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 trapezoidal-shaped loading elements and cylindrical outer conductor has attractive properties such as low and well-balanced 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.
Highlights
The early application of deflecting/crabbing cavities was in rf deflecting systems designed to separate high energy particle beams [1]
In the 0-mode the transverse electric field is canceled between the bars (Fig. 5), there is a longitudinal component remaining near the ends of the cavity so this mode would operate as an accelerating mode
The rf-dipole design with trapezoidal-shaped bars geometry with the cylindrical outer conductor has been shown to have significantly improved properties compared to other geometries
Summary
The early application of deflecting/crabbing cavities was in rf deflecting systems designed to separate high energy particle beams [1]. According to the Panofsky-Wenzel theorem [18,19], under the assumption that the particle traverses the cavity in a straight line at constant velocity, the transverse momentum imparted on the particle is related to the transverse gradient of the longitudinal voltage gain It can be generated by a TM-type deflecting/crabbing cavity or by a cavity operating in TEM-type mode. Cavity designs with pure TE-type operating mode do not generate a transverse momentum as the net effect from the electric field is canceled by the magnetic field component when integrated along the beam line. The magnetic field is zero on the midplane along the beam line and maximum at the top and bottom planes
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