Half wave helix loaded superconducting resonator for the Saclay heavy ion linac

The main characteristics and performance of the helix superconducting resonators designed and mounted in the new Saclay Booster Linac, the first European heavy ion superconducting accelerator, are reported. Half-wave resonators have been tested with a continuous ¹²C beam delivered by the FN tandem. The behavior is very similar to the theoretical calculations done with field distribution measurements. The accelerating field achieved is 2.15 MV/m, corresponding to an energy gain of 535 keV/charge. The complete booster, which now has 16 half-wave resonators in the first and last large cryostats, makes it possible to extend the mass range from A=12 up to at least A=80 with excellent optical and dynamical beam qualities. The important advantages of the new structures are the broadness of the transmit time factor curve, which makes it possible to accelerate low-velocity beams with good efficiency, and the simplicity of the mechanical design which only requires two helix welds