Design evolution and properties of superconducting parallel-bar rf-dipole deflecting and crabbing cavities

Abstract

Deflecting/crabbing cavities serve a variety of purposes in different accelerator applications, primarily in separating a single beam into multiple beams and in rotating bunches for head-on collisions at the interaction point in particle colliders. Deflecting/crabbing cavities are also used for transverse and longitudinal emittance exchange in beams, x-ray pulse compression, and for beam diagnostics. Compact superconducting deflecting/crabbing cavities are under development due to strict dimensional constraints and requirements for higher field gradients with low surface losses. The TEM-like superconducting parallel-bar cavity supports low operating frequencies, thus making the design favorable for many of the deflecting/crabbing cavity applications. The design of the parallel-bar cavity based on cylindrical straight loading elements and rectangular outer conductors has evolved and been adapted to improve the design properties by modifying the design geometry. The improved design with trapezoidalshaped loading elements and cylindrical outer conductor has attractive properties such as low and wellbalanced peak surface fields and high transverse shunt impedance. Additionally, the wide separation of modes in the higher-order mode spectrum and the absence of lower-order mode are advantageous in high current applications. The evolution of the parallel-bar geometry into an rf-dipole geometry is presented with a detailed analysis of the properties for each design.

Effect of crab cavity high order modes on the coupled-bunch stability of High-Luminosity Large Hadron Collider

“…High-Luminosity LHC employs two sets of crab cavities, each consisting of four cavities per IP and per beam: one set with the crossing in the horizontal and the other -in the vertical plane. Currently, there are two different designs of the crab cavities being considered: Double Quarter Wave (DQW) [18] and RF Dipole (RFD) [19][20][21][22]. Both designs feature a large number of high order modes, some of which might be dangerous for the coupled-bunch stability.…”

Design studies of a compact superconducting rf crab cavity for future colliders using Nb/Cu technology

“…This requirement follows from the LHC specifications of a rf frequency equal to 400 MHz while the distance between the two beam pipes at the foreseen cavity locations is about 194 mm [3]. Three designs have been evaluated, fabricated, and rf tested so far: (i) The double quarter wave crab cavity (DQWCC) developed at BNL in Upton, New York, USA [4,5], which will be used for the above mentioned proof-of-principle test [6], (ii) the rf dipole crab cavity (RFDCC) developed in collaboration between the Old Dominion University (ODU) in Norfolk, Virginia, USA and SLAC National Laboratory in Menlo Park, California, USA [7], and (iii) the four-rod UK crab cavity (4RCC) developed at the Lancaster University in Bailrigg, Lancaster, UK in collaboration with the Cockcroft Institute in Daresbury, Warrington, UK [8].…”

Design and vertical tests of double-quarter wave cavity prototypes for the high-luminosity LHC crab cavity system

“…The crabbing system of HL-LHC will follow the local scheme [1]. The IP1 will be equipped with a set of Double-Quarter Wave (DQW) cavities [2] while IP5 will have a set of RF Dipole (RFD) cavities [3]. The four-rod crab cavity [4] was also considered for the HL-LHC crabbing system and then downselected in favor of the DQW and RFD cavities.…”