Multi-bunch Energy Compensation*

To obtain a luminosity of 1034cm-2sec-’ in a TeV Linear Collider (TLC), it will probably be necessary to accelerate many bunches in one filling of the RF structure. This has the effect of extracting more energy from the structure and thus enhances the overall efficiency of the accelerator. However, this leads to many problems. First, the train of bunches is subject to cumulative beam breakup transversely. This can be controlled by damping the transverse modes with slots in lY2 !he irises coupled to waveguides. In addition, the energy of the bunches must be. kept the same to high precision. For the fundamental mode, this entails adjusting the timing of the RF fill and also the bunch spacing. The higher longitudinal modes, although they do not induce instability, also may lead to bunch-to-bunch variations in energy. However, it also seems possible to damp these modes to cure this problem.’ Of course, there are also problems associated with damping a train of bunches in a damping ring.