Task 6: Short Period Nb 3 Sn Superconducting Helical Undulator Dr Owen Taylor Institutes Science and Technology Facilities Council (STFC) UK –Daresbury.

Task 6: Short Period Nb3Sn Superconducting Helical

Undulator

Dr Owen TaylorInstitutes

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

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Outline of Presentation• Motivation and Task 6. Objectives

• Summary of existing NbTi helical undulator

• Nb3Sn wire choice

• Manufacturer / Size

• Nb3Sn operating margin in undulator

• Summary

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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

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Task 6. Objectives• Increase the achievable magnetic field of

undulator with use of Nb3Sn

• Higher field – Increased positron yield / savings• Create short (~300 mm) Nb3Sn prototype and

test magnetically• Design iterated to make (~500 mm) Nb3Sn

module with maximum field / shortest period possible• Comparison with excising NbTi magnet

• Make final report with full description of study made

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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

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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

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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

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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%

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Nb3Sn 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 %

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Nb3Sn Performance• Nb3Sn Availability

• EAS Bruker do not make Nb3Sn smaller than Ø0.7 mm

• Supercon Inc. and Oxford Instruments Superconducting Technology (OST) make Ø0.4 mm and Ø0.5 mm respectively• Nb3Sn 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

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Nb3Sn Performance• Supercon 0.5 mm Nb3Sn ‘Internal Tin’

Performance

• Critical current data at 4.2 K (data from Supercon brochure)

• Difficult to extrapolate to down to 3 T

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Nb3Sn Performance• Supercon 0.5 mm Nb3Sn ‘Internal Tin’

Performance

• Data with Kramer extrapolation where B0.25 Ic0.5

• Can not trust extrapolation

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Nb3Sn Performance• Supercon 0.5 mm Nb3Sn ‘Internal Tin’

Performance

• Supercon performed performance tests for us down to 3 T

• Can see extrapolation is not so good at low fields

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Nb3Sn Performance• Supercon 0.5 mm Nb3Sn ‘Internal Tin’

Performance

• Solid line shows Kramer fit to all data

• Ic = 1120 A at 3 T, 4.2 K

Nb3Sn Performance• 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)

• Need to do low field measurements of OST wire

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Nb3Sn Diameter & Margin• Nb3Sn 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 Ioperate/Ic) for hex-packingWire Diameter 0.4 mm 0.5 mm 0.6 mm

Winding & Ioperate 39 wires at 452 A

27 wires at 658 A

18 wires at 981 A

Supercon Ic & Margin

547 A (83 %) 855 A (76 %) 1231 A (80 %)

• OST wire – larger margin / higher field / shorter period

Summary• Single wire winding rather than ribbon – hex

packing

• We have low field performance data for Supercon Nb3Sn 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?