INTERACTION OF THE RF SYSTEM OF STORAGE-RINGS AND LINACS WITH LONGITUDINAL BUNCH OSCILLATIONS

The RF amplifier feeding a synchrotron, a storage ring or a linac is t he source not only of the beam energy, but also of the energy of misma tch oscillations, which lead to emittance growth if they are not dampe d. The steering mechanism for the energy flow is a first of all partic le dynamics and resistivity of the beam environment. Also the properti es of the amplifier play a role; the Robinson criterion is an example. Longitudinal mismatch can be excited as well by cavity as by amplifie r properties. The mechanism can be very easily demonstrated and unders tood in case of a storage ring with a one-gap RF cavity. In case of a linac of finite length, the effect is evaluated statistically. Excitat ion of mismatch occurs already below the << Robinson threshold >>. At the Robinson threshold it becomes catastrophic: the beam vibrates. We discuss measures to suppress the growth of mismatch.