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Machine-Detector Interface

Machine-Detector Interface. W. Kozanecki, CEA-Saclay. Issues Machine Backgrounds, Present & Future BaBar involvement in Accelerator Performance Improvements Summary. The Issues Backgrounds  operational efficiency (this coming run) long-term projections (2005 & beyond) New IR design

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Machine-Detector Interface

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  1. Machine-Detector Interface W. Kozanecki, CEA-Saclay • Issues • Machine Backgrounds, Present & Future • BaBar involvement in Accelerator Performance Improvements • Summary

  2. The Issues • Backgrounds •  operational efficiency (this coming run) • long-term projections (2005 & beyond) • New IR design • background simulations: can BaBar live with predicted levels? • make it all fit (unavoidable hardware changes!)[this topic likely togrowin importance] • Accelerator Performance Improvements • background remediation • beam dynamics • instrumentation • IR geometry, orbits & optics • BaBar-based accelerator diagnostics

  3. Backgrounds: what has happened so far • Try & revive the ‘Background Group’ • Strong (and largely successful) effort at • awareness-raising in BaBar (“work on backgrounds? why?”) • recruiting help • Identified subdetector background contact persons (SBC) • Regular MDI meetings (~ every other week) • Background Workshop: 22-24 Sep 03 http://www.slac.stanford.edu/BFROOT/www/Public/Physics/bgd2003_workshop/agenda_items/agenda.html • In-depth review of radiation-abort policies: “make BaBar & PEP-II transparent to each other” • Run-4 backgrounds: operational issues, vulnerabilities, long-term projections • Launch the background-simulation effort

  4. Background Sources I () • Synchrotron-radiation X-rays • Power: mostly separation dipoles • Background: mostly HER IP quadrupoles • Duck it if you can! else mask it, but watch out for multiple bounces • Masking very effective: SR backgrounds not a problem in BaBar so far • Cool it well - or else! • Lost-particle backgrounds • Bremsstrahlung: e + gas -> e’ +  (E’ < E) By now, almost exclusively from the last few (tens of) m ==> vacuum! • Coulomb scattering: e + gas -> e’ (E’ = E, but ) Potentially from the whole ring, depending on limiting apertures and on pressure profile. In practice no longer an issue • Touschek :similar to bremsstrahlung BaBar: neglected so far. Should be checked for very-high current operation. • Luminosity (e+ e- => e+’ e-’) • Elm shower debris (radiation + occupancy) + beam-wall p’s (trigger)

  5. # Xtls > 10 MeV % occpcy (> 1 MeV) Two-beam backgrounds Single-beam backgrounds IDCH vs.I+ L1 trigger rate vs. I- (I+ = 1100) EMC vs. I+,I- EMCvs. I (I+ = 1100)-

  6. Background Projections(based on bgds measured in 2000, then 2002) High-Luminosity Model(JS, PEP-II AP Note 130) combined with ( - I- + - I-2 ) +(+ I+ + + I+2 ) + L Drift Chamber Bakground Projection (July 2000 characterization)

  7. SVT Bakground Projection DIRC Bakground Projection Pain threshold: ∫dose ~ 2 MRad Pain threshold: PM rate ~ 200 kHz (dead time ~ % @ 300 kHz, 20% @ 500 kHz) • Horiz. plane: ~ 2 MRad by 2003-4, then 0.5 - 1 MRd/y • Other : ~ 0.25 MRad by 2004, then ~ 0.1 MRad/y July 2000 characterization Note how different the relative contributions are between subdetectors

  8. Recent background history: DCH Compare measured DCH background to that expected at the same LER current, HER current & Luminosity, based on the Feb. 2002 characterization

  9. Background Sources II() • Lost-particle backgrounds (continued) • Beam-beam (?) tails ~ Coulomb-like signature==> collimation ? ( LER !) • elm shower debris in incoming detector straight (esp. LER?) • ‘steady state’ : DCH, IFR – but also SVT (dose + occupancy) • Spikes & fluctuations  DCH, TRG • Radiation bursts • spikes (“fast aborts”) • trapped events • Injection backgrounds • 30-90% of SVT dose • 45% of EMC dose (CsI calorimeter) • ~ 50% radiation aborts

  10. measured predicted (2002) Recent background history: SVT, IFR SVT IFR endcap

  11. HER lifetime DCH current steady-state level 400 sec Radiation bursts Fast (auto) abort Manual abort

  12. SVT Radiation dose from January to June 2003 (Numbers are in krad, (%) is of dose in stable beams) Injection Backgrounds

  13. Backgrounds  operational efficiency (’03-’04) Beam-beam tails Radiation bursts Radiation-abort strategy • SR + beam gas + “Lumi” (e+e- e+ e-g) (“traditional”) • not an issue  ’05 w/ present IR geometry (& b* !) • however beam-gas in the LER may become a major contributor to the SVT • integrated dose • occupancy once the LER current is raised significantly • Beam-beam tails (SVT occupancy, DCH spikes, dead-time bursts, IFR currents) a growing limitation (including for BaBar data quality) • Interplay between BaBar radiation-abort strategy, and (primarily) • radiation bursts (spikes/trapped evts) ==> significant source of beam aborts • difficult injection (poor injection efficiency, high backgrounds, repeated aborts) ==> major inefficiencies Injection backgrounds

  14. Backgrounds: long-term projections I • Experimental background extrapolations • 2005 (2009) Currently based on 2002 bkgd data. An updated characterization will be carried out once PEP-II stabilizes. • BaBar hardware/performance limitations? • 2005 (2009) (see W. Wisniewski’s talk) • extrapolation of ‘traditional’ backgrounds(in present geometry)valid 200x ? • b* ==> Coulomb still OK? • can one extrapolate beam-beam backgrounds – at all? • how to take into account evolution of injection losses • any limitations/vulnerabilities in Babar hardware or physics performance? • radiation damage? • operational limitations (power supplies, trigger/dataflow bandwidth,...) • physics performance (tracker occupancy/efficiency/resolution, calorimeter resolution)

  15. SVT elx threshold problem ? Projected integrated dose in SVT midplane (Basis: 2002 characterization, no beam-beam tails, no injection improvements)

  16. 50 mR/s ~ 10% chip occupancy Projected SVT data quality (Basis: 2002 characterization, no beam-beam tails) Extrapolated dose rates in the SVT mid-plane (stable beams) “BaBar needs to better understand the implications of high beam occupancies”

  17. Projected DCH currents & data-flow dead time (Basis: 2002 characterization, no beam-beam tails) remedy under active study

  18. Backgrounds: long-term projections II SR simulations (an intrinsic part of the new-IR design) • Beam-gas simulations • ring: Turtle • IR  Geant4 Beam-beam? Lattice mods? (dynamic aperture) • 2 themes... • validate IR upgrade design • make sure that what we install in ’05 does not suffer from built-in flaws... • ...at least for those processes we can calculate (SR, beam-gas) • understand / improve backgrounds in present machine • ...that are intimately intertwined • validation requires credibility • update “old” simulations to incorporate what we learnt • simulations of present machine/detector configuration better get the ‘right’ answer (when confronted with measurements)... • ...if we want to believe predictions for the upgraded IR • improve those backgrounds we canNOT calculate • both for today’s and for tomorrow’s sake!

  19. EMC L1 trigger rate BaBar involvement in Accelerator Performance Improvements (I) • Background analysis & mitigation [BP, LP, TG: some just starting, but too few...] • Background simulations [RB, MB, GC, SM + SLAC (TF/GB)] • Fast monitoring of machine backgrounds  PEP-II [MW, C’OG, AP, GDF,...] • injection quality (SVT, EMC: dDose /dIb ) • time distribution of injection triggers • data quality: occupancies, dead time,... • for the stored beams • in the ‘trickle’ window • more operator-friendly displays (& controls) of radiation inhibits/aborts

  20. BaBar involvement in Accelerator Performance Improvements (II) • Beam dynamics • beam-beam simulations [IN (Caltech), YC (Slac ARD)] • beam-beam experiments, monitoring of beam-beam performance • Instrumentation • gated camera in LER & HER [D. D., Slac Exptl Grp C + A. Fisher +...] • beam-beam effects (flip-flop, ‘raining buckets’, parasitic crossings) • electron-cloud effects • development of an X-ray beam-size monitor for the LER: SLAC + • zone-plate approach: J A (Caltech) • pin hole approach: JK (LBL), HDS • SVTRAD sensor & electronics upgrade [B P et. al. (Stanford); MB/DK et. al. (Irvine) (initiated & funded by BaBar)] • CsI background sensors [JV, Slac Exptl Grp B] • IR geometry, orbit & optics • IR orbit monitoring & stability, IP & ring orbit feedbacks • on-line monitoring of IP position  PEP-II control system [RB, Slac; GDF, Caltech; ..] • on-line monitoring of luminous spot sizes  PEP-II control system [MW (Slac); GDF (Caltech); MB/GR (Nikhef);...]

  21. Summary • BaBarians... • ...have (re-started) contributing significantly to the machine • “BaBar-based machine diagnostics “ a growing & important effort • But more help is needed, esp. on medium- & long-term issues • BaBar vulnerabilities better understood • short term: SVT elx chip, DCH data flow, IFR aging • medium term: SVT (& EMC ?) integrated dose, tracker occupancies, physics systematics • ?? implications of lattice mods (a dyn. aperture) for backgrounds? • Most urgent short-term gains • injection (lack of reproducibility, abort cascades, ++dose, fatigue) • beam-beam tails (more agressive and/or upgraded collimation) • radiation bursts (“dust events”) • Most significant long-term gain potential • LER vacuum in last 20 m (?) [tbc by updated bgd characterization] • injection (30-90% of integrated dose in SVT & EMC)

  22. Appendix: radiation bursts (aka ‘dust’ events)

  23. Statistical study of trapped event properties (T. Schietinger, 1999)

  24. SVT diode pattern during trapped events • typical, but not universal

  25. An odd sequence of slow radiation bursts (2003) ? ?

  26. An odd sequence of slow radiation bursts (c’td) ?

  27. A collection of fast radiation spikes (stored beams)

  28. Geometry of some detectors useful for such studies (East)

  29. Radiation bursts: “summary” • Statistical study of trapped event properties (T. Schietinger, 1999) http://www.slac.stanford.edu/~schieti/background/trapped • SVT diode pattern during trapped events http://www.slac.stanford.edu/~schieti/background/trapped/svt_response.html • A collection of recent slow & fast radiation bursts • Some guesses... • NEG dust from near IR pumps? • gas ‘bubbles’? (would explain correlation with current increases) • possibly some incorrectly latched fast beam instabilities (RF, TFB ?) • ...but certainly no coherent picture nor robust interpretation

  30. Spare slides

  31. RF System Ron Akre Ray Larsen Lattice/Model Tor Raubenheimer Uli Wienands Feedback Systems Eric Colby Dmitry Teytelman Reliability/Uptime Roger Erickson Name #2 Diagnostics Mark Ross Steve Smith Vacuum Systems Nadine Kurita Scott DeBarger Injection Franz-Josef Decker Name #2 Controls Tom Himel Rusty Humphrey Machine/Detector Interface Witold Kozanecki Guy Wormser New IR Design Mike Sullivan Name #2 stricly speaking PEP-II Mid-Project Evaluation Resources Ewan Paterson, TD Persis Drell, RD Bill Wisniewski, Babar Jonathan Dorfan, Co-ordinator Parameters, LdtJohn Seeman, Stan Ecklund

  32. Brian Petersen, 3 Oct 03 Fast Abort Changes • Will leave abort settings during stable beams unchanged • Forgiveness (2 Rad) cannot be increased as that endangers the SVT • Increasing threshold (~1 R/s) could result in running at >1R/s for 10 minutes, which we do not want to try • We can try to change settings during injection • There is no immediate danger to the SVT as it is not biased • The increase in dose (a few krad/year) would be regained if we can get rid of 10-20% of the aborts • Suggested change: • Increase forgiveness by factor 3 over stable beams (e.g. 6-8 rads) • Set threshold at 2 times stable beams (~2rad/s) instead of 5 times • Would like to have causes of aborts, which still occur be identified and logged by operators

  33. Brian Petersen, 3 Oct 03 Slow Abort Changes • We will enable “extend” button for 10-minute timer, but restrict it to 10 additional minutes • We will monitor it for abuse (of course) • Activate 10 minute timer for the diamonds • Suggest to replace BW:MID diode with BW diamond • Use threshold of 75 mrad/s? Changes can be implemented by next week

  34. Brian Petersen, 3 Oct 03 Possible Longer Term Changes • Should separate “forgiveness” from protection against very fast spikes • Very quickly abort beams on dose rates of 0.1 to 1krad/s • Allow rates of 1-100 Rad/s for a little longer (x2-4?) than today • Requires the SVTRAD1.5 • Abort only one beam? • Not clear that HER and LER always clearly separated during aborts • Gain in integrated dose will be minimal as most aborts would be of the HER • Would require new electronics in IR-2 alcove (previous electronics were done by Mark Petree)

  35. MID Radiation Doses Until Now Budget is set to reach 4 Mrad by 7/1-2005 (to be lowered?) FW:MID is consistently overestimated in Run 3

  36. TOP Module Doses until 2009 TOP modules look OK, except if FE:TOP becomes MID module BW:TOP and FW:TOP doses are probably overestimated 85-90% of the dose is supposed to come from injection

  37. G. Wormser, Bgd Workshop summary, 24 Sep 03 BABAR scorecard today X: visible effect with non-zero impact - : visible effect with no impact ? : yet unknown fixed: det upgrade to fix a significant issue

  38. G. Wormser, Bgd Workshop summary, 24 Sep 03 BABAR scorecard July 2004

  39. G. Wormser, Bgd Workshop summary, 24 Sep 03 BABAR scorecard July 2006

  40. G. Wormser, Bgd Workshop summary, 24 Sep 03 BABAR scorecard 2009

  41. Architecture of background simulations (1) • Synchrotron Radiation • MAGBENDS / QSRAD: stand-alone programs • SR background calculations: an intrinsic component of IR re-design • shouldn’t these be interfaced to GEANT? • Beam-gas • step 1: LP-TURTLE transports particles around 1 ring turn • full model of ring optics (treated as transport line) • start with ‘nominal’ beam at IP • beam-gas scattering randomly around ring (bremsstrahlung or Coulomb scattering)  transport ‘secondaries’ (e’, g) • simplified model of IR apertures (simple geometry, no showering!) • those particles lost ‘near’ the IP are • saved @ scoring plane • input to step 2 • step 2: full GEANT simulation of detector + near-IR (+- 8.5 m) • see Mario Bondioli’s talk

  42. Architecture of background simulations (2) • Beam-beam • full simulation of beam-beam tails impractical • focus on collimation studies • optimize collimator placement/relocation (SM) • understand main characteristics of collimator secondaries (HB) • provide guidance for machine experiments • use Turtle machinery • Strategy considerations • improve/update description of magnetic fields & apertures (TF, GC) • many fundamental features easier to understand at Turtle level •  first round of IR-upgrade design validation will be done this way (RB) • GEANT-level simulation essential (MB, GB, GC) • to benchmark computations against data • to make sure there are no “alligators” hiding in new design • absolute background predictions always suspect • even when benchmarked against experiments. However... • ...ratios (new design /present machine) much more reliable.

  43. Coulomb scattering in Arcs (y-plane) IP e-Brems-strahlung in last 26 m (x-plane) Vacuum pipe / mask apertures Lost-particle backgrounds Normalized to: - uniform pressure profile of 1 nT - 1 A beam current IP

  44. Zone 3 X (mm) Zone 2 X (mm) Zone 1 X (mm) Zone 4 IP The “Background Zones” reflect the combined effect of.... • beam-line geometry (e.g. bends) • optics at the source and at the detector • aperture restrictions, both distant(good!) & close-by (bad!) Bremmsstrahlung Bremmsstrahlung in field-free region Coulomb scattering in Arcs Bremmsstrahlung

  45. Benchmarking of simulations: comparing “predicted” and measured background levels • Radiation patterns • for a given sensor type: independent of absolute calibration • among different sensors: compare fractional derivatives • Absolute background levels • sensor calibration! • absolute pressure profile ! • Global consistency/sanity checks • operational experience in MCC

  46. Vacuum gauge reading (nT) Abort diode signal (mR/s) Pressure-bump experiment: NEG heating in BaBar straight • Create localized P-bumps • NEG heating • DIPS on/off • Measure response of  background monitors • Compare relative measured & simulated monitor response to validate Monte Carlo • Different • regions • ==> • diff. patterns • diff. abs. levels

  47. Understandingthe absolute level of HER backgrounds (Sep 99) • Compare measured & predicted dose rates in HER: • Monte Carlo lost-particle simulation (Turtle + BBSIM) validated by p-bump experiments • Computed pressure profile in detector straight section (N2-equivalent, not vac.-gauge units!) • Average ring pressure (from lifetime) for arcs & distant straights

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