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Collimation MD’s and Preparation of Review

Collimation MD’s and Preparation of Review. R. Assmann et al Collimation Study Group, 23.5.2011. MD Sat – Mon. Status 9.5.2011, 08:00. Nominal collimation, single b tune shift (Coll, Imp.). Initial blow-up tests with transverse damper. Injection scraping during short delay from injectors.

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Collimation MD’s and Preparation of Review

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  1. Collimation MD’s and Preparation of Review R. Assmannet al Collimation Study Group, 23.5.2011 CWG 23.5.2011

  2. MD Sat – Mon Status 9.5.2011, 08:00 CWG 23.5.2011

  3. Nominal collimation, single b tune shift (Coll, Imp.) • Initial blow-up tests with transverse damper. • Injection scraping during short delay from injectors. • Nominal 3.5 TeV collimation settings achieved for b1 &b2: • TCP = 5.7 sigma (nom), TCSG = 6.7 sigma (nom) • TCLA = 9.7 sigma (nom), IP6 = 7.2/7.7 sigma (nom) • Octupoles trimmed to 350A for beam 1. • For b1 moved towards nominal 7 TeV settings. Limited by TCSG losses close to IP7. Valid setup reached: • TCP = 4.0 sigma (nom), TCSG = 6.0 sigma (nom) • TCLA = 8.0 sigma (nom), IP6 = 7.0/7.5 sigma (nom) • Smallest gap: 2.2 mm • Beam lifetime: > 100 hours • Tune shift measured: ~2e-4 • Efficiency measured: 3e-5 – 1e-4 CWG 23.5.2011

  4. Settings b1 first loss-maps CWG 23.5.2011

  5. Vertical tune shift – collimator movement CWG 23.5.2011 Clearly seen in vertical plane when moving collimtors out by 4 sigma and back in, etc… Magnitude: ~0.0003

  6. Efficiency measured – here b1, horizontal 4e-5 CWG 23.5.2011

  7. Losses in Dispersion-Suppressor (Coll+BLM+MP) • BLM thresholds adjusted on 120 BLM’s, based on old data. • Created fast (~2 s) beam losses at primary collimators. • 3 bunches, b2 loss • Loss rate: 1.5e11 p/s • 20 times below BLM limits, 10 times below assumed quench limit, • 16 bunches, b2 loss • Loss rate b2: 2.5 – 3e11 p/s, 6e11 p/s • Reached 505 kW loss • Beam dump after damper switched on, b2 still on 1/3 resonance. • 16b (b1) and 21b (b2): CWG 23.5.2011

  8. Beam Loss with 16 bunches, 3.5 TeV Loss rate: 9e11 p/s @ 3.5 TeV  505 kW CWG 23.5.2011

  9. Losses into DS (beam 2): No quench! 505 kW – Primary beam loss IR7 peak in 1 s no correction BLM response IR6 336 W – Q8 35 W – Q11 Power load [kW] 5 W – Q19 CWG 23.5.2011

  10. Update Performance Reach: 3.5 TeV Cleaning efficiency: Gain factor 4.3 (MD result) Min. lifetime: Gain factor 2 (2011 operation) Quench limit times dilution length: Gain factor 14.3 (MD result) CWG 23.5.2011

  11. Update Performance Reach: 7 TeV Cleaning efficiency: Gain factor 4.3 (MD result) Min. lifetime: Gain factor 2 (2011 operation) Quench limit times dilution length: Gain factor 14.3 (MD result) CWG 23.5.2011

  12. Request for Checks • Important estimates for the June review! Please check! • Conditions apply (are they reasonable?): • Same minimum beam lifetime at 3.5 TeV and 7 TeV. • Minimum beam lifetime independent from intensity. • No disturbing effect from much larger impedance. • Theoretical scaling of cleaning efficiency and quench limit. • Same spatial distribution of losses in SC magets at 3.5 TeV and 7 TeV: • Loose factor 1.4 due to smaller beam emittance (single diffractive losses form line with vertical extent given by vertical beam size)… • Any other effects for losses with higher density at 7 TeV? • Peak MD performance achievable in routine operation and at 7 TeV. • No disturbing effect from smaller impact parameters at 7 TeV. • Both beams behave the same. • Same locations for peak loss into SC magnets. • No other performance limits included (IR1/5, ions, …). CWG 23.5.2011

  13. Assign Margins • For the first time room for some small margins! • Margins and effect on predictions: • Smaller V beam size: factor 1.4 • Stability efficiency: factor 2 • Lower beam lifetime: factor 2 • With these margins would loose factor 5.6 in predicted performance… • These margins are somewhat arbitrary, still small and not complete (no margin for uncertainties in theoretical scaling to 7 TeV). • Still better than nothing… • Also note: we did not quench, so we have determined a lower limit (quench margin might still be higher). CWG 23.5.2011

  14. Performance Reach with Margins: 7 TeV Cleaning efficiency: Gain factor 4.3 (MD result) Min. lifetime: Gain factor 2 (2011 operation) Quench limit times dilution length: Gain factor 14.3 (MD result) CWG 23.5.2011

  15. Why Large Changes in Prediction? • This is a complicated prediction. It involves: • Beam loss rate. • Cleaning efficiency of a 4 stage collimation system. • Spatial and temporal distribution of leakage losses in super-conducting magnets. • Quench limit of super-conducting magnets, versus time and energy. • That is why we always pointed out large error bars and need for experimental data. • Last memo included the request for MD’s to get more reliable data. • Biggest concerns: achievable cleaning efficiency, distribution of losses in DS and quench limit in DS • That is why we refused a decision before the June review! • Now with the new experimental data we have for the first time sufficient data base for a decision. • Ions are assumed to be behave similarly. CWG 23.5.2011

  16. What Do We Conclude? • LHC collimation is working very well, close to the predicted theoretical limits  excellent work by all of you.Outstanding success: factor 200 beyond WR in one go! • We seem to have sufficient cleaning efficiency but setup accuracy and stability are found to be limited • Seen in operation and MD • Limits seen with tolerances relaxed by factor 4 compared to what is used for performance reach estimates • The job is not over: • Large amount of work to keep system working like in MD for years • Must still improve various aspects of the system to achieve goals CWG 23.5.2011

  17. Review https://indico.cern.ch/event/collreview2011 CWG 23.5.2011

  18. Review https://indico.cern.ch/event/collreview2011 CWG 23.5.2011

  19. Review Committee Chair: Mike Seidel (PSI) Committee: T. Camporesi (CERN) W. Fischer (BNL) M. Lamont (CERN) T. Markiewicz (SLAC) N. Mokhov (FNAL)plus a few to be confirmed CWG 23.5.2011

  20. DRAFT New Memo under Preparation Sufficient data with the LHC beams has been recorded and the requested beam tests for LHC collimation have been performed. The results allow an update of the LHC performance reach calculation. This calculation is still affected by uncertainties but for the first time provides reasonable certainty for being used as a basis for decisions. A 9-point plan for LHC collimation is proposed, including important adjustments in the foreseen work. Based on present best knowledge and understanding, this 9-point plan is compatible with nominal LHC performance at 7 TeV in 2014 and ultimate LHC performance in 2017. At the same time the workload is reduced (e.g. no IR3 upgrade of dispersion suppressors in 2013) and collimation work is reoriented at the directions that are most efficient for optimizing LHC performance. It is noted that a small performance risk for the LHC cannot be fully excluded. However, this risk is deemed acceptable. Lower risks can only be achieved by upgrading the LHC dispersion suppressors as soon as possible, i.e. IR3 during the first long shutdown. CWG 23.5.2011

  21. DRAFT 9 Point Plan: 1 – 3 Action: Cancel the collimation upgrade for the IR3 dispersion suppressors during the first long shutdown in 2014. Complete ongoing prototyping work.Justification: Within reasonable uncertainties it is expected that nominal LHC luminosity can be reached without this work. This conclusion is based on the new results from the May 2011 machine studies. Action: Cancel the temporary installation of vertical collimators into IR3.Justification: The need for temporary relocation of betatron cleaning into IR3 due to SEU issues in IR7 was not demonstrated by beam experience so far. Action: Review priority and direction for work on crystal collimation for the LHC.Justification: Setup of crystal collimators is more complicated than for standard collimators, where limits are seen. The improvement in cleaning efficiency in IR3/7 is not required. Crystal collimators cannot help to reduce losses into DS’s of IR1/2/5. CWG 23.5.2011

  22. R2E Input? Do we need the IR3 temporary cleaning upgrade? Limits in IR7 electronics confirmed or not? No problem for 500 kW loss but what about extrapolation to long-term? Does R2E agree with the action no. 2? CWG 23.5.2011

  23. 9 Point Plan: 4 – 6 DRAFT Action: Start an overall study for the upgrade of the LHC DS’s with collimators in IR1/2/3/5/7, developing a coherent approach. Develop and prototype adequate collimator hardware for readiness in 2016, in close contact with GSI. Justification: The urgency in IR3/7 DS’s is lower than anticipated and upgrades of other DS’s might become more urgent.  Action: Reinforce the work towards second generation collimators with beam position buttons in their jaws, aiming for first installations in 2014.Justification: Overcome the limitations in collimator setup. Allow for best efficiency and small b* at 7 TeV. Avoid lengthy collimator setup periods and win in integrated luminosity. Action: Reinforce the work towards second generation collimators with robust collimator materials or damage handling concepts, with EuCARD + LARP collaborators. Readiness goal is 2016.Justification: Prepare for LHC beams with higher than ultimate brightness. CWG 23.5.2011

  24. DRAFT 9 Point Plan: 7 – 9 Action: Accelerate work on radiation measures with first installations in 2013 and readiness for 2016.Justification: The success of the LHC leads to a faster intensity ramp up and activation of collimators. Action: Start work on design and development of hollow e-beam scrapers for the LHC. Readiness goal is 2016.Justification: Hollow e-beam scrapers are an inexpensive and safe way to reduce the magnitudes of peak beam loss. Provides insurance against risks taken in action 1, in particular against possible surprises when going from 3.5 TeV to 7 TeV. Action: Assign additional dedicated CERN staff resources to the setup and optimization of the existing collimation system. Justification: Not implementing the IR3 upgrade in the DS’s implies that the associated efficiency gain of a factor 10-30 will not come. The existing system must then be operated much longer than foreseen, at the limits of its capabilities. This imposes heavy additional workload for manual setup and optimization. CWG 23.5.2011

  25. Other Work DRAFT • It is noted that the nine points proposed do not describe the full collimation work plan. Additional work packages exist on various topics: • collimation setup in the control room • modeling of performance • optimization of setup accuracy and speed • various small collimation upgrades (e.g. IR2) • IR upgrades within HL-LHC design study • These work packages are not affected by the proposed changes in work plan and it is assumed that they are continued as planned. CWG 23.5.2011

  26. Next Steps • Check technical results for review meeting. • Any additional info to be included? • Define program of talks and presentations: • Please send proposals to me… CWG 23.5.2011

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