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This article discusses the monitoring of e-cloud phenomenon and pressure rise in the coating industry. It provides insights on pressure variations during different conditions and compares data from various experiments. The article also highlights the effect of e-cloud on different types of coatings.
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SPS MD run w17: e-cloud monitors and pressure rise Coating news By M.T.
MBB dipoles uncoated uncoated new a-C coated q 51340 51480 51540 ECM P 51824 StSt StSt
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)
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)
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?
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
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
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
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
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
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)
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
