Thanks for discussion and input to: Oliver Bruning, Stephane Fartoukh, Ray Veness, Serge Claudet, Roberto Saban, Ralph Assmann, Andy Butterworth

Transcription

1 LHC - BOLD BEGINNING Mike Lamont Thanks for discussion and input to: Oliver Bruning, Stephane Fartoukh, Ray Veness, Serge Claudet, Roberto Saban, Ralph Assmann, Andy Butterworth Lend thy fresh beams our lagging months to cheer LOOK WITH FAVOR UPON A BOLD BEGINNING Virgil

2 Reasonably good start

3 Even before the drawing-board stage, the farsighted John Adams noted in 1977 that the tunnel for a future large electron positron (LEP) collider should also be big enough to accommodate another ring of magnets. REALLY BOLD BEGINNINGS

4 Challenges Accepted High magnetic field 2-in-1 magnet design Superfluid helium (After some debate!) LEP isn t even installed yet but we re going to start work on an accelerator which needs: a magnet design we re not sure works; fields we can t yet produce; to be cooled by superfluid helium in 27 km tunnel deep underground.

5 1984 Since it is very difficult to handle more than one event per bunch crossing for experiments that can accept a higher <n>, luminosities of up to 1.5 x cm -2 s -1 could possibly be reached It took a very long time - 10 years - from this starting point for the project to be approved. During most of this time Giorgio Brianti led the LHC project study. However, we should not forget the enormous debt we owe to Carlo Rubbia in the second half of that decade for holding the community together behind the LHC against all the odds. Lyn Evans

6 Parameters through the years Giorgio Brianti

7 June 1994 first full scale prototype dipole June 2007 First sector cold ECFA-CERN workshop April 2008 Last dipole down 1994 project approved by council (1-in-2) SSC cancelled Some of us practiced on a 27 km warm version First set of twin 1 m prototypes Over 9 T 2002 String 2 Main contracts signed November delivered September 19, 2008

8 Courtesy Luca Bottura

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10 Technology: beautiful, when well done! 25 March 2003 Lucio Rossi - Superc. Mag. 10

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12 48 warm magnets have come from TRIUMF, Vancouver; 40 from the Institute for High Energy Physics in Protvino, near Moscow; and 65 from the Budker Institute of Nuclear Physics in Novosibirsk, Russia. Warm quadrupole magnets in IR3 and IR7 - challenging 2-in-1 design Significant international effort

13 Triplets Two separate designs: FNAL had a good field quality didn t initially reach the design gradient KEK reached the design gradient but had field quality issues Following the triplet construction was Tom Taylor and Ranko Ostojic. The upshot of the above challenges was the decision to mix the triplet magnets: KEK magnets at Q1 and Q3; FNAL magnets at Q2. Impact on the powering scheme of the triplet (both designs require different currents for the same gradient) key player here was Jean-Pierre Koutchouk.

14 Magnets++ Field quality tracking and adjustment Field quality vitally important for beam stability - good after adjustments and faithful to the tight specifications Sorting: not all magnets are created equal geometry - aperture b3 - dynamic aperture/resonance driving terms b1 closed orbit perturbations a2 coupling, vertical dispersion Magnetic measurement and modelling Characterize the important dynamic effects in anticipation of correction All important magnetic strength versus current calibration

15 Dipole Skew Dipole Quadrupole Skew Quadrupole Sextupole Skew Sextupole Octupole Skew Octupole Decapole Skew Decapole Quattuordecapole

16 b3 integral (units) 10 5 Firm 1 Firm 2 Firm 3 Collared coil 0-5 average upper limit for systematic lower limit for systematic -10 Xs1 Xs2 Xs Collared coil progressive number AT-MAS & MTM Plus: main field, magnetic length, quadrupole, octupole, decapole, skew quadupole, skew sextupole, skew octupole! Courtesy Ezio Todesco et al

17 QUALITY CONTROL Strong anomalies all along the magnet axis (-13 units of b2, -5 units of b3, 16 units of a2, 12 units of a3, 7 of a4, ). After decollaring, it has been found that a copper wedge of type 2 has been put at the place of the type 1 wedge (see Fig. 32). Courtesy Ezio Todesco et al

18 Magnet sorting - geometry Measured the curved aperture of dipoles: 3 classes: GOLD SILVER MID-CELL MQ MB MB MB MB MB MB G S SL G,S SL,SR MC G S SR MQ G S SL G,S SL,SR MC S. Fartoukh for the MEB G S SR MQ

19 Magnet sorting - b3 Very efficient flip-flop pairing: effective random b3 reduced by a factor 2-3, further improved by super-imposing p-pairing for the outliers in sectors78/81/34 Typical p-pairing + flip-flop Few Xs3 s Xs1 Noell magnets Sector 78: ap. V1 Courtesy Stephane Fartoukh

20 Magnet measurements and modeling 10 years of measurements, dedicated instrumentation R&D, 4.5 million coil rotations, 50 GB of magnetic field data, 3 Ph.D.s and a few Masters Theses on the subject, 2 years of data pruning and modeling, collaborations and participation in runs in Tevatron and RHIC today we have the most complex and comprehensive forecast system ever implemented in a superconducting accelerator Luca Bottura 2008 for the FIDEL team

21 CRYOGENICS

22 24 km of superconducting K 88 tons of superfluid helium at 1.9 K 8 x 4.5 K superconducting magnets Courtesy Serge Claudet

23 Cryogenic vacuum Good beam lifetime in a cryogenic system where heat input into the 1.9 K helium circuit must be minimized and where significant quantities of gas can be condensed on the vacuum chamber Constraints: heat input (beam screen); resistivity (copper layer); beam stability (impedance); Beam screen as seen by the beam BS cooling pipes Slots (3% surface) Cold Bore (2K)

24 Room temperature vacuum ~6 km of room temperature vacuum chambers Same requirements in terms of beam lifetime and stability as the cold sectors, but do not benefit from cryo-pumping. A new technology: sputtered non-evaporable getter, was developed for the LHC

25 Foreseen limitations At low energy the main limitation for the beam lifetime comes from the machine non-linearities, i.e. the magnetic field errors At collision energy the limiting effects are caused by the beam-beam interaction Head-on conservative approach based on previous experience long range interactions - limiting factor performance. Electron cloud only identified as a problem for the LHC in the late 90ies Pioneering work by Francesco Ruggiero & Frank Zimmermann

26 Optics and beam dynamics Major effort to optimize the optics: Which crossing scheme is preferred? What is the effect of triplet errors? Which is the preferred working point? What are the best integer tunes? Major simulation effort to study: Particle stability (dynamic aperture), beam instabilites Effect of triplet errors, head-on beam-beam, long-range beam-beam development of simulation tools (MAD and SIXTRACK) and the build up of computing resources (Frank Schmidt and Eric McIntosh) Specification of corrector circuits and strategy Jean-Pierre Koutchouck et al

27 Jacques Gareyte

28 Dynamic aperture In collisions, dynamic aperture largely constrained by the long range beam-beam effects and the field errors in the low beta triplets Phase-space plot simulated using a 2- dimensional model of the long-range beambeam force Y. Papaphilippou & F. Zimmermann

29 Long range encounters give rise to a well defined border of stability at the diffusive aperture Diffusion rate Particle amplitude Y. Papaphilippou & F. Zimmermann

30 POWERING TESTS INTERCONNECTION And then a miracle occurred QRL COOL DOWN

31 Alignment HLS linked by two hydraulic networks Beam through Alice and to the end of sector 23 first shot 8/8/2008

32 Preparation: beam tests through the years 2003:TT :TI8 CNGS 2005: FIRST HOLE TI2 2008: FIRST BEAM TO LHC 2008: FIRST BEAM TO IR3 2008: SEPT : FIRST IONS TO LHC 2009: Sector test 2009!

33 MAGNET CIRCUIT TESTS++ Transfer lines Injection, Extraction RF, injection sequence Timing System Beam Interlock System Collimators Vacuum Interlocks, SIS BLMs, BPMs BTV, BCT Beam dump Powering Groups of Circuits Magnet model Sequencer, alarms Controls, logging, DBs LSA, optics model, YASP Preparation: HWC and machine checkout RF frequency is nearly fixed. Just jump to the next bucket. This can only happen if the SPS is empty PSB VCO CPS Source Next SPS target bucket FREV bucket FREV Time difference to digital convertor SB-Frev jumps to the next LHC TB-Frev Jump SPS SBF Target bucket revolution frequency CPS Re-phase with beam ~20ms Target Bucket FREV + - LHC TBF Batch 1 CPS RF Reference frequency Jump LHC TBF SPS SBF Batch 2 Re-phase with beam ~50ms RF SPS SPS RF BA3 Rephase with beam: The time difference between the target bucket FREV and the source bucket FREV is measured by a TDC. The TDC value then changes the RF frequency so that they come in line. This takes time to complete, and disturbs the orbit. ABORT GAP Filling LHC Ring 1 R1 Bucket from telegram Target bucket revolution frequency In LHC RF SR4 Batch 3 Batch 4 Batch 5 Injection Kicker Batch 1 Batch 4 Out Kicker tail is to long to allow inserting batch 4 between batch 3 and batch 5 Batch number to Bucket number conversion Bucket = K + h/n h = RF Buckets n = 12 Batches K = 121 Approx (Offset) Re-phasing in the SPS: Batch 2 Batch 3

34 August 2008 First injection test November 29, 2009 Beam back August, e33, 2.6 fb bunches September 10, 2008 First beams around April 2010 Squeeze to 3.5 m October e bunches June bunches September 19, 2008 Disaster Accidental release of 600 MJ stored in one sector of LHC dipole magnets March 30, 2010 First collisions at 3.5 TeV November 2010 Ions

35 September 10 th, 2008 Bold or foolhardy? James Gillies & team: the creation of a global brand. IR7 IR3 IR6 First turn!

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37 2009: besides massive repair and consolidation Understanding the problem Copper stabilizer issue identified Measurement campaign warm and cold Simulations Test set-up (FRESCA) Prevention Deployment of new Quench Protection System (design, prototyping, production, deployment, testing) Allows online measurement of the cold splice resistance on the nano-ohm level. Heroic effort from Knud, Reiner and team Caution Run at 3.5 TeV

38 2009: That which does not kill us Beam based systems Injectors & transfer lines Instrumentation: BPMs, BLMs Beam interlock System RF Collimators Controls & software Sequencer Injection sequencer Settings management Middleware Timing Software interlocks Magnet model On-line model Logging Dry runs, system tests and hardware commissioning (bis) RF frequency is nearly fixed. Just jump to the next bucket. This can only happen if the SPS is empty SB-Frev jumps to the next LHC TB-Frev Jump Jump LHC TBF LHC TBF SPS SBF SPS SBF Target Bucket FREV Target bucket revolution frequency Batch 1 SPS SPS RF BA3 ABORT GAP Filling LHC Ring 1 R1 Bucket from telegram Target bucket revolution frequency LHC RF SR4 Batch 1 Batch 2 Batch 3 CPS Batch 4 PSB VCO CPS Source Next SPS target bucket FREV bucket FREV Time difference to digital convertor Re-phase with beam ~20ms + - CPS RF Batch 2 Re-phase with beam ~50ms RF Rephase with beam: The time difference between the target Unprecedented state of readiness Reference frequency bucket FREV and the source bucket FREV is measured by a TDC. The TDC value then changes the RF frequency so that they come in line. This takes time to complete, and disturbs the orbit. In Batch 3 Batch 4 Batch 5 Injection Kicker Out Kicker tail is to long to allow inserting batch 4 between batch 3 and batch 5 Batch number to Bucket number conversion Bucket = K + h/n h = RF Buckets n = 12 Batches K = 121 Approx (Offset)

39 Early commissioning Marked by phenomenally swift deployment of tools to measure, correct, and verify: Optics, magnet model, polarities (!), aperture Fabulously fast turnaround on problem resolution Ramp, squeeze commissioning eased by availability of feedbacks Underpinned by instrumentation and software Experience meets youthful enthusiasm, talent, and stamina

40 Feb 27 Beam back March 30 First collisions 3.5 TeV June Commission nominal bunch intensity CONSOLIDATION November 4 Switch to lead ions February March April May June July August September October November April Commission squeeze September Crossing angles on October Luminosity production 2010

41 2010 integrated luminosity CONSOLIDATION COMMISSIONING and frantic debugging EXPLOITATION

42 Optics Optics stunningly stable and well corrected Two measurements of beating at 3.5 m 3 months apart Local and global correction at 1.5 m R. Tomas, G. Vanbavinckhove, M. Aiba, R. Calaga, R. Miyamoto

43 Reproducibility LHC magnetically reproducible with rigorous pre-cycling - set-up remains valid from month to month 7 e-3 Tune corrections made by feedback during squeeze Courtesy Stefano Redaelli

44 Nominal cycle 2011 Beam dump Squeeze Stable beams Collide Ramp down/precycle Ramp Ramp down Injection 35 mins ~30 mins Injection Ramp Squeeze 17 mins 8 mins Collide 1 mins Stable beams 0 30 hours Fastest turn around down from 3h40m in 2010 to 2h7m in 2011 after optimization

45 Transfer & injection 2011: 144 bunches of 1.4e11 ppb MJ IR8 Possibly the best studied, best optimized transfer lines in the history of accelerator physics Injection kicker Fast extraction kicker SPS 6911 m 450 GeV / 400 GeV Switching magnet CNGS Target Transfer line LHC Injection kicker IR2 Transfer line HiRadMat Fast extraction kicker 1 km

46 Injection Complex process wrestle with: Re-phasing, synchronization, transfer, capture Timing, injection sequencing, interlocks Injection Quality checks SPS and LHC Abort gap keeper Beam losses at injection, gap cleaning Full program of beam based checks performed Carefully positioning of collimators and other protection devices Aperture, kicker waveform Transfer line collimator SC magnets armed with beam loss monitors TCDD absorber TDI collimator 4 x KICKERS 5 x SEPTA

47 Ramp Power converters (all magnet circuits), magnet model, RF, collimators, beam dump, transverse damper, orbit and tune feedback, BLM thresholds etc. Reproducible and essentially without loss (after a lot of work) Ions this morning (after less than a week in the machine)

48 Current [A] Tracking between the three main circuits of sector Quadrupole Circuits (RQF, RQD) ppm Dipole Circuit (RB) 1000 Main bend power converters: tracking error between sector 12 0 & 23 in ramp to 1.1 TeV 19:00 19:30 20:00 20:30 21:00 21:30 Phenomenal performance from the power converters Courtesy Freddy Bordry & Dave Nisbet

49 Magnet model Knowledge of the magnetic machine is remarkable All magnet transfer functions, all harmonics including decay and snapback Tunes, momentum, optics remarkably close to the model Model based feed-forward reduces chromaticity swing Courtesy Luca Bottura & Ralph Steinhagen

50 Tune and orbit feedback Mandatory in ramp and squeeze Commissioning not without some issues but now fully operational Courtesy Ralph Steinhagen

51 RF Beam-induced voltage and load power dealing with over half nominal intensity RF feedback working as designed to cope with transient beam loading The broadband RF noise is reduced to a level that makes its contribution to beam diffusion in physics well below that of Intra Beam Scattering. Capture losses are also under control, at well below 0.5%. Longitudinal emittance blow-up operation needed for ramping of nominal bunch intensity 1.2 ns Courtesy Philippe Baudrenghien Bunch length in ramp with blow-up

52 Courtesy Andy Butterworth

53 Courtesy Andy Butterworth

54 Transverse position Transverse dampers Injection oscillations Working extremely well to damp the TCBI mode 0 Hump suppression Abort gap and injection gap cleaning Coherent instabilities Blow-up for loss maps Vital and working very well OFF ON Injection oscillations Turn number Courtesy Wolfgang Hofle & Daniel Valuch

55 Beam Instrumentation: brilliant the enabler Beam Position Monitors Beam loss monitors Base-Band-Tune (BBQ) Synchrotron light Longitudinal density monitor Wire scanner

56 Machine protection the challenge Beam 100 MJ Situation at 3.5 TeV (in August 2011) Not a single beam-induced quench at 3.5 TeV YET SC Coil: quench limit mj/cm 3 56 mm 11 magnet quench at 450 GeV injection kicker flash-over

57 Beam Interlock System Safe Beam Parameter Distribution Jaw Position Temperature Safe LHC Parameter Software Interlock System Operator Buttons CCC Vacuum System Screens and Mirrors beam observation RF System (f_rf + P) Access System Collimation System Special BLMs Safe Beam Flag Beam Interlock System Beam Dumping System Powering Interlocks superconducting magnets Magnet protection system (20000 channels) Powering Interlocks normal conducting magnets Magnets Power Converters ~1600 Power Converters AUG UPS Fast Magnet Current change Monitor Cryogenics some channels BPMs LHC Experiments Beam Loss Monitors BCM Beam loss monitors BLM Monitors aperture limits (some 100) Monitors in arcs (several 1000) Injection Interlock Timing System (Post Mortem Trigger) Courtesy Rudiger Schmidt, Bruno Puccio, Ben Todd

58 Beam Dump System (LBDS) Absolutely critical. Rigorous and extensive program of commissioning and tests with beam. Expected about two asynchronous dumps per year one to date with beam IR6 H Beam2, extracted

59 Collimation 1.2 m Two warm cleaning insertions IR3: Momentum cleaning 1 primary (H) 4 secondary (H,S) 4 shower abs. (H,V) IR7: Betatron cleaning 3 primary (H,V,S) 11 secondary (H,V,S) 5 shower abs. (H,V) Local IP cleaning: 8 tertiary coll. Total = 108 collimators About 500 degrees of freedom. beam

60 Collimation cleaning at 3.5 TeV Generate higher loss rates: beam across the 3rd order resonance. Beam 1 Betatron TCTs Off-momentum Dump TCTs TCTs TCTs Legend: Collimators Cold losses Warm losses Outstanding performance: No beam-induced quenches in 2010/2011

61 ns 50 ns 4. Increase bunch intensity 1. Increase number of bunches 3. Squeeze further 2. Reduce beam size from injectors

62 Total intensity At injection dynamic aperture is clearly greater than aperture defined by collimators: Excellent field quality and correction of non-linearities Dynamic effects well under control (FIDEL) Low tune modulation, low power converter ripple, low RF noise Number of issues during the ramp-up in the number of bunches: Instrumentation response Vacuum activity UFOs Beam induced heating Single Event Effects (SEE) Machine protection performing impeccably Routine collimation of 110 MJ LHC beams (50 times HERA/Tevatron) without a single quench from stored beams.

63 The LHC Success of Stored Energy factor ~50 no quench with stored beam at LHC Courtesy Ralph Assmann

64 Beam from injectors This year we ve mostly been taking the 50 ns beam. Excellent performance better than nominal bunch intensity and less than nominal beam size Years in the preparation

65 Beam stability Even with well over nominal bunch intensity instabilities under control via Landau damping (octupoles) and transverse feedback TSBI of HT mode m = -1 from machine impedance predicted without octupoles and intrinsic nonlinearities (Elias Metral) Lots of care during design to minimize the machine impedance. Lot of effort to study and simulate potential limitations. Francesco Ruggiero (impedance police) and Fritz Caspers (RF contact specifications)

66 COLLISIONS Beam-beam Can collide well over nominal bunch intensity with smaller that nominal emittances Head-on: no problem up to ~0.0075, ~0.02 total tune shift with offset collisions in LHCb and Alice Put this down to excellent field quality and sufficient long range separation 25 hours

67 Squeezing further Aperture compatible with a well-aligned machine, a well centred orbit and close to design mechanical aperture Together with collimation, this opened the way to a squeeze from 1.5 to 1.0 m. (50% increase in luminosity.) Stefano Redaelli, Massimo Giovannozzi, Jorg Wenninger et al

68 Operational robustness Injecting dangerous beams routinely vigilance always required Ramp & squeeze & collide essentially without loss Excellent reproducibility and stability Feedbacks (tune, orbit, transverse) indispensable Almost exclusive coverage by the sequencer for nominal operation Software, controls, databases, measurement and analysis tools provide rich functionality

69 Efficiency/Availability 30% efficiency for stable beams during 180 days for physics (54 days in stable beams) Other scheduled periods: 18 days technical stops 10 days scrubbing run ~17 days of MD Pretty good!

70 Availability LHC Cryo global availability Major stops: PLC-SEU: 5 Cryo: 5 EL: 4 24-Jan 21-Feb 21-Mar 18-Apr 16-May 13-Jun 11-Jul 8-Aug 5-Sep 3-Oct 31-Oct 28-Nov 2010: Nice learning curve 2011: Direct effect of high luminosity since spring, partially treated now and to be continued at Xmas break Between TS 2010 Scheduled Stops Weekly 2011 Between TS 2011 Courtesy: Serge Claudet

71 PERSONAL COMPETANCIES Leadership Teamwork Ability to relax

72 Maslow s Hierarchy of Needs Tee Shirts Experience Expertise Resources

73 We delivered 5.6 fb -1 to Atlas in 2011 and all we got was a blooming tee shirt

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