Beam operation with crab cavities at KEKB

Nuclear and Particle Physics Proceedings, 2016

The numerous parasitic encounters near interaction points of some particle colliders can be mitigated by introducing a crossing angle between beams. However, the crossing angle lowers the luminosity due to reduced geometric overlap of the bunches. Crab cavities allow restoring head-on collisions at the interaction point, thus increasing the geometric luminosity. Crab cavities also offer a mechanism for luminosity leveling. KEKB was the first facility to implement the crab crossing technique in 2007, for the interaction of electron and positron beams. The High Luminosity Large Hadron Collider (HL-LHC) project envisages the use of crab cavities for increasing and leveling the luminosity of proton-proton collisions in LHC. And crab cavities have been proposed and studied for future colliders like CLIC, ILC and eRHIC. This paper will review the past, present and future of crab cavities for particle colliders.

2008

2008

Physical review accelerators and beams, 2021

R. Calaga , A. Alekou, F. Antoniou, R. B. Appleby, L. Arnaudon, K. Artoos, G. Arduini, V. Baglin, S. Barriere, H. Bartosik, P. Baudrenghien, I. Ben-Zvi, T. Bohl, A. Boucherie, O. S. Brüning, K. Brodzinski, A. Butterworth, G. Burt, O. Capatina, S. Calvo, T. Capelli, M. Carlà, F. Carra, L. R. Carver, A. Castilla-Loeza, E. Daly, L. Dassa, J. Delayen, S. U. De Silva, A. Dexter, M. Garlasche, F. Gerigk, L. Giordanino, D. Glenat, M. Guinchard, A. Harrison, E. Jensen, C. Julie, T. Jones, F. Killing, A. Krawczyk, T. Levens, R. Leuxe, B. Lindstrom, Z. Li, A. MacEwen, A. Macpherson, P. Menendez, T. Mikkola, P. Minginette, J. Mitchell, E. Montesinos, G. Papotti, H. Park, C. Pasquino, S. Pattalwar, E. C. Pleite, T. Powers, B. Prochal, A. Ratti, L. Rossi, V. Rude, M. Therasse, R. Tomás, N. Stapley, I. Santillana, N. Shipman, J. Simonin, M. Sosin, J. Swieszek, N. Templeton, G. Vandoni, S. Verdú-Andrés, M. Wartak, C. Welsch, D. Wollman, Q. Wu, B. Xiao, E. Yamakawa, C. Zanoni, F. Zimmermann, and A....

2010

With lower betas at collision points or longer bunches, luminosity loss due to the crossing angle becomes important. Crab cavities could minimize the loss. The scenarios for a crab crossing implementation in the LHC, the expected performance gain, hardware implications, R&D plan is presented. Some aspects related to machine protection, collimation, aperture constraints, impedance, n oise effects to ensure safe beam operation with crab cavities are also addressed.

2010

Key conclusions have been stated by S. Myers (Director of Accelerator and Technology, CERN) following the advisory board recommendations along with future R&D objectives for the LHC crab cavity program. 5. High reliability of the crab cavities is essential; the trip rate should be low enough not to perturb LHC beam operation. 6. Validation cavity tests in the LHC itself are not deemed essential. It is considered plausible to install a new system in the LHC without having tested a prototype in the LHC beforehand. As in all new colliders, this has been done with many other components. 7. Demonstration experiments should focus on the differences between electrons and protons (e.g.effect of crab-cavity noise with beam-beam tune spread; impedance; beam loading) and on reliability & machine protection which are critical for the LHC. 8. A beam test with a KEKB crab cavity in another proton machine is considered useful, meaningful and sufficient (for deciding on a full crab-cavity implementation in LHC) if it addresses the differences between protons and electrons. 9. Possible modifications of LHC Interaction Region 4 during the 2013/14 shutdown should be studied to evaluate the feasibility of installing and testing crab-cavity prototypes, and of accommodating a possible global crab-cavity scheme. 10. The timing of the crab-cavity implementation should be matched to the short and long-term goals and to the overall CERN schedule, and be in phase with the experiment upgrades. 11. The crab-cavity infrastructure should be included in all other LHC upgrades scenarios. 12. Crab cavities can increase the LHC luminosity without an accompanying increase in beam intensity, thereby avoiding negative side effects associated with high intensity and high stored beam energy. This opinion has been endorsed by the general-purpose highluminosity experiments. A working group has been established within CERN to study the feasibility of the KEK-B crab cavities in the SPS to test possible differences between electrons and protons in the presence of crab cavities. The working group is led by Elias Metral and has a mandate to conclude on the feasibility study by the end of 2009. The working group activities are documented at the following hyperlink: http://emetral.web.cern.ch/emetral/CCinS/CCinS.htm The members of the working group constitute: Rama Calaga (Crab cavity expert and possible measurements)-BNL&USLARP Nicolas Delruelle (Cryogenics)-TE/CRG Nicolas Gilbert (Space and integration)-EN/MEF Elias Metral (Chairman, beam dynamics issues and SPS availability)-BE/ABP Joachim Tuckmantel (Crab cavity expert and RF)-BE/RF Frank Zimmermann (Crab cavity expert, measurements and linkman with KEK)-BE/ABP Olivier Brunner (Klystrons and superconducting cavities)-BE/RF Giovanna Vandoni (Vacuum)-TE/VSC Jorg Wenninger (Machine protection)-BE/OP The summaries prepared by the session conveners and additional material from the discussions during the workshop are presented in this document. The meeting minutes drafted by F. Zimmermann were substituted for summaries not provided by the conveners.

2008

Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favour a 3.9 GHz superconducting, multi-cell cavity as the solution for ILC, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are fundamental issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.

TU5PFP040, …

The planned luminosity upgrade to LHC is likely to necessitate a large crossing angle and a local crab crossing scheme. For this scheme crab cavities align bunches prior to collision. The scheme requires at least four such cavities, a pair on each beam line either side of the ...

… -Report-2006-058, 2006

In order to achieve acceptable luminosity for ILC crossing angles greater than ~2 mrad, RF deflection cavities must be used to rotate electron and position bunches leading up to the IP. A bunch that passes through a deflection cavity at a phase where the deflection averages to zero, receives a crab kick leading to a finite rotation at the IP. For a beam energy of 500 GeV and a crossing angle of 20 mrad the required crab kick is about 11.4 MV at 1.3 GHz and 3.8 MV at 3.9 GHz. Cavities are needed on both beams and are likely to be positioned about 12 m before the IP. Any RF phase error between the bunch and the cavity leads to a deflection of the bunch in addition to a rotation of the bunch. Any differential phase error between the cavities leads to differing deflections and consequential loss in luminosity. An updated analysis of system requirements and phase tolerances with respect to original calculations [1] is given. Issues on cavity and frequency choice are discussed.

The present approach to a CESR B-factory is to divide the desired beam current of 1-2 amps into a large number of low current bunches, which helps reduce detector backgrounds. To fit 230 bunches into the CESR size ring, they need to be very closely spaced, eliminating room for any conventional separators. Instead, a small (12 mr) crossing angle is considered, which may cause harmful coupling between synchrotron and betatron motion [1]. By rotating the bunches before collision ("crabbing") so they collide head-on, and then rotating them back, so they pass through the arcs normally, this dangerous coupling can be eliminated [2]. We show that the needed transverse kick of ~ 2 MV can be achieved with one single cell superconducting cavity, operating in the TM110 mode at 500 MHz, while keeping the surface electric field below 25 MV/m to avoid excessive field emission. The cell design allows all modes higher in frequency than the crab mode to propagate out the beam pipe and be damped outside the cryostat with ferrite beam pipe absorbers. 1.5 GHz niobium cavities have been tested to study the multipacting behavior of the TM110 mode.