lessons of sps scraping with lhc beams
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Lessons of SPS Scraping with LHC Beams. V. Kain, K . Cornelis , L . Drosdal , M. Meddahi , A. Mereghetti , O. Mete, E. Veyrunes. SPS Scraping – Experience from LHC Run I. Systematically large non-Gaussian tails in particle distribution for LHC beams High beam losses at injection LHC - PowerPoint PPT PresentationTRANSCRIPT
Lessons of SPS Scraping with LHC Beams
1
V. Kain, K. Cornelis, L. Drosdal, M. Meddahi, A. Mereghetti, O. Mete, E. Veyrunes
SPS Collimation Review 2
SPS Scraping – Experience from LHC Run I
Systematically large non-Gaussian tails in particle distribution for LHC beams– High beam losses at injection LHC– High beam losses during squeeze in the LHC with tight collimators
Transverse beam scraping in the SPS for LHC beams became essential.
November 2013
Example of collimator scanin the LHC at 450 GeV
With and without scraping in the SPS
L. Drosdal, B. Salvachua, G. Valentino
SPS Collimation Review 3
SPS Scraper in SPS LSS1
Horizontal and vertical graphite fingers that can be moved into the beam
November 2013
The scraping occurs at the end of the ramp to get rid of the off-momentum scattered particles.
BCT during a 50 ns LHC cycle in the SPS:about 3 % of the intensity is scraped.
~10 mm
SPS Collimation Review 4
SPS scraping towards the end of the ramp
The scraping process starts at energy 409 GeV and lasts for about 250 ms.
November 2013
SPS Collimation Review 5
How is the scraper setting chosen?
The scrapers scrape at about ~2.5 – 2.9 s The settings are chosen such to remove the tails but not to impact
on the core of beam
November 2013
Results of scraper setting versus emittance after scraping and losses in the LHC transfer lines
% of dump threshold in the LHC for 144 bunch injection
SPS Collimation Review 6
ISSUES WITH SPS SCRAPING
November 2013
SPS Collimation Review 7
Beam Loss around the SPS Ring
Losses recorded during MD of scraping whole beam in the SPS– Numbers need to be scaled to operational scenario
Scattered particles are lost all around machine Peak loss obviously in point 1
November 2013
Need to increase several BLM thresholds for the whole cycle to be able to deal with scraping losses.
Sun glasses?Is under study.
A. Mereghetti
SPS Collimation Review 8
Evolution of Scraper Setting and Scraped Intensity
Settings of scrapers in H and V change Partly due to reduce scraped intensity: mainly in V
– was reduced through the autumn from 3 % to about 2 % In H scraper setting is following the change of the SPS orbit
November 2013
SPS Collimation Review 9
Change of H Scraper Setting and Beam Position
November 2013
issue with dp/p
Horizontal setting evolution
Horizontal beam position at scraper fitted from surrounding BPMs
Position can change by ~ 1mm in one week
SPS Collimation Review 10
Consequences and Origin of Orbit Movement
Scraper needs setting up/ verification before EACH LHC filling– …and the LHC beam is only scraped at one moment in the cycle not
throughout the whole energy range
Origin of orbit movement not identified yet Possibly only an issue for cycles with LHC optics and not fixed
target beams– Tune close to integer– Possibly generated by LHC extraction equipment in LSS6– Would LSS2 extraction equipment do the same thing?
November 2013
SPS Collimation Review 11
Limit on maximum Number of Scraper Cycles
Current SPS scraper is moved by a stepping motor in and out of beam every LHC cycle
It is only used for LHC cycles during LHC filling
Theoretical limit of number cycles: ~400’000
Number of cycles by end of February 2013: 187’000
If it has to be used on a more regular basis and the number of cycles before system fatigue becomes limit: magnetic bump instead of mechanical system– Concept is available– More complicated (machine
protection), more space required in the machine
– Could bring more absorption
November 2013
SPS Collimation Review 12
Conclusion
The SPS scrapers are systematically used to prepare the LHC beams
The system has proven to be operationally reliable and robust for the current mode of operation:– Only high intensity LHC beams– Only one energy– Only for LHC filling
The big inconvenience for scraping/collimation in the SPS:– Lack of sufficient orbit stability– To make the systems do their job, they need continuous tuning
November 2013
SPS Collimation Review 13
EXTRA SLIDES
November 2013
SPS Collimation Review 14
SPS Scraper is robust
A robustness test was carried out at the end of LHC run I Scraping the whole beam: 288 bunches The spare system was used Result: the scraper survived. Detailed investigation still to come.
November 2013
Signs of discoloration.Indication of state change?
SPS Collimation Review 15
Losses on the transfer line collimators
November 2013