High energy accelerator research organization, KEK, has developed new separation dipole magnets, D1, for the High Luminosity Large Hadron Collider (HL-LHC). The existing LHC Nb-Ti technology is utilized for the D1 in order to generate a field integral of 35 T·m at the nominal operating current and temperature of 12 kA and 1.9 K, respectively. The corresponding central field is equivalent to 5.6 T. Prior to fabrication of the first full-scale prototype, which has begun in 2020, three magnets of 2 m-long short-scale models have been developed since 2015. The stored energies of the full-scale and short-scale magnets are estimated to be 2.13 MJ and 0.568 MJ, respectively. One of the challenges in beam operation is protecting coils from quench: the stored energy has to be dissipated only by quench protection heaters (QHs) and without energy extraction despite the high engineering current density of 600 A/mm~2.
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