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LHC achievements, status and plans

LHC achievements, status and plans. J. Wenninger BE OP group. Outline. Machine protection (driven) commissioning Setting up for trains Train operation The last week of protons Ion run. The target. >10 32 cm -2 s -1. (> 1 fb -1 for 2011). Machine protection driven commissioning.

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LHC achievements, status and plans

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  1. LHC achievements, status and plans LHC Status - ATLAS France J. Wenninger BE OP group

  2. Outline Machine protection (driven) commissioning Setting up for trains Train operation The last week of protons Ion run LHC Status - ATLAS France

  3. The target >1032 cm-2s-1 LHC Status - ATLAS France (>1 fb-1for 2011)

  4. Machine protection driven commissioning • MP phase 1: low intensity MP commissioning. • Commissioning of the protection systems. • Low intensity single bunch commissioning of the systems, including beam tests (manually triggered failures). • MP phase 2: MP running in with gradual intensity increase. • Intensity increase in steps, factor 2 – 4, up to ~ MJ stored energy. • Stability run of a few weeks around 1-3 MJ. • MP Phase 3: intensity increase to 10’s MJ regime. • Intensity increase in steps of 2-3 MJ (1 TEVATRON beam). • Initially planned one step every 1-2 weeks. • With the good MPS performance, agreed to reduce the step to: • 3 fills and 20 hours of stable beams. This span is also driven by operational considerations, as conditions can change drastically with large number of trains. LHC Status - ATLAS France

  5. Machine protection: some statistics • More than 270 dumps above injection energy. • Between March and end of August over 70% of the beams above injection energy were dumped by the MPS ! • The MPS has caught all events perfectly, even some weird operational mistakes. • Remaining worries arise from COMBINED failures, most scenarios involve an injection or a dump error (asynchronous dump). • That is why we carefully track anomalies in the present period of rapid intensity increase. Beam dumps > 450 GeV ‘False’ dumps LHC Status - ATLAS France Beam monitoring HW surveillance Operator MPS test

  6. UFOs • On 7th July we observed the first occurrence of fast beam loss events in the super-conducting regions of the ring: • Beam loss at a SC magnet. • Fast loss over ~0.5-2 ms. • Most events during stable beams: no power converter changes, orbit rock-stable, no lifetime issue before the event… • Loss at regions of very large aperture > 40 beam sigma (collimators between 6 and 15 sigma). • The hypothesis quickly emerged that it is not the beam that moves to the aperture, but rather the opposite ! • ‘Dust’ particles ‘falling’ into the beam, estimated size ~100 mm think Carbon-type object. • Two events in perfect coincidence (time & space) with TOTEM roman pot movements make this hypothesis rather convincing. LHC Status - ATLAS France

  7. Example of a 152 bunches UFO Beam loss monitor post-mortem LHCb IR7 IR1 Arc Arc LHC Status - ATLAS France s Time evolution of loss 1 bin = 40 ms 0.5 ms Dump trigger

  8. A worrying correlation… T. Baer LHC Status - ATLAS France One of the reasons why we want to observe the beams for 20 hours before increasing intensity!

  9. UFO near threshold About 50% of the UFOs lead to dumps while the loss is decaying… IR1 ALICE IR3 Arc LHC Status - ATLAS France Time evolution of loss 1 bin = 40 ms Dump trigger The dump is triggered on the loss integral !

  10. UFO and BLM thresholds • 2 weeks ago we had accumulated 12 UFO events ( beam dumps). • But there was no quench – the BLMs always triggered first. • In many cases the signal was just above threshold of the BLMs… • Therefore we decided 2 weeks ago to increase the dump thresholds of most BLMs at super-conducting elementsby a factor 3. • Initial thresholds were set to 30% of quench level – we are now essentially at the estimated quench level. • New models of the magnet cooling indicate more margin than initially estimated, and the BLM response is tuned on a different loss scenario. • Since then there was only one UFO dump in the IR8 triplet, but from LHCb BCM (machine BLMs far below threshold). • The rate of UFOs (the ones that dump + the ones that are below dump threshold) increases with intensity: • With 250 bunches there are ~0.8 UFOs/hour LHC Status - ATLAS France

  11. Outline Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run LHC Status - ATLAS France

  12. Crossing angles • Until end of August the large bunch spacing did not require Xing angles. • A Xing angle was used in stable beams to avoid some parasitic encounters from the ‘democratic’ filling scheme. • To operate with closely spaced bunches (trains) a Xing angle is required to avoid parasitic encounters in the common vacuum chamber. • Xing angle value is a compromised between maximizing aperture and minimizing beam-beam effects. LHC Status - ATLAS France ‘long-range beam-beam’ ½ crossing angles (sign  B1) For 150 ns spacing, the first encounter is at 22.5 m from the IP

  13. Separation and crossing in ATLAS Horizontal plane: the beams are combined and then separated ATLAS IP 194 mm ~ 260 m LHC Status - ATLAS France Common vacuum chamber During injection, ramp & squeeze there is an additional parallel separation of  2 mm in the horizontal plane ! Vertical plane: the beams are deflected to produce a crossing angle at the IP Not to scale ! ~ 7 mm

  14. Crossing angles : injection ATLAS ALICE CMS LHCb B1 Hor 10 mm B1 Vert LHC Status - ATLAS France B2 Hor B2 Vert

  15. 150 ns beam structure • PSproduces trains of m bunches (spacing 150 ns). • m = 8 or 12. • m is fixed for a given filling sequence. • SPSassembles nPS trains of m bunches • n = 1,2,3 or 4. So far we use only 1 and 2. • train spacing defined at injection to SPS, presently 300 ns. • n may change for each cycle. • LHCrequests pSPS train groups • n may vary from one injection to the next. LHC Status - ATLAS France Very flexible – can produce a large variety of patterns in the LHC m m m m m m m m m LHC m m m m m m m m m SPS or or m PS Circumference

  16. Overview of proposed 150ns “structure” one train of m bunches shifted by -3 x 25ns slots -3 LHC Status - ATLAS France +3 -3 k -3 -3 m m m • n PS trains of each m bunches • N = n x m = tot nr of bunches • M = N – n/4 = nr of collisions in each of IP1, IP5 and IP8 • example (N=48): n = 12 & m = 4 => M = 45 n = 4 & m = 12 => M = 47 • NB: m=12 is max for 150ns • Add k bunches for ALICE, typically k = ~ N/16 & k  ~16 • NB: the N bunches will give parasitic encounters at IP2: +/-11.25 m, +/-33.75 m, … IP1,5,8: +/-22.5m, +/-45m, …

  17. A possible evolution 2/3 equalitarian 4-fold symmetric private IP2 LHC Status - ATLAS France M. Ferro-Luzzi

  18. 312 bunches Beam 1 LHC Status - ATLAS France

  19. 8.5s 6.7s Secondary (robust) 15.0s 12.0s Absorber (W metal) LHC aperture and collimator settings 5.7s 5.7s 12.5s 15s Tertiary (W metal) Primary (robust) Beam halo ➠ ARC ARC ARC Beam halo ➠ IP & Triplets ARC ARC ARC ±8.5 σ IP & Triplets Injection LHC Status - ATLAS France b* 3.5 m 3.5 TeV ±18 σ TCP TCSG TCLA TCT Courtesy S. Redaelli

  20. Machine protection setup/tests for trains • Collimator setup. • IR7(betatron [transverse] cleaning) and IR3(off-momentum cleaning) untouched wrt pre-train period. Exception for beam 2 in IR3 due to a collimator hierarchy issue (relative retraction). • Tertiary collimator setup at injection, at 3.5 TeV un-squeezed and for collisions. Positions are interpolated in ramp and for the squeeze steps. • 8 collimators per beam (2 per IR and per beam). • Collimator and dump setup validation. • Large losses induced by crossing resonance to verify collimator setup (loss maps). • De-bunch beam to fill abort gap and trigger dump to verify protection by absorbers (and collimators). • Very time (beam) consuming exercise. Minimum of 10 cycles. • Used up a large part of the train setup. LHC Status - ATLAS France

  21. Good setup - hierarchy respected IP7 TCPs TCSGs TCLAs Normal cond. magnet cleaning insertion IP1 IP2 IP3 IP4 IP5 IP6 IP7 IP8 β cleaning Δp/p cleaning Dump TCTs TCTs TCTs LHC Status - ATLAS France Beam 1 The collimator hierarchy is verified with dedicated loss maps induced by artificially high loss rates: record beam losses around the ring while crossing betatron resonances.

  22. Cleaning inefficiency evolution Courtesy D. Wollman Example of the loss leakage on the horizontal tertiary collimators (sum over all IRs) over 2 months. LHC Status - ATLAS France • Leakage into cold aperture around 2e-4. • Stable over 2 months.

  23. 10.5 s Dump protection Dump protection and b* 15s Tertiary (W metal) Beam halo ➠ IP & Triplets • b* at the IR is limited by the beam size in the triplet. • Beam size in triplet  1/b*. • b* reduction is limited by the aperture in the triplet and the tolerances for collimators, protection devices (dump) and orbit movements. • Tolerances are not too aggressive to avoid constant OP interruptions for alignment verification and checks. LHC Status - ATLAS France LHC Status - ATLAS France b* 3.5 m ±18 σ = orbit tolerances 1-2 s s  0.3 mm at TCT. TCDQ TCT

  24. What is an Asynchronous Beam Dump? LHC Status - ATLAS France TCSG

  25. What is an Asynchronous Beam Dump? Abort gap =3 ms Bunched beam and perfect synchronization with RF LHC Status - ATLAS France Bunches Bunches TCSG Empty region

  26. What is an Asynchronous Beam Dump? Abort gap =3 ms Loss of synchronization with RF or RF off  Unbunched beam filling the abort gap LHC Status - ATLAS France Unbunched beam Unbunched bean TCSG

  27. Protection in case of an asynchronous beam dump Estimated occurrence : at least once per year, 0 events up to now! LHC Status - ATLAS France TCDQ + TCSG to protect downstream SC magnet (Q4) TCSG TCDQ = 6 m long one-sided collimator TCSG = 1 m long two-sided collimator

  28. Asynchronous dump test • De-bunch a low intensity beam and fire the dump. • Verify that losses are contained in dump and collimation regions. • This is re-checked for EVERY dump using the small amount of beam present in the abort gap. dp/p cleaning betatron cleaning dump ATLAS ALICE CMS LHCb LHC Status - ATLAS France

  29. Outline Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run LHC Status - ATLAS France

  30. Injection • Injection is becoming more critical: • Injected beams have now some damage potential. • Losses at injection collimators become more critical – LHCb BCMs can tell some stories… • De-bunching of the already circulating beam can lead to beam dumps during injection. • Abort gap cleaning by exciting particles in the gap ( collimators) may soon become mandatory. • Frequent cause of dumps at injection. • Injection was going rather well until an aperture restriction was suddenly observed some 10 days ago near the injection septum of beam1. • Led to excessive losses and beam dumps during injection. LHC Status - ATLAS France

  31. Injection region • The injection septum (MSI) bends the injected beam parallel to the circulating beam in the horizontal plane. • The injection kicker (MKI) is deflecting the injected beam into the plane of the LHC (vertical deflection). • The TDI injection absorber is protecting the machine from damage in case of MKI ‘failures’ (not rare !!). • The TDI also intercepts the circulating bunch during over-injecting. LHC Status - ATLAS France

  32. Injection area investigations at the MSI Beam 1 : circulating & injected beam LHC Status - ATLAS France Beam 2 Suspected aperture restriction at the transition of injection septa magnets (MSIB-MSIA).

  33. Injection area investigations at the MSI LHC Status - ATLAS France Circulating b1 Injected b1 There is a problem with the RF fingers at the transition. Not clear how did it get worse suddenly. Must be repaired >> technical stop advanced to this Tuesday (18.10).

  34. Injection septum loss mapping • Scan of losses versus beam position (injected beam) clearly show obstruction. Steered beam down and towards left  sort of OK again. • Unfortunately this lasted only about one day, then the beam to be moved further down and more to the left (last Saturday). • 4 mm Vertical • +1 mm Horizontal High losses High losses LHC Status - ATLAS France old old new new No losses No losses

  35. Ramp rate • At the start of the run the ramp rate had to be limited to 2 A/s (1.2 GeV/s) for magnet protection reasons. • Ramp duration 0.45-3.5 TeV: 46 minutes • Since mid-July the rate for down-ramps and magnet pre-cycles (magnetic history reset) was increased to nominal value of 10 A/s (6 GeV/s). • Ramp speed with beam now to 10 A/s (6 GeV/s). • Pure ramp duration 0.45-3.5 TeV: 16 minutes. LHC Status - ATLAS France 3500 GeV 2 A/s 10 A/s 450 GeV

  36. From injection to collisions TCT = Tertiary Collimator LHC Status - ATLAS France 100/110 • 4 stops on the flat top for feedbacks and collimators.

  37. Emittance • Injected emittance can be reduced to less than 1.5 mm – almost a factor 3 below nominal value (3.5 mm). • Emittances for 50, 75 and 150 ns are lower than for 25 ns (injectors). • Rather strong beam-beam was observed in one fill with emittances at 3.5 TeV below 2 mm. Losses lead to beam dump – curable since thresholds were too low on some normal conducting elements in IR7. • Presently we aim for/inject beams with emittances of ~2 mm. • Emittance increase to collisions under control (transverse damper) – routinely start collisions with emittances around 2.5 mm (better for B1 than for B2). • Since Luminosity ~ 1/emittance  ~30% gain of luminosity. LHC Status - ATLAS France

  38. The good news : beam-beam, lifetimes • Beam current lifetimes in collisions now ≥ 25 hours. • No or very small lifetime dips when bringing beams into collisions. • Excellent news is that the beam-beam effects (both head-on and long-long range) seem much less critical than anticipated. • >> Can think of more bunch current, smaller emittance ! • Luminosity decay dominated by emittance growth, • Current decay ~30-40% • Emittance growth ~60-70% LHC Status - ATLAS France

  39. High intensity issue: vacuum activity IR1 • Vacuum pressure increase observed around the 4 experiments since LHC switched to train operation – issue becomes more and more critical as the intensity increases. • Local pressure bump around  60 m from the IP. • In the region of an uncoated segment of vacuum chamber at the warm-cold transition (after triplet). • Pressure rise driven by the presence of both beams. • No significant effect with a single beam. • Signs of cleaning by beam, and dependence on intensity (bunch/total). • Suspicion that this might be electron clouds ! LHC Status - ATLAS France

  40. Intensity and vacuum over 2 weeks 3.e13 p+ LHC Status - ATLAS France 3.5·10-7 mbar

  41. Electron clouds • … affect high intensity beams with positive charge and closely spaced bunches. • Electrons are generated at the vacuum chamber surface by beam impact, photons… • If the probability to emit secondary e- is high (enough), more e- are produced and accelerated by the field of a following bunch(es). Multiplication starts… • Electron energies are in the 10-100 eV range. • The cloud of e- can drive the beam unstable, and at the LHC, overload the cryogenic system by the heat deposited on the chamber walls ! •  The cloud can ‘cure itself’ because the impact of all those electrons cleans the surface, reduces the electron emission probability and eventually the cloud disappears ! LHC Status - ATLAS France Bunch N+2 accelerates the e-, more multiplication… Bunch N+1 accelerates the e-, multiplication at impact Bunch N liberates an e- e- e- N+2 N+1 N ++++++ ++++++ ++++++ e-

  42. Electron cloud • In principle no electron cloud expected with 150 ns beams. • Room temperature vacuum chambers are coated with a NEG that kills/reduces the likelihood of electron clouds. • But not the few pieces at the transition after the triplet… • The fact that the pressure increases with two beams, is close to a parasitic encounter and in a region without coating makes e-cloud a possible a candidate… • The vacuum group installed small solenoids around the chamber in IR1 during a cryo stop to test the hypothesis of electron cloud build-up (standard cure). • The presence of e-clouds could be demonstrated: with solenoid the vacuum is orders of magnitude better. • Brought a significant improvement of the vacuum and background for ATLAS. • The fact that the effect is much less visible in CMS could be due to the CMS solenoid STRAY field (to be confirmed). LHC Status - ATLAS France

  43. Solenoids between DFBX and D1 in IR1L M. Jimenez LHC Status - ATLAS France

  44. Solenoid A4R1 - ON Solenoid A4L1 - ON LHC Status - ATLAS France

  45. Peak luminosity performance Peak luminosity = 1.31032 cm-2s-1 (312 bunches/beam, 295 colliding bunches) LHC Status - ATLAS France

  46. Stored energy Peak ~20 MJ (TEVATRON ~2 MJ) The present beam intensity will slice open a vacuum chamber even at injection. LHC Status - ATLAS France

  47. Integrated luminosity Integrated luminosity ~23 pb-1 (17.10.2010) A fill with 250 bunches delivers 2 pb-1 in ~7-8 hours LHC Status - ATLAS France

  48. Outline Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run LHC Status - ATLAS France

  49. Plans Advanced technical stop 104 200 296 248 344 152 LHC Status - ATLAS France 312 • We are only at 312 bunches due to the injection problems. But with the smaller emittance we exceeded 1032. • If in the next 2 weeks, we make 6 fills per week it is possible to collect ~40 pb-1 more since for ≥ 350 b fills will deliver ~3-4 pb-1 / 12 hour.

  50. The next 2 weeks • Continue intensity increase towards ~400+ bunches. • Determine limits on b* for 2011: • Consolidate recent aperture measurements at injection confirming that we have more space than ‘designed’ – much better orbit, better alignment. • May reduce b* to 2 m in 2011 while keeping the same margins/tolerances. • Test physics fills with 50 ns trains. • Start with ~50 bunches, then increase in few steps to 300+ bunches. • Precious experience if we want to push intensity further and anticipate train effects (vacuum…). • Quench tests. • Test b* = 90 m optics (TOTEM, total cross section). • Feedback improvements for tune and orbit (could also be done during ion period). LHC Status - ATLAS France

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