Determination Of Low Level Rf Control Requirements For Superconducting Cavities From Microphonics Measurements

In lightly beam loaded superconducting accelerators the rf power requirements are dictated by the maximum amount of microphonics that the system must be able to control and by the energy content of the cavity. In previous machines, such as heavy-ion boosters, the energy content of the cavities was relatively small and one could afford to specify a large control window and still use low power ((almost equal to)100 W) rf sources. In newer accelerators that are being contemplated--such as the CEBAF 12 GeV upgrade or RIA--the energy content of the cavity is quite large requiring rf sources in excess of 10 kW. Conservatism in the control window specification would be quite costly; on the other hand loss of lock could have adverse effect on machine availability or beam property or even, in some cases, result in activation. We present a model to estimate the requirements to be placed on the rf control system based on the properties of the cavities, the frequency tuning system, and the characteristics of the accelerator.