vacuum observations during the 7 5 and 50 ns bunch spacing operation (md 17-20 nov 2010)

LHC Beam Commissioning WG- 23 Nov 2010

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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 bunch spacing2. 50 ns bunch spacing

3. Test ramp with 50ns_109b_12_90_12bpi10inj2. Conclusion

LHC Beam Commissioning WG- 23 Nov 2010

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1. 75 ns bunch spacing

LHC beam commissioning 19 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

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Conditionning at 680b1+680b2

• Reduction of ~ a factor 2 at D1 LSS2 and LSS8

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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

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Pressure increase comparison

• Threshold at 9-10 1010 p/b for 75 ns beams• Beam conditioning Losses ?

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VGPB.2.5L3.B

Ellipse 52x30 mm

BPMWE

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2. 50 ns bunch spacing

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Pressure increase comparison

• Higher slope for 50 ns than 75 ns• A factor 2 between the slopes

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3. Test ramp with 50ns_109b_12_90_12bpi10inj

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Fill 1500 – 19th November • Only SR desorption • in LSS2• in LSS3&5• In LSS6&7

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Fill 1500 – 19th November • Pressure increases at VGI in A4L1• But remains lower than 7E-10 mbar

Bunch lengthincreases

SR at ~ 2 TeV

Bunch lengthdecreases during ramp

Up to 1 TeV

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Fill 1500 – 19th November • During ramp, bunch length decrease at 19:36 and flattens at 19:40

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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)

Bunch lengthincreases

SR at ~ 2 TeV

Bunch lengthdecreases during ramp

Up to 1 TeV

LHC Beam Commissioning WG- 23 Nov 2010

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Same ramp the 31th October

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Fill 1459 – 31th October • 50ns_109b_12_90_12bpi10inj - Trains well separated i.e. no discussion between trains• Pressure up to 2e-8 mbar

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4. Conclusions

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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 WG- 23 Nov 2010

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Backup slides :Same ramp the 31th October

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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