DRESSING COIL PROTOTYPE

Riccardo SchmidDressing Coil prototype construction and mapping

nEDM Meeting Nov. 2nd, 2007 M.I.T./Bates

Dressing Coil Issues• Oscillatory B field induces eddy currents on FM Shield• Necessary to limit the dissipative heating to < 1W• It is possible to shield the B field using additional Active Shield Coils. • Important to keep B field uniformity high in the measurement cells.

N=34 Cosθ saddle coils

Cryoperm 1 mm

Current density distribution on FM shield(Unshielded)

Finite element analysis using ELEKTRA (Vector Fields) from ASU (R. Alarcon, S. Balascuta )

FM Shield

Dressing Coil

Active Shield

Demonstrate Active Shield efficiency by building a prototype.

Out[150]=

Active Shield3D Model

Shown:5 Active Shield contour pairs

UPDATED Power DissipationPower dissipated on the FM shield can be estimated to be

The effectiveness of the Active Shield increases as more windings are added to the shield.

NOTE: the data shown are from calculations for the new nEDM coils geometryR1 = 50cm L1 = 300cm (N=34 Cosθ)R2 = 55.9 cm L2 ~ 400 cm

Prototype ConstructionInner Dressing Coil:8-turn Cosθ coilR1 = 8.75 cmL1 = 49.6 cmOuter Active Shield:Contour coilR2 = 9.69 cmL2 ~ 64 cm

Active Shield outline printed on poster paper and wrapped around Al cylinder.Cu wires glued on paper.

Al Cylinder

Cu wires glued on paper

Posterprintout

Active Shieldwith 5 contour coil pairs

INSIDE FIELDPrototype MappingInner Dressing Coil (Cos coil) with a 1.5A current (fixed)Outer Active Shield (Contour Coil) variable current

B field mapping inside cylinders for comparison with calculations.

Only x component of the field measured inside the coils (By << Bx inside)

z

y

x

Nominal B field in x direction

Mapping field inside coils (Z axis)

INSIDE FIELDPrototype MappingInner Dressing Coil:8-turn Cosθ coilR1 = 8.75 cmL1 = 49.6 cmOuter Active Shield:Contour coilR2 = 9.69 cmL2 < 64 cm

Note: Mapping of x component of B field

Inner Field mapping

4.0E-024.2E-024.4E-024.6E-024.8E-025.0E-025.2E-025.4E-02

-7 -2 3 8 13

B (G

auss

)

Z (cm)

Data

Theory

4.54E-014.55E-014.56E-014.57E-014.58E-014.59E-014.60E-01

-7 -2 3 8 13B

(Gau

ss)

Z (cm)

Z Profile

Data

Theory

I1=1.5AI2=0.0A

I1=1.5AI2=-1.2A

Inner Coil only

Inner Coil + Active Shield

Normalization Needed

OUTSIDE FIELDPrototype MappingInner Dressing Coil (Cos coil) with a 1.5A current (fixed)Outer Active Shield (Contour Coil) variable current

Field mapping outside to measure shielding effectiveness at the FM shield radius.Measurements on 1/8 of the area of FM surface:R3 = 13cmL3 = 60 cm

( Inner: R1 = 8.75 cm and L1 = 49.6 cm)( Outer: R2 = 9.69 cm and L2 < 64 cm)

Measure Bx and By separatelyInterested in <|B|> at FM shield radius

NormalizationCurrent in inner dressing coil fixed at 1.5A

Current in outer Active Shield varied from 0A to -1.4A

Field at center of coils changes with Active Shield current – Linear Dependence

Need to normalize (scale) outside field measurements so that field at center is the same for all currents.

Outside Field MappingAverage Magnitude of Bx outside Dressing Coils at a radius of 13cmNormalized to the value of Bx for I2=0

Outside Field MappingAverage Magnitude of By outside Dressing Coils at a radius of 13cmNormalized to the value of Bx for I2=0

Conclusions

• Mapping of prototype shielding agrees with calculations

• Demonstrated one approach to the construction of Active Shields on printed paper

? Field Uniformity ? Test Dressing Fields with AC currents