a-Cvalues describe: a-C on Cu
Big science (accelerators, light sources, public fusion)
What it enables
Secondary electron yield near 1 with no activation bake: electron cloud suppression where you cannot heat.
Status and pusher
Deployed in the SPS and part of the HL-LHC toolkit, with years of beam exposure and no degradation. Pushed by CERN.
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 | substrate cleaned to UHV standard before sputtering; the film tolerates a solvent wipe |
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| Forbidden | abrasives |
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| Limit | adhesion, set by substrate preparation |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 5e-10 mbar·L/s/cm² |
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| Outgassing, baked | 5e-13 mbar·L/s/cm² |
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| Vapour pressure | none |
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Temperature
| Bake, assembled | 300 °C |
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| Vacuum degas | substrate |
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| Metallurgical limit | graphitises above 400 °C |
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Thermal
| CTE | substrate |
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| Thermal conductivity | substrate |
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| Specific heat | 710 J/kg·K |
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| Emissivity | 0.8 |
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Mechanical
| Strength | coating |
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| Elongation | nil |
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| Hardness | 1500–2500 HV |
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| Density | 2 g/cm3 |
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Electrical and magnetic
| Relative permeability | 1.0 |
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| Resistivity | 1e-2–1e2 Ω·cm |
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Engineering
| Corrosion | inert |
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| Joining | sputtered in situ |
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| Process notes | SEY below 1.1 as deposited, with no activation and no capacity limit |
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| Availability and cost | CERN-derived, few sources |
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Sources · 1
- NEG and carbon coatings for accelerators, review
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