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

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

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

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

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

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

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

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

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?

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

Cross-section of first winding

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