1. Development of the EuCARD Nb 3 Sn Dipole Magnet FRESCA2 P. Ferracin, M. Devaux, M. Durante, P. Fazilleau, P. Fessia, P. Manil, A. Milanese, J. E. Munoz Garcia, J. C. Perez, L. Oberli, J. M. Rifflet, G. de Rijk, F. Rondeaux, E. Todesco, and the whole team of the Magnet Design and Technology (MDT) Section EUCARD-WP7-HFM 9 th collaboration meeting LASA, Milan 18 September, 2012

2. Introduction European Coordination for Accelerator R&D (EUCARD) Project – R&D on new technologies for future upgrades of the European accelerators Work Package 7 dedicated to superconducting high field magnets for higher luminosities and energies Key objective: fabrication and test of FRESCA2 – Upgrading the CERN cable test facility FRESCA 88 mm  100 mm aperture 10  13 T bore field NbTi  Nb 3 Sn superconducting technology – Provide the background field for an HTS coil insert R&D towards 20 T magnet 18/09/2012 Paolo Ferracin2

3. Introduction Overview of magnet design Target: 13 T in 100 mm clear bore OD: 1.030 m; length: 2.255 m Al shell, 65 mm thick, 1.6 m long Iron yoke – Holes for axial rods Horizontal stainless steel pad – 3 bladders, 75 mm wide – 2 load keys Vertical iron pad – 2 bladders, 60 mm wide – 2 load keys Auxiliary bladders between yokes Four double-layer coils Iron and Ti alloy central posts 18/09/2012 Paolo Ferracin3

4. Conductor and cable parameters Both PIT an RRP procured Strand diameter: 1 mm Cu/Sc: 1.3  56% Cu Strand #: 40 Bare width after cabling: 20.900 mm Bare thickness after cabling: 1.860 mm Insulation: 0.200 mm Assumed growth during HT – 4% in thickness and 2% in width Bare width after HT: 21.400 mm Bare thickness after HT: 1.934 mm 18/09/2012 Paolo Ferracin4 PIT strand

5. Superconductor properties J c of virgin strand (4.2 K) without self field (s.f.) correction (PIT) – 2400 A/mm 2 at 12 T – 1400 A/mm 2 at 15 T Self field corr. of 0.41 T/kA ~5% cabling degradation Resulting J c for comp. – 2450 A/mm 2 at 12 T – 1400 A/mm 2 at 15 T 18/09/2012 Paolo Ferracin5

6. Dilatation test Goal: measure cable longitudinal length variation during reaction – Feed-back on coil and tooling design 1.5 m of cable wound around 700 mm long winding pole – Stainless steel, iron, Ti alloy – Gaps vs. no-gaps First (out of 3) heat treatment completed, analysis in progress 18/09/2012 Paolo Ferracin6

7. Coil design Two double-layers with 36 and 42 turn Coil aperture 116 mm, bore 100 mm Iron and Ti (or SS) poles Inter-coil gap and mid-plane “tailored” shim 730 mm of straight section Hard-way bend of 700 mm 17  inclined ends Overall coil length of 1.6 m 18/09/2012 Paolo Ferracin7

8. Magnet parameters Operational conditions (13 T) – I op : 10.9 kA – B peak_op : 13.4 T – 79% of I ss at 4.2 K B bore : 16.0 T – 72% of I ss at 1.9 K B bore : 17.2 T; 15 T bore field: 86% of 1.9 K I ss Peak field in layer 1 1% homogeneity in 2/3 of aperture and 540 mm length 10% of margin in the ends 18/09/2012 Paolo Ferracin8

9. E.m. forces and support structure E.m. forces in straight section directed outwardly – Max. “accumulated” stress of 100 MPa Horizontal bladders pressurized to 30 MPa – Insertion of a shim in hor. load keys of 0.6 mm Shell  from 65 (293 K) to 185 (4.2 K) MPa Axial force: 2.8 MN – LHC (8.3 T, 1 aperture): 0.25 MN – HQ (170 T/m): 0.8 MN Axial piston used to pre-load the rods – 60 mm diameter Rod  from 150 (293 K) to 260 (4.2 K) MPa 18/09/2012 Paolo Ferracin9

10. Coil stress 2D and 3D mechanical model Goal: contact pressure (or tension <20 MPa) between pole turn and pole pieces – From straight section to hard- way and easy-way bent Coil peak (equiv.) stress – 140-150 MPa – Maximum stress moves to low field region at full field 18/09/2012 Paolo Ferracin10 -137 MPa 134 MPa 154 MPa -139 MPa

11. Coil fabrication status Winding on 3 bolted blocks Stainless steel fixture (top plates and side rails) for reaction – Mica sheets for sliding Same parts in aluminium for impregnation Design completed, procurement in progress One set of coil part successfully fabricated – Plasma spray for insulation 18/09/2012 Paolo Ferracin11

12. Support structure fabrication Yoke and shell 18/09/2012 Paolo Ferracin12 10 strain gauge stations Azimuthal, axial with T comp. Straight section and ends Total: 20 gauges

13. Support structure fabrication Yoke and shell 18/09/2012 Paolo Ferracin13

14. Support structure fabrication Coil-pack with dummy coils 18/09/2012 Paolo Ferracin14 14 strain gauge stations Azimuthal, axial with T comp. Straight section and ends Total: 28 gauges

15. Support structure fabrication Coil-pack with dummy coils 18/09/2012 Paolo Ferracin15

16. Support structure fabrication Axial support system 18/09/2012 Paolo Ferracin16 2 strain gauge per rod Axial direction. Total: 8 gauges

17. Quench protection At nominal field, total stored energy of 4.6 MJ – 3.7 m long LARP LQ features: 1.4 MJ – But, comparable the stored energy density Protection system: 95 mΩ dump resistor and quench heaters on all layers – 50 W/cm 2 and 50% coverage 150 or 200 K of peak T with t detection of 40 or 100 ms 18/09/2012 Paolo Ferracin17 Traces with 4 heaters – Wiggling shape for better coverage 9 voltage taps per layer – Monitor pole turn and external turns

18. Conclusions and future plans Design of Nb 3 Sn dipole magnet FRESCA2 completed – Goal: 13 T in 100 mm bore According measured strand properties, the magnet operates with more than 20% of current margin Fabrication of coil fabrication tooling in progress Structure components and parts for the first coil delivered Next steps – First coil wound with a copper cable early next year – In parallel, support structure assembled, pre-loaded and cooled- down to 77 K around aluminium dummy coils. Results to be used to validate models and define procedures and pre- load levels 18/09/2012 Paolo Ferracin18