Download presentation
Presentation is loading. Please wait.
Published byAlexandrina Cain Modified over 9 years ago
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.