1. 18.10.2010 LHC Status - ATLAS France 1 LHC achievements, status and plans J. Wenninger BE OP group

2. Outline 18.10.2010 LHC Status - ATLAS France 2 Machine protection (driven) commissioning Setting up for trains Train operation The last week of protons Ion run

3. The target 18.10.2010 LHC Status - ATLAS France 3 >10 32 cm -2 s -1 (>1 fb -1 for 2011)

4. Machine protection driven commissioning 18.10.2010 LHC Status - ATLAS France 4  MP phase 1: low intensity MP commissioning. o Commissioning of the protection systems. o Low intensity single bunch commissioning of the systems, including beam tests (manually triggered failures).  MP phase 2: MP running in with gradual intensity increase. o Intensity increase in steps, factor 2 – 4, up to ~ MJ stored energy. o Stability run of a few weeks around 1-3 MJ.  MP Phase 3: intensity increase to 10’s MJ regime. o Intensity increase in steps of 2-3 MJ (  1 TEVATRON beam). o Initially planned one step every 1-2 weeks. o 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.

5. Machine protection: some statistics 18.10.2010 LHC Status - ATLAS France 5  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. Beam dumps > 450 GeV Operator MPS test HW surveillance Beam monitoring ‘False’ dumps  Remaining worries arise from COMBINED failures, most scenarios involve an injection or a dump error (asynchronous dump). o That is why we carefully track anomalies in the present period of rapid intensity increase.

6. UFOs 18.10.2010 LHC Status - ATLAS France 6  On 7 th July we observed the first occurrence of fast beam loss events in the super-conducting regions of the ring: o Beam loss at a SC magnet. o Fast loss over ~0.5-2 ms. o Most events during stable beams: no power converter changes, orbit rock-stable, no lifetime issue before the event… o 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 ! o ‘Dust’ particles ‘falling’ into the beam, estimated size ~100  m think Carbon-type object. o Two events in perfect coincidence (time & space) with TOTEM roman pot movements make this hypothesis rather convincing.

7. Example of a 152 bunches UFO 18.10.2010 LHC Status - ATLAS France 7 LHCb Arc s IR1IR7 Time evolution of loss 1 bin = 40  s 0.5 ms Dump trigger Beam loss monitor post-mortem

8. A worrying correlation… 18.10.2010 LHC Status - ATLAS France 8 T. Baer One of the reasons why we want to observe the beams for 20 hours before increasing intensity!

9. UFO near threshold 18.10.2010 LHC Status - ATLAS France 9 About 50% of the UFOs lead to dumps while the loss is decaying… Dump trigger Time evolution of loss 1 bin = 40  s ALICE Arc IR3IR1 The dump is triggered on the loss integral !

10. UFO and BLM thresholds 18.10.2010 LHC Status - ATLAS France 10  2 weeks ago we had accumulated 12 UFO events (  beam dumps).  But there was no quench – the BLMs always triggered first. o 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 elements by a factor 3. o Initial thresholds were set to 30% of quench level – we are now essentially at the estimated quench level. o 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: o With 250 bunches there are ~0.8 UFOs/hour

11. Outline 18.10.2010 LHC Status - ATLAS France 11 Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run

12. Crossing angles 18.10.2010 12 LHC Status - ATLAS France IRPlaneInjection & ramp Squeeze & collisions 1V-170-100 2V 170 110 5H 170 100 8H-170-100 ½ crossing angles (sign  B1)  Until end of August the large bunch spacing did not require Xing angles. o 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. o Xing angle value is a compromised between maximizing aperture and minimizing beam-beam effects. ‘long-range beam-beam’ For 150 ns spacing, the first encounter is at  22.5 m from the IP

13. Separation and crossing in ATLAS LHC Status - ATLAS France 13 Horizontal plane: the beams are combined and then separated Vertical plane: the beams are deflected to produce a crossing angle at the IP ~ 7 mm Not to scale ! 194 mm ATLAS IP ~ 260 m Common vacuum chamber 18.10.2010 During injection, ramp & squeeze there is an additional parallel separation of  2 mm in the horizontal plane !

14. Crossing angles : injection 18.10.2010 LHC Status - ATLAS France 14 ATLASALICECMSLHCb  10 mm B1 Vert B1 Hor B2 Vert B2 Hor

15. 150 ns beam structure 18.10.2010 LHC Status - ATLAS France 15  PS produces trains of m bunches (spacing 150 ns). o m = 8 or 12. o m is fixed for a given filling sequence.  SPS assembles n PS trains of m bunches o n = 1,2,3 or 4. So far we use only 1 and 2. o train spacing defined at injection to SPS, presently 300 ns. o n may change for each cycle.  LHC requests p SPS train groups o n may vary from one injection to the next. m mm PS SPS LHC mmmmmmm m Circumference mm or Very flexible – can produce a large variety of patterns in the LHC or mmmmmm

16. LHC Status - ATLAS France one train of m bunches shifted by -3 x 25ns slots one train of m bunches shifted by -3 x 25ns slots Overview of proposed 150ns “structure”  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, … -3 +3 -3 m k m m 18.10.2010 16

17. A possible evolution bunches per LHC injection LHC injections x bunches ( per beam) Total bunches per LHC beam LHC inj. Collisions in IP1,5,8 Collisio ns in IP2 83 x8 24 3 16 84x8 +3x8 56 7 47 16 8 or : 8 & 8+8 12x8 + 1x8 or : 4x8+4x(8+8) + 1x8 104 13 9 93 8 8 or : 8 & 8+8 16x8 + 3x8 or : 8x(8+8) + 3x8 152 19 11 140 16 8 & 8+84x8+10x(8+8) + 1x8 200 15 186 8 8 & 8+8 or : 8 & 8+8+8 4x8+12x(8+8) + 3x8 4x8+8x(8+8+8) + 3x8 248 19 15 233 16 etc…etc 312 19 290 16 2/3 equalitarian 4-fold symmetric private IP2 M. Ferro-Luzzi 18.10.2010 17 LHC Status - ATLAS France

18. 312 bunches 18.10.2010 LHC Status - ATLAS France 18 Beam 1

19. LHC aperture and collimator settings 19 Injection 3.5 TeV 5.7  8.5  15.0  15  5.7  6.7  12.0  12.5  Primary (robust) Secondary (robust) Absorber (W metal) Tertiary (W metal) ARC Beam halo ➠ ARC IP & Triplets Beam halo ➠ ±8.5 σ ±18 σ 18.10.2010 LHC Status - ATLAS France Courtesy S. Redaelli  * 3.5 m TCP TCSG TCLA TCT IP & Triplets

20. Machine protection setup/tests for trains 18.10.2010 LHC Status - ATLAS France 20  Collimator setup. o 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). o Tertiary collimator setup at injection, at 3.5 TeV un-squeezed and for collisions. Positions are interpolated in ramp and for the squeeze steps. o 8 collimators per beam (2 per IR and per beam).  Collimator and dump setup validation. o Large losses induced by crossing resonance to verify collimator setup (loss maps). o De-bunch beam to fill abort gap and trigger dump to verify protection by absorbers (and collimators). o Very time (beam) consuming exercise. Minimum of 10 cycles. o Used up a large part of the train setup.

21. LHC Status - ATLAS France Good setup - hierarchy respected 21 IP4IP5IP6IP7IP8 β cleaning Δp/p cleaning Dump TCTs IP1IP2IP3 Beam 1 IP7 TCPs TCSGs TCLAs Normal cond. magnet cleaning insertion 18.10.2010 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 18.10.2010 22  Leakage into cold aperture around 2e-4.  Stable over 2 months. Courtesy D. Wollman LHC Status - ATLAS France Example of the loss leakage on the horizontal tertiary collimators (sum over all IRs) over 2 months.

23. Dump protection and  * 18.10.2010 LHC Status - ATLAS France 23 LHC Status - ATLAS France IP & Triplets Beam halo ➠ 10.5  15  Dump protection Tertiary (W metal) ±18 σ TCDQ TCT   * at the IR is limited by the beam size in the triplet. o Beam size in triplet  1/  *. o  * reduction is limited by the aperture in the triplet and the tolerances for collimators, protection devices (dump) and orbit movements.  * 3.5 m = orbit tolerances 1-2   0.3 mm at TCT.  Tolerances are not too aggressive to avoid constant OP interruptions for alignment verification and checks.

24. What is an Asynchronous Beam Dump? TCSG 18.10.2010 24 LHC Status - ATLAS France

25. TCSG What is an Asynchronous Beam Dump? Abort gap =3  s Bunches Empty region Bunched beam and perfect synchronization with RF 18.10.2010 25 LHC Status - ATLAS France

26. TCSG What is an Asynchronous Beam Dump? Abort gap =3  s Unbunched beamUnbunched bean Loss of synchronization with RF or RF off  Unbunched beam filling the abort gap 18.10.2010 26 LHC Status - ATLAS France

27. TCSG Protection in case of an asynchronous beam dump TCDQ = 6 m long one-sided collimator TCSG = 1 m long two-sided collimator TCDQ + TCSG to protect downstream SC magnet (Q4) Estimated occurrence : at least once per year, 0 events up to now! 18.10.2010 27 LHC Status - ATLAS France

28. Asynchronous dump test 18.10.2010 LHC Status - ATLAS France 28  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. ATLASALICECMSLHCb dp/p cleaning betatron cleaning dump

29. Outline 18.10.2010 LHC Status - ATLAS France 29 Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run

30. Injection 18.10.2010 LHC Status - ATLAS France 30  Injection is becoming more critical: o Injected beams have now some damage potential. o Losses at injection collimators become more critical – LHCb BCMs can tell some stories… o De-bunching of the already circulating beam can lead to beam dumps during injection. o Abort gap cleaning by exciting particles in the gap (  collimators) may soon become mandatory. o 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. o Led to excessive losses and beam dumps during injection.

31. Injection region 31  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 !!). o The TDI also intercepts the circulating bunch during over-injecting. 18.10.2010 LHC Status - ATLAS France

32. Injection area investigations at the MSI  Suspected aperture restriction at the transition of injection septa magnets (MSIB-MSIA). Beam 2 Beam 1 : circulating & injected beam 18.10.2010 32 LHC Status - ATLAS France

33. Injection area investigations at the MSI  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). Injected b1 18.10.2010 33 LHC Status - ATLAS France Circulating b1

34. Injection septum loss mapping 18.10.2010 LHC Status - ATLAS France 34 old new High losses No losses High losses No losses -4 mm Vertical +1 mm Horizontal  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).

35. Ramp rate 18.10.2010 LHC Status - ATLAS France 35  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. o 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). o Pure ramp duration 0.45-3.5 TeV: 16 minutes. 2 A/s10 A/s 450 GeV 3500 GeV

36. From injection to collisions 18.10.2010 LHC Status - ATLAS France 36  4 stops on the flat top for feedbacks and collimators. 100/110 TCT = Tertiary Collimator

37. Emittance 18.10.2010 LHC Status - ATLAS France 37  Injected emittance can be reduced to less than 1.5  m – almost a factor 3 below nominal value (3.5  m). o Emittances for 50, 75 and 150 ns are lower than for 25 ns (injectors). o Rather strong beam-beam was observed in one fill with emittances at 3.5 TeV below 2  m. 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  m. o Emittance increase to collisions under control (transverse damper) – routinely start collisions with emittances around 2.5  m (better for B1 than for B2). o Since Luminosity ~ 1/emittance  ~30% gain of luminosity.

38. The good news : beam-beam, lifetimes 18.10.2010 LHC Status - ATLAS France 38  Beam current lifetimes in collisions now ≥ 25 hours. o No or very small lifetime dips when bringing beams into collisions. o 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, o Current decay ~30-40% o Emittance growth ~60-70%

39. 18.10.2010 LHC Status - ATLAS France High intensity issue: vacuum activity IR1 39  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. o 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. o 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 !

40. Intensity and vacuum over 2 weeks 18.10.2010 LHC Status - ATLAS France 40 3.5·10 -7 mbar 3.e13 p+

41. Electron clouds 18.10.2010 LHC Status - ATLAS France 41 N e- N+1 e- N+2 e- Bunch N liberates an e- Bunch N+1 accelerates the e-, multiplication at impact Bunch N+2 accelerates the e-, more multiplication… ++++++ … 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… o 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 !

42. Electron cloud 18.10.2010 LHC Status - ATLAS France 42  In principle no electron cloud expected with 150 ns beams. o Room temperature vacuum chambers are coated with a NEG that kills/reduces the likelihood of electron clouds. o 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). o The presence of e-clouds could be demonstrated: with solenoid the vacuum is orders of magnitude better. o Brought a significant improvement of the vacuum and background for ATLAS. o The fact that the effect is much less visible in CMS could be due to the CMS solenoid STRAY field (to be confirmed).

43. Solenoids between DFBX and D1 in IR1L M. Jimenez 18.10.2010 43 LHC Status - ATLAS France

44. Solenoid A4L1 - ONSolenoid A4R1 - ON 18.10.2010 44 LHC Status - ATLAS France

45. Peak luminosity performance 18.10.2010 LHC Status - ATLAS France 45 Peak luminosity = 1.3  10 32 cm -2 s -1 (312 bunches/beam, 295 colliding bunches)

46. Stored energy 18.10.2010 LHC Status - ATLAS France 46 Peak ~20 MJ (TEVATRON ~2 MJ) The present beam intensity will slice open a vacuum chamber even at injection.

47. Integrated luminosity 18.10.2010 LHC Status - ATLAS France 47 Integrated luminosity ~23 pb -1 (17.10.2010) A fill with 250 bunches delivers 2 pb -1 in ~7-8 hours

48. Outline 18.10.2010 LHC Status - ATLAS France 48 Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run

49. Plans 18.10.2010 LHC Status - ATLAS France 49 104 152 200 248 296 344  We are only at 312 bunches due to the injection problems. But with the smaller emittance we exceeded 10 32.  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. 312 Advanced technical stop

50. The next 2 weeks 18.10.2010 LHC Status - ATLAS France 50  Continue intensity increase towards ~400+ bunches.  Determine limits on  * for 2011: o Consolidate recent aperture measurements at injection confirming that we have more space than ‘designed’ – much better orbit, better alignment. o May reduce  * to 2 m in 2011 while keeping the same margins/tolerances.  Test physics fills with 50 ns trains. o Start with ~50 bunches, then increase in few steps to 300+ bunches. o Precious experience if we want to push intensity further and anticipate train effects (vacuum…).  Quench tests.  Test  * = 90 m optics (TOTEM, total cross section).  Feedback improvements for tune and orbit (could also be done during ion period).

51. Outline 18.10.2010 LHC Status - ATLAS France 51 Machine protection commissioning Setting up for trains Train operation The last week of protons Ion run

52. Early ion scheme 18.10.2010 LHC Status - ATLAS France 52 J. Jowett  Peak luminosity ~10 25 cm -2 s -1, integrated L ~ few  b.  Bunch charge corresponds ~6E9 – equivalent to a pilot proton bunch. o Visible on beam position system only down to ~2-3E9 (with good quality !)

53. Ions are like protons at the LHC 18.10.2010 LHC Status - ATLAS France 53  At the LHC the difference between Pb ions and protons is very small because of the high energy. o Same orbit, tunes, optics, geometrical emittance…  Main difference between ions and protons is the RF frequency (revolution frequency): o RF frequency swing 5 kHz instead of 800 Hz (wrt 400 MHz). o Difference in frequency is vanishing at 3.5 TeV : ~ 10 Hz.  It is possible to reuse almost all proton settings for ions !

54. Ions are almost like protons at the LHC 18.10.2010 LHC Status - ATLAS France 54 Some changes wrt protons:  We may remove the crossing angle – partly your choice. o ALICE wants to run with 0 effective angle. They need the external (machine) crossing angle bump to compensate their spectrometer crossing angle.  Collimation does not work well for ions due to fragmentation. o Basically a single stage system. Details of settings not finalized yet. o Collimation setup must be completely redone, but it will be simpler. o ALICE has a problem with the vertical TCT that shadows spectator neutrons in their ZDC. o Request to retract TCT as no fast loss (asynch. dump) in vertical plane. This will probably be accepted.  MPS issues are minor – no special setup. o But we will keep our eyes open !

55. A 128 bunches/ring scheme  Basic building block: –Four bunches spaced by 500 ns –Injection kicker: 975 ns  9 such blocks fill exactly one LHC quarter.. 18.10.2010 55 LHC Status - ATLAS France

56. Commissioning of ions 18.10.2010 LHC Status - ATLAS France 56  Commissioning should be feasible in one week. 3 weeks of good running…  Intensity increase should be fast – over a couple of fills. o Clearly no serious MP issue here. o Possibly driven by operational aspects (injection etc).

57. Summary 18.10.2010 LHC Status - ATLAS France 57  L = 10 32 cm -2 s -1 achieved !  So far possible obstacles have been solved: o UFOs – the BLM threshold increase helped – we were bloody lucky! >> But at 7 TeV this could become a serious issue !! o Vacuum – solenoids help against e-cloud.  Major test in the last 2 weeks: 50 ns operation test.  Injection problem to be fixed during the technical stop.  Switch over to ion should be fast – 1 week. o Some details to be finalized (Xing angle or not). o Possibility to increase bunches from 62 to 140 is on the table.

58. Outlook 2011 18.10.2010 LHC Status - ATLAS France 58 Possible gains in luminosity:  50 ns trains x 3   * = 2 m x 1.7  Lower emittance – already used(x 1.3)  Bunch charge to 1.3x10 11 p x 1.4 Totalx 7 ! Total intensity may be limited by collimation or lifetime considerations – we may not gain the full factor !

59. 18.10.2010 LHC Status - ATLAS France 59 Spares

60. Lifetime versus crossing angle 18.10.2010 LHC Status - ATLAS France 60 Test with 3 batches of 8 bunches each, spacing 150 ns at injection  up to 6 long range interactions per bunch. 100  rad 170  100  rad 80  rad 70  rad 60  rad 50  rad 40  rad 30  rad 20  rad 90  rad At injection the minimum Xing angle with 150 ns trains is 100  rad. It was decided to use the nominal value of 170  rad to gain experience. Aperture was found not to be a problem.

61. Beam loss in collisions – 104 bunches 18.10.2010 LHC Status - ATLAS France 61 ATLASALICECMSLHCb dp/p cleaning betatron cleaning Luminosity driven ! One can clearly determine the collimation efficiency online (not IRs !)

62. Example of global aperture measurement LHC Status - ATLAS France 62 TCPV = 15 sig TCPV = 13 sig TCPV = 12 sig Q4.R6 Loss at Q4 higher than at TCP Loss at Q4 about same as TCP Loss at Q4 lower than at TCP Beam 2, V plane 18.10.2010

63. Measured 450 GeV Aperture LHC Status - ATLAS France 63  No aperture bottlenecks in triplets.  On momentum aperture ≥ 3 sigma larger than ‘predicted’ Main reason: much better orbit (≥ 2 sigma gain) Beam / planeLimiting element Aperture [  ] Beam 1 HQ6.R212.5 Beam 1 VQ4.L613.5 Beam 2 HQ5.R614.0 Beam 2 VQ4.R613.0 18.10.2010