Superconducting rf system for the cesr luminosity upgrade : design , status , and plans *

The CESR Luminosity Upgrade Plan consists of several consecutive steps, or phases [1]. At the present time, this program is in Phase II. The next step, Phase III, would yield a luminosity of 1x1033cm-2sec-1 with 45 bunches in each beam for a total current of 1 A. This plan utilizes four superconducting single-cell cavities with an accelerating gradient of 6 MV/m, which corresponds to a peak accelerating voltage of 1.8 MV per cell. The power transferred to the beam in each cavity would be 325 kW. Some machine and RF parameters are given in Table 1. The use of only four superconducting RF (SRF) cells with more strongly damped higher-order modes (HOMs), as compared to the present twenty normal conducting (NRF) copper cells, decreases both the broad band and narrow band impedances sufficiently to allow stable operation at the high current levels. The name BB1 has been assigned to the Cornell superconducting 500 MHz single-cell cavity shape. One can find a detailed description of the cavity elsewhere [2]. Two cavities have been manufactured to date: the first, BB1-1, by Dornier, and the second, BB1-2, by ACCEL. The BB1-1 cavity and prototype RF window, cryostat, HOM loads and beam line components were subjected to a beam test in CESR in August 1994 [3]. This experience allowed us to complete the design of the SRF system, which is described in this paper.