After an introduction on the design of the Grenoble 43 T Hybrid Magnet based on a large bore Nb-Ti superconducting outer coil of 1100 mm internal diameter and 2 sets of copper alloys resistive inserts, we will focus on the first 3 years of operation of its cryogenic system.

The cryoplant is constituted of a stand-alone liquid helium liquefier with an adjustable production capacity from 70 to 150 litres/hour, an helium pumping system of 5000 m3/h, a recovery system with balloon, compressors and high pressure tanks, a cryogenic satellite to produce the superfluid pressurised liquid helium static bath at 1,8 K with a cooling power greater than 60 W, to allow the superconducting coil to be operated at this temperature.

The cryostat containing the vessel with the superconducting coil and 1400 litres of liquid helium is equipped with two sets of thermal screens actively cooled to 40 K and 90 K by a circulation of gaseous helium.

The entire process is controlled via a PLC and a human-machine interface with home-made programs specifically designed and developed for this application.

The Hybrid magnet is operated twice a year during several weeks : once during spring and once during autumn. Between these periods, the 24 tons cold mass including the superconducting coil is partially warmed-up and maintained at 95 K with the help of a liquid nitrogen circulation prior being re-cooled down to 1.8 K and maintained at this temperature during all the operational phases.

The whole cryogenic process and the main problems/issues encountered during these 3 years of operation will be described in detail with an emphasis on lessons learned to benefit to similar further projects.

Keywords
1.8 K|Hybrid Magnet|Operation|Cryogenics