An RF cavity for the NLC damping rings

Abstract

We report on the design and development of a strongly HOM damped copper RF cavity for the NLC damping rings. The cavity is based on the successful PEP-II RF cavity but incorporates many simplifications and improvements. The cavity is designed for a frequency of 714 MHz, gap voltage of 500 kV and beam current of 800 mA. We present the RF design and HOM impedance calculations done in MAFIA, the RF, thermal and stress analyses performed in ANSYS and the simplified mechanical design and assembly process. Designs for the RF window, HOM loads and tuners are described. Options for increasing the stored energy or further lowering the HOM impedance are discussed. This design could easily be scaled up or down in frequency and could be useful for other projects such as new light sources.

U.S. Linear Collider Technology Options Study

“…Adjacent cavities are separated by 3.75 wavelengths allowing pairs of cavities to be fed from a single klystron via a "magic T". It is assumed at present that the cavities are the same design as used in the main damping rings [21,22], being HOM-damped structures based on the PEP-II design. Studies of instabilities driven by modes in the cavities have yet to be carried out for the pre-damping ring, though we note that in the case of the main damping rings, only a few modes transverse and longitudinally are above the damping threshold [23], and growth rates for these modes can readily be dealt with by feedback systems.…”

The Next Linear Collider damping ring lattices

“…In the wiggler straight, the wiggler itself provides the vertical focusing. The three RF cavities [4] are located before the extraction components, so that there are no transient changes in the loading on the cavities during an injection/extraction cycle. The RF frequency is 714 MHz, so that within a bunch train, every RF bucket is filled to give a bunch separation of 1.4 ns.…”

Electromagnetic, thermal, and structural analysis of RF cavities using ANSYS

“…The solid model may be "cut" in order to create a symmetry section before or after importing into ANSYS, though it is usually faster to perform the cut in the solid modeler, as it reduces the size of the transfer file. Figure 1 shows the original solid model and the portion of the model that is imported into ANSYS for the Next Linear Collider (NLC) damping ring RF cavity design [3,4].…”