Magnet development experiments

B. Plaster

Last collaboration meeting (February 2007)

x : field direction y : “vertical” z : axial

N = 40 cos θ coil 1/7-prototype r = 8.75 cm ℓ/r = 10

Coil + 3x Metglas Shield at 300 KCoil + 3x Metglas Shield at 77 K

Investigated Source of Asymmetry

Perc

enta

ge D

evia

tion [

%]

of

Bx

Thermal contraction of wires

B. Plaster

Originally: Cu magnet wire wound on Al frame

Al CTE: 24 ppm/K Cu CTE: 17 ppm/K

300 K

77 K

Prediction

Perc

enta

ge D

evia

tion [

%]

of

Bx

Coil with Cu wire No ferromagnetic

shield

Thermal contraction of wires

B. Plaster

Improvement: Al magnet wire

Perc

enta

ge D

evia

tion [

%]

of

Bx

300 K

77 K

Prediction

Coil with Al wire No ferromagnetic

shield

Shielding factor attenuation

B. Plaster

For (cos θ coil + 3x Metglas) studies

Metglas shielding factor decreases ~10 at 77K

Reduced attenuation of (non-uniform ) background fields

Perc

enta

ge D

evia

tion [

%]

of

Bx Coil (Al Wire) +

3x Metglas at 77 K

~ 1 mGauss

Shielding factor attenuation

B. Plaster

Field

Devia

tion [

Gauss

] of

Bx

Room Background

~ 4 mGauss ~ 0.7

mGauss

Shielded 77K Background

Need Background Gradient 0.5

mGauss

~ 0.5 mGauss

For (cos θ coil + 3x Metglas) studies

Metglas shielding factor decreases ~10 at 77K

Reduced attenuation of (non-uniform ) background fields

Shielding factor attenuation

B. Plaster

Improvement: more (multi-layer) shielding

3-layer shield: inner Metglas, Cryoperm, outer Metglas

77K background attenuated by factor of ~10

300 K

77 K

Prediction

Future “small-scale” experiments

B. Plaster

In process of fabricating (~90% complete) ~ 17%-scale prototype with optimized N = 34, ℓ/r = 6.4 [r ~ 11 cm]

Nℓ / r

global minimu

m

cell~ 0.04 mGauss

1.5 Gauss

Factor of ~12 more uniform

Other “experiments”

B. Plaster

Wire “droop” and tensioning required for 1/2-scale

• Diameter ~ 26”, length ~ 7 feet

Wire Tension Test

m

~ 6 feet

I-bolt

fixed anchor point

fixed

heights fixed with level

floor

wire “droop” from level measured with transit

as function of m

mass droop from level

50 g 0.209” = 5.31 mm

100 g 0.134” = 3.40 mm

150 g 0.104” = 2.64 mm

200 g 0.084” = 2.13 mm

250 g 0.072” = 1.83 mm

300 g 0.061” = 1.55 mm

350 g 0.051” = 1.30 mm

mass droop from level

400 g 0.041” = 1.04 mm

450 g 0.034” = 0.86 mm

550 g 0.012” = 0.31 mm

650 g 0.006” = 0.15 mm

750 g 0.003” = 0.08 mm

850 g 0.000” = 0.00 mmBob Carr / Brad Plaster

Feb. 22-23, 2007

Wire specs:

SC-T48B-6-0.4mm from Supercon

0.44 mm diameter Formvar insulation

TOSCA modeling indicated two possible sources of asymmetries:

• Welds on shield cylinders

• Mis-alignment of axis of coil relative to shield

Cryoperm

shield

coil

Sample TOSCA result

Importance of co-axial

alignment !! (see R. Alarcon TOSCA talk)

welds

October 2006 Collaboration Meeting

New idea

• “Wind” Metglas strips directly onto surface of cos coil support frame

• Monolithic design guarantees co-axial alignment

• Also desirable as comes in 0.8-mil thick strips, few layers sufficient; thin shield desirable for Eddy current heating

Metglas

winding

cos coil support frame

October 2006 Collaboration Meeting

Office of Nuclear Physics

Pre-proposal: Cylindrical superconducting shield surrounding cos θ coil• Mirror currents in superconductor result in worsening of field uniformity

Now: Ferromagnetic shield surrounding cos θ coil• Mirror currents in ferromagnetic material result in improved field uniformity

Impact of inner ferromagnetic shield

Results of initial TOSCA calculations confirmed improvement in field uniformity for cos θ coil + ferromagnetic shield

prototype-sized coil dimensions

cos θ coil only

cos θ coil + shield