A Tuner for the 350 MHz Superconducting CH-Structure

The superconducting CH multi-cell prototype cavity, which has passed a very succesfull power test recently leading to an accelerating gradient of Ea = 7 MV/m, will be equipped with a frequency tuning system [1]. The rftuning during operation bases on the principle of a slight elastic deformation at both ends of the tank. This is causing a change in the gap width of the first and last accelerating cell and the accompanying variation of capacity finally results in a frequency shift. The mechanical resonances of the cavity have been investigated experimentally in the environment of an acoustical laboratory at room temperature and within the vertical cryostat at 4 K. Moreover, an active periodic cavity detuning provided by the piezo tuners was implied, while stable superconducting cavity operation was kept by a frequency control loop acting on the rf-frequency oscillator.