Geometric optimization of the 56 MHz SRF cavity and its frequency table

Abstract

It is essential to know the frequency of a Superconducting Radio Frequency (SRF) cavity at its 'just being fabricated' stage because frequency is the key parameter in constructing the cavity. In this paper, we report our work on assessing it. We can estimate the frequency change from stage to stage theoretically and/or by simulation. At the operating stage, the frequency can be calculated accurately, and, from this value, we obtain the frequencies at other stages. They are listed in a table that serves to check the processes from stage to stage. Equally important is optimizing the geometric shape of the SRF cavity so that the peak electric-field and peak magnetic-field are as low as possible. It is particularly desirable in the 56MHz SRF cavity of RHIC to maximize the frequency sensitivity of the slow tuner. After undertaking such optimization, our resultant peak electric-field is only 44.1MV/m, and the peak magnetic-field is 1049G at 2.5MV of voltage across the cavity gap. To quench superconductivity in an SRF cavity, it is reported that the limit of the peak magnetic-field is 1800G [1], and that of the peak electric-field is more than l00MV/m for a SRF cavity [2]. Our simulations employed the codes Superfish and Microwave Studio.