GSI, Darmstadt, Germany
TEMF, TU Darmstadt, Darmstadt, Germany
IPHT, Jena, Germany
FSU Jena, Jena, Germany
IOQ, Jena, Germany
HIJ, Jena, Germany
Supracon AG, Jena, Germany
Accurate non-destructive measurement of the absolute intensity of weak ion beams (< 1 uA) in storage rings is often restricted to special beam conditions and, even then, is associated with large uncertainties and tedious calibration procedures. However, experiments with rare ions in particular depend on excellent current resolution. In order to make these beams accessible, the Cryogenic Current Comparator (CCC) monitors deviations of the DC beam current on a scale of nA and compares the signal to a calibrated reference current. At the heavy-ion storage ring CRYRING at GSI a CCC prototype for FAIR was installed and first results of the commissioning are reported here. Preceding the operation with beam, a careful design of the beamline helium cryostat was required to provide the stable cryogenic environment needed for CCC operation. Mechanical and electro-magnetic perturbations that interfere with measurement of the beam’s faint magnetic field are suppressed by the internal structure of the system and a superconducting magnetic shield, while the remaining interference can be filtered with adequate signal processing. In this way, a current resolution in the nA range was demonstrated.
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