Task 6: Short Period Nb3Sn Superconducting Helical Undulator George Ellwood 26-11-2010 1.
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Transcript of Task 6: Short Period Nb3Sn Superconducting Helical Undulator George Ellwood 26-11-2010 1.
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Task 6: Short Period Nb3Sn Superconducting Helical Undulator
George Ellwood26-11-2010
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Outline of presentation
• Background• Objectives• NbTi Undulator• Nb3Sn Wire Choice• Wire tests• Winding trials• Ceramic Insulation• Summary
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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
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Task 6 Objectives• Increase the magnetic field of an undulator by using
Nb3Sn• 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
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NbTi Study• Many prototypes were to perfect the
manufacturing technique. • Scaled up to a 4m cryomodule containing two
1.75m magnets. •23rd September 2010 a milestone was reached:
•Both magnets were powered to 215A individually
•Both magnets were then powered to 215A
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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%
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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• 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 %
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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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Supercon 0.5mm Internal Tin wire performance
• Solid line shows Kramer fit to all data• Ic = 1120 A at 3 T, 4.2 K
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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)
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OST Wire
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• 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.
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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.
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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 2010.
• 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
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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.• 11.5 mm period.• This has been wound, potted and sectioned to
check groove width.
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Aluminium Former
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First to helical former to be manufactured by external company rather than RAL workshop
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Winding with OST wire
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Potted using Mix71A
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This potting was done to allow the undulator to be sectioned and didn’t use a mould.
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Sectioning of sample
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1 (F) 2 (R) 3 (F) 4(R)
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Sectioning results 1 & 2
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1 2
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.
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Sectioning results 3 & 4
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3 4
Similar differences between groove 3 and 4The 5 wires are not flat in groove 3.
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Sectioning• The winding groove is consistently less than
the 3.7-3.8mm 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
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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.
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Sectioning of ceramic insulation
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The packing of the wire is not evenTwo wires appear to be almost touching, continuity test required
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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.
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Thank you for your attention
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