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Some thoughts on the evolution of LHC scrubbing

Some thoughts on the evolution of LHC scrubbing. G. Rumolo, G. Iadarola , H. Bartosik. Record intensity: 2.7 x 10 14 p. Beam 1. Beam 2. After injection and transverse damper set up, 3.5 days of 25ns beam at 450 GeV (6 – 9 December, 2012)

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Some thoughts on the evolution of LHC scrubbing

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  1. Some thoughts on the evolution of LHC scrubbing G. Rumolo, G. Iadarola, H. Bartosik

  2. Record intensity: 2.7 x 1014p Beam 1 Beam 2 • After injection and transverse damper set up, 3.5 days of 25ns beam at 450 GeV(6 – 9 December, 2012) • Fast intensity ramp up: only one fill with trains of 72 bunches, then trains of 288 bunches • Several fills with maximum number of bunches (2748) • Very good efficiency • Injection time limited by vacuum in the MKI (beginning), then by time required by cryo to re-adjust to the increasing heat load

  3. Beam 1 Beam 2 • Scrubbing progress from heat load • Clear improvement during the first 60 – 70 hours • Slow-down of the process in the last part of the scrubbing Normalized heat load in Sector 5 – 6

  4. Beam quality evolution • Overview on lifetimes during scrubbing • Also from the lifetimes, after a clear improvement at the beginning, the process seems to significantly slow down

  5. Reconstructing the SEY evolution during the scrubbing run • Starting from an initial value of 1.55, the dmax in the arc dipoles seems to quickly flatten at a value slightly below 1.45 • Unexpected leveling of the process • From heat load measurements and PyECLOUD simulations

  6. Vacuum evolution (I) • Significant improvement seen in the vacuum (pressure gauges used for the SEY analysis in the LSS). Thanks to O. Dominguez, V. Baglin

  7. Vacuum evolution (II) • Clearer trend in terms of normalized pressure(pressure gauges used for the SEY analysis in the LSS). Thanks to O. Dominguez, V. Baglin

  8. Heat load in the arcs when ramping up the energy • Enhanced heat load probably due to photoelectrons (804 bunches at 4 TeV produce the same heat load as 2748 bunches at 450 GeV) • Violent transient during the ramp (limit of the # of bunches) • Not much additional scrubbing visible … 804b 804b 372b 156b 84b Thanks to L. Tavian

  9. Beam quality evolution • Between the test ramps at 4 TeV and the physics run, there were three more fills at 450 GeV (14 – 15 December, 2012) • Heat load as high as in previous fills with 2748 bunches • Emittance degradation still present with 288b fills Fill 3437: four trains of 288b + one of 144b Thanks to T. Rijoff, H. Maury-Cuna

  10. Electron cloud in the arcs elsewhere than in the dipoles? • Quadrupoles, multipoles • Modeling of the SEY curve • What happens at low energies? • Re-diffused electrons • Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces • The COLDEX experience

  11. Electron cloud in the arcs elsewhere than in the dipoles? • Quadrupoles, multipoles • Modeling of the SEY curve • What happens at low energies? • Re-diffused electrons • Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces • The COLDEX experience

  12. Possible interpretation • Cells composed of 80% dipoles, but also 6% quadrupole + 14% drift & multipoles • SEY thresholds are different in dipole/drift (1.45) or quadrupole (1.2) • Electron cloud in dipoles is dominant (1-2 orders of magnitude) as long as dmax > 1.5 in dipole chambers • But now quadrupoles (and multipoles?) could be dominant … • This could explain • Saturation of scrubbing process (scrubbing curve becomes very steep for SEY below 1.3) • Long memory between trains • Horizontal blow up

  13. Electron cloud in the arcs elsewhere than in the dipoles? • Quadrupoles, multipoles • Modeling of the SEY curve • What happens at low energies? • Re-diffused electrons • Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces • The COLDEX experience

  14. ELECTRON CLOUD STUDIES AND BEAM SCRUBBING EFFECT IN THE SPS J.M. Jimenez, G. Arduini, P. Collier, G. Ferioli, B. Henrist, N. Hilleret, L. Jensen, J-M. Laurent, K. Weiss, F. Zimmermann https://cds.cern.ch/record/615159?ln=it The Effect of Gas Ion Bombardment on the Secondary Electron Yield of TiN, TiCN and TiZrV Coatings For Suppressing Collective Electron Effects in Storage Rings F. Le Pimpec, R.E. Kirby F.K. King and M. Pivi https://cds.cern.ch/record/924733?ln=it

  15. THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTS V. Baglin, J. Bojko1, O. Gröbner, B. Henrist, N. Hilleret, C. Scheuerlein and M. Taborelli https://cds.cern.ch/record/466534?ln=it

  16. THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTS V. Baglin, J. Bojko1, O. Gröbner, B. Henrist, N. Hilleret, C. Scheuerlein and M. Taborelli https://cds.cern.ch/record/466534?ln=it MEASUREMENTS AT EPA OF VACUUM AND ELECTRON-CLOUDRELATED EFFECTS V. Baglin, I. R. Collins, O. Gröbner, C. Grünhagel, B. Henrist, N. Hilleret and B. Jenninger Chamonix XI

  17. R=1

  18. THE CHEMICAL ORIGIN OF SEY AT TECHNICAL SURFACES R. Larciprete, D. R. Grosso, M. Commisso, R. Flammini, R. Cimino Proceedings of ECLOUD12

  19. Usual Cos Flat

  20. Electron cloud in the arcs elsewhere than in the dipoles? • Quadrupoles, multipoles • Modeling of the SEY curve • What happens at low energies? • Re-diffused electrons • Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces • The COLDEX experience

  21. q Ep secondaries rediffused elastically reflected

  22. Re-diffused electrons are not included in our models… With re-diffused, POSINST model (G. Bellodi, 2004, ISIS studies) • Re-diffused electrons enhance the build up • Can impact up to a factor 2 on heat load calculations (e.g. LHC, PS2) • In the present ECLOUD/PyECLOUD model, electrons are either reflected or cause secondary emission No re-diffused (present model)

  23. Effect of re-diffused electrons: LHC heat load simulations (M. Furman)

  24. Electron cloud in the arcs elsewhere than in the dipoles? • Quadrupoles, multipoles • Modeling of the SEY curve • What happens at low energies? • Re-diffused electrons • Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces • The COLDEX experience

  25. ELECTRON CLOUD AND BEAM SCRUBBING IN THE LHC N. Hilleret, O. Bruning, F. Caspers, I.R. Collins, O. Grobner, B. Henrist, J.-M. Laurent, M. Morvillo, M. Pivi, F. Ruggiero, X. Zhang

  26. MEASUREMENTS AT EPA OF VACUUM AND ELECTRON-CLOUDRELATED EFFECTS V. Baglin, I. R. Collins, O. Gröbner, C. Grünhagel, B. Henrist, N. Hilleret and B. Jenninger Chamonix XI THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTS N. Hilleret , V. Baglin, J. Bojko, O. Gröbner, B. Henrist, C. Scheuerlein, M. Taborelli LHC Project Report 433 (2000)

  27. C. Yin Vallgren, Ph.D. thesis, CERN-THESIS-2011-063 (2011) • Scrubbing of Cu measured with e- at 500eV R. Cimino, A surface study on the origin of SEY reduction on accelerator walls, in Electron Cloud Simulations Meeting, 29/07/2011 Dose [C/mm2]

  28. THE CHEMICAL ORIGIN OF SEY AT TECHNICAL SURFACES R. Larciprete, D. R. Grosso, M. Commisso, R. Flammini, R. Cimino Proceedings of ECLOUD12

  29. Measurements of scrubbing on warm surfaces • In general (Cu on StSt): • E > 100 eV • About 10-2 C/mm2 • dmax below or about 1.2 • Scrubbing curve flattens for doses above 10-3 C/mm2 (dmax below 1.3)

  30. THE LATEST NEWS ON ELECTRON CLOUD AND VACUUM EFFECTS J.M. JIMENEZ, on behalf of the AT Department/Vacuum Group Chamonix XIII

  31. Latest results from COLDEX V. Baglin APC, 16/05/2005

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