1. Task 6: Short period helical superconducting undulator
Simon Canfer
EUCARD Meeting
CERN 29 September 2009

2. Motivation
The ILC requires unprecedented numbers of positrons when compared with present day sources
If the positrons can be polarised then the physics reach of the collider can be enhanced
ILC Baseline – Synchrotron radiation from an undulator
Very high energy electrons
Short period undulator
Lots of Periods for high intensity
Helical undulator  circularly polarised photons

3. Institutes STFC Daresbury Laboratory (DL)
Rutherford Appleton Laboratory (RAL)

4. Aim
The aim of this programme is to fabricate and test a short helical undulator prototype wound with Nb3Sn wire.
The geometry of the undulator will be similar to that achieved under the current programme i.e. with an 11.5mm period.
We would like to achieve much higher fields than possible with NbTi (~1.15T achieved, quench limit)
Ultimate goal is to reduce period to ~10mm
NbTi undulator, cryostat and team

5. Challenges
Primary challenge with any Nb3Sn magnet is the insulation system and compatiblity with heat treatment
Former insulation (was challenging with NbTi, clean winding area required)
Turn-to-turn insulation
Secondary challenge is to make an insulation that is thin enough to give a current density advantage over NbTi

6. Work Plan Design Study Prototype Helical Final Report
Source suitable conductor and procure
Study on insulation systems that will not compromise the fill factor
Test wind and react on planar undulator D former
Design iteration
Prototype Helical
Manufacture suitable test former for helical undulator
Wind and react on short section (300mm) helical undulator former
Test undulator
Iterate design and incorporate improvements
Wind and react on short section (500mm) helical undulator former
Final Report

7. Progress Magnetic modelling work
Winding and potting trials on dummy conductor
Research on suitable insulation

8. Magnetic modelling Comparison of NbTi and Nb3Sn Super conductor type
Operating
Temp (K)
Wire
Section
WireØ
(mm)
Insulation
Thickness (μm)
Cu:Sc Fraction
Packing factor
Wire current (A)
Operating point
(% Of short sample)
NbTi
4.2
round
0.4 20
0.9
0.65
271 99
rectangular
0.4x0.72
0.85
452 81
1.8 75 62
Nb3Sn 50
0.5
350 77 70
0.43
408 86

9. Nb3Sn Wire choice Relatively small diameter, because:
Maximum current 500 amps, driven by heat load on chosen HTC current leads
Winding radius to suit D-shaped tool
Can we roll to a rectangular section to increase packing factor?

10. Winding and potting trials on dummy conductor
D-shaped former and potting jig to examine packing factor and tolerances on straight section

11. Cross-section of first winding

12. Insulation research Requirements:
Reliable
Thickness less than 70um to compete with NbTi
Compatible with heat treatment
Available
Vapour deposition techniques are promising, but not yet available for coating wire
Glass or ceramic fibre braid