SRF CAVITY TUNING FOR LOW BEAM LOADING

The design of 5-cell elliptical 650 MHz β=0.92 cavities to accelerate H- beam of 1 mA average current in the range 467-3000 MeV for the Project X Linac is currently under development at Fermilab [1]. The low beam current enables cavities to operate with high loaded Q’s and low bandwidth, making them very sensitive to microphonics. Mechanical vibrations and the Lorentz force can drive cavities off resonance during operation; therefore the proper design of the tuning system is very important part of cavity mechanical design. In this paper we review the design, performance, operation, reliability and cost of fast and slow tuners for 1.3 GHz elliptical cavities. We also present a design of the slow and fast tuners for 650 MHz β=0.9 cavities based on this experience. The helium vessel (HV) in the new design is equipped with the tuners located at the end of the cavity instead of the initially proposed blade tuner located in the middle. We will present the results of ANSYS analyses of mechanical properties of tuners.