R3B-Glad Magnet R&D Tests Program: Thermosiphon Loop With Horizontal Section, Superconducting Cable Joints at 3600 A, and Reduced Scale “Coil in its Casing” Mock-Up

The R3B-Glad magnet is part of a large acceptance spectrometer devoted to the physics of exotic nuclei, under construction at CEA Saclay (France) for the future FAIR facility at GSI (Darmstadt, Germany). The R3B-Glad project is in its final phase where the magnet cold mass is achieved and will be tested at 4.6 K and nominal current in the fall of 2011. We present the results of the R&D tests programs that were implemented to answer some issues raised after the technical design review. First, this superconducting dipole will be cooled down by indirect cooling, and its 22 tons cold mass maintained at 4.6 K by means of a two-phase helium thermosiphon loop. An experimental model set-up has been specifically built to demonstrate the cooling efficiency despite the presence of large quasi-horizontal sections in the circuit. Then the superconducting Rutherford cable joints, required between the 26 coil double pancakes, were designed and tested to minimize their electrical resistance. Finally a reduced scale mock-up of a coil in its casing, with a general design similar to the final magnet, was tested at low temperature to validate the indirect cooling and the mechanical blocking system of the coil in its casing by differential thermal shrinkage. This test was performed at a higher current (8800 A) than the nominal one (3600 A) to reach the same value of temperature margin before quenching, together with similar high level of magnetic forces on the coil (100 to 200 t/m in final magnet).