Broad-Band, Multi-Kilowatt, Vacuum, HOM Waveguide Loads for the PEP-II RF Cavity *

For the HOM damping waveguides in the PEP-II RF cavity to work effectively as high-pass filters a broad-band, low-reflection, load is required with a VSWR less than 2:l in the frequency range 700 MHz to 2500 Mhz. .4dditional design constraints are vacuum operation, thus eliminating an RF window and a potential source of reflections, and the capability of dissipating up to 10 kW of HOM power. A compact baseline design using a lossy dielectric is proposed which fulftlls these requirements based on results from numerical simulations. We present the electrical properties of such a load, discuss its thermal properties under high power conditions, and detail a fabrication technique for brazing the lossy dielectric onto the copper walls of the HOM waveguide. Finally, simulation results of an alternative design utilizing ferrites are presented. The dedicated HOM dampers in the PEP-II RF cavity are designed to lower the impedances of the cavity HOM’s below the level at which the feedback system can damp the beam oscillations while preserving the shunt impedance of the accelerating mode. In practice, this can only be achieved if the coupling waveguides are terminated in broadband, Iowreflection loads; high reflections degrade the effectiveness of the HOM damping scheme since they can increase the Qext of the cavity HOMs. The loads will be designed to dissipate up to 10 kW of power spread out across the frequency range