Radiation Heat Loads to Superconducting Quadrupoles for BigRIPS In-Flight Separator at RIKEN

The BigRIPS fragment separator in the RIKEN RIBF project is characterized by fourteen superconducting triplet quadrupoles (STQ's) with large apertures and high-field gradients. While the five STQ's on the first stage of the BigRIPS are cooled by a liquid helium cryogenic plant, the nine STQ's on the second stage are cooled by small cryocoolers on their cryostat. This first stage serves to produce and separate RI beams, so that the first two STQs are exposed to the high radiation from the production target and beam dumps, which causes radiation heat loads as well as radiation damages. Measurements of the radiation heat loads to the cryostats of the first two STQs during commissioning operations of the RIBF facility are reported.