3391
play

3391 3397 2.5 3390 Total intensity [p] 2 3396 3394 3389 1.5 - PowerPoint PPT Presentation

May 31, 2023 •558 likes •874 views

3407 3392 3401 14 x 10 3398 3405 3395 3406 3391 3397 2.5 3390 Total intensity [p] 2 3396 3394 3389 1.5 1 0.5 0 10 20 30 40 50 60 70 80 3438 3437 Time [h] Inten. [p x10 13 ], Energy [TeV] 20 3439 15 10 3436 3425

  1. 3407 3392 3401 14 x 10 3398 3405 3395 3406 3391 3397 2.5 3390 Total intensity [p] 2 3396 3394 3389 1.5 1 0.5 0 10 20 30 40 50 60 70 80 3438 3437 Time [h] Inten. [p x10 13 ], Energy [TeV] 20 3439 15 10 3436 3425 3427 3428 3429 5 0 170 180 190 200 210 220 230 Time [h] 3457 Inten. [p x10 13 ], Energy [TeV] 8 6 3441 3442 3453 4 2 0 5 10 15 20 25 30 35 40 Time [h]

  2. 25 ns in the LHC in 2012 Overview MDs Scrubbing run 12 – 15 Dec 2012 Physics run 6 – 10 Dec 2012 15 – 17 Dec 2012 1) S crubbing speed : why has the scrubbing process seemingly stopped in the LHC ? 2) Behavior of the heat load/stable phase shift with the beam energy

  3. Scrubbing Run Heat load in the arcs 14 x 10 2.5 Total intensity [p] 2 1.5 1 0.5 0 10 20 30 40 50 60 70 80 Time [h] Thanks to L. Tavian 60 Heat load [W/hc] 40 20 0 10 20 30 40 50 60 70 80 Time [h]

  4. Scrubbing Run Heat load in the arcs 14 x 10 2.5 Total intensity [p] 2 1.5 1 0.5 0 10 20 30 40 50 60 70 80 Time [h] -13 x 10 2.5 HL/I [W/(hc p)] 2 1.5 1 0.5 0 10 20 30 40 50 60 70 80 Time [h] Improvement Saturation

  5. Scrubbing Run Beam lifetimes Improvement Saturation

  6. Scrubbing Run Stable phase shifts Power loss from stable phase shift (Beam1 and Beam2) Total power loss from Total power loss from heat load in the arcs stable phase shift Ratio between power losses in above graph Beam 1 loses more power than Beam 2  Thanks to J. Esteban-Müller, consistent with worse lifetime E. Shaposhnikova

  7. Scrubbing Run Stable phase shifts Information on the build up of the e-cloud from the bunch-by- Thanks to J. Esteban-Müller, bunch measurements: saturated within the first four batches E. Shaposhnikova Could explain better lifetime of last injected batches

  8. Scrubbing Run Stable phase shifts Information on the build up of the e-cloud from the bunch-by- Thanks to J. Esteban-Müller, bunch measurements: still building up, not yet in saturation E. Shaposhnikova Could explain worse lifetime of last injected batches

  9. MDs at 4 TeV Heat load Inten. [p x10 13 ], Energy [TeV] 8 6 4 2 0 0 5 10 15 20 25 30 35 40 45 50 Time [h] Heat load enhanced and 60 Thanks to L. Tavian nearly flat at 4 TeV !!!! Heat load [W/hc] 40 20 0 0 5 10 15 20 25 30 35 40 45 50 Time [h]

  10. Fill 3429 Inten. [p x10 13 ], Energy [TeV] 8 800 bunches@4 TeV for 8h 6 4 Electron dose of about 2.4 x 10 -3 C/mm 2 2 (estimated by simulations) 0 0 20 25 30 2 Time [h] C. Yin Vallgren, Ph.D. thesis , CERN-THESIS-2011-063 (2011) 1.8 60 1.6 Heat load [W/hc] SEY max 40 1.4 20 1.2 0 1 -8 -6 -4 -2 0 10 10 10 10 10 Dose [C/mm 2 ] 0 20 25 30 Time [h]

  11. Fill 3429 Inten. [p x10 13 ], Energy [TeV] 8 800 bunches@4 TeV for 8h 6 4 Electron dose of about 2.4 x 10 -3 C/mm 2 2 (estimated by simulations) 0 0 20 25 30 Time [h] THE CHEMICAL ORIGIN OF SEY AT TECHNICAL SURFACES R. Larciprete, et al., Proceedings of ECLOUD12 60 Heat load [W/hc] 40 E-cloud threshold in dipoles 20 0 0 20 25 30 Time [h]

  12. Scrubbing Run Stable phase shifts Power loss from stable phase shift (Beam1 and Beam2) Total power loss from stable phase shift Total power loss from heat load in the arcs Ratio between power losses in above graph Transverse emittances (from BSRT) were Thanks to J. Esteban-Müller, not much degraded for this fill E. Shaposhnikova

  13. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

  14. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

  15. Scrubbing Run Stable phase shifts Power loss from stable phase shift (Beam1 and Beam2) Total power loss from stable phase shift Total power loss from heat load in the arcs Ratio between power losses in above graph Transverse emittances (from luminosity) Thanks to J. Esteban-Müller, were degraded for this fill E. Shaposhnikova

  16. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

  17. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

  18. Scrubbing Run Stable phase shifts Fill 3457 has about the same number of Thanks to J. Esteban-Müller, bunches as Fill 3429 (but BCMS) E. Shaposhnikova

  19. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

  20. (Power loss from phase shift)/(Heat load) 2.50 Data only from end of the fills… 2.00 1.50 Ratio 1.00 Flat bottom Flat top 0.50 0.00 3380 3390 3400 3410 3420 3430 3440 3450 3460 Fill number

  21. Why scrubbing stops • Electron cloud in the arcs elsewhere than in the dipoles? → Quadrupoles, multipoles • Modeling of the Secondary Emission process → What happens at low energies? → Re-diffused electrons • Scrubbing behaviour → Cold surfaces?  Lab measurements suggest similar scrubbing curves  The COLDEX experience  slow decay of heat load … → Scrubbing relies on the presence of C  Do we have formation of a C layer in the LHC BS ? 21

  22. → Contribution from quads?  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 d max > 1.5 in dipole chambers  But now quadrupoles (and multipoles ?) could be dominant … 4 10 Dipole Quadrupole Drift 2 10 Heat load [W/hc/beam] 0 10 -2 10 → Consistent with -4  Saturation of scrubbing process (scrubbing 10 1 1.5 2 2.5 curve becomes flat for SEY below 1.3) SEY  Long memory between trains  Stand-alones 22

  23. Standalones (SAM) – examples

  24. Standalones (SAM)

  25. Standalones (SAM)

  26. Standalones (SAM)

  27. Standalones (SAM) Heat loads in D3 and arcs exhibit a sharp increase on the ramp, heat load in the quads seems unaffected

  28. Energy dependence • Effect of the beam size? → Bunch length is about constant, transverse sizes decrease → Simulations seem not to confirm effect of transverse size • Dependence of surface properties on magnetic field → SEY would affect multipacting • Photoelectrons → Would only affect seed electrons and the time to reach saturation → No threshold effect observed at around 2 TeV → Dipole edge effects cause photoelectrons already at 450 GeV? • Probably seen only close to threshold (also based on SPS experience, though with shortening bunches) 28

  29. Influence of low energy electrons Usual Cos Flat 29

  30. 2 10 Scrubbing dose (50eV) [mA/m] 0 10 -2 10 -4 10 72bpi - cos low en. 288bpi - cos low en. 72bpi - usual mod. 288bpi - usual mod. -6 10 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 SEY 2 10 1 10 Scrubbing dose (50eV) [mA/m] 0 10 -1 10 -2 10 72bpi - flat low. en. 288bpi - flat low. en. -3 10 72bpi - usual mod. 288bpi - usual mod. -4 10 30 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 SEY

  31. Scrubbing Run Stable phase shifts Thanks to J. Esteban-Müller, E. Shaposhnikova

More recommend