A Highly Efficient Interdigital-H-Type Resonator for Molecular Ions

For accelerating molecule ions with low charge to mass ratio highly efficient resonators are needed to keep the accelerator length short and to decrease power consumption. Therefore we used a modified interdigital-H-type structure (TE111 excitation) to build a high power prototype for CO+ molecules. We measured a surprisingly high bare shuntimpedance of 700 M¿/m at 108.5 MHz. By using a proper design of drifttubes and stabilizing rods to fix the support stems, we obtained a nearly constant axial field distribution. The resonator will be used for postacceleration of CO+ molecules - which are preaccelerated to 153 keV/N by a CN Van de Graaff - up to 224 keV/N requiring less than 15 kW RF power, corresoonding to a total cavity voltage of 3 MV and a resonator length of about 1 m.