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Introduction, requirements of the LHC and LHC injectors’ challenges

OPERATION OF THE LHC BEAMS IN THE SPS. E. Métral. Introduction, requirements of the LHC and LHC injectors’ challenges The LHC zoo  Many (proton) beams required & LHC commissioning Main SPS supercycle foreseen in 2008 & user names Some procedures & references for the nominal beam

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Introduction, requirements of the LHC and LHC injectors’ challenges

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  1. OPERATION OF THE LHC BEAMS IN THE SPS E. Métral • Introduction, requirements of the LHC and LHC injectors’ challenges • The LHC zoo  Many (proton) beams required & LHC commissioning • Main SPS supercycle foreseen in 2008 & user names • Some procedures & references for the nominal beam • Some words about the ion beams (~ early ion beam produced in the SPS in 2007)

  2. Many thanks to many colleagues from OP, ABP, RF, BI … for their explanations & help during the 2007 run & preparation of this course! • See also procedures & references (from 2007) done by Magali: http://sps-documentation.web.cern.ch/SPS-documentation/ • Please do not hesitate for any comment!

  3. INTRODUCTION (1/13) • 2 main challenges involved in the design of the LHC • Very high magnetic field to reach the collision energies in the TeV range • Very high luminosity necessary to provide significant event rates at this energy Beam current Brightness = transverse bunch density It is limited by : - Space-charge effects in the injectors... - Head-on beam-beam interaction at collision It is limited by : - Collective instabilities - Cryogenic load (synchrotron radiation and wall current) - S.C. magnet quench

  4. INTRODUCTION (2/13)  LHC injectors’ challenges • “Preservation” of the transverse emittance (brightness) • Generation of the longitudinal structure (25 ns bunch spacing)

  5. INTRODUCTION (3/13) SPS operates above transition (~ 21 GeV) for LHC-type beams Duoplasmatron = Source  90 keV (kinetic energy) LINAC2 = Linear accelerator  50 MeV PSBooster = Proton Synchrotron Booster  1.4 GeV PS = Proton Synchrotron  25 GeV SPS = Super Proton Synchrotron  450 GeV LHC = Large Hadron Collider  7 TeV LHC (proton) beam in the injector chain

  6. INTRODUCTION (4/13)  TRANSVERSE EMITTANCE PRESERVATION • The initial transverse emittance is given by the duoplasmatron source • The beam is then adiabatically bunched and accelerated in a Radio Frequency Quadrupole (RFQ2) under high space charge conditions • Fine-tuning of the 50 MeV Drift Tube Linac (DTL) and of the transfer line to the PSB Normalised, at 1 Depends on extraction aperture, electrode shape and space charge   

  7. INTRODUCTION (5/13)  TRANSVERSE EMITTANCE PRESERVATION • The beams in the Linac2 are quasi square pulses with a length which varies depending on the user (the beam length varies between 25 μs and 120 μs and it is limited at the source) • The nominal LHC requirement is a beam of 180 mA in 30 s at the entrance of the PSBooster • The transverse normalised rms beam emittance is 1.2 m  Challenge of transverse emittance preservation in the injectors - PSBooster ejection  2.5 m - PS ejection  3 m - SPS ejection  3.5 m - LHC top energy  3.75 m

  8. INTRODUCTION (6/13)  LONGITUDINAL BEAM STRUCTURE • The generation of the nominal bunch train for LHC (25 ns bunch spacing) is done in the PS • Double-batch injection from PSBooster due to space charge in the PSBooster  Rings 3-4-2-1-3-4 • Bunch splittings used instead of debunching / rebunching due to longitudinal microwave instability Must be the 1st! LHC Design Report, Ch. 7, p. 45

  9. + MKE kickers issues INTRODUCTION (7/13) SPS CHALLENGES • Impedance reduction programme in the SPS has made a major contribution to the ability of the SPS to produce the LHC beam • Shielding of specific equipment, such as the magnetic septa, identified as an impedance source • Shielding of some 900 intermagnet pumping ports has reduced significantly the resonant impedance in the machine and increased the stability of the LHC beam • The nominal beam has successfully been accelerated to 450 GeV/c, despite the discovery that the electron cloud effect is a major issue for the SPS Continued machine development to understand and cure the phenomena in the SPS has been accompanied by additional studies using the SPS as a test-bed for the LHC. Periods of beam conditioning are now routinely used to “scrub” the surface of the vacuum chambers, reduce the secondary electron yield and minimise the vacuum pressure rise

  10. INTRODUCTION (8/13)  SPS BEAM PARAMETERS Tolerance in bunch intensity: 10% Tolerance in trans. emittance: 20% Tolerance in long. emittance: 20%

  11. INTRODUCTION (9/13)  NOMINAL LHC FILLING SCHEME • PS cycle length = 3.6 s • SPS cycle length = 21.6 s • LHC filling time (for the 2 rings) = 8 min 38 s (= 12 SPS cycles of 21.6 s per beam  24 in total, i.e. a filling time of 24  21.6 s = 518.4 s)

  12. INTRODUCTION (10/13)  ~ NOMINAL LHC BEAM IN THE SPS IN 2004 ~ 3.3 1013 p at 450 GeV/c (i.e. 4  72 = 288 bunches with ~ 1.151011 p/b)

  13. INTRODUCTION (11/13)  ~ NOMINAL LHC BEAM IN THE SPS IN 2006 ~ 3.6 1013 p at 450 GeV/c (i.e. 4  72 = 288 bunches with ~ 1.241011 p/b)

  14. INTRODUCTION (12/13)  NOMINAL (LOW INTENSITY) BEAM EXTRACTED FROM THE SPS IN 2007 Shown by S. Myers on 26/02/08 (AB meeting)

  15. INTRODUCTION (13/13)  NOMINAL (LOW INTENSITY) BEAM EXTRACTED FROM THE SPS IN 2007 Shown by S. Myers on 26/02/08 (AB meeting)

  16. M. Benedikt, LHC-OP-ES-0002 rev 1.0 (2004) THE LHC BEAM ZOO (1/4) Pilot =“safety beam” • Interest in the 50 ns variant has been resuscitated (since few months) to try and satisfy the need for low luminosity in IP2!

  17. Needed before each physics coast THE LHC BEAM ZOO (2/4)

  18. THE LHC BEAM ZOO (3/4)

  19. THE LHC BEAM ZOO (4/4)

  20. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (1/6) 26 GeV/c or acceleration up to 37 GeV/c • SFTLONG1 (13 BP) + CNGS1 (5) + CNGS2(5) + CNGS3 (5) + LHCFAST1 (7) + MD1/2 (5) = 40 BP = 48 s • Later, when LHC is filling properly we will have to switch to an LHC filling supercycle

  21. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (2/6) • In 2007 • SPS timing user names changed to beam-type names • At the same time we got the possibility via LTIMs to activate a given RF MMI stack for a given timing user  Tended to 'decouple' the RF MMI stack name from the timing user name • The BI settings are organized by beam type and can be loaded to any timing user  This also decouples the BI settings from the timing user names • In 2008  The idea is to go back to a given timing user associated to a certain SPS magnetic cycle more than to a certain beam type • LHC1 & LHC2 for nominal MAGNETIC LHC cycles • LHCFAST1 & LHCFAST2 for the short LHC MAGNETIC cycles • LHCION1 & LHCION2 for ion MAGNETIC cycles • …

  22. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (3/6) For the short magnetic cycles 24 in 2007 32 in 2008

  23. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (4/6)  Example of a Long MD cycle in 2008 • Timing user LHC1. LSA settings mapped to that user • If we take a nominal beam on the cycle, RF MMI stack for LHC1 mapped to stack LHC25NS. BI settings for LHC-NOMINAL mapped to LHC1 • If we take a pilot beam on the cycle, RF MMI stack for LHC1 mapped to stack LHCPILOT. BI settings for LHC-PILOT mapped to LHC1 • 'Early' LHC filling SC with two fast LHC cycles. Cycles are mapped to timing users LHCFAST1 & LHCFAST2. LSA settings mapped to those users • If we take a pilot beam on the 2 cycles, RF MMI stack for LHCFAST1 & LHCFAST2 mapped to stack LHCPILOT. BI settings for LHC-PILOT mapped to LHCFAST1 & LHCFAST2 • If we take an individual bunch on the 2 cycles, RF MMI stack for LHCFAST1 & LHCFAST2 mapped to stack LHCINDIV. BI settings for LHC-INDIV mapped to LHCFAST1 & LHCFAST2 • If we take 12 bunches (1 PSB ring) on the 2 cycles, RF MMI stack for LHCFAST1 & LHCFAST2 mapped to stack LHC25NS. BI settings for LHC-NOMINAL mapped to LHCFAST1 & LHCFAST2

  24. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (5/6) Different acceleration between NOMINAL and FAST cycles 4320 (or 15120) 7590 (or 18390) 60 (or 10860)

  25. MAIN SPS SUPERCYLE FORESEEN IN 2008 & USER NAMES (6/6) The (proton) LHC user names in the PS & PSB

  26. SOME PROCEDURES & REFERENCES FOR THE NOMINAL (4  72 BUNCHES) BEAM ALTERNATIVE FILLING SCHEME! To see how things vary in this case FILLING PATTERN (1/3) NOMINAL FILLING SCHEME!

  27. FILLING PATTERN (2/3) 4  72 bunches

  28. FILLING PATTERN (3/3) 5  48 bunches 58 115 172 229 9 9 9 9 Batch 5 48 48 48 48 48 ~ 1.2 s ~ 1.2 s ~ 1.2 s ~ 1.2 s ~ 1.2 s 570 285 855 1140

  29. PROCEDURE TO SET UP THE INJECTION (1/4) • Check that the PS is not in simulated frequency 6 BPM of TT2 + 4 BPM in TT10 • TT10 BP settings Last 10 BPM of TT10 Couplers with logarithmic amplifiers in TT10  No gain

  30. PROCEDURE TO SET UP THE INJECTION (2/4) • Injection kickers settings The first 3 kickers can give until 11 s, whereras the 4th one gives 2.5 s

  31. PROCEDURE TO SET UP THE INJECTION (3/4)

  32. PROCEDURE TO SET UP THE INJECTION (4/4)

  33. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (1/13) ENERGY MATCHING PROCEDURE - Inject the beam. Adjust BSPS till the first turn is centered - Switch on RF (if not already done) - Measure the orbit (about 100 ms after injection) - Check the position at which the beam is captured If the beam is not centered, (that means the energy in the PS is such that the revolution period in the SPS does not correspond to the RF frequency in the SPS), adjust BSPS till the beam is centered after capture - The first turn is then no longer centered - BPS should be adjusted (so as to adjust the beam energy). - An excel spreadsheet can be used to determine by which amount BPS should be changed

  34. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (2/13) • Tunes (measured)  To avoid slow beam losses from resonances (ecloud, space charge… tune spreads) • SPS Control  → SPS Beam Control → New Trim editor • Qx  26.13 • Qy  26.185 • When there are more than 1 injection, Qx increases with the intensity and Qy decreases with the intensity (Laslett tune shift)  One has to compensate for this effect • In order to keep the coherent tune constant the Qx settings need to be decreased by 0.008 in correspondence of every injection and Qy must be increased by 0.005 •  Jorg added in 2007 a menu in the MultiQ to correct the tune shift for each injection: GO in the 'Tools' menu (main program toolbar) and check the box 'Show LHC beam "Injection Q"....'. This will make the appropriate menu/DV plot appear/disappear

  35. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (3/13) • Chromaticities (measured)  To stabilize the beam with respect to the instabilities due to single bunch (effects from electron cloud) • SPS Control  → SPS Beam Control → New Trim editor • x  + 0.2 • y  + 0.4 • BEWARE: DO NOT TRIM THE RADIAL STEERING BEFORE THE LAST INJECTION (even for chromaticity measurements). This would change the RF frequency we are sending to the PS - and the 40 and 80 MHz cavities will not like it!!! The radial position can be trimmed after the last injection • Octupoles settings  To achieve a machine as linear as possible • SPS Control  → SPS Beam Control → New Trim editor • H: ~ - 1 m-4(Settings are not critical, but they shouldn't be too high  Not larger than about 1 m-4) • V: ~ 0

  36. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (4/13) • Transverse dampers  The transverse dampers are essential in the horizontal direction in order to damp the instabilities due to coupled bunches (effects from electron clouds and resistive wall). In the vertical plane they are mainly used to damp resistive wall instability • Gain (for the nominal beam): • Horizontal: 23 dB • Vertical: 15 dB • For 1 bunch or 12 bunches: OFF • For 72 bunches  There are 2 pairs of transverse dampers per plane. They should be ON during the whole cycle

  37. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (5/13) • Timings  SPSOP CCM → Working Set → RF-SPEC → SPS:RF7 • Switching on timings: • "tdamper h1 on opera" • "tdamper h2 on opera" • “tdamper v1 on opera” • “tdamper v2 on opera" • Settings: • Timings defined with respect to event SIX.F1KFO-CT • Coarse delay: 995 ms ( i.e. 5 ms before 1st injection) • Switching off timings: • "tdamper h1 off opera" • "tdamper h2 off opera" • “tdamper v1 off opera” • “tdamper v2 off opera" • These should always be ENABLED • Settings: • Timings defined with respect to event SIX.F1KFO-CT • Coarse delay: 20000 ms Forewarning 1000 ms before first occurence of injection OFF timing should be a few ms after the timing of the standard dump

  38. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (6/13) • MOPOS settings

  39. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (7/13)

  40. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (8/13) Averaging over 5 orbits

  41. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (9/13) BEAM DUMP SETTINGS

  42. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (10/13) TT2 / TT10 LINE May be not the latest optics!

  43. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (11/13) Max [x] = QF = EVEN number Max [y] = QD = ODD number SPS RING   90º SPS transverse tune  6  (18 / 4) = 27!  Qx  26.13 and Qy  26.18

  44. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (12/13) TI2

  45. PROCEDURE TO SET UP THE MACHINE TRANSVERSALLY (13/13) TI8

  46. PROCEDURE TO SET UP THE MACHINE LONGITUDINALLY (1/13) • RF loops • PHASE LOOP (measures the difference between the phase of the RF and the phase from the beam and tries to minimize it) • SYNCHRO LOOP  We stay always on the synchro loop instead of going at some point on the radial loop for acceleration (we cannot do this with the FT beams because transition is crossed) • BTRAIN is enabled at the beginning the ramp and switch off at the end of the ramp (Bup and Bdown are 0.1 Gauss)

  47. PROCEDURE TO SET UP THE MACHINE LONGITUDINALLY (2/13) • 200 MHz TWC • Feedforward (not used on FT beam) + 1-turn delay feedback together (send correction to the cavity through a transmitter)  To combat the beam loading • Long. feedback (called also damper)  Used since the injection, and then the gain is adjusted (high gain around the injections for injection damping), to combat coupled-bunch instabilities • Injection into 2 MV bucket (mismatched) • 800 MHz TWC • Bunch shortening mode Matched voltage is < 1 MV

  48. PROCEDURE TO SET UP THE MACHINE LONGITUDINALLY (3/13) • Timings • At - 425 ms RF ON (TWC200) • Phase loop ON (fprog) synchro loop ON • 4 injections • Before TWC 800 ON in bunch shortening mode after the 4th inj. Now it is ON already from the beginning due to the MKE kickers • Max Bdot = 0.35 T/s • At 270 GeV/c, longitudinal blow-up done with phase modulation on 200 MHz (to have the shortest bunch length on the flat-top, otherwise one has coupled-bunch instabilities). It is active for ~ 100-200 ms, with an efficient time of ~ 10-20 ms • L ~ 0.45 eVs at the end of the flat-bottom and it is ~ 0.6-0.7 eVs on the flat-top • Synchro with LHC • Adiabatic voltage to send the shortest bunch lengths

  49. PROCEDURE TO SET UP THE MACHINE LONGITUDINALLY (4/13)  Example of bunch length with nominal (472 bunches) beam but low intensity (~ 2.5E13 p) V200MHz [104 V] Full (4) bunch length [ns/100] V800MHz [103 V] Beam momentum [GeV/c] Must enter in the LHC 2.5 ns bucket

  50. PROCEDURE TO SET UP THE MACHINE LONGITUDINALLY (5/13) • Injection frequency • - Value = 200.264550 MHz injection B field : 1170.3 Gauss) • - Setting: SPS Control → SPS Equipment Control → SPS RF • → SPS RF Control → RF Synchro → Injection B field • → select appropriate MMI target (MD1, or LHC25ns, ...) • → Write:1170.3 Gauss (corresponds to 200.264550 MHz) • Injection pulses  Sets the delay on top of the prepulse sent by • the PS machine, in bucket number • - Value = 5500 • - Setting:SPS Control → SPS Equipment Control → SPS RF → SPS RF Control → RF Synchro → Injection pulses • → select appropriate MMI target  (MD1, or LHC25ns, ...) • → Write: 5500

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