Task 6: Short Period Nb3Sn Superconducting Helical Undulator George Ellwood

Outline of presentation Background Objectives NbTi Undulator Nb3Sn Wire Choice Wire tests Winding trials Ceramic Insulation Summary 2

Background 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 3

Task 6 Objectives Increase the magnetic field of an undulator by using Nb 3 Sn Increased positron yield -> more efficient Create & test a short prototype (~300mm) Design iterated to make (~500 mm) Nb3Sn module with maximum field / shortest period possible Comparison with existing NbTi magnet 4

5 NbTi Study Many prototypes were to perfect the manufacturing technique. Scaled up to a 4m cryomodule containing two 1.75m magnets. 23 rd September 2010 a milestone was reached: Both magnets were powered to 215A individually Both magnets were then powered to 215A

6 NbTi Study Final Parameters: Beam tube ID: 4.7 mm Winding ID: 6.35 mm Field on axis: 0.86 T Peak field in conductor: 2.74T Predicted margin with this conductor: 25%

7 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%

8 Nb 3 Sn Conductor Size What wire diameters fit in existing 3.25 mm groove? 0.4 bare (0.55 insulated) Square packing 3.3 mm wide PF = 42 % Hex packing 3.3 mm wide PF = 43 % 0.5 bare (0.65 insulated) Square packing 3.25 mm wide PF = 46 % Hex packing 3.25 mm wide PF = 48 % 0.6 bare (0.75 insulated) Square packing 3.0 mm wide PF = 50 % Hex packing 3.0 mm wide PF = 49 %

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 9

Supercon 0.5mm Internal Tin wire performance Solid line shows Kramer fit to all data I c = 1120 A at 3 T, 4.2 K 10

OST 0.5 mm Nb3Sn Performance, two grades of wire Large extrapolation to available data OST R2006: Ic ~ 1000 A at 3 T, 4.2 K (Jc ≈ 1600 A/mm2, 4.2 K 12 T) OST E2004: Ic ~ 2000 A at 3 T, 4.2 K (Jc ≈ 2900 A/mm2, 4.2 K 12 T) 11

OST Wire 12 Purchased 1 km of Ø0.5 mm (Ø0.63 mm with glass braid) E2004 RRP wire from OST. Recommended heat treatment: 210°C/48hr + 400°C/48hr + 650°C/50hr Received on 4th June 2010.

Modelling using extrapolated low field values Field strength and Ic at 1 kA. Winding ID: Ø6.35 mm. Field on axis: 1.54 T. Peak field in conductor: 4.42 T. Operating at 82% of Ic. 13

Wire Tests We need to know low field performance of OST wire Karlsruhe Institute of Technology have measured this using different heat treatments in November We’ve just received the results and will discuss in more detail at the next EuCARD meeting. 210°C/48hr + 400°C/48hr + 650°C/50hr 14

Winding Trial Need to do a trial winding to confirm groove dimensions. This used an Aluminium former with similar dimensions to the NbTi helical undulator. 32 OST 0.5mm wires in winding mm period. This has been wound, potted and sectioned to check groove width. 15

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Aluminium Former 17 First to helical former to be manufactured by external company rather than RAL workshop

Winding with OST wire 18

Potted using Mix71A 19 This potting was done to allow the undulator to be sectioned and didn’t use a mould.

Sectioning of sample 20 1 (F) 2 (R)3 (F) 4(R)

Sectioning results 1 & Groove 1 is larger than groove 2 at the top and middle but smaller at the bottom. The 5 wires are not flat in groove 1.

Sectioning results 3 & Similar differences between groove 3 and 4 The 5 wires are not flat in groove 3.

Sectioning The winding groove is consistently less than the mm specified. There are noticeable differences between the first groove and second cut. This is believed to be due to wear of the cutting tool. This may be avoided with more frequent changes in cutting tool. – Checked by using before and after short lengths 23

Ceramic Insulation Copper wire with enamel was wet- wound onto a former using Pyro-Putty 677 ceramic. Heat treatment was performed at 650°C in vacuum. The former was impregnated with epoxy and cured to allow it to be sectioned. 24

Sectioning of ceramic insulation 25 The packing of the wire is not even Two wires appear to be almost touching, continuity test required

Summary We plan to use Ø0.5 mm E2004 RRP wire from OST. – The low field performance has been measured by KIT. – We’ll review the results and incorporate into design. Winding trial has shown issues with tool wear – This can be monitored and can be resolved. Ceramic insulation looks promising but requires further work. 26

Thank you for your attention 27