Rf Control Requirements for the Cebaf Energy Upgrade Cavities*

The 6 GeV CEBAF accelerator at Jefferson Lab is arranged in a five-pass racetrack configuration, with two superconducting radio frequency (SRF) linacs joined by independent magnet transport arcs. It is planned to increase the accelerator energy to eventually support 12 GeV operations. To achieve this, a new 7-cell superconducting cavity is being built to operate at an average accelerating gradient of 12.5 MV/m with an external Q of 2.2 x 10. The present RF system, composed of an analog control loop driving a 5 kW klystron, will not easily support the narrower bandwidth cavities at the higher gradients. A new RF control system that may incorporate digital feedback, driving an 8 kW klystron is being proposed. In designing a system it is important to understand the control limitations imposed by the cavity, such as microphonics, Lorentz force detuning and turn-on transients. This paper discusses these limitations and the resulting design constraints for new RF controls.