RF cavity R&D at LBNL for the NLC Damping Rings,FY2000/2001

Abstract

This report contains a summary of the R&D activities at LBNL on RF cavities for the NLC damping rings during fiscal years 2000/2001. This work is a continuation of the NLC RF system R&D of the previous year [1]. These activities include the further optimization and fine tuning of the RF cavity design for both efficiency and damping of higher-order modes (HOMs). The cavity wall surface heating and stresses were reduced at the same time as the HOM damping was improved over previous designs. Final frequency tuning was performed using the high frequency electromagnetic analysis capability in ANSYS. The mechanical design and fabrication methods have been developed with the goals of lower stresses, fewer parts and simpler assembly compared to previous designs. This should result in substantial cost savings. The cavity ancillary components including the RF window, coupling box, HOM loads, and tuners have been studied in more detail. Other cavity options are discussed which might be desirable to either further lower the HOM impedance or increase the stored energy for reduced transient response. Superconducting designs and the use of external ''energy storage'' cavities are discussed. A section is included in which the calculation method is summarized and its accuracy assessed by comparisons with the laboratory measurements of the PEP-II cavity, including errors, and with the beam-sampled spectrum.