Highly Sensitive Measurements of the Dark Current of Superconducting Cavities for TESLA Using a SQUID Based Cryogenic Current Comparator

A newly high performance SQUID based measurement system for detecting dark currents, generated by superconducting cavities for the upcoming TESLA project (XFEL) at DESY Hamburg, is proposed. It makes use of the Cryogenic Current Comparator principle and senses dark currents in the pA range with a measurement bandwidth of up to 70 kHz.