Superconducting Magnet System for J-PARC Neutrino Beam Line

A helium cryogenic system has been constructed to circulate 300 g/s of Supercritical Helium (SHe) at 4.5 K through a series of superconducting magnets for a neutrino beam line at J-PARC. The conceptual cryogenic system design, considering the cooling characteristics of the magnets, was defined in 2005. The engineering design was subsequently carried out by Taiyo Nippon Sanso Corp. The main elements are a screw compressor with a capacity of 160 g/s at 1.4 MPa, a refrigerator with a capacity of 1.5 kW at 4.5 K and a centrifugal SHe pump with a flow rate of 300 g/s. After system integration in 2008, performance tests were conducted. In a preliminary cooling test to confirm the cryogenic capacity, the cryogenic system successfully performed to the required specifications by circulating a supercritical helium flow of 300 g/s at 0.4 MPa and 4.5 K through a bypass line with a simulated heat load of 520 W and simulated pressure drop of 0.85 MPa. Following this, a full system test with the magnets was carried out. The magnets were pre-cooled from the ambient temperature for eight days and were kept below 4.8 K by circulating pumped SHe. The measured heat leakage at the magnets during these tests, including SHe transfer lines, was 210 W. Since the maximum beam loss predicted is 150 W, the cooling capacity of the cryogenic system is large enough to manage beam operations expected in the future.