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Magnetic fields R&D update. Results from prototype studies of a 1/6-scale B 0 coil with. (∂B x /∂x)/B 0 ~ 3 x 10 −5 cm −1 over scaled fiducial volumes. Results from 4-Kelvin test of a prototype system. cos θ coil + ferromagnetic shield + Pb superconducting shield.
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Magnetic fields R&D update Results from prototype studies of a 1/6-scale B0 coil with (∂Bx/∂x)/B0 ~ 3 x 10−5 cm−1 over scaled fiducial volumes Results from 4-Kelvin test of a prototype system cos θ coil + ferromagnetic shield + Pb superconducting shield nEDM November 2007 Collaboration Meeting B. Plaster
Completed Summer SURF Last collaboration meeting In process of fabricating (~90% complete) a 17%-scale prototype with optimized N=34, ℓ/r = 6.4 [ r = 10.9 cm, ℓ = 69.7 cm ] Model Prediction cell cell global minimum ~ 2 10−6 cm −1 Factor of ~20 more uniform along x-axis than previous prototypes ℓ / r N nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile First-iteration map nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile nEDM November 2007 Collaboration Meeting B. Plaster
First-iteration map Second-iteration map N=34, ℓ/r = 6.4 field profile Mispositioned groove predicted to generate gradient of wrong sign Correction should exacerbate gradient !! nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile Instead of trying to achieve “perfection”, instead decided to correct with a gradient coil Unwanted gradient ~linear Will no doubt face similar problems in “real” experiment Gradient coil N=2 cos θ coil winding, but as an “anti-Helmholtz” pair Current ratios 1.0 A in N=34 12 mA in N=2 nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile uniformity ~ 4 10−5 (∂Bx/∂x)/B0 ~ 3 x 10−5 cm−1 desired (∂Bx/∂x)/B0 scale-up to full-size (∂Bx/∂x)/B0 ~ 5 x 10−6 cm−1 1 10−6cm−1 nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile Test at 77 K nEDM November 2007 Collaboration Meeting B. Plaster
N=34, ℓ/r = 6.4 field profile With ferromagnetic shield at 300 K Known for some time that N=34 uniformity worsens in presence of ferromagnetic shield Hence, reason for design of “modified” cos θ coils with wire positions offset from nominal ASU, S. Balascuta TOSCA Caltech, M. Mendenhall nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests Pb superconducting shield 4K dewar from J. Eisenstein group (Caltech condensed-matter) Radius = 9.5 cm Length = 100.0 cm Baffled heat-shield neck (5 layers of Cu-coated PCB) Accommodates N=40 prototype cos θ coil + ferromagnetic shield Feedthroughs for probe (z-motion only), leads, sensors, etc. Pb Tc = 7.2 K 1/16”-thick, on Al frame nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests One initial test, (only) Earth’s field locked-in during transition through Tc First set of tests, August 2007 Initial cooldown of Pb shield from ~100K required ~60 ℓ of LHe Probe oriented for axial measurements, Bz(z) Only one temperature sensor mounted at top of shield 80 Gauss axial field (Helmholtz coil) applied after T < Tc consistent with residual background top of shield 80 G Lower limit on axial shielding factor of ~ 200 (limited by power supply) nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests Second set of tests, early-September 2007 Setup to test N=40 cos θ coil + ferromagnetic shield mounted within Pb shield Idea was to map Bx(z) for coil+ferro+Pb, compare with TOSCA Received 2 new temperature sensors, mounted near bottom/middle of Pb Test failed, unable to cool entire assembly to 4 K with 120 ℓ LHe Later hypothesized that an Al plate that coupled cos θ coil onto its support stand obstructed flow of LHe to bottom of dewar nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests Third set of tests, mid-September 2007 Coupler support plate reamed out Identical setup of N=40 + ferro + Pb Leads for 3 temperature sensors, cos θ coil DC leads, degaussing coil AC leads, magnetometer probe, etc. Successfully cooled entire assembly from ~100 K to 4 K with 120 ℓ LHe T < Tc for ~30 hours No LHe level sensor nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests Map of Bx(z) for N=40 cos θ coil + Metglas + Pb at 4 K Precision limited by “hand mapping” Thanks to S. Balascuta (ASU) for TOSCA calculations nEDM November 2007 Collaboration Meeting B. Plaster
Pb superconducting shield tests During warmup, field at center recorded every ~3 seconds Demonstration of effectiveness of superconducting shield at screening time-varying backgrounds Power supply stability better than ~5 × 10−5; fluctuations at T > Tc from background fluctuations leaking through ferromagnetic shield nEDM November 2007 Collaboration Meeting B. Plaster
Future R&D work Attention now focused on construction of a 1/2-scale prototype modified cos θ coil and ferromagnetic shield Not “true” cos θ coil; wire positions optimized for uniformity in presence of ferromagnetic shield acrylic tube 24” O.D. 3-ring set of acrylic “rings” 6’ + 1.5’ (glued) nEDM November 2007 Collaboration Meeting B. Plaster
Future R&D work Status Machining to be done at the Caltech HEP shop Acrylic materials on hand since August 2007 Plagued by delays at machine shop (i.e., were considered low priority) Recently (last week, after 2-month delay) HEP shop arranged for outside shop to start machining on the acrylic rings Also in process of upgrading our automated mapping system to accommodate the 1/2-scale coil and the 1/2-scale dewar 25’-tall structure, Caltech HEP high-bay area Goal is first results (perhaps not best !!) by April/May/June time-scale nEDM November 2007 Collaboration Meeting B. Plaster
