BEAM COUPLING IMPEDANCES OF FAST TRANSMISSION-LINE KICKERS

Fast transmission-line kickers contain no ferrite and consist of two long metallic parallel plates supported by insulators inside a beam pipe. A beam is deflected by both the electric and magnetic fields of a TEM wave created by a pulse propagating along the strips in the direction opposite to the beam. Computations of the beam coupling impedances for such structures are difficult because of their length. In the paper, the beam coupling impedances of transmission-line kickers are calculated by combining analytical and numerical methods: the wake potentials computed in short models are extended analytically to obtain the wakes for the long kickers, and then the corresponding beam impedances are derived. At very low frequencies the results are compared with simple analytical expressions for the coupling impedances of striplines in beam position monitors. 1 TRANSMISSION-LINE KICKERS In the planned Advanced Hydrotest Facility (AHF) [1], the 20-ns beam bunches will be extracted from the 50GeV main proton synchrotron and then will be transported to a target by an elaborated transport system. The beam transport system splits the beam bunches into equal parts in its splitting sections so that up to 12 synchronous beam pulses can be delivered to the target for the multi-axis proton radiography. The fast beam extraction from the synchrotron will be provided by the transmission-line kickers. The traveling-wave ferrite-free kickers consist of two long metallic parallel plates supported by ceramic insulators inside a beam pipe. The metallic plates (strips) together with the vacuum chamber walls form two 50-Ω transmission lines, Fig. 1, and have matching terminations at their ends. The beam bunches are deflected by the combined action of the electric and magnetic fields of a TEM wave created by a voltage pulse propagating along the strips in the direction opposite to the beam.