EDMS Id: 1232723
Minutes of Beam Loss, Protection, Transfer Lines LIU-SPS Working Group Meeting
Notes from the meeting held on
18 July 2012
Present: Lene Drøsdal, Lars Jensen, Malika Meddahi, Alessio Mereghetti, Öznur Mete,
Helmut Vincke, Jörg Wenninger.
Excused: Wolfgang Bartmann, Brennan Goddard, Verena Kain, Fausto Lorenzo
Maciariello, Yannis Papaphilippou, Helga Timko.
1- Comments and Matters Arising – All
The minutes of the previous meeting were approved.
2- SPS beam scraping: more on observations/ measurements and outcomes for the
LIU operation – Lene Drøsdal
The beam scraping test results were updated with the addition of new scans (slides).
Lene reminded that during the LHC beam injection process, if the losses at the transfer
line collimators are above the LHC-BLM thresholds, the beams are dumped. The high
losses are mostly correlated to large tails of the SPS beams. In order to prevent these
losses, high intensity LHC beams are scraped in the SPS before the injection, typically to
1-3%.
Assuming that the SPS beam is stable, the scraper jaws should be set at a fixed position.
However, as the beam position is varying in the SPS, the scraper jaw position has to be
adjusted very regularly, and the operators cannot rely on a fixed scraping procedure.
Therefore the investigation of the SPS beam stability is essential for the correct setting up
of the beam scraper jaws as well as their important outcomes for the LIU operation. This
stability study is in progress (Lene).
Weekly beam scraping tests are performed to investigate the SPS beam stability and tails.
During the scraping tests, the jaw in one plane was retracted to decouple the contribution
from scraping in both planes, while the other jaw was moved stepwise towards the beam
centre. The beam size and the centre can be extracted from the Gaussian fit of the
measured tail distribution up to 30% of the beam. According to the tail scans over the
period of May/June 2012, the beam centre has moved by ~0.7 mm. However, further
investigations are necessary to determine how much the beam centre measurements are
biased by the tail population. Performing beam scraping closer to the beam core –up to
60% of the distribution- reveals the presence of large tail population. Using these data, a
better fit could be made. The beam size measurements were correlated with the wirescanner measurements. The tests showed that scraping only 30% of the beam leads to an
overestimation of the beam size in case of large tail population. In this case, only full beam
scans are sufficient to determine the beam centre and the size.
More full scans will be done in the upcoming tests in order to better characterize the beam
stability and sizes. Meanwhile an orbit stability crosscheck with the BPM readings will
provide important information. The full beam scan method will be improved by analyzing
the measured distribution as a double Gaussian, defining the beam core and the tails as
different Gaussian distributions.
3- Update on Fluka studies – Alessio Mereghetti
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Previously, the beam impact at 5σ onto the jaw of the TCDIH.NEW1 collimator in TI8
under Q20 optics was investigated. Despite the fact that the nominal LIU case results in
the higher peak energy deposition (per impacting particle), it is the maximum LIU case
which causes a higher temperature increase on the impacted collimator jaw.
In the update, the difference in the temperature increase was correlated with the
compensation between the beam size and the bunch population provided by different
beam parameters (Nominal or Maximum LIU) (slides). From nominal to maximum LIU
parameters the beam spot area increases by a factor of 2.5. This is consistent with the
previous findings where increasing beam dimension compensates for the increasing
bunch population and yields higher values of the temperature increase.
A parametric study was performed and presented in order to further investigate the case.
A slab of graphite with the same composition as the TCDIx collimators was taken into
account. The peak energy deposition and the temperature increase were computed for the
same simulation settings used for TCDIx collimators (the same scoring mesh). The
nominal LIU parameters were considered as the reference case for the computations. A
search was conducted in order to determine the bunch population resulting with the same
temperature increase with the reference case as the beam dimension increases.
As a result, for the relatively low dispersion values where the beam size is dominated by
the emittance, the increase in the bunch population may lead to a higher increase in the
temperature at the location of the peak energy deposition.
4- Status of the TCDI Ansys studies – Fausto Maciariello
This contribution was postponed for the next meeting.
5- Update on Scraper Studies including Orbit Effects – Oznur Mete
The LIU scraper system studies were updated taking into account orbit effects (slides).
The resulting orbit deviations due to the misalignment of the SPS quadrupoles were
calculated. Misalignment errors (Gaussian distribution 1σ = 200μm) were assigned
randomly to all SPS quadrupoles. A thousand different seeds were used within the 6σ
reach of the distribution. In the current design, in order to move the beam to the point of
interception with the fixed scraper, a negative and a positive local orbit bump are used for
H and V plane respectively. Consequently, a 3σ deviation of 19 mm and -16 mm, in the H
and V planes were considered as the worst cases for further analysis.
Additional local orbit bumps were used to correct the orbit in its worst case. The same
knobs as used for the scraping bumps were utilized and required bumper strengths for the
correction were calculated. The resulting orbit in the SPS was calculated for each plane,
considering the components of 3σ deviated orbit, correction bumps at the location of the
scrapers and the bumps to move the beam further onto the scrapers. The resulting case
was analyzed in terms of the total required magnet strengths and the beam clearance.
For the scenario where both a correction and the bump are involved in their worst cases
the amount of possible scraping for H and V planes were found to be 5σ and 6σ of the
beam, respectively. The horizontal bumpers in the LSS6 were found to be sufficiently
strong to provide the required kicks. However, MPSH.62199 might constitute a bottleneck
for the LIU operation due to the necessity of usage of 99% of its capacity for the worstcase correction and full scraping. The existing bumpers for the vertical plane are not
strong enough to provide needed strengths. Therefore four new bumpers were proposed
with the determined strengths to be utilized both for worst-case orbit correction and the full
beam scraping plus a tolerance of 20%.
The beam clearance of the horizontal plane is larger than 3σ when the errors and both
bumps are switched on. However, the clearance is not sufficient for the vertical plane. It
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was suggested to use in the simulation only half of the maximum errors (20 mm offset
have been used, as 10 mn could be considered – in regular operation the orbit is corrected
to about 3-4 mm).
6- A.O.B.
None.
7- List of Actions
Actions for SPS beam tests: Karel Cornelis, Lene Drøsdal, Verena Kain, Öznur Mete
- Beam tests:
 Scraping the full beam away (low Intensity) –(to be concluded in two weeks)
 Beam loss location measurements during the ramp, with high and low intensity
(Helga Timko) (to be scheduled)
Actions depending on the discussions:
 Confirm the reliability of the acquisition from BPV.60508.
 Investigation of the scraper scans considering a model of double Gaussian
distribution to better explain the tails.
 Crosscheck the orbit stability with the BPM readings.
- Tests in the SPS on the cycle without beam:
 Timing of the bumpers (switch of the polarity) (to be finalized)
Actions for FLUKA studies: Alessio Mereghetti.
 Short term: TED Dump
 Energy deposition / thermal load on TED dumps and upstream vacuum window, for
the smallest beam size / highest beam intensity; considered dumps: TED.29133
and TED.87765.
 Medium-long term: TI2/TI8, Energy deposition on the LHC magnets due to full beam
impact on a TCDIx collimator, close to LHC, for both Q20 and Q26:
 TI2: impact on the TCDIH.29050 collimator (i.e. the last collimator in the upgraded
collimation scheme), with special attention to Q8 and Q7 (Left of Point 2).
 TI8: impact on the TCDIH.87904 collimator, with special attention to Q7 and Q6
(Right of Point 8),
 TI8: impact on the TCDIH.88121 and TCDIV.88123 collimators, with special
attention to Q5 (Right of Point 8).
 Medium-long term: SPS Scrapers
 Energy deposition / thermal load on the scraper, and loss pattern around the SPS
ring, for horizontal and vertical scraping, focusing on LSS6; priority to Q20 optics;
tool: coupling of Fluka to SixTrack. Worthwhile to consider all the cases, in order to
correctly identify the key parameters ruling the patterns to be found.
 Actions arising during the discussions
 The situation with the MSI magnets in the TI2 to be checked;
 Taking into consideration the LHC BLMs, when computing the effect on LHC
magnets;
 For the Fluka and SixTrack coupling, a realistic beam profile to be obtained with the
contribution from Yannis Papaphilippou.
– Effect on the downstream elements induced by a full beam dump on the TED; Get
in contact with O. Aberle for first feedbacks about results on the TED. (done)
– Provide Oliver with the energy deposition maps. (done)
Actions for studies on LIU scraper: Öznur Mete
Simulations (ongoing):
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 Feasibility of the LIU scraping system, in the presence of the orbit effects: consider
decreasing the misalignment error and repeat the same investigation.
 Search for the possibility of flat interception of the beam with the scraper instead of
the current tilted case.
Actions for dose rate estimations: Helmut Vincke.
– Estimation of the doses in the LSS6 considering a possible future scraping activity
in the area (when final location will be confirmed).
Actions for ANSYS studies: Fausto Maciariello.
– TCDI Ansys simulations.
– Explore the possibility of a beam-based test to identify the reliability and robustness
of the concerned graphite material. (Timing for the test and the required beam
properties will be discussed with Malika Meddahi, Verena Kain, Oliver Aberle).
Next meeting:
Wednesday 1st August 2012 (TBC), from 10:30 to 11:30, in 865-1D17. The agenda will be
communicated in due time.
Öznur Mete
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