1. D. Arbelaez for the LBNL LCLS SCU team Mar. 3, 2016 1

2. Outline Magnetic design – Periodic section – End design and corrections – Periodic field corrections Coil fabrication Quench protection Coil testing Undulator assembly Measurement results 2

3. Coil Optimization Find optimal number of turns per layer and total layers necessary to meet peak field requirement (1.86 T @ λ = 19.0 mm, g = 8.0 mm) Wire diameter = 0.6 mm, insulation thickness = 60 μm 5 layers is sufficient to operate at 80 % of load line margin Modest gains margin can be obtained by adding more layers Number of layers Number of turns per layer Load Line Margin 3 Load Line Comparison On-Axis Field Peak Conductor Field Critical Current

4. End Designs and Non-Ideal Effects Saturation of the undulator core and poles leads to non- ideal effects – Pole saturation changes the local kick strength – Pole and core saturation leads to non-ideal global effects Variation in Pole Saturation No Core Saturation near end Flux through the end  2D calculations are shown to demonstrate the principles  For accurate results 3D calculation must be used 4

5. Global Field Effects B z On-Axis Field Profile B z Even # of poles, Odd # of coils Odd # of poles, Even # of coils cw ccw cwccw cwccw Number of turns are chosen to cancel these effects in an ideal case Global field effects are present due to saturation 5

6. End Design Principles 2 Independent Correctors Correction of global field effects – 1 corrector (coil at each end wired in series) is used for correction of the global field effect – corrector produces both a local kick and a global field – In principle the two ends can be wired independently to produce both a constant and linearly varying global fields Correction of local end kick – 1 corrector at each end wired independently for entrance and exit kick correction – This correction is decoupled from the main core and produces no global fields – Field clamps are included for this corrector in order to avoid interference with nearby magnetic components 6

7. Effect of end corrector global field local kicks odd# of poles Global Field Correction Coils are wound in first and last pocket of each core Produces a global correction + local kick Strength is chosen to cancel only global field error 7

8. Local End Kick Correction Magnetically decoupled from main undulator core Produces only local kicks Field clamps are used to minimize stray field Compact design (fits under splice joint in Nb 3 Sn device) Effect of end corrector no global field local kicks odd# of poles 8

9. Switch-Based Tuning Concept One superconducting path - with heater One resistive path (low resistance) When heater is on the superconducting path becomes resistive (high resistance) Superconducting path Resistive solder joint (low resistance) Heaters ON 9 Heaters OFF Current

10. Current path via lithography on YBCO Tapes Commercial tape from SuperPower Inc. Masks designed for photolithography process Chemical etching used to remove Copper, Silver, and YBCO layers where desired Solderable thin film heaters were developed for efficient and reliable fabrication Laser cutting is used to separate joint section 10

11. Undulator Coil Fabrication: Magnet Core Mandrel is machined from a single piece of steel Tight fabrication tolerances were met by the vendor CMM inspection of the magnet cores was done at various steps to verify the quality of the parts Worked with a plasma spray vendor to develop the coating process to protect against high potential to the magnet core during a quench 11

12. Undulator Coil Fabrication: Winding Computer controlled winding machine is used 1.6 km of wire are used for a single core (~ 8000 turns) Wire braid insulation trials were performed to develop a thin and robust insulating layer on the wire Increasing braid angle (with respect to wire axis) Final braid insulation 12 0.71 mm

13. Undulator Coil Fabrication: Heat Treatment Wind and react process Large furnace at LBNL can accommodate these coils Coils are compressed in steel tooling Heat treatment performed in Ar atmosphere at 650 degrees for 50 hours (total cycle time is ~ 7 days) 13

14. Undulator Coil Fabrication: Epoxy Impregnation Coils are transferred to impregnation tooling Solder joints are made at the ends to flexible NbTi lead cables Instrumentation wires are installed in the coils Impregnation process is carried out 14

15. Quench Protection The Nb 3 Sn undulator operates at extremely high current densities in the wire (nearly a factor of two greater than NbTi) Hot spot temperature scales with current squared Fast detection time and current decay are necessary to protect the Nb 3 Sn undulator Hot Spot Temperature Magnet Protection Requirement Safe Area 15 Safe temperature [A 2 s] NbTi

16. Quech Protection System and Test Results Quench Protection system uses state of the art electronic components – Precision isolation amplifiers (Allow high voltage signals) – IGBT solid state switches (fast switching) – Dump resistor (fast decay) Dump resistor value is chosen for fast decay but voltage must also be kept at reasonable values Protection system was tested on a four period undulator half – The coil reached a maximum current of 930 A – At high currents the rate of decay increases after a short time (suggest quench back behavior) Current Decay for short undulator half 16

17. Coil Testing Magnet test facility at LBNL used to test individual coils for transport current Quench protection system was implemented to protect the full length coils 17

18. Coil Test Results Quench protection system was successfully applied to the full length coils 550 mΩ resistor was selected (max. voltage = 430 V) Coil 1 reached 766 A after two quenches Coil 2 reached 729 A after 80 quenches 18

19. Corrector Fabrication Process to adhere correctors to the vacuum chamber was developed (correctors and glue take up 0.2 mm of excess thickness) Short prototypes were fabricated and successfully tested in cryogen free cryostat 19

20. Undulator Assembly (Cooling System) Copper plates in contact with undulator poles (Indium interface) Copper plates are split in order to reduce the effect of thermal contraction mismatch between materials Thermal links are used to transfer heat from the plates to the LHe pipe 20

21. Final Undulator Assembly 21 Undulator Assembly at LBNL Lead Connection and LHe Tank Assembly at ANL

22. End Corrections End corrector response as expected for decoupled end correctors Observed hysteresis effects for the on-board end correctors – Higher than expected quadratic component in the magnetic field along the length – The effect could be minimized with a hysteresis cycle 22 On-Board End Corrector ResponseDecoupled End Corrector Response

23. Magnetic Measurement Results Hall probe measurements performed at 500 A with coupled end corrector at 2.5 A De-coupled end corrector is not energized (second field integral corrected numerically) Later measurements verified that the sensitivity and strength of the de-coupled end correctors is sufficient to meet the first and second field integral specifications 23 Magnetic Field First Field Integral Second Field Integral Phase Error

24. YBCO Field Corrector The YBCO correction network was powered to 50 A Six of the single-turn correction coils were wired and the functionally of all six was verified Two correctors were powered with a main undulator current of 300 A The two correctors gave a field integral of 30 μTm at 50 A 24 Effect of Two Correctors on the Second Field Integral of the Undulator Derived from Hall Probe Measurements

25. Conclusions Developed basic undulator design and correction methods – End corrections – YBCO switch network (central field corrections) Developed fabrication and processing techniques for Nb 3 Sn undulators – Wire and core insulation – Winding, reaction, epoxy impregnation Developed quench protection system for high current density undulators Individual coil test performance was good (~ 95% of design value) although training behavior between two coils was very different Good intrinsic field quality was obtained with the Nb 3 Sn device Functionality of the YBCO field corrector system was demonstrated High field in test at ANL was not achieved – The current limiting is indicative of a local problem (not a fundamental problem with the technology) – Will further investigate the cause of the lower than expected current limit 25