sps scrubbing experience: electron cloud observables l. mether on behalf of the liu-sps e-cloud team...
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![Page 1: SPS scrubbing experience: electron cloud observables L. Mether on behalf of the LIU-SPS e-cloud team LIU SPS scrubbing review, September 8, 2015](https://reader030.vdocuments.mx/reader030/viewer/2022020320/56649ea75503460f94ba96c1/html5/thumbnails/1.jpg)
SPS scrubbing experience: electron cloud observables
L. Mether on behalf of the LIU-SPS e-cloud team
LIU SPS scrubbing review, September 8, 2015
![Page 2: SPS scrubbing experience: electron cloud observables L. Mether on behalf of the LIU-SPS e-cloud team LIU SPS scrubbing review, September 8, 2015](https://reader030.vdocuments.mx/reader030/viewer/2022020320/56649ea75503460f94ba96c1/html5/thumbnails/2.jpg)
Outline
• Outline
• Electron cloud • Electron cloud monitors• Electron cloud evolution during cycle• Electron cloud evolution over scrubbing
• Arc pressures• Pressure gauges• Pressure evolution during cycle• Pressure evolution over scrubbing
• Summary
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Electron cloud monitors• Large aperture dipole magnets installed in a
straight section• Vertical magnetic fields, set to B = 0.12 T, field
in SPS bends at injection
• Each magnet is equipped with a liner…• Stainless steel MBA/MBB type vacuum
chamber, with holes drilled along the side
• …with a strip detector on the outside• 48 channels
• Signal integrated over multipleturns (20 – 200 ms)
• Provide transverse profile of electron distribution
• Help to understand the e-cloud evolution and scrubbing process in SPS bends
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Electron cloud during SPS cycle• Nominal SPS 25 ns cycle
• 4 batches of 72 bunches, 1.2x1011 p+/bunch
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Electron cloud during SPS cycle• Electron cloud signal along nominal 25 ns cycle
• E-cloud signal low, but still visible• Large enhancement during ramp to flat top, mainly due to bunch shortening
Ramp
Nominal intensityMBBMBA
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Electron cloud during SPS cycle• Horizontal profile of electron cloud signal
MBA
MBB
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Electron cloud with high-intensity beam• During the four scrubbing runs this year, the machine was run mainly
with a high-intensity beam, with around 2x1011 p+/bunch
• For this purpose a scrubbing cycle with up to 4 batches of 72 bunches, at flat bottom was used
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• E-cloud signal in MBA and MBB monitors along scrubbing cycle
Ramp
• Electron cloud twice as strong as for nominal intensity beam
• Significantly more electron cloud in MBB chamber than in MBA
High intensity
Nominal intensity
Electron cloud with high-intensity beam
MBBMBA
MBBMBA
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Electron cloud with high-intensity beam• Horizontal profile of electron cloud signal
• Electron cloud extends beyond region scrubbed with nominal intensity beam
High intensity
Nominal intensity
MBA MBB
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Electron cloud with high-intensity beam• Horizontal profile of electron cloud signal
• This region has been effectively scrubbed!
High intensityW50
Nominal intensity
MBA MBB
High intensityW25
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Electron cloud evolution during scrubbing• Study the evolution of signal in electron cloud monitors over scrubbing period
• MBA and MBB chambers• Two observation points:
− Signal after first injection− Maximum signal along cycle
MBBMBA
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Electron cloud evolution during scrubbing• E-cloud signal in MBA monitor after injection of first batch
W16 W17 W23 W25
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Electron cloud evolution during scrubbing• Maximum e-cloud signal in MBA monitor
First batch
Maximumsignal
W16 W17 W23 W25
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Electron cloud evolution during scrubbing• E-cloud signal in MBB monitor after injection of first batch
W16 W17 W23 W25
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Electron cloud evolution during scrubbing• Maximum e-cloud signal in MBB monitor
First batch
Maximumsignal
W16 W17 W23 W25
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Outline
• Outline
• Electron cloud • Electron cloud monitors• Evolution during cycle• Evolution during scrubbing
• Arc pressures• Pressure gauges• Evolution during cycle• Evolution during scrubbing
• Summary
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Arc pressures• Pressure gauges located between dipole magnets in each arc
• We follow two families of gauges:
X2940
MBA MBB
X0660
MBB
MBB
• Located between an MBA and an MBB dipole
• Located between 2 MBB dipoles
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Arc pressures along cycle• Pressures during nominal intensity cycle with ramp
and high-intensity flat-bottom scrubbing cycle• Gauges X0660 (MBB-MBB)
High intensityNominal intensity
Ramp
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Arc pressure evolution during scrubbing• Pressure rise over scrubbing cycle at gauge 40660
• Located between two MBB dipoles
W16 W17 W23 W25
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Arc pressure evolution during scrubbing• Pressure rise over scrubbing cycle at gauge 42940
• Located between an MBA and an MBB dipole
W16 W17 W23 W25
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Summary & conclusion• Electron cloud with high-intensity beam
• Electron cloud is more than doubled with high intensity vs nominal intensity at flat bottom− MBB type chamber more prone to e-cloud than MBA type chamber
• Scrubbing efficiency • Based on data from electron cloud monitors and pressures:
− Conditioning seen mainly in the first week of high-intensity beam− Full suppression not seen over four batches
• E-cloud monitors provide information also along the cycle:− Significant improvement seen after the injection of one batch:
full suppression in MBA, significant reduction in MBB
• Conclusion • SEY lowered during scrubbing, but not sufficiently to fully suppress e-cloud • Effect of scrubbing seems to level off
− If further scrubbing can be done, required timescales much longer than days/a few weeks
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Thank you for your attention!