High Inductance Cryogenic Current Comparators for Beamlines

The Cryogenic Current Comparator (CCC) for beamlines is designed for the non-destructive, highly sensitive, and absolute measurement of bunched (AC) and un-bunched (DC) beam current of charged particle in the nA range using the external magnetic field of the beam. Niobium based CCCs are running at the CERN-Antiproton Decelerator (beamline diameter of 100 mm) and are tested at the CRYRING@ESR. CCCs of the xD-series (extended dimension) can support the new facility for antiproton and ion research (FAIR) at GSI (Gesellschaft fur Schwerionenforschung) in Darmstadt with a 150 mm beamline diameter. The large FAIR-Nb-CCC-xD has an inductance of 80 mu H. An effective way to increase the sensitivity is to increase the inductance of the pickup coils. The two first CCCs of the new Sm-series (smart & small) have overall inductances of 200 and 300 mu H. This work describes the individual development steps, starting with the superconducting pickup coils. For CCCs with a flux concentrating core in the pickup coil, the subsequent current noise of the CCC is determined by the cores parameter. On the basis of low-temperature LsRs-measurements on pickup coils, it is shown how the fluctuation-dissipation theorem (FDT) can be used to infer the current noise of the CCC. For the first time a white noise of 1 pA(rms)/root Hz could be achieved. A superconducting, meandering shield filters the circular magnetic field and suppresses interference fields. Through step-by-step setup and measurements, it follows how this affects CCC system parameters. Finally, it was possible to measure current impulses below 1 nA(pp) in the laboratory.