S-band HOM-damper calculations and experiments

Damper cells for higher order modes are necessary for the S-band linear collider to suppress higher order dipole modes, which are harmful to the beam. It is foreseen to employ two single cell damper stations in the whole 6m-structure. One is posed at cell 25 and the other at cell 106. In order to investigate the effect of a single damper cell within a stack of undamped cells, a 12-cell constant impedance structure loaded by a single wall slotted damper cell was built and analyzed experimentally, numerically and analytically. The goal of the investigations was to optimize the damping effect for the first dipole passband, which contains the (most dangerous) synchronous 11/12 π-mode. The first problem is to find the appropriate single damper cell Q-value, which is needed for a certain cell-to-cell coupling to maximize the energy flow into the damper cell. The second problem is to find the optimum tuning position in order to achieve the best over all damping effect for the first dipole passband without disturbing the accelerating mode. Several wall slotted damper cells have been built and examined