Coherent-Instability-Induced Radiation

Abstract

We explore here the possibility of using the coherent instability in a storage ring as the source of a coherent light. A coherent instability is always associated with a loss of beam revolution energy. If the cause of the instability is an evanescent impedance, for example, the RF cavity modes below the beam pipe cutoff, then the energy lost by the beam is deposited into the impedance source. On the other hand, if the instability is caused by radiation impedance [1], then the energy lost by the beam is turned into radiation that propagates around the storage ring in synchrony with the coherent beam oscillation. The radiation mode discovered by the authors of ref.[1] has a nonvanishing longitudinal component of the electric field. Hence, the radiation inevitably transfers energy back to the particle beam. If this feedback mechanism causes the amplitude of the beam coherent motion to grow, we have a coherent instability. The amplitude of the induced field will grow with the same growth rate.