E-Cloud Monitors and Pressure Rise in Coating News

1. SPS MD run w17: e-cloud monitors and pressure rise Coating news By M.T.

2. MBB dipoles uncoated uncoated new a-C coated q 51340 51480 51540 ECM P 51824 StSt StSt

3. Static pressure and start of MD, unstable beam, large losses q Highest pressure in freshly inserted ECM StSt 51340 51480 51540 Highest pressure in freshly inserted uncoated dipole P[mbar] lowest pressure in old conditioned uncoated inserted dipole 27.04 -Static pressure as usual (for instance w25/09 or w45/09)

4. Second night of MD, stable beam, very low losses 29.04.10 -Conditioning is very weak -Difference in dynamic pressure due to history more than coating -large pressure rise in ECM (as before)

5. E-cloud monitors StSt. Unit: integrated electron current over supercycle (nC) integrated FBCT over supercycle (1e10protons/bunch) x104 a-CNe13 a-CZr • Almost no conditioning of StSt; one monitor with 2 times more signal than the other • Decrease in current in carbon monitors …due to (weak) pressure decrease?

6. Pressure rise comparison: data of MD w25/09 3b 4b 2009 w25 2010 w17 - No significant differences except for the higher pressure in the recently inserted dipole51480

7. Fast pressure acquisition (300Hz) 4 batches with acceleration Synchronization with FBCT clearly shows the effect of each batch The minimum of pressure is at second injection The differences in individual shapes are not understood P[mbar] Intensity 1010p/b

8. Comparison fast and normal (PVSS, 1s) acquisition Synchronization accuracy 1s due to PVSS (1s resolution) Still some calibration to be corrected on data of 51480

9. Next liners after w22 2 half shells • Partial a-C coating to verify the effect of e-cloud close to a-C: • non uniform in lateral direction to profit of resolution of strip detector StSt grooves insert, (M.Pivi) Inserts just arrived at CERN

10. Coatings • half-length chamber with MBB profile coated (SEM for thickness profile in progress): more uniform with rectangular cathodes than cylindrical excepted for the gap between rods (see figure). • 7m prototype next week; then 7 m real MBB chamber (with rectangular cathodes) • Coated 2 liners for ECM in the SPS: SEY=0.95 after one week air exposure! (high power => high deposition rate and high resulting substrate temperature ~250C) • Coated tube for ion induced desorption experiment in Linac 3 (running) • Characterization: pumpdown measurements done on CNe53 (round tube) confirm 10x higher outgassing of a-C wrto unbaked StSt • Asked two firms for a sample with alumina plasma spray to test first degassing and dielectric strength

11. Coating with rectangular cathodes Defects of the substrate “plasma rings” at extremities Defects due to a gap in the cathode (new cathode design tested today)

12. Next on SPS : • w22: replace the ECM and intermediate section with a-C coated ECM and measure again the dynamic pressure simultaneously with e-cloud • w22: remove dosimeters (measurements of dose to identify possible location of RGA electronics to identify desorbed gases) • -w26: extract removable sample for SEY analysis (to verify the effect of e-bombardment on the a-C coating) • -w30: insertion of coated MBB (3 m prototype OK, tubes ready for end of May probably with rectangular cathodes) • -w26 or w30: replacement of a-CZr ECM with half-coated ECM • -at the next venting of dipoles we could isolate a pumping port (pressure gauge+ion pump) through a manual valve from the main vacuum system of the machine to verify the behavior with beam and magnet ramp

14. Effect of the magnets on the gauge signals