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Update on coatings for SPS

Update on coatings for SPS. M.Taborelli for SPSU. Present status for the carbon coatings. SEY measurements in the lab: δ max= 0.9-1.1 for all coatings, as received, after 2h air aging in water vapour is worse than in air; the mechanism is not clear aging is different for different coatings

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Update on coatings for SPS

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  1. Update on coatings for SPS M.Taborelli for SPSU

  2. Present status for the carbon coatings • SEY measurements in the lab: • δmax= 0.9-1.1 for all coatings, as received, after 2h air • aging in water vapour is worse than in air; the mechanism is not clear • aging is different for different coatings • E-cloud monitors (ECM) • -carbon coatings suppress e-cloud (10-3-10-4 compared to StSt) • -central stripe of 40 mm almost sufficient • -no aging observed for more than 1 year of operation • NB1: no field ramp (injection energy value), few electrons extracted from the e-cloud for the measurement • NB2: no pressure data in ECM • Prototype coated MBB dipoles in SPS • dynamic pressure rise in coated very similar to uncoated • microwave transmission shows 10 times less e-cloud related signal in coated • NB1: coating is different from ECM due to B-geometry and T limitation

  3. Mobile sample -showed strong aging (SEY up to 1.5); coating is still there, with more O than before on the surface NB1: coated as a liner, but exposed to air for months before insertion in SPS NB2: was facing StSt, so it was submitted to e-cloud “irradiation” Coating techniques -coatings in liner can be considered as good -coating in long pipes, as dipoles, is not uniform yet -in assembled dipole more difficult that in separated tube

  4. Ongoing activities and news: • -cut open the magnet chamber (extracted from the dipole this week) • -new mobile a-C sample inserted in SPS • (without long venting before insertion) • -cut open the e-cloud monitor • with a-C strip and measure SEY • dosimeters placed in spots of BA5 • cavern to identify spot to place RGA • electronics • -pressure rise and e-cloud measured • during LHC test beam • -proposal for diagnostics with multipactor • -second series of aging tests in the lab (in air, vacuum, N2, H2O vap)

  5. SEY of a sample cut from liner History: the liner was 1 year in SPS + 1 month in air Both spots on the pieces cut out of the liner strip have still low SEY

  6. Effect of air exposure after irradiation (in the lab) on SEY Inspired by the bad result of the mobiles sample: now on sample extracted from SPS liner Irradiated with 1E-1 C/mm2 The aging is still rather slow (ex: MBB witness samples went to 1.2-1.3 after one month in air without irradiation)

  7. SPS, 36 bunches, 50 ns spacing, 1 batch E-cloud current FBCT Un-un Co-Co E-cloud current Un-un FBCT Very likely change of gain in FBCT It is transparent in the acquisition!

  8. E-cloud vs bunch spacing and conditioning of StSt

  9. Proposal for diagnostics on dipoles (coated, uncoated) ex-situ (F.Caspers) • Use the dipole as waveguide and measure multipacting (MP) properties • diagnostics through reflected power or independent travelling wave transmission at different frequency • no beam necessary • -can measure in the dipole with the coating on the dipole or with a coated test-liner inserted, with/without B-field • -can measure a sample submitted to e-cloud-like irraidiation in the dipole vacuum to see potential aging effects • -non destructive, non polluting (no wire inside): can be used later for quality control f

  10. First estimate of necessary power -Dipole cross-section ~ WR510 (129 x 64 mm2) - 1.5 GHz -power to induce MP is about P=30 KW travelling wave and SEY of 2 (copper) (ESA MP calculator)  use standing wave mode and profit of Q factor Q factor estimate from losses: - for Cu 0.005 dB/m - for StSt we have 50-70 times lower conductivity, so 8 times higher losses Q0= 2π = 4500 (in Neper/m, 1dB=8.68 Nep)) λ·loss (H.Meinke, F.Gundlach, Tachenbuch der HF technik) The loaded Q is Q0/2 (critical coupling) Can be done with a large safety margin with the available 100W power

  11. Next • Results of cut dipole chamber • Aging in various environments (SEY in the lab) • Irradiation in the lab of MBB test samples and aging to compare with liner sample. Irradiation of a liner sample which has been long time in air before • Test coatings configurations to improve uniformity of coating in long chambers with 2 (3) types of cathodes: (permanent magnets) loops and straight rods (only for coating chamber alone). Insert 2-3 dipoles coated in the best way we can in SPS in winter stop 2010-11 • - 2 runs of test of gas desorption with heavy ions on a-C coated chambers foreseen in Linac3

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