Capture Solenoid Discussion A look at Operating Margins in the SC Coils

1. Capture Solenoid DiscussionA look at Operating Margins in the SC Coils Peter Loveridge P.Loveridge@rl.ac.uk Rutherford Appleton Laboratory UKNF Meeting, Lancaster April-2009

2. Introduction Would like to define a realistic operating surface (J,B,T) for SC capture solenoid coils To understand operating margins To enable study of alternative coil configurations Strategy: Performance of Nb3Sn strands developed for ITER Define a “Neutrino Factory” cable Extrapolate cable performance from strand data

3. Study-2 Capture Solenoid Hybrid 20 Tesla Solenoid Magnet NC insert generates ~6 Tesla SC “Outsert” generates ~14 Tesla, Nb3Sn Combination of high field, large bore, presents a real challenge Pion capture is related to B x R Huge inter-coil forces >10,000 Tonnes Lorentz forces are related to B2 x R Magnet optimisation? Study-2 capture solenoid

4. ITER Central Solenoid Model Coil In Study-2 (2001), Capture Solenoid performance “Based on” ITER CSMC Taken as “State-of-the Art” Nb3Sn strands 5 stage cable = 3 x 3 x 4 x 5 x 6 = 1080 strands Conduit dimensions 50 mm x 50 mm ITER Central Solenoid Model Coil (CSMC) tested 19 Apr 2000 Achieved 46 kA @ 13 Tesla ITER Central Solenoid Model Coil (CSMC) Conductor ITER Central Solenoid Model Coil Assembly in Test Facility

5. A Critical Surface Definition for NF Solenoid 190 A @ 4.2K, 12 T Data scaled from ITER VAC strand measurements [Courtesy Durham, Supercond. Sci. Technol. 18 (2005) S241-S252] STRAND Assume ITER strand specification (TF cable) 190 A @ 4.2 K and 12 Tesla 0.82 mm diameter strand Cu:Non-Cu ratio = 1 CABLE Assume a “CSMC like” Cable Strand Diameter = 0.82 mm Strand Area = 0.528 mm2 Total Strands = 1080 No. SC strands = 720 (2/3) No. Cu strands = 360 (1/3) Conduit Dims: 50 mm x 50 mm Conduit Area = 2500 mm2

6. Strain Degrades Nb3Sn Strand Performance! Nb3Sn Strand performance is very sensitive to applied strain! Sources of strain: Cabling Jacketing Thermal strain (650˚C to 4.2 K) Lorentz Forces ITER experience: Operating strain in the strand of the order -0.75 % Cable degradation is large (50% not unheard of…) Difficult to predict cable performance from strand data! Illustration of Strain Degradation in Modern Nb3Sn Strands (Courtesy ITER Organisation)

7. Coil Operating Conditions Cable degradation Study-2 SC Coil 23.4 A/mm2 ITER CSMC Achieved 46 kA @ 13 T Note: 5 % margin on load-line ~ 0.7 Kelvin temp margin

8. Coil Shielding Issues – Temperature Margin Shielding designed to mitigate beam heating of SC coils Steady-state Instantaneous (pulsed) Note: a reasonable temperature margin to aim for ~ 1K ~ 1 mJ/cc could cause a quench! Link with FLUKA power deposition studies Note: Bmax at Rmin Material Properties at 4 Kelvin Specific heat of coil materials is dramatically reduced at low temperature

9. Summary Would like to define a realistic operating surface (J,B,T) for the SC capture solenoid coils But… strain degradation in cable is large, and not easy to quantify! Difficult to extrapolate cable performance from strand data In any case, Study-2 magnet performance already looks optimistic compared to ITER technology Questions & Next Steps • Need to understand what level of strain degradation to expect! • Look at “whole cable” test data • Interpret SULTAN (PSI) short-sample tests • Is the coil shielding sufficient? • Small heat capacity in SC coil • Space constraints for shielding in magnet bore