New Design for the SIS100/300 Magnet Cooling

Two superconducting synchrotrons, SIS100 and SIS300, are planned for the new International Accelerator Facility of Antiprotons and Heavy Ions (FAIR) at GSI, Darmstadt. These accelerator rings, operating at liquid helium temperatures, are placed in one tunnel of 1100 m length. The SIS100 structural superferric dipoles and quadrupoles are based on the Nuclotron-type hollow NbTi composite multi wire cable and cooled in parallel with two-phase helium flows. The peak operating mode for the SIS100 dipoles corresponds to B_max=2 T, dB/dt=4 T/s, f=1 Hz. Fast-ramped dipoles ( dB/dtap1 T/s, fap0.05 Hz) with a field strength of 4 T and above are required for the SIS300 ring. A 4.5 T, costhetas-style, curved magnet with a coil made of a high current hollow cable cooled with two-phase helium flow is proposed for SIS300. The necessary modifications of the magnet cooling scheme are presented and discussed. General optimization of the SIS100/300 cryogenic system namely cooling with three refrigerators, the number of parallel channels, the length of helium transfer lines, and a closed nitrogen loop for the heat shield cooling is considered. The new design will make it possible to reduce the FAIR project cost