HIJ, Jena, Germany
GSI, Darmstadt, Germany
IOQ, Jena, Germany
IPHT, Jena, Germany
FSU Jena, Jena, Germany
Supracon AG, Jena, Germany
Cryogenic Current Comparators (CCC) are presently used at CERN-AD (100 mm beamline diameter) and in the FAIR project at CRYRING (150 mm beamline diameter) for non-destructive absolute measurement of beam currents below 20 ’A (current resolution 10 nA). Both sensor versions (CERN-Nb-CCC and FAIR-Nb-CCC-XD) use niobium as superconductor for the DC-transformer and magnetic shielding. The integrated flux concentrators have an inductance of below 100 ’H at 4.2 Kelvin. The new Sm-series (smart & small) is designed for a beamline diameter of 63 mm and uses lead for the superconducting shield. The first sensor (IFK-Pb-DCCC-Sm-200) has two core-based pickup coils (2x 100 µH at 4.2 K) and two SQUID units, to eliminate Barkhausen current jumps as part of the low frequency 1/f-noise. During the construction some basic experiments on noise behavior (fluctuation’dissipation theorem, white noise below 2 pA/sqrt(Hz)) and magnetic shielding (flux concentrator and shielding as LC circuit resonance , additional mu-metal shielding) were undertaken, the results of which are presented here. Finally, a current resolution of 500 pA could be achieved in the laboratory.
