Superconducting twin quarter wave resonator for acceleration of low velocity heavy ions

We have designed and fabricated a superconducting twin quarter wave resonator (Twin-QWR) made of niobium and copper for the acceleration of low velocity heavy ions. The resonator has two inner conductors and three acceleration gaps, which give a resonant frequency of 129.8 MHz and an optimum beam velocity of 6% of the light velocity. Each inner conductor resonates like in a coaxial quarter-wave line resonator. The resonator was designed to have a separable structure so that we could treat the inner conductor's part fully made of high purity niobium apart from the outer conductor made of niobium and copper. We obtained an acceleration field gradient of 5.8 MV/m at an RF power input of 4 W.