RF system considerations for a large hadron collider

Abstract

The radio‐frequency (rf) system of a large hadron collider is require to operate in three different modes. It must capture and accumulate in stationary buckets (closed trajectories in longitudinal phase space) successive groups of bunches from its injector; accelerate these bunches in moving buckets up to the design energy; and finally store them, for several hours, while maintaining a minimum ratio of bunch‐to‐bucket area. In the storage mode it provides the nominal energy gain per turn required to make up for synchrotron radiation losses and for the power loss due to voltages induced in the impedances presented to the beam by the vacuum chamber and accelerating structures. In what follows then, we shall discuss how we arrive at a particular choice of voltage and frequency; the type of accelerating structure that would be suitable for obtaining the required voltage and resonant impedance; static beam loading including a simplified beam stability criterion involving the beam current and total rf system shunt impedance; the basic principle of rf phase and frequency control loops; and the effect of rf noise and its interaction with these loops. Finally, we shall consider the need for and design of rf systems to damp independently coherent oscillations of individual bunches or groups of bunches. (AIP)