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Vacuum observations during the 7 5 and 50 ns bunch spacing operation (MD 17-20 Nov 2010)

Vacuum observations during the 7 5 and 50 ns bunch spacing operation (MD 17-20 Nov 2010). V. Baglin, G. Bregliozzi, P. Chiggiato, J-M. Jimenez, G. Lanza. CERN TE-VSC , Geneva. 1. 75 ns bunch spacing 2. 50 ns bunch spacing 3. Test r amp with 50ns_109b_12_90_12bpi10inj 2. Conclusion.

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Vacuum observations during the 7 5 and 50 ns bunch spacing operation (MD 17-20 Nov 2010)

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  1. Vacuum observations during the 75 and 50 ns bunch spacing operation (MD 17-20 Nov 2010) V. Baglin, G. Bregliozzi, P. Chiggiato, J-M. Jimenez, G. Lanza CERN TE-VSC, Geneva 1. 75 ns bunchspacing 2. 50 ns bunchspacing 3. Test rampwith50ns_109b_12_90_12bpi10inj 2. Conclusion LHC Beam Commissioning WG- 23 Nov 2010

  2. 1. 75 ns bunch spacing LHC Beam Commissioning WG- 23 Nov 2010

  3. Stacking 48b to 680 with gaps of 1.85 microsec • Injection of 24+24 bunches separated by 75 ns and 225 ns between b24 and b25 • 1.85 µs between trains • Machine full with 2x680b after 14 injections LHC beam commissioning 19 nov 2010

  4. Stacking 48b to 680 with gaps of 1.85 microsec • Average bunch current 0.9 E11 p/bunch • Below interlock level (4e-7 mbar) when machine filled with 2 x 680 b • Mainly pressure increases at D1 and less in other areas • Stayed for ~ 2h before beam dumped LHC beam commissioning 19 nov 2010

  5. Conditionning at 680b1+680b2 • Reduction of ~ a factor 2 at D1 LSS2 and LSS8 LHC beam commissioning 19 nov 2010

  6. Pressure increase with machine full • Linear trend in pt1, 3 • Except for pt2, pt 8 where threshold at ~ 70 mA (248+248 b) • No pressure increase in pt5 & 7 LHC beam commissioning 19 nov 2010

  7. Pressure increase comparison • Threshold at 9-10 1010 p/b for 75 ns beams • Beam conditioning Losses ? LHC beam commissioning 19 nov 2010

  8. VGPB.2.5L3.B BPMWE Ellipse 52x30 mm LHC beam commissioning 19 nov 2010

  9. 2. 50 ns bunch spacing LHC Beam Commissioning WG- 23 Nov 2010

  10. Pressure increase comparison • Higher slope for 50 ns than 75 ns • A factor 2 between the slopes LHC beam commissioning 19 nov 2010

  11. 3. Test ramp with 50ns_109b_12_90_12bpi10inj LHC Beam Commissioning WG- 23 Nov 2010

  12. Fill 1500 – 19th November • Only SR desorption • in LSS2 • in LSS3&5 • In LSS6&7 LHC beam commissioning 20 nov 2010

  13. Fill 1500 – 19th November • Pressure increases at VGI in A4L1 • But remains lower than 7E-10 mbar SR at ~ 2 TeV Bunch length increases Bunch length decreases during ramp Up to 1 TeV LHC beam commissioning 20 nov 2010

  14. Fill 1500 – 19th November • During ramp, bunch length decrease at 19:36 and flattens at 19:40 LHC beam commissioning 20 nov 2010

  15. Fill 1500 – 19th November • Some activity in MKIR8 intermodule stimulated by ramp and SR • Start ramp, pressure increase starting from ~ 550 GeV (19:36) • But flattens at 800– 1000 GeV (19:40) SR at ~ 2 TeV Bunch length decreases during ramp Up to 1 TeV Bunch length increases LHC beam commissioning 20 nov 2010

  16. Same ramp the 31th October LHC Beam Commissioning WG- 23 Nov 2010

  17. Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains • Pressure up to 2e-8 mbar LHC beam commissioning 20 nov 2010

  18. 4. Conclusions LHC Beam Commissioning WG- 23 Nov 2010

  19. Conclusions • 2x680 b were injected with 75 ns, pressure remained below interlock level • Beam conditioning was observed during ~ 2h storage time • At 75 ns, threshold around 9-10 1010 p/bunch • At 50 ns, the pressure rise per mA is ~ 2 x the 75 ns pressure rise per mA • The test ramp of 50 ns_109b_12_90_12bpi10inj exhibits no pressure rise larger than • 7 10-10 mbar • Beam conditioning is ongoing LHC beam commissioning 20 nov 2010

  20. Backup slides : Same ramp the 31th October LHC Beam Commissioning WG- 23 Nov 2010

  21. Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains • Pressure up to 2e-8 mbar LHC beam commissioning 20 nov 2010

  22. Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains • Pressure increases due to ecloud in the 1e-9 mbar region SR at ~ 2 TeV LHC beam commissioning 20 nov 2010

  23. Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains • Pressure 4e-9 mbar SR at ~ 2 TeV LHC beam commissioning 20 nov 2010

  24. Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains SR at ~ 2 TeV LHC beam commissioning 20 nov 2010

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