N.M.KROLL**, D.C.VIER (UCSD), C-K.NG (SLAC)
Electrical discharge damage has been commonly observed in the coupler cells of accelerator structures and has been attributed to field enhancement noted in simulations. In studies of coupler design simulations for both damped detuned structures and photonic band gap structures we find that the field magnitude on axis is an unreliable guide to surface field enhancement. We will report the effect of eliminating quadrupole fields in the coupler cell, of enlarging the beam iris separating the the coupler cell from the adjacent accelerator cell, and of reducing the phase advance in the cell adjacent to the coupler. It appears that one or a combination of these expedients will eliminate the problem. A new simulation procedure for matching the coupler to the accelerator structure will be described. It has greatly facilitated the many matching adjustments required to carry out this investigation.
* Work supported at SLAC under U.S.DOE contract DE-AC03-93SF00515 and at UCSD under U.S.DOE grants DE-FG03-93ER40759 and DE-FG03-93ER40793
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