1. Conceptual Design of the Neutron Guide Holding Field Christopher Crawford, Yunchang Shin University of Kentucky nEDM Collaboration Meeting 2009-06-19

2. Outline  Issues: constraints adiabaticity / abruptness field gradients  Design: DSCTC steel flux return taper in DSCTC DSCTC 2m 1010 steel flux return  -metal ext.

3. Constraints  preserve neutron polarization (holding field) Larmor precession -adiabatic– field uniformity -abrupt– field smallness Majorana transitions ?  avoid gradients in measurement cell from: holding field coils (left on)– field fringes magnetized Metglas (HF off)– field fringes magnetic material– no magnetic material  spin dressing field uniformity– no conductors in B 0 region  neutron guide construction – no current sheets in guide  SM polarizer – 300 G – 100 mG field taper

4. Issue – adiabaticity / abruptness  100 mG doldrums too large for abrupt changes too low for adiabatic rotation in cryostat could try and ‘steer’ spins into fringe with exit fringe either or both conditions will preserve polarization:

5. Field and neutron spin direction – 100 mG

6. Field and neutron spin direction – 70 mG

7. Field and neutron spin direction – 40 mG

8. Polarization vs Field (corner of guide)

9. Field lines in double-cos-theta coil  require: B=0 outside B=B 0 inside  solve  M with B r boundary conditions  calculate j from B t boundary using  M  1” flux return                                                                   

10. Current windings on end face  B t =0 on ends so solution is axially symmetric  equipotentials  M =c form winding traces for current on face n£(H=r  M )  end plates connect along inside/outside

11. Issue – gradients  Design – DSCTC  guide field ~ dipole directly affects B 0 field if left on magnetizes Metglas if turned on and off repeatedly  flux return ~ quadrupole magnetic material in cryostat distorts the field currents – DSCTC similar to dressing coil design arbitrary geometry inner coils – guide field outer coils – flux return end-caps – contain B-field current sheet omitted

12. Integration of DSCTC and steel flux return

13. Issues – current sheet / spin dressing coils  guide field should terminate at beginning of B 0 field:  conductors inside spin-dressing coils perturb RF field  to match up and cancel out fringes  don’t want current-sheet on end-cap of the DSCTC complicates neutron guide need to cancel B 0 fringe  quadrupole residual direct – gradient indirect – magnetization = +

14. Stray fields from DSCTC B(15cm, 15cm, 25cm) = (456,15.3, 149) x 10 -8 G dB x dB y dB z /dx 3.1 1.0 10. /dy 1.0 1.0 0.5 x10 -8 G/cm /dz 10. 0.5 4.1 No Shields dB x dB y dB z /dx 0.4 128? 0.8 /dy 0.1 0.1 0.2 x10 -8 G/cm /dz 0.9 0.2 0.7 Shield & B 0 (40 mG) Septimiu Balascuta

15. Lab Setup “quadrupole loops” triple-axis fluxgate magnetometer deguassing coils H. Yan, B. Hona, B. Plaster 1) 25.5” O.D., 67.5” long, 1.6 mils (2 layers) 2) 17.25” O.D., 48.5” long, 2.4 mils (3 layers) Nested Metglas shields:

16. B x (z) B y (z) B z (z) quadrupole at this end Step #1: Quadrupoles off (baseline) Step #2: Quadrupoles on (impact) Step #3: Quadrupoles off (hysteresis) Note: x = vertical, y = horizontal

17. B x (x) B y (x) B z (x) Results along y-axis are similar Shapes (  gradients) similar Probably should be repeated for higher precision, test repeatability Step #1: Quadrupoles off (baseline) Step #2: Quadrupoles on (impact) Step #3: Quadrupoles off (hysteresis)

18. Holding field downstream of bender  5 G holding field in 10 m of guide downstream of bender  external 1010 steel yoke, 1/16” x 42.5 cm x 42.5 cm  40 cm x 1 mm Al winding 160 A-turns top and bottom 92  /m, 4.7 W/m  coil vs. permanent magnets: allows use of steel on all four sides of guide for both internal and external shielding can be turned off during measurement cycle low power  lightweight – 31 kg/m mount on guide housing  horizontal vs. longitudinal field double-cos-theta-coil transition need same current as solenoid only on top and bottom each side can mount separately

19. External shielding  factor of 10 shielding of Earth’s magnetic field  B y /B x = 50 mG / 5 G  0.57 ± perturbation of holding field angle only matters at interface with double-cos-theta coil

20.              x z y z Top view Side view B J B J beam left beam right guide bottom guide top  y x    Issue – field taper

21. Calculation – optimal taper

22. Results – optimal taper

23. Design – DSCTC taper 1.16 A 50 windings 0 m – 100 mG 1 m – 189 mG 2 m – 460 mG 3 m – 2.4 G 4 m ~ 10 G j max =152 A/m P max =11.3W/m 2 P ~ 100 W

24. Design – DSCTC taper flux return lines

25. Extra Slides: B 0 field alone / with DSCTC at x=12.5, y=12.5 cm (worst case)

26. B 0 =100mG+DSCTC x=12.5 cm

27. B 0 +DSCTC, x=12.5 cm

28. B 0 =100mG+DSCTC, x=6.25 cm

29. B 0 =DSCTC, x=6.25 cm

30. B 0 +DSCTC – 100 mG

31. B 0 +DSCTC – 40 mG