Fe3O4values describe: NiZn ferrite
Big science (accelerators, light sources, public fusion)
Why it wins
Inside cavities and kickers, unwanted RF must die somewhere: HOM absorber ferrites and lossy dielectrics turn beam-induced modes into heat on purpose.
Why not the alternative
Unloaded cavities ring; external loads cannot reach trapped modes.
Watch out
Outgassing and brazability of ferrites are their own qualification campaigns.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: CERN Accelerator School, vacuum and materials proceedings.
Wet cleaning
| Recipe | solvent wipe, dry; porous grades bake rather than wash |
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| Forbidden | aqueous soak: porosity holds water; and check for zinc before any hot service |
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| Limit | the Curie point sets the bake, and the bake sets the cleaning that is possible |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 5e-9 mbar·L/s/cm² |
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| Outgassing, baked | 5e-12 mbar·L/s/cm² |
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| Vapour pressure | zinc-bearing ferrites are a vapour risk hot: check the composition |
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Temperature
| Bake, assembled | 200 °C |
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| Vacuum degas | 400 °C |
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| Metallurgical limit | Curie 100–400 °C by grade; above it the damping is gone |
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Thermal
| CTE | 8–10 ppm/K |
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| Thermal conductivity | 3–6 W/m·K |
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| Specific heat | 750 J/kg·K |
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| Emissivity | 0.9 |
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| Melting / softening | 1400 dec. °C |
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Mechanical
| Strength | 50–100 flex MPa |
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| Elongation | nil |
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| Young's modulus | 150 GPa |
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| Hardness | 600 HV |
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| Density | 4.8–5.2 g/cm3 |
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Electrical and magnetic
| Relative permeability | the whole point: 100–2000 initial |
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| Resistivity | 1e5–1e8 Ω·cm |
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Engineering
| Corrosion | good |
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| Joining | clamped or bonded |
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| Process notes | damps HOM and parasitic modes in RF structures |
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| Availability and cost | RF component suppliers |
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Grades
| CMD5005 class ferrite | kicker and absorber heritage grade |
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| TT2-111R class | SRF HOM absorber ferrite |
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| AlN-SiC lossy ceramics | brazable absorbers where ferrites fail |
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Sources · 1
- CERN Accelerator School, RF systems
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