Theory and 3-D simulations of an RF accelerating cavity with asymmetric power feed

The authors investigate the transverse wake potential of a side-coupled RF accelerating cavity both analytically and using a 3-D gridded code. They find that the asymmetry leads to a transverse wakefield which is not 90 degree out of phase with the accelerating potential. As a result, there is a net deflection, as well as a transverse tilt, of a micropulse whose center is in phase with the peak of the accelerating potential. The transverse tilt can be reduced to zero using a dummy compensating stub. The net deflection, however, is not affected by such a stub, and depends only on the average power flow into the cavity. The analytic model predicts values of the cavity Q and the amplitude and phase of the transverse wakefield which agree well with the 3-D simulations. Results for a 1 MV accelerating cavity are given