In September the Superconducting Magnet Team at INFN-LASA completed the assembly and test of the so called “Round Coil Superferric Magnet” (RCSM) corrector, a very unconventional concept of magnet that allows to create the desired multipole field through a three dimensional shaping of the iron, which are excited by simple round coils. The RCSM realized at LASA is particularly innovative for the use of a coil in MgB2 (Magnesium di-Boride based superconductor). MgB2 superconductor, which is prone to degradation if it is wound with relatively low curvature radius, has demonstrated now to be a practicable option in accelerator magnets with this kind of configuration.
The RCSM had been considered a possible option for the HL-LHC high order corrector magnets, whose design and construction was assumed by INFN-LASA. However computations showed that, for the necessity to increase efficiency in terms of longitudinal space available for corrector-package, the classical superferric option with Nb-Ti and standard two dimensional iron shaping was preferred; nonetheless, the MgB2 RCSM prototype magnet has remained in the development line to explore the manufacturing aspects of this design, and to have a MgB2 magnets available for high energy accelerators, a prima for this technology.
Last year a single coil, wound with MgB2 conductor produced by Columbus Superconductors (Genova), was tested in LASA without the iron yoke, and the news was reported in Accelerator News 24 (link: https://acceleratingnews.web.cern.ch/article/new-step-towards-successful-mgb2-superconducting-coils). Now an entire module of the magnet, composed by poles, yoke a single round coil, has been completed, and the test demonstrated the feasibility of this kind of technology. The magnet, cooled at 4.2 K with liquid helium, reached without any training quench the design current (“ultimate current”, 161 A) and demonstrated to be able to operate stable for one hour at the ultimate current. The coil was then energized to larger currents to investigate the limiting current, which resulted 236 A, corresponding to the 78% of the intersection of the load line with the critical current for virgin, not-degraded, conductor (the theoretical limit, in practice never reached in real magnet). It is notable that this current limit has been reached without intermediate quench (no training).
