AC losses measurement of the DISCORAP model dipole magnet for the SIS300 synchrotron at FAIR

Considerable attention has been paid in the last years to the development of fast-cycled superconducting magnets for future accelerators, leading to the design and construction by INFN and GSI of a 3.8-m-long prototype of a 4.5 T, 1 T/s, dipole magnet, for the SIS300 synchrotron of the FAIR facility (Darmstadt, Germany). This ramp-rate is 20-100 times higher than the one used in other superconducting synchrotrons like RHIC or LHC. Being operated at rather large dI/dt, these magnets are subjected to a wide spectrum of ac dissipation, taking place in the superconductor as well as in the metallic components of the mechanical structure, requiring the development of specialized superconducting cables and a careful consideration of the other aspects of the structural design. Between July and September 2012, the dipole magnet prototype has been subjected to a test at LASA laboratory (INFN Milan, Italy), during which it was successfully operated at current ramp rates as high as 0.7 T/s (the power supply limit). In this paper, we describe the V-I apparatus used to assess the dissipations within the magnet during the ac regime, the measurement results, and their comparison with the values expected from the design and on the basis of superconducting cable qualification results.