Development of a new B-Mapping System for SRF Cavity Vertical Tests

Magnetic flux trapped in the Niobium bulk material of superconducting radio frequency (SRF) cavities degrades their quality factor and the accelerating gradient. The sensitivity of the surface resistance to trapped magnetic flux is mainly determined by the pre-treatment, the cavity geometry and the Niobium grain size and orientation. To potentially improve the flux expulsion characteristics and hence the efficiency of future accelerator facilities further studies of the trapping behavior are essential. For this purpose a so-called "B-Mapping System" to monitor the magnetic flux along the outer cavity surface of SRF 1.3 GHz TESLA-Type single-cell cavities is currently under development at DESY. Contrary to former approaches, this system digitizes the sensor signals already inside of the cryostat to extensively reduce the number of required cable feedthroughs