Support Structure of Cold-Mass for Superconducting Ring Cyclotron and Electromagnetic Force Measurements With Strain Gauges

The superconducting ring cyclotron (SRC), which is the last-stage accelerator of the RIKEN RI-beam factory, was commissioned in December 2006, and it has since been operated for approximately five months each year. The SRC comprises six superconducting sector magnets, and the maximum magnetic field strength in the beam orbit region and the stored energy are 3.8 T and 240 MJ, respectively. The total weight is 8300 t. The cold-mass in each sector magnet consists of upper and lower main coils connected to each other at liquid helium temperature, and it weighs 24 t. The cold-mass is supported by eight titanium-alloy rods each in the vertical and azimuth directions, and with a stainless steel multifolded pipe in the radial direction to resist large electromagnetic forces. In order to measure the stress and movement in the cold-mass, a total of 208 strain gauges were attached on the main coil vessel, supports, etc., during construction. The strains generated during the excitation of the magnets were almost the same as the calculated values. Furthermore, there were negligible changes in the strains at all positions during the excitation measured in 2006 and 2013. These results verify the design effectiveness of the cold-mass support structure.