Anticrab cavities for the removal of spurious vertical bunch rotations caused by crab cavities

Many particle accelerators are proposing the use of crab cavities to correct for accelerator crossing angles or for the production of short bunches in light sources. These cavities produce a rotation to the bunch in a well-defined polarization plane. If the plane of the rotation does not align with the horizontal axis of the accelerator, the bunch will receive a small amount of spurious vertical bunch rotation. For accelerators with small vertical beam sizes and large beam-beam effects, this can cause significant unwanted effects. In this paper we propose the use of a 2nd smaller crab cavity in the vertical plane in order to cancel this effect and investigate its use in numerical simulations.

Figure 1

The ILC crab-cavity midcell shape.

Figure 2

The ILC BDS lattice showing the beta functions.

Figure 3

The horizontal offset against longitudinal position for the macroparticles in a bunch at the IP of the ILC.

Figure 4

The vertical offset against longitudinal position for the macroparticles in a bunch at the IP of the ILC where the crab cavity has a 10 mrad roll misalignment.

Figure 5

Luminosity reduction factor for various roll misalignments of the ILC crab cavities comparing simulations and analytic calculations.

Figure 6

Luminosity reduction factor for various roll misalignments of the ILC crab cavities as a function of bunch charge.

Figure 7

The vertical offset against longitudinal position for the macroparticles in a bunch at the IP of the ILC where the crab cavity has a 10 mrad roll misalignment and there is an anticrab cavity correction.

Figure 8

Luminosity reduction factor as a function of the amplitude error on one anticrab cavity for a 10 mrad roll misalignment of the ILC crab cavity.

Figure 9

Luminosity reduction factor as a function of the phase error on one anticrab cavity for various roll misalignments of the ILC crab cavity.