1. End Design Discussion D. Arbelaez (LBNL) Oct. 7, 2014 1

2. Basic End Design Kicks (ideal) Potentials at Poles: 0, ½, -1, +1, … 0 1/2 +1 Even poles Odd poles # of coil turns: ¼, ¾, 1 … 0 1/4 -3/4 +1 Even poles Odd poles Potentials at Poles: 0, ¼, -3/4, +1, -1, … # of coil turns: 1/8, ½, 7/8, 1 … # of coil turns is given by the difference in neighboring pole potentials

3. End Design Including Local End Errors 3 Kick and displacement errors at the ends due to non-ideal effects Even or Odd number of poles – Even – zero net steering, non-zero net displacement – Odd – zero net displacement, non-zero net steering 2δ Even number of poles δ +K -K Odd number of poles +K +δ -δ Steering + Displacement Displacement Only Ideal δ

4. Undulator Pole/Core Saturation 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

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

6. Scaling of Global Field Effects with Undulator Length Magnetic field was calculated with two different length undulators (second one is twice as long) The effect of the end coil corrector is shown Slope of the distributed field scales approximately with 1/L Second field integral scales with slope*L 3 ≈ L 2 Slope = 0.17 G/mm Slope = 0.28 G/mm I2 dev α slope  L 3 Magnetic Field Variation First Field Integral Variation End kick strength Even # of poles

7. LBNL 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

8. 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 Effect of end corrector global field local kicks odd# of poles

9. 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

10. Glass Braid Insulation Update 4 braiding angles were tested on 0.6 mm diameter copper wire by New England Wire Company SCD 450 fine filament Glass yarn was purchased from AGY The final braid thickness was 55 μm with excellent coverage Increasing braid angle (with respect to wire axis) Final braid test