CuSSvalues describe: Cu on 316LN
Big science (accelerators, light sources, public fusion)
Why it wins
The LHC answer to a cold bore: a high-Mn austenitic screen colaminated with about 75 microns of OFE copper, pumping slots to the 1.9 K bore behind, sawtooth facing the synchrotron light. Image currents see copper, cryogenics sees a shield.
Why not the alternative
Bare steel screens would cook the beam with resistive wall impedance; bare cold bore would cryosorb and then avalanche.
Watch out
HL-LHC adds amorphous carbon on top for e-cloud: a three-material laminate.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: CERN vacuum group compilations and coating programme; CERN Accelerator School, vacuum and materials proceedings.
Wet cleaning
| Recipe | as OFE on the copper face, with the steel side protected |
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| Forbidden | anything that lifts the bond |
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| Limit | bond integrity, checked before and after |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 1e-9 mbar·L/s/cm² |
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| Outgassing, baked | 5e-12 mbar·L/s/cm² |
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| Vapour pressure | negligible |
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Temperature
| Bake, assembled | 300 °C |
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| Vacuum degas | 600 °C |
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| Metallurgical limit | the copper layer recrystallises from 200 °C |
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Thermal
| CTE | 16–17 copper face ppm/K |
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| Thermal conductivity | 391 in the copper skin W/m·K |
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| Specific heat | 400 J/kg·K |
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| Emissivity | 0.05 copper face |
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| Melting / softening | 1085 (Cu) °C |
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Mechanical
| Strength | set by the steel substrate |
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| Density | 8.4 composite g/cm3 |
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Electrical and magnetic
| Relative permeability | <1.005 on a 316LN substrate |
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| Resistivity | 1.71 in the skin, which is the point |
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Engineering
| Corrosion | the copper face oxidises |
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| Joining | the colaminate is the joint |
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| Process notes | low surface resistance on a strong low-μr substrate |
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| Availability and cost | specialist rolling, accelerator supply chain |
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Grades
| P506-class high-Mn steel plus OFE Cu colamination | the LHC arc screen construction |
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Sources · 1
- HL-LHC project, vacuum and beam screens
← The Matter