# Presentation: 544287

## The Four-Layer Conventional Magnetic Shield

- Brad 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

- superconducting 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 ]
- ...

## 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 Gauss |  |  |  |

*Ideal 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”

- 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

## 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

- 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