The Four-Layer Conventional Magnetic

ShieldBrad Plaster, Caltech

May 25, 2006

“Current” design Estimated shielding factors Production and time-scale Estimated costs $$$

Overview of current design

Layer Radius [cm]

1 96.7

2 101.8

3 106.8

4 111.9

Upper cryostat cylinders[ J. Boissevain, 13:17 EDT Today !!! ]

~7.5 m

~5.0 m

Layer Radius [cm]

1 106.9

2 111.9

3 117.0

4 122.1

62-mil layer thickness → ~5.5 English Tons

Lower cryostat cylinders

Δ ~ 5.1 cm

Δ ~ 5.1 cm

~2.5 m

9 panels around

circumference

μ-metal tubes around

penetrations

Overview of current design

Lower cryostat inner shielding

Proposed upper cryostat inner shielding [ferromagnetic shield] Improve field uniformity from

3He spin-holding cos θ coil Dimensions driven by size of

3He spin-holding cos θ coil

ferromagnetic shield superconductin

g shield

Item Radius [cm]

Superconducting

62.9

Ferromagnetic 62.2

B0 cos θ coil 61.0

Lengths little less than 4.0 m

4K shield

[ J. Boissevain, March 2006, NCSU ]

Estimated shielding factors: I Transverse shielding factor, ST, for n-layer configuration of

infinitely-long concentric cylinders Sumner, Pendlebury, and Smith, J. Phys. D 20, 1095 (1987)

Proper evaluation requires a value of μi for each layer μn = μ(H) for H = Hext

μn-1 = μ(H) for H = Hext / [ shielding from nth layer alone ]

μn-2 = μ(H) for H = Hext / [ shielding from nth + (n-1)th layers ]

…

μ-metalCryoperm at 4K

Estimated shielding factors: I Results for lower cryostat shielding

Four-layer conventional shield + 4K ferromagnetic [ Cryoperm ] shield Presence of superconducting shielding ignored

Layer r [cm] μ(H) Accumulated ST

4 122.1 15900 Layer 4: 11.3

3 117.0 170000 Layers 4+3: 221.2

2 111.9 100000 Layers 4+3+2: 1663.7

1 106.9 70000 Layers 4+3+2+1: 10116.8

C 62.2 70600 Layers 4+3+2+1+C: 6.60 х 105

Residual Shielded Field = 7.6 х 10-7 GaussIdeal case: infinitely-long cylinders, no

penetrations, no end-caps

Estimated shielding factors: I Results for upper cryostat shielding

Four-layer conventional shield only

Layer r [cm] μ(H) Accumulated ST

4 111.9 15900 Layer 4: 12.2

3 106.8 170000 Layers 4+3: 261.8

2 101.8 100000 Layers 4+3+2: 2282.4

1 96.7 70000 Layers 4+3+2+1: 1.61 х 104

Residual Shielded Field = 3.1 х 10-5 Gauss

Ideal case: infinitely-long cylinders, no penetrations, no end-caps

Proposed inner ferromagnetic shield will provide greater shielding factor, comparable to lower

cryostat

Estimated shielding factors: II Zeroth-order finite-element analysis calculation of

shielding factors [TOSCA → ASU collaborators] Finite-length concentric cylinders without end-caps Lower and upper cryostats considered separately

4-layer conventional shield

Cryoperm shield

H = 0.5 Gauss transverse field

Estimated shielding factors: II Results for lower cryostat shielding

Four-layer conventional shield + 4K ferromagnetic [ Cryoperm ] shield Presence of superconducting shielding ignored

TOSCA result for residual field in the center of symmetry of the five concentric layers

1.77 х 10-6 Gauss

Within factor of ~2 of estimation assuming infinitely-long cylinders

TOSCA results as function of length of

the four-layer conventional shield

Estimated shielding factors: II Results for upper cryostat shielding

Four-layer conventional shield only

TOSCA result for residual field in the center of symmetry of the four concentric layers

2.10 х 10-3 Gauss

Calculation probably not that realistic Lengths of cylinders (~2.5 m)

taken to be distance from top of upper cryostat to lower-cryostat, upper-cryostat “tee”

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 500 1000 1500 2000 2500

Length [cm]

Res

idu

al F

ield

[G

auss

]

TOSCA results as function of length of

the four-layer conventional shield

Shielding factor optimization

Inspection of the formulas for the transverse shielding factor suggests that ST can be enhanced via a judicious choice of the radii

If (rj/rk) sufficiently small, ST ~ Si

T SjT Sk

T ...

Shielding factor optimization

Inspection of the formulas for the transverse shielding factor suggests that ST can be enhanced via a judicious choice of the radii

If (rj/rk) sufficiently small, ST ~ Si

T SjT Sk

T ...

Carried out a grid search over radii of four-layer shield 4K ferromagnetic shield and

inner-most layer of four-layer shield radii fixed

Baseline configuration ~220 m2 for lower cryostat ~ 67 m2 for upper cryostat

Computed ST for the radii of each grid combination, then estimated cost by scaling material costs to surface areas→ ~70% of the cost for the

shield will be material cost (more later about costs…)

Shielding factor optimization

Lower cryostat

Upper cryostat

Calculations: future TOSCA First approximation

Finite-length cylinders, no end-caps Ignore lower-cryostat and upper-cryostat connecting

“tee” Transverse and axial shielding factors Verify results of layer spacing optimization

Second approximation Add end-caps with geometry similar to that in Jan’s

“latest reference design” Optimize the geometry of the end-caps

Full model Join the lower-cryostat and upper-cryostat cylinders Model penetrations through the structure

Production of the shield Vendor selected is Amuneal

Located in Philadelphia (in the north-side ghetto…) Magnetic shields we have procured from Amuneal for our R&D

activities have all been delivered on-time Recently, have provided a free Cryoperm shield (valued at

~$3000) as part of joint R&D efforts between Caltech and Amuneal Delivered a ~1/4-scale multi-layer shield to J. Kirschvink at

Caltech (geophysics) Provided magnetic shielding for JLab, BNL, SNS (Beam Line 15),

… ; now in discussions of magnetic shielding requirements for the ILC

Preliminary design review conducted on-site at Amuneal on March 6, 2006 B. Filippone, J. Boissevain, W. Sondheim, S. Currie, and BP

Production of the shield Driving constraint for production is the size of their furnace

5’ diameter х 12’ long Assembly will consist of many “panels” For magnetic continuity, Amuneal has proposed using 4”-wide

battens along the circumferential and horizontal seams to be tightened with aluminum clamps

Envisage an Al support structure for the shield Tied into the main support structure for the lower and upper

cryostats, without transferring any of the load from the cryostats onto the μ-metal

Implicit that Amuneal will provide the Al spacers between the layers

Also implicit that Amuneal will construct the Al support structure, and “protective covering” for outer-most layer

Assembly issues Modular assembly

Lower cryostat shielding around the measurement cells → permits B-field tests, etc. in lower cryostat

Region near “rear” end-caps easily removable

Upper cryostat shielding, after ready to drop in upper cryostat “guts”

“Top” end-caps

“Rail system” for removing “rear” end-caps for access to B-field coils and measurement cells

Upper cryostat “cut in half”, for access to interior after installation

Serious integration issues !!

Time scale Now – April 2008: Design for shield, support structure,

degaussing system, integration issues, etc.

April 2008 – December 2008: Procurement period Cost fixed at time of PO

Shielding shipped via semi-truck to Caltech for test assembly/installation starting January 2009 in high-bay area Measure residual fields Shielding used for tests of all B-field coils to be fabricated at

Caltech/ASU

Installation of shielding structure and magnets at ORNL beginning November 2009

Expected cost $$$ Prior to February 2005

review, quote obtained from Amuneal

Expected cost $$$ Prior to February 2005

review, quote obtained from Amuneal

Design to be delivered to Amuneal in early-June, quote to be generated for CD-1 Review

$800 to $900 k

Expected cost $$$

Quote for Feb. 2005 Review

Saturation ?

Long-Standing Problem

• Motivation to investigate impact of weld beads/seams on N=20 cos θ coil + shield uniformity came from March 6 meeting at Amuneal

μ-metal

Cryoperm

Long-Standing Problem• TOSCA results

– Modeled cos θ coil + 62-mil thick μ-metal shield WITH 102-mil thick weld seam

μ-metal