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 für Schwerionenforschung) in Darmstadt with a 150 mm beamline diameter. The large FAIR-Nb-CCC-xD has an inductance of 80 µH. 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 µH. 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 L
_s
R
_s
-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
/√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.