DEVELOPMENT OF BEAM CURRENT MONITOR WITH HIGH-Tc SQUID AT RIBF

A highly sensitive beam current monitor with a highcritical-temperature (high-Tc) superconducting quantum interference device (SQUID) and a high-Tc current sensor, that is, a high-Tc SQUID monitor, has been developed for use in the radioisotope beam factory (RIBF) at RIKEN. As reported in the present work, the high-Tc SQUID monitor allows us to measure the DC of high-energy heavy-ion beams nondestructively in such a way that the beams are diagnosed in real time and the beam current extracted from the cyclotron can be recorded without interrupting beam user experiments. Both the high-Tc magnetic shield and the high-Tc current sensor were fabricated by dip-coating a thin layer of Bi2-Sr2-Ca2-Cu3-Ox (2223-phase, Tc=106 K) on a 99.9% MgO ceramic substrate. Unlike other existing facilities, all the high-Tc devices are cooled by a lowvibration pulse-tube refrigerator, enabling us to downsize the system. Last year, aiming at its practical use, the highTc SQUID monitor was installed in the RIBF. Using the monitor, a 1 μA Xe beam intensity (50 MeV/u) was successfully measured with 100 nA resolution. Here we report the present status of the facility, details of the highTc SQUID monitoring system and the results of the beam measurement.