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New Collaring and Coil Pre-stress Limit for a Nb3Sn Magnet Alexander Zlobin Technical Division Fermilab
Introduction Fermilab is developing a new generation of accelerator magnets based on Nb3Sn superconductor • LHC luminosity upgrade • Muon Collider New recent results within the Fermilab’s base High Field Magnet (HFM) program • Assembly and test of Nb3Sn Quadrupole model (TQC) with dipole style collar and coil alignment • Study of the effect of coil pre-stress on magnet performance
Quadrupole collar • Collaring using short vertical 4-jaw press with partial coil compression along the length • Requires additional horizontal to vertical handling of the coils • Time consuming process for Nb3Sn magnets with many (~6-8) passes and some risk of damage to coils
Dipole-style collar Dipole-style collar: • Similar for Dipole and Quadrupole magnets • Collaring using full-length horizontal press • Collaring with a single pass reducing coil degradation risks and construction time (<1 week)
Effect on QP and FQ • Multiple handling and test cycles => robust technology • Consistent coil quench performance in shell and collar structures • No significant field quality distortions related to the dipole style
Nb3Sn TQC vs. NbTi HGQ Nb3Sn TQC is modification of NbTi LHC IRQ (MQXB) HGQ (MQXB): • 70-mm NbTi IRQ • Cable 15 mm wide • Gop=200 T/m @ 11.1 kA • Top=1.9K • Margin ~20% dTc~2K TQC: • 90-mm Nb3Sn IRQ • Cable 10 mm wide • Gop=200 T/m @12.0 kA • Top=4.5K, 5% Ic margin, dTc~2K • Top=1.9K, 15% Ic margin, dTc~6K • Nb3Sn TQC: • Gmax~211 T/m at 4.5 K • Instabilities at T<3K • Gmax~217 T/m at 3.2K • Gmax~230 T/m at 1.9 K with stable conductor
Coil pre-stresses in Quadrupole mirror • Quadrupole mirror based on TQC quadrupole structure • Quadrupole coil made of improved (more stable) RRP 108/127 Nb3Sn strand • Different warm and cold coil pre-stress (see Table)
Effect of coil pre-stress • Small (<5%) Ic degradation in conductor at coil pre-stress up to ~190 MPa. • Noticeable degradation of conductor stability at T<3 K => more stable conductor for operation at 1.9 K and ~200 MPa.
Conclusions and Plans • Dipole style collar design and collaring process were successfully tested at Fermilab using 90-mm Nb3Sn TQ coils • Quench performance and field quality are consistent with the test results for models based on shell (TQS02a/c) and quadrupole collar (TQC02Ea) structures • Gmax=217 T/m (Bmax~12 T) => higher with better conductor • Dipole style collar structure can be easily adopted for long Nb3Sn quadrupole (and dipole) magnets => important for LARP and LHC upgrade needs • Coil pre-stress limit for Nb3Sn magnets is larger than 150 MPa (up to ~190 MPa) => • Possibility of higher field/field gradient • More room for pre-stress variation in long magnets • Next step: • Assemble and test in FY2011 a 4-m long quadrupole based on dipole style collars (recycle LARP LQ coils) • Continue work on Nb3Sn strand and cable improvement