1. Task 6: Short Period Nb 3 Sn Superconducting Helical Undulator Dr Owen Taylor Institutes Science and Technology Facilities Council (STFC) UK –Daresbury Laboratory (DL) Jim Clarke, Duncan Scott –Rutherford Appleton Laboratory (RAL) Tom Bradshaw, Owen Taylor, Elwyn Baynham, Geoff Burton, Steve Carr, Matt Hills, Steve Watson, Simon Canfer, George Ellwood

2. 2 Outline of Presentation Motivation and Task 6. Objectives Summary of existing NbTi helical undulator Nb 3 Sn wire choice Manufacturer / Size Nb 3 Sn operating margin in undulator Summary

3. 3 Motivation ILC requires unprecedented numbers of positrons when compared with present day sources If positrons can be polarised then the physics reach of the collider can be enhanced ILC Baseline – Synchrotron radiation from a Helical Undulator –Very high energy electrons –Short period undulator –Lots of Periods for high intensity (~200 m long undulator) –Helical undulator  circularly polarised photons

4. 4 Task 6. Objectives Increase the achievable magnetic field of undulator with use of Nb 3 Sn Higher field – Increased positron yield / savings Create short (~300 mm) Nb 3 Sn prototype and test magnetically Design iterated to make (~500 mm) Nb 3 Sn module with maximum field / shortest period possible Comparison with excising NbTi magnet Make final report with full description of study made

5. 5 Existing Studies Team has been working on superconducting helical undulator development for ILC since 2004 (Supported by STFC & EUROTeV) Exclusively NbTi so far Several short prototypes have been constructed and tested Following this R & D phase a full scale module has been designed and constructed

6. 6 NbTi Study Many prototypes were made and sectioned to perfect winding 4 m Cryomodule made Contains two 1.75 metre helical magnets Wound with NbTi wire with 11.5 mm period Final stage of commissioning

7. 7 NbTi Study Field strength, critical current Beam tube ID: 4.7 mm Winding ID: 6.35 mm Field on axis: 0.86 T Peak field in conductor: 2.74 T Predicted margin with this conductor: 25% Quench tests successful

8. 8 NbTi Winding Wound with 7 wire ribbon, 8 layers Ø0.4 mm NbTi wire, with 25 µm enamel (Ø0.45 mm when insulated) 3.25 mm wide winding Packing factor of 62%

9. 9 Nb 3 Sn Conductor Size Needs to be reacted at ~700°C after it has been wound Can be bought with braided “S” glass insulation, thickness ~ 75µm Ribbons not possible – single wire winding What wire diameters fit in existing 3.25 mm groove? 0.4 bare (0.55 insulated) 0.5 bare (0.65 insulated)0.6 bare (0.75 insulated) Square packing 3.3 mm wide PF = 42 % Hex packing 3.3 mm wide PF = 43 % Square packing 3.25 mm wide PF = 46 % Square packing 3.0 mm wide PF = 50 % Hex packing 3.25 mm wide PF = 48 % Hex packing 3.0 mm wide PF = 49 %

10. 10 Nb 3 Sn Performance Nb 3 Sn Availability EAS Bruker do not make Nb 3 Sn smaller than Ø0.7 mm Supercon Inc. and Oxford Instruments Superconducting Technology (OST) make Ø0.4 mm and Ø0.5 mm respectively Nb 3 Sn Performance Due to small winding area, need large currents to achieve ~1 T on axis Need to know critical current in winding at ~4 T No companies have data for performance below 9 T Large extrapolation needed – no confidence Supercon Inc. made measurements from 3 T for us

11. 11 Nb 3 Sn Performance Supercon 0.5 mm Nb 3 Sn ‘Internal Tin’ Performance Critical current data at 4.2 K (data from Supercon brochure) Difficult to extrapolate to down to 3 T

12. 12 Nb 3 Sn Performance Supercon 0.5 mm Nb 3 Sn ‘Internal Tin’ Performance Data with Kramer extrapolation where B 0.25  I c 0.5 Can not trust extrapolation

13. 13 Nb 3 Sn Performance Supercon 0.5 mm Nb 3 Sn ‘Internal Tin’ Performance Supercon performed performance tests for us down to 3 T Can see extrapolation is not so good at low fields

14. 14 Nb 3 Sn Performance Supercon 0.5 mm Nb 3 Sn ‘Internal Tin’ Performance Solid line shows Kramer fit to all data I c = 1120 A at 3 T, 4.2 K

15. Nb 3 Sn Performance OST 0.5 mm Nb 3 Sn Performance, two grades of wire Large extrapolation to available data OST R2006: I c ~ 1000 A at 3 T, 4.2 K (J c ≈ 1600 A/mm 2, 4.2 K 12 T) OST E2004: I c ~ 2000 A at 3 T, 4.2 K (J c ≈ 2900 A/mm 2, 4.2 K 12 T) Need to do low field measurements of OST wire

16. 16 Nb 3 Sn Diameter & Margin Nb 3 Sn Diameter Choice Require diameter large enough that single wire winding is possible Want high current density without too large operating current Supercon margin if Undulator peak field = 4 T This equates to bore field of ~ 1.25 T (i.e. 45% higher than NbTi) Table shows critical current (percentage I operate /I c ) for hex-packing Wire Diameter0.4 mm0.5 mm0.6 mm Winding & I operate 39 wires at 452 A27 wires at 658 A18 wires at 981 A Supercon I c & Margin547 A (83 %) 855 A (76 %) 1231 A (80 %) OST wire – larger margin / higher field / shorter period

17. Summary Single wire winding rather than ribbon – hex packing We have low field performance data for Supercon Nb 3 Sn wire but not OST 0.5 mm (0.65 mm when insulated) wire offers best compromise for size Supercon wire with 11.5 mm winding period – margin of 24 % with 1.25 T bore field Purchase OST wire for low field study & final winding?