A prototype of a highly sensitive cryogenic current comparator with a HTS SQUID and HTS magnetic shield

A highly sensitive cryogenic current comparator (CCC) for the measurement of the intensity of faint beams, such as a radioisotope beam, was developed for the RIKEN RI beam factory project. This monitor is composed of a high-temperature superconducting (HTS) magnetic shield and an HTS current sensor including an HTS superconducting quantum interference device (SQUID), which are cooled by a low-vibration pulse-tube refrigerator. Both the HTS magnetic shield and the HTS current sensor based on Bi-2-Sr-2-Ca-2-Cu-3-O-x, (Bi-2223) were fabricated by dip-coating, on a 99.9% MgO ceramic substrate. Recently, a prototype of the HTS SQUID CCC system was completed and we carried out the first measurements using DC ion beams in the current range of 0.5-20 muA, which were produced by the ECR (electron cyclotron resonance) ion source in the CNS experimental hall. After the measurement was successfully carried out in the CNS, we installed the system into the beam transport line of the RIKEN Ring Cyclotron (RRC) to measure the current of the high-energy heavy-ion beam which has a bunched microstructure. In this paper, we describe the performance and the present status of the prototype of the HTS SQUID CCC system and the results of the ion beam measurement.