gives the number of potential collisions per surface unit over a given period of time. In other words, the higher the luminosity, the higher the number of collisions and the more data the experiments can gather. This will allow researchers to observe rare processes that occur beyond the LHC’s present sensitivity level. Physicists will also be able to perform precise studies of the new particles observed at the LHC, such as the Higgs boson. The newly developed crab cavities will play an important role to increase the luminosity.

The University of Manchester was involved in the beam dynamics modelling, and understanding how to measure the crabbing. Dr Rob Appleby, from the high energy particle physics group of the University of Manchester and HL-LHC-UK spokesperson, explained: “This is a world-first result and we in HL-LHC-UK look forward to working with CERN into the future to build HL-LHC in order to significantly improve the LHC performance”

Dr Graeme Burt from Lancaster University is HL-LHC-UK project manager and UK crab leader. He added: “The importance of this ground-breaking result cannot be underestimated; I am delighted the UK team could contribute in all phases of this experiment through the HL-LHC-UK project in support of our CERN colleagues.”

Engineers at Lancaster were involved in, and in many cases led, the design of a number of the subsystems, and in all phases of testing from sub-systems to the final test.

Professor Carsten Welsch, Head of Liverpool’s Physics department which had a key role in the measurements through a member of his QUASAR Group, Dr Lee Carver, based at CERN, said: “This fantastic result will help make the LHC an even better accelerator in the future. It was made possible by close collaboration between UK institutions contributing to the High Luminosity upgrade and CERN.”

STFC contributed to the development of the cryomodule that encloses the crab cavities and keeps them cool with superfluid liquid helium. A team of engineers from STFC’s Daresbury Laboratory has been a key player in the international collaboration at every stage of developing the cryomodule from developing basic concepts, undertaking extensive engineering analysis to developing key components such as the cold magnetic shielding.

Shrikant Pattalwar is a Senior Cryogenic engineer at STFC and Crab Cavity Cryomodule UK task leader. He believes the team was a key part of this successful step: “This result reflects excellent coordination between the UK, CERN and the US teams. We are really proud to be a part of such an exciting collaboration.”

In the coming months, the cavities will be commissioned to their nominal voltage of 3.4 million volts and will undergo a series of tests to fully validate their operation for the HL-LHC era. A total of 16 such cavities will be installed in the HL-LHC – eight near the ATLAS experiment and eight near CMS.