Magnetic fields R&D update B. PlasternEDM November 2007 Collaboration Meeting Results from prototype studies of a 1/6-scale B 0 coil with Results from 4-Kelvin test of a prototype system cos θ coil + ferromagnetic shield + Pb superconducting shield (∂B x /∂x)/B 0 ~ 3 x 10 −5 cm −1 over scaled fiducial volumes

Last collaboration meeting B. Plaster 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 ] N ℓ / r global minimum Factor of ~20 more uniform along x-axis than previous prototypes nEDM November 2007 Collaboration Meeting cell ~ 2  10 −6 cm −1 Completed Summer SURF Model Prediction

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting First-iteration map

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting Mispositioned groove predicted to generate gradient of wrong sign First-iteration map Second-iteration map Correction should exacerbate gradient !!

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting Instead of trying to achieve “perfection”, instead decided to correct with a gradient coil Unwanted gradient ~linear Gradient coil N=2 cos θ coil winding, but as an “anti-Helmholtz” pair 1.0 A in N=34 12 mA in N=2 Current ratios Will no doubt face similar problems in “real” experiment

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting uniformity ~ 4  10 −5 (∂B x /∂x)/B 0 ~ 3 x 10 −5 cm −1 (∂B x /∂x)/B 0 ~ 5 x 10 −6 cm −1 scale-up to full-size desired (∂B x /∂x)/B 0 1  10 −6 cm −1

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting Test at 77 K

N=34, ℓ/r = 6.4 field profile B. PlasternEDM November 2007 Collaboration Meeting 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

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting Pb superconducting shield Radius = 9.5 cm Length = cm Accommodates N=40 prototype cos θ coil + ferromagnetic shield 4K dewar from J. Eisenstein group (Caltech condensed-matter) Baffled heat-shield neck (5 layers of Cu-coated PCB) Feedthroughs for probe (z-motion only), leads, sensors, etc. Pb T c = 7.2 K 1/16”-thick, on Al frame

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting First set of tests, August 2007 Initial cooldown of Pb shield from ~100K required ~60 ℓ of LHe Only one temperature sensor mounted at top of shield One initial test, (only) Earth’s field locked-in during transition through T c 80 Gauss axial field (Helmholtz coil) applied after T < T c Probe oriented for axial measurements, B z (z) Lower limit on axial shielding factor of ~ 200 (limited by power supply) top of shield consistent with residual background 80 G

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting Second set of tests, early-September 2007 Setup to test N=40 cos θ coil + ferromagnetic shield mounted within Pb shield 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 Idea was to map B x (z) for coil+ferro+Pb, compare with TOSCA

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting Third set of tests, mid-September 2007 Identical setup of N=40 + ferro + Pb Coupler support plate reamed out 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 < T c for ~30 hours No LHe level sensor

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting Map of B x (z) for N=40 cos θ coil + Metglas + Pb at 4 K Thanks to S. Balascuta (ASU) for TOSCA calculations Precision limited by “hand mapping”

Pb superconducting shield tests B. PlasternEDM November 2007 Collaboration Meeting 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 > T c from background fluctuations leaking through ferromagnetic shield

Future R&D work B. PlasternEDM November 2007 Collaboration Meeting Attention now focused on construction of a 1/2-scale prototype modified cos θ coil and ferromagnetic shield acrylic tube 24” O.D. 6’ + 1.5’ (glued) 3-ring set of acrylic “rings” Not “true” cos θ coil; wire positions optimized for uniformity in presence of ferromagnetic shield

Future R&D work B. PlasternEDM November 2007 Collaboration Meeting Status Acrylic materials on hand since August 2007 Machining to be done at the Caltech HEP shop 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 Goal is first results (perhaps not best !!) by April/May/June time-scale 25’-tall structure, Caltech HEP high-bay area