A TUNER FOR A SUPERCONDUCTING CH-PROTOTYPE CAVITY

The superconducting CH multi-cell prototype cavity will be equipped with a frequency tuning system. 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 effects on rf-frequency and field distribution have been measured and were compared with previous calculations. The tuning system implies two stages, a slow mechanical device and a fast piezo system, all parts were manufactured already. Additionally, the mechanical resonances of the cavity have been investigated experimentally in the environment of an acoustical laboratory at room temperature and recently 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.