LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 118. July 2012

SPS: BEAM STABILITY AND TAIL POPULATION AT

SCRAPERS

Lene Drosdal+Verena Kain, Karel Cornelis,

Eric Veyrunes…

LIU-SPS-BL-P-TL

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 218. July 2012

Outline

• Beam scraping in the SPS for LHC injection• Scraper scans to measure beam parameters• Stability of beam parameters over time• Full beam scan• Measurement errors• Stability from 100% scans• Summary and outlook

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 318. July 2012

Beam ScrapingHigh intensity LHC beams are scraped in the SPS

before the end of the ramp (403 GeV)

Typical intensity scraped: 1-3 %

SPS cycle with scraping:

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 418. July 2012

LHC Injection QualityParticles from the tails are lost at the transfer line collimators close to the LHC and can trigger a protection beam dump. For un-scraped beam:• 12 bunches, operational emittance: ~10 %• 12 bunches, nominal emittance (blow-up): ~26 %

Not possible to inject full intensity without beam scraping!

Injection losses – scrapers out [Injection quality MD 2011]

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 518. July 2012

Scraping strategyCorrect scraper position:

Injection losses can be reduced to an acceptable level while preserving the emittance

Injection quality MD 2011

If beam is stable: Keep scraper fixed at correct position, BUT the scraping is not constant and scrapers need to be moved Need to investigate stability of beam

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 618. July 2012

Scraper scansProcedure: Scraper in one plane retracted, the other

is moved step-wise towards the beam centre:

For each step the scraped intensity is calculated, 3 measurements are used per step

A Gaussian fit is calculated to find the beam size s and beam centre x0 with respect to the scraper

PLOTS

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 718. July 2012

Beam stability 1Scraper scans were done throughout May/June:

Beam centre seem to be moving by ~0.7mm

BUT.. we assumed that tails are not over-populated and scraping up to ~30% is enough to fit – Only if we assume Gaussian beams!

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 818. July 2012

Beam stability 2Scraping at setting:

Scrapers are moved because beam is changing Scraping is not constant

Result of beam centre moving or are the beam estimates biased from a large tail population?

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 918. July 2012

Impact of large tail populationIf the beam has very large tails the beam size is over-

estimated by our fits! A better fit can be found only using parts of the measurements closer to the core:

Fit of all points Cut-off at 60%

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1018. July 2012

Matching with the wire scanners

Using only the beam core (>60%) we match the wire scan measurement:

Expected s at scraper location:s = 0.360 * = 0.429

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1118. July 2012

Errors from scraping only until x% • If we scrape only until 30% the beam size is largely

overestimated if we have tails!• Beam position also moved by ~0.8 mm

Same magnitude as estimated variations!

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1218. July 2012

Large tails method break-down

If the tails population is large only a complete scan can be used to estimate the beam parameters and tail population: Do we always have large tails? Is the beam position stable?

If we have large tails scraping at a fixed % is also not a sufficient to define the scraper settings

Full beam scans to be repeated• More time consumed than for 30% scans• BLM thresholds need to be opened

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1318. July 2012

Stability from full scansScraper scan 9 July:

•36 bunches, horizontal plane•Average intensity per bunch: 1.48 e11•Scraper position: -8.2mm•Beam size from wire scan: 0.429mm

•Fit [50, 100%]:• X0 = -5.925mm• s = 0.453mm

Scraper scan 17 July:•36 bunches, horizontal plane•Average intensity per bunch: 1.53 e11•Scraper position: -8.3mm•Beam size from wire scan: 0.462mm

•Fit [50, 100%]:• X0 = -6.574mm• s = 0.539mm

Beam has moved by ~0.6mm

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1418. July 2012

Vertical planeScraper scan 17 July:

•36 bunches, vertical plane•Average intensity per bunch: 1.52 e11•Scraper position: 3.2mm

•Fit [50, 100%]:• X0 = 5.590mm• s = 0.425mm

Only one scan done in the vertical plane:

• Large tails also in the vertical plane

• Need to check wire scan measurement

• Need more scans..

LIU-SPS-BL-P-TL: SPS – Beam Stability And Tail Population At Scrapers 1518. July 2012

Conclusions & Outlook• Full beam scans show that we have large tails• Necessary to do a full scan to measure beam parameters• Scraping at 1-3% is not sufficient to setup the scrapers• Where are the tails coming from?

• The beam centre is moving at the scrapers (H)• Further scans will be done to measure the stability• Orbit stability (BPMs) needs further attention• Use the full beam scan as a tool to estimate the tail

population using a double Gaussian fit:I(x) = +