Investigation of a Modified Helix Loaded Superconducting Resonator for Acceleration of Heavy Ions

A modified helix loaded cavity was developed. The design is a compromise between a rather simple construction, rigidity and small size on one hand and a reasonably good acceleration of low velocity ions on the other hand. It contains a tapered helix to reduce the ratio of peak electric to effective accelerating field to ~7.1 at an optimum relative charged particle velocity of ß = 0.092. Field measurements at room temperature have been performed as well as first measurements at 4.2 K. The rigidity of the helix was increased resulting in a typical frequency noise smaller ± 175 Hzpeak at the fundamental frequency of 142 MHz. The design accelerating field is 2.25 MV/m at a peak electric field of 16 MV/m leading to an optimum accelerating potential of 538 kV. In laboratory test measurements an effective accelerating field of 2.36 MV/m was achieved. This corresponds to an accelerating potential of 566 kV at a peak electric surface field of ~17 MV/m.