Ernie Ihloff 21 May 08

Preliminary Heat Shield Design for nEDM

Ernie Ihloff 21 May 08

Heat Shield Design Choices

• Meets Physics requirement for experiment• Limits heat load to inner volumes • Reliable design; no leaks or failures• Manufacturability, Serviceability and Cost• Support scheme that addresses movement • Number of heat shield and temperatures• LN2 shield or not• Cool down requirements

Ernie Ihloff 21 May 08

Layout

Ernie Ihloff 21 May 08

Heat Shield Material Choices

• OFHC copper for outermost shield if it meets experiment requirements (MIT recommendation)

• Aluminum alloy for inner shields only if required• Support scheme and materials that limit heat load • Copy support designs from SRF community

Ernie Ihloff 21 May 08

OFHC Copper as heat shield

• Proven in most SRF cavities worldwide. Jlab, SNS, Cern, and Desy

• Does it meet Physics requirements ???• Braze with Sil-fos or other lower temperature alloy• Lower CTE than Aluminum Alloys• Very reliable • Thermal Conductivity Copper vs. Aluminum

At 40K, 5 times better ( 2000 W/ cm-K)

At 80K, 2 times better ( 600 W/cm-K)

Ernie Ihloff 21 May 08

Aluminum Heat ShieldsThermal Conductivity Comparison

Ernie Ihloff 21 May 08

Aluminum Heat ShieldsMaterial Comparison

Aluminum 5083Aluminum, Al 92.4 - 95.6 %Chromium, Cr 0.0500 - 0.250 %Copper, Cu <= 0.100 %Iron, Fe <= 0.400 %Magnesium, Mg 4.00 - 4.90 %Manganese, Mn 0.400 - 1.00 %Other, each <= 0.0500 %Other, total <= 0.150 %Silicon, Si <= 0.400 %Titanium, Ti <= 0.150 %Zinc, Zn <= 0.250 %

Aluminum 1100Aluminum, Al >=99%Beryllium, Be <= 0.000800 %Copper, Cu <= 0.05 %Manganese, Mn <= 0.05%Other, each <= 0.0500 %Other, total <= 0.150 %Silicon, Si <= 0.95 %Zinc, Zn <= 0.10 %

Aluminum 6061Aluminum, Al 95.8 - 98.6 %Chromium, Cr 0.0400 - 0.350 %Copper, Cu 0.150 - 0.400 %Iron, Fe <= 0.700 %Magnesium, Mg 0.800 - 1.20 %Manganese, Mn <= 0.150 %Other, each <= 0.0500 %Other, total <= 0.150 %Silicon, Si 0.400 - 0.800 %Titanium, Ti <= 0.150 %Zinc, Zn <= 0.250 %

Aluminum 3003Aluminum, Al 96.7 - 99.0 %Copper, Cu 0.0500 - 0.200 %Iron, Fe <= 0.700 %Manganese, Mn 1.00 - 1.50 %Other, each <= 0.0500 %Other, total <= 0.150 %Silicon, Si <= 0.600 %Zinc, Zn <= 0.100 %

Ernie Ihloff 21 May 08

Aluminum Fabrication Issues

• Need to narrow alloy choices for fabrication tests

• Try all in small 1 foot square tests

• Try different tubing attachment processes

Clamp (Poor thermal contact)

MIG or TIG weld (hard)

Braze (vacuum braze)

1100 Aluminum best choice

Ernie Ihloff 21 May 08

Heat Shield Temperature and Load

Ernie Ihloff 21 May 08

Heat Shield Design Parameters

Outer Cryostat - 6061 Aluminum, emissivity = .2

50K shield - OFHC Copper emissivity = .07(polished copper) 3 mm thick (.118) 22.2 mm tubing (1.0 mm thick) Initial design 40 Square meters 1000 kg.

4.5K shield - 1100 aluminum with brazed tubing 9.5 mm thick 400 kg

.3-.5K Central Volume – Composite emissivity = 1.00

Vacuum better than 5 x 10e-5 torr

Double Aluminized Mylar (DAM) 25 micronsPolyester 75 micron spacerEmissivity = .035

Ernie Ihloff 21 May 08

Summary

• Use proven designs as guidance, Mostly Jlab• Suggest use of OFHC copper outer shield• Use 1100 Aluminum where necessary

Tasks to complete concepual design• Finish hand calculations (June 08) Not ready to release today• Do FEA on heat transfer and structure (June-July)• Work with Jan on supports (thermal and mechanical)