Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN R. Salemme, V. Baglin, G. Bregliozzi on behalf of TE-VSC group Electron Cloud Meeting #18 CERN December 04 th 2014

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN First COLDEX experimental run during SPS Scrubbing Run I (03-10/11) COLDEX inserted on Monday 3 rd at 12:00: no impact on beam lifetime COLDEX sector extracted on Monday 10 th, at 6:00 Objectives and achievements Accumulation of beam time and electron dose → Time integrated beam current exceeds 4 A∙h → different, in some cases limited, circulation time before dump (at flat bottom, at flat top) Study with different SPS parameters (beams and intensities) → from 1 to 5 batches of 72 bunches, 25 ns bunch spacing, up to 1.3E+11 ppb → mainly at 26 GeV/c, but also with acceleration to 450 GeV/c Study at 2 beam screen temperatures: ~50 K, then ~5-10 K Study with doublet beams (5+20 ns hybrid spacing) → observed limited effects due to field-free and a-C coated region COLDEX: SPS Scrubbing Run I 2

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN COLDEX Measurements 3 Total pressures along the vacuum system: VGIs Partial pressures in the RT and cryogenic parts: RGAs Electron activity on the middle electrode: chimney biased electrode BS and CB temperatures: CERNOXs Heat load on the beam screen

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Preliminary Results: overview 4 50 K 5 K 10 K

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Preliminary Results: at 50 K 5

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Preliminary Results: H2 evolution 6

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Preliminary Results: at 5K 7

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Preliminary Results: H2 evolution 8

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Conclusions for Scrubbing Run 1 ● Within the beam time obtained during the first SPS Scrubbing Run, first observations of a-C coating at 50 K and 5-10K with LHC type beams and doublet beams did not reveal strong effects of vacuum degradation imputable to electron cloud ● Along the scrubbing run, significant pressure rises were observed outside the COLDEX system, while in COLDEX a pressure rise has been observed mainly due to H 2 gas accumulation at 50 K ● No appreciable electron activity was observed on the RT electron collector of COLDEX: below 50 nA ● Observed dissipated heat loads along the a-C coated beam screen are smaller than 1 W/m 9

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN Future perspectives: 2014 ● Participation to second SPS Scrubbing Run: ?/12 →longer studies with BS at 10 K, CB at 3 K →more interested in higher beam intensities rather than doublets (low effectiveness for COLDEX location and set-up)  (gradually) increase of bunch intensity: > 1.3∙10 11 ppb  inject 4 batches or more →long beam circulation time before dump is essential  Operate with maximum achievable beam dump time to get cycle close to 100 % ● Improve understanding of dynamic effects linked to H 2 → in-situ different gas injections and evolution follow-up during Xmas TS → simulations 10

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN 11 Future perspectives: 2015 ● COLDEX is not compatible with LHC PHYSICS operation (too much time for extraction/insertion) ● Participation to SPS Scrubbing Runs in Preliminary schedule sees:  w.16 → but LHC re-commissioning with beam: compatible?  w.22 → depending on LHC Technical Stop 1 (Mo-Fr) ● Perform specific studies e.g. gas accumulation, different BS temperature ranges, coating ageing, etc. during 2015 MDs →~ 5 x (8-12) hours “fully dedicated” MDs with LHC type beams →possible allocation: before LHC operation (February) and close to LHC TSs?

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN 12 Future perspectives: 2016 ● During last IEFC (28/11), L. Rossi approved COLDEX runs also for 2016 (Crab Cavities will be installed in SPS LSS4 in EYETS )

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN 13 Acknowledgments ● Strong support and commitment of many CERN groups for COLDEX refurbishment and operation: TE-VSC, TE-CRG, BE-OP, BE-ABP, TE-EPC, EN- ICE ● Thanks to L. Rossi, HL-LHC project leader, Crab Cavities, WP 4, and Cryogenic, WP9, projects for their support to operate COLDEX during 2016