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Machine-Detector Interface (MDI) report

Machine-Detector Interface (MDI) report W. Kozanecki, CEA-Saclay Operational issues radiation aborts radiation-dose history injection & stored-beam background history Background characterization characterization experiments long-term projections & vulnerabilities outgassing storms

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Machine-Detector Interface (MDI) report

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  1. Machine-Detector Interface (MDI) report W. Kozanecki, CEA-Saclay • Operational issues • radiation aborts • radiation-dose history • injection & stored-beam background history • Background characterization • characterization experiments • long-term projections & vulnerabilities • outgassing storms • Simulations • Accelerator performance enhancements

  2. Stable-beam “genuine” radiation aborts: • 0.9 / day • ~ 60% of these may actually be sympathetic • “Genuine” injection aborts: 0.4 / day ...to be compared to an average of 7 aborts/day from all sources

  3. HER trickle starts Run-4 radiation-dose history HER trickle starts Outgassing storms

  4. Trickle-injection background Veto windows • The background generated by the trickle injection is concentrated in a narrow time window corresponding to revolutions of the injected bunch. • BABAR vetoes this window during data taking to avoid high dead time • BABAR rejects a larger region at the analysis phase to guarantee good data quality. • The total loss is around 1.5%

  5. Monitor using injection-gated triggers (1 ms x 20 ms) Injection- & trickle- background history DCH trigs LER trickle EMC trigs (always on) LER trickle EMC trigs (always on) HER trickle DCH trigs HER trickle

  6. IDCH, msrd/pred Normalized DCH current Stored-beam background history 20% 20% SVT ocp’cy @ f = p (HEB-sensitive) SVT ocp’cy @ f = 0 (LEB-sensitive) 10%

  7. Background sources in PEP-II • Synchrotron radiation (this bkg negligible in PEP-II, but not in KEKB) • Beam-gas (bremsstrahlung + Coulomb) • HEB only: BHbg ~ IH * (pH0 + PHDyn * IH) Note: p0 = f(T) ! • LEB only: BLbg ~ IL * (pL0 + PLDyn * IL) Note: p0 = f(T) ! • beam-gas x- term: BLHbg ~ cLH * IL * IH (LEB+HEB, out of collision) (?) • Luminosity (radiative-Bhabha debris) – major concern as L  • BP ~ dP * L (strictly linear with L) • Beam-beam tails • from LER tails: BL, bb ~ IL * fL(xL,H+/-) • from HER tails: BH, bb ~ IH * fH(xL,H+/-) • Trickle background: BLi ,BHi(injected-beam quality/orbit + beam-beam) • Touschek: BLT(signature somewhat similar to bremsstrahlung; so far small)

  8. Data: Jan 04 (bef. therrmal outgassing crisis) Background characterization measurements Step 1: Beam-current scans  single-beam terms

  9. Total occupancy • HER single beam • LER single beam • Beam-beam term • present in all subdetectors • fluctuations, short - & long-term •  parametrization optimistic ? Step 2: L & beam-beam terms EMC cluster multiplicity SVT occupancy (FL1 M01-f)

  10. IDCH = DCH Step 3: Background Parametrizations • DCH example: total current & occupancies Step 4: Background Extrapolations 60 L Tracking efficiency drops by roughly 1% per 3% occupancy PEP-II parameter projections LER contribution very small

  11. Luminosity background e+ e- e+e-g • elm shower debris • neutrons! • no contribution from coasting HEB or LEB • maydominate DCH, DIRC rate

  12. Neutron Background Effort underway to measure neutron background in BaBar BF3 counter installed on fwd Q4 Sees large rate (>10 kHz) during colliding beams, not single beam Rate only seen with polyethylene moderator~1MeV neutrons Neutrons thought to be from radiative Bhabhas hitting Q2 septum mask and inside support tube - Shielding of BaBar is being investigated

  13. DCH + TRG When combined with higher trigger rates, long read-out time leads to unacceptable deadtime. A major DCH elx upgrade is now in progress.

  14. Backward: East Top West Bottom Background strongly - dependent By 2007 predict 80% occupancy right in MID-plane In layer 1, 10% will be above 20% occupancy NOW 2004 2005 2006 2007 Forward: East Top West Bottom Integrated dose will be more than 1 Mrad/year by 2007 SVT Background now is ~75% HEB [LEB negligible (!)] In 2007, it will be 50% HER, 50% L • It has recently been realized that • in the SVT (but not in other subdetectors), a large fraction of the “Luminosity”background is most likely due to a HER-LER beam-gas X-term (but: similar extrap’ltn). • the HER single-beam background in run 4 is about 2x what it was in 2002  improve?

  15. Outgassing storms • New (?) major background source: thermally-enhanced beam-gas • in incoming LER straight (exacerbated by NEG activation; OK for now) • sensitive to LER current; several time constants in a time-dependent mix • suspect: NEGs (MS’s talk), ion pumps, collimator jaws, misc. vac. pipe secs •  SVT dose + occupancy (E-MID); minor impact on dead time • in incoming HER straight (triggered the NEG activation; OK for now) • sensitive to HER current, very long time constants •  BaBar dead time + SVT occupancy (W-MID) • in (or very close to) the shared IR vacuum system • sensitive to both beam currents; at least 2 time constants • suspect: NEG + complicated IR ‘cavity’ (Q2L  Q2R) + HOM interference •  BaBar dead time + SVT occupancy (W-MID + E-MID) • HOM dominant heating mechanism • mostly long to very long time constants (30’-3 h): suggests low power • sensitive to: bunch pattern, VRF, collimator settings, Z(IP), hidden var’s • Many “??”(minor, inocuous changes  large effects, good or bad)

  16. Fill: March 28, 12-3 pm mRad/s Data points End of injection Fit 200 VP3044 10 VGCC3027 VP3147 0 1 2 3 h Days in March (April 1=32) Time evolution of the thermal outgassing background • The different time dependences of the pressure readings allowed to fit the background sensor (Backward East diamond) as a linear combination of 4 LER gauges, on a fill by fill basis • The sensitivity coefficients for each gauge were then extracted. They represent the N2-equivalent pressure integral with the same time dependence as the gauge reading. The background problem was not related to a Pressure increase (as indicated by the gauge readings) but to a huge increase in background sensitivy

  17. HOM interference in IR Data: 12 Apr 04 VGCC2187 (HER sensitive) VGCC3027 (incoming LEB) BW diamond [+ dead time] (HEB sensitive) BE diamond (LEB sensitive)

  18. HOM interference in IR VGCC2187 (HER sensitive) VGCC3027 (incoming LEB) Collision phase <ZIP> (BaBar) BE diamond (LEB sensitive) BW diamond (HEB sensitive)

  19. Background simulations Background is coming from: HER & LER beam-gas, luminosity, and beam-beam tails Important to understand/quantify these backgrounds What will be the effect of the IR upgrade on beam-gas (& b-b) bgds? Can the luminosity background be explained by radiative Bhabhas ? Which way does it enter the detector ? What is the n spectrum? Can we shield or reduce this background source ? Can we mitigate beam-beam backgrounds with improved collimation ? Substantial effort in reviving/updating simulation infrastructure! Status: Turtle optics updated to 2003 HER beam line (LER in progress) Description of masks & apertures under detailed review (bugs found) Beam line up to Q5 (mostly) implemented in Geant4 simulation of BaBar detector –validation of geometry & magnetic tracking in progress post-2005 configuration is awaiting a finalized IRdesign Significantly more detailed simulation compared to the old Geant3 simulation used until 2000

  20. Example: Coulomb scattering background in the HER (Turtle level, ’04 config.) Where do scattered e-come from ? Where do scattered e-hit?

  21. G4 simulation: status • Simulation integrated inside the BaBar standard Geant-4 environment. • magnets added in the region from backward-Q5 to forward-Q5 • background sensors (PIN diodes, diamonds, quartz & CsI) added & validated • beamline elements from -Q5 to +Q5 included • validation of magnetic field description (incl. Q1-Q5) in progress Decision made to import beamline elements from CAD files  tools written to allow automatic translation from Solid Edge files to G4 C++ Correction of some G4 geometry ‘features’ (!) Main steps Retrieval of CAD files: HER OK, LER downstream Q4-Q5 not yet available Simplification & translation of CAD files to C++ source: done on all available parts Debugging of geometry problems : done up to Q2s

  22. Ongoing Background Simulation Studies Beam-gas • Single beam background comes from Coulomb scattering and bremsstrahlung • Study relative contributions at various locations at the IP and where in the ring the original scattering happens So far only studied at Turtle level: HER (2003), LER (1998) Radiative Bhabha background • Where does the electrons/positrons end up after scattering? • What kind of backgrounds are produced and can it be shielded? • How much neutron radiation is generated? What is the neutron spectrum? • Will the 2005 IR upgrade make it worse? This simulation effort is just starting up. Beam-beam collimation • Beam-beam background can be reduced with collimators • LER collimator usage limited by background in IFR end cap • Can the collimators be moved downstream of BaBar? First results look encouraging!

  23. BaBar involvement in Accelerator Performance Improvements (I) • Background analysis & mitigation [BP, MC/TG, NB, JM/JV, RM, LP, WK/GW] • Background simulations [RB, MB, GC, WL, SM, PR/AS, WK + SLAC (TF/GB)] • Fast monitoring of machine backgrounds  available online in PEP-II CS [MW, C’OG, AP, GDF,...] • injection & trickle quality variables: SVT, DCH, EMC • subdetector occupancies: SVT, DCH, EMC, DIRC • BaBar dead time • more operator-friendly displays (& controls) of radiation inhibits/aborts • BaBar-based machine diagnostics • time distribution of injection triggers [LP, BP, ...] • Online centroids & sizes of luminous region using Babar dimuons [C’OG, BV, AP, IN, MB,...]

  24. <xIP > Luminous-region history <yIP > <zIP > <sLx > <sLz >

  25. BaBar involvement in Accelerator Performance Improvements (II) • Beam dynamics • beam-beam simulations [IN (Caltech), YC (Slac ARD), WK] • beam-beam experiments, monitoring of beam-beam performance [WK] • e & b* measurements using dimuons [just starting] • Instrumentation • Gated camera: now operational in both in LER & HER [DD, Slac Exptl Grp C] • LER interferometer software [AO, Orsay] • Development of an X-ray beam-size monitor for the LER [Caltech + LBL + SLAC] • SVTRAD sensor & electronics upgrade [BP et. al. (Stanford); MB/DK et. al. (Irvine) (initiated & funded by BaBar)] • CsI background sensors , n detectors & shielding [JV, Slac Exptl Grp B]

  26. Summary (I) • Stable-beam (genuine) radiation aborts are down to < 1/day • Trickle injection • is a major success in terms of improving • machine stability + abort frequency  integrated L • overall injection quality • accumulated SVT dose • The associated detector backgrounds appear largely negligible (most – but not all – of the time) • Present stored-beam bgds (dose rate, data quality, dead time) • OK most of the time (& better w/ trickle)- for now (thermal outgassing!) • Background characterization experiments • were highly valuable in identifying the origin, magnitude & impact of single- & two-beam backgrounds. • On the long term, the dominant backgrounds are expected to be, in order of decreasing importance: • radiative-Bhabha debris (all subdetectors), incl. a significant neutron flux • HER beam-gas (SVT, TRG), especially if thermal outgassing resurfaces • beam-beam tails & their fluctuations (DCH, EMC, TRG, IFR  wall!)

  27. Summary (II) • In the medium term (2005-07), the main vulnerabilities are • beam-gas backgrounds from HOM-related thermal outgassing as I+,- • high dead time associated with DCH data volume & trigger rates (addressed by DCH elx upgrade) • high occupancy and radiation ageing in the mid-plane of the SVT, • possibly leading to a local loss of tracking coverage. •  reduce the HER single-beam background back to 2002 levels (/1.5-2) ? • a high flux of ~ 1 MeV neutrons in the DCH (wire aging from large pulses, possibly also contributions to occupancy) • Background simulations • large investment in reviving/updating tools + rebuilding the group • ‘almost’ ready to evaluate backgrounds in IR upgrade • manpower limited • BaBar-based accelerator performance enhancement • common BaBar-PEPII diagnostics greatly improved, starting to pay off • very significant involvement of BaBarians in beam instrumentation & simulation

  28. Spare slides

  29. Run-4 radiation-abort history (automated script) • Stable-beam aborts: 280 • stable beams: 56% of the time • includes trickle • radiation-driven manual aborts (trapped events) not included • Injection aborts & inhibits: 301 • inject: 24% of the time • note: dominated by pre-trickle

  30. Radiation signatures: stable-beam aborts, sympathetic Compiled by B. Petersen  1000 X stored beam  150 X stored beam  5000 X stored beam 15 / 22 6 / 22 1 / 22

  31. Radiation signatures: stable-beam aborts (I), radiation only Compiled by B. Petersen  50 X stored beam  80 X stored beam 3/28 6/28

  32. Radiation signatures: stable-beam aborts (II), radiation only ? Compiled by B. Petersen  10000 X stored beam  10000 X stored beam  1000 X stored beam 7/28 4/28 6/28 Could 17/28 radiation-only aborts be sympathetic?

  33. Typical radiation signatures: injection aborts Most of the recent injection aborts look like this  5000 X stored beam  100 X stored beam  50 X stored beam

  34. Injection aborts: a typical example (EOIC summary for 3/23/04) • tune management • non-reproducibility of thermally-induced IP motion • difficult for 1 operator to “keep all balls in the air”

  35. Stable-beam aborts: remediation avenues • Need better understanding/characterization • 40-50% of the radiation aborts were found to be sympathetic... by manually scanning logs • 60% of the ‘radiation-only’ aborts may be sympathetic as well • < # ‘radiation-only’ aborts > ~ 1/day  2-3 % inefficiency (counting all, and adding manual aborts for trapped events) •  can we learn to use the radiation signature to diagnose the source? •  can we automate the categorization of aborts? • easier (automated?) identification/logging of T/L instabilities • data entry • Improved diagnostics: SVTRAD 1.5 elx upgrade coming soon

  36. Implies replacement of mid-plane modules during 2005 shutdown SVT: projected integrated dose Dose projections assume negligible injection background

  37. HER single-beam background: possible improvements ? • now (Jan 2004) ~ 1.6 x Feb 2002 (@ 1 A) • mostly linear with IH dominated by base pressure (thermal outg’sg) • dynamic pressure term (~ SR  IH2) unchanged since Feb 2002 - no plausible improvement (short of $$) • radial ion pumps repair: regain ~ 20% ? • requires removing support tube ( > July 2005) • feasibility of repair tbc • high-vacuum (TSP) section (PR02 7039 to 7042) • TSP’s flashed on 5 + 27 Jan ’04 – no detectable improvement in pressure (p0 ~ 5E-10) • There may be some to gain from more frequent NEG activation • at best, will return to Feb 2002 levels, but not for long • # NEG cycles is finite  NEG activation expensive

  38. Drift Chamber current as function of Luminosity during a X scan (all currents constant) DCH current (microA) Luminosity

  39. DCH/TRG background extrapolations • HER single-beam & lumi (bkg + physics) terms dominate • Trickle: only average shown. Must be able to accomodate large fluctuations. • Beam-beam: only best case shown. Data taken since then show beam-beam can easily be 2 x larger – not counting short-term fluctuations. • LER single beam: small (mostly beam-gas), no fluctuations expected

  40. EMC Looked at number of crystals with any/significant energy and clusters Small quadratic term from single beam data # of crystals used in cluster finding Currently physics events have ~110 digis and 8 clusters Long term impact on physics analysis not clear yet

  41. 12 hours Thermal time constants VGCC3027  (incoming LEB) BE diamond  (LEB sensitive) LER current VGCC2187 (HER sensitive)  BW diamond [+ BBR dead time] (HEB sensitive)

  42. Detailed study of the time evolution of the thermal outgassing related background Fill March 28, 12pm-3 pm • The different time dependences of the pressure readings allowed to fit the background sensor (Bacward East diamond) as a linear combination of 4 Pumps*LER, on a fill by fill basis • The 4 pumps are located on the incoming LER straight and all exhibit HOM related thermal outgassing (eg, change of pressure associated with change of bunch length) • A very satisfactory description of the background was thus obtained in all cases • The sensitivity coefficients for each pump were then extracted. They represent the N2-equivalent pressure integral with the same time dependence as the pump reading. mRad/s Data points End of injection Fit VP3044 VGCC3027 VP3147 0 1 2 3 hours

  43. Evolution of the sensitivity coefficients • The coefficients are normalised to their pre-NEG activation values , indicated by the red line (1 point per long fill) • The background problem was not related to a Pressure increase (as indicated by the pump readings) but to a huge increase in background sensitivy • The problem was solved by: • -continued processing • Collimator jaw opening • Change in bunch pattern These changes has different actions on the various background drivers VP3044 VGCC3027 200 10 Days in March (April 1=32) Days in March (April 1=32)

  44. BE diamond (LEB sensitive) VGCC3027 (incoming LEB) NEG actvtd NEG actvtd NEG actvtd NEG actvtd BW diamond (HEB sensitive) VGCC2187 (HER sensitive) Mismatch (x 10-100) betw. time evolution of msrd p and of bkgd demonstrated by detailed analysis of local pressure contributions to background signals

  45. NEG actvtd NEG actvtd NEG actvtd NEG actvtd Large variety of processing times, mechanisms, & bkg sensitivities

  46. 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!

  47. 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

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