1. 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 K Coil + 3x Metglas Shield at 77 K Investigated Source of Asymmetry Percentage Deviation [%] of B x

2. Thermal contraction of wires B. Plaster Originally: Cu magnet wire wound on Al frameAl CTE: 24 ppm/K Cu CTE: 17 ppm/K 300 K 77 K Prediction Percentage Deviation [%] of B x Coil with Cu wire No ferromagnetic shield

3. Thermal contraction of wires B. Plaster Improvement: Al magnet wire Percentage Deviation [%] of B x 300 K 77 K Prediction Coil with Al wire No ferromagnetic shield

4. 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 Percentage Deviation [%] of B x Coil (Al Wire) + 3x Metglas at 77 K ~ 1 mGauss

5. Shielding factor attenuation B. Plaster Field Deviation [Gauss] of B x 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

6. 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

7. 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] N ℓ / r global minimum cell ~ 0.04 mGauss 1.5 Gauss Factor of ~12 more uniform

8. Other “experiments” B. Plaster Wire “droop” and tensioning required for  1/2-scale Diameter ~ 26”, length ~ 7 feet

9. 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 massdroop from level 50 g0.209” = 5.31 mm 100 g0.134” = 3.40 mm 150 g0.104” = 2.64 mm 200 g0.084” = 2.13 mm 250 g0.072” = 1.83 mm 300 g0.061” = 1.55 mm 350 g0.051” = 1.30 mm massdroop from level 400 g0.041” = 1.04 mm 450 g0.034” = 0.86 mm 550 g0.012” = 0.31 mm 650 g0.006” = 0.15 mm 750 g0.003” = 0.08 mm 850 g0.000” = 0.00 mm Bob Carr / Brad Plaster Feb. 22-23, 2007 Wire specs: SC-T48B-6-0.4mm from Supercon 0.44 mm diameter Formvar insulation

10. 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

11. 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

12. 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