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Simulation of the spark rate in a Micromegas detector with Geant4

Simulation of the spark rate in a Micromegas detector with Geant4. Sébastien Procureur CEA-Saclay. Motivation. From JLab review (May 2009):. “We suggest the following further simulation studies: […]

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Simulation of the spark rate in a Micromegas detector with Geant4

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  1. Simulation of the spark rate in a Micromegas detector with Geant4 Sébastien Procureur CEA-Saclay

  2. Motivation FromJLabreview (May 2009): • “We suggest the following further simulation studies: • […] • Study the rate of production of highly-ionizing particles (e.g. low energy protons or alpha particles) which might • cause sparking; for example, from elastic e-p events or from scattering from nuclear targets. A study of the rate of • highly ionizing events and their energy deposition profile in the detector at CLAS12 design luminosity could provide • an estimate of dead-time losses due to sparking and could lead to a better overall detector design.” → This requires to first estimate, with a simulation, the measuredspark rates Spark rate simulations CT review, 12/02/2009 S.Procureur

  3. Outline Introduction – existing data on sparks Geant4 simulation of a MM in hadron beams (Gemc) • HighlyIonizingParticles (HIPs) production - Depositedenergy Spark rate estimation • Normalized and real gains • Comparisonwith data • Systematics (production threshold, integration size) Predictions and conclusion • Bulk vs non bulkMicromegas • Effect of the drift electrodematerial • Applicability for CLAS12? (+ 1 slide on the tracking) Spark rate simulations CT review, 12/02/2009 S.Procureur

  4. Sparks in Micromegas • a spark/dischargeis a rapid breakdown appearing in the amplification gap • (seeBrahim’s talk), usuallywith hadron beams • pioneeringwork: D. Therset al., NIM A469 (2001), 133 → Spark rate is a power law of the gain → Strongdependencewith Z (gas) « A likelyexplanationis that a discharge is triggered when an energy of a few hundred keV is released in the detector conversion gap resulting in a large number of primary ions » This behaviourwasconfirmed by severalexperiments (+ additionalstudieswithα sources… similar conclusions) Spark rate simulations CT review, 12/02/2009 S.Procureur

  5. Geant4 simulation of a MM (Gemc) Simulation of the detector tested by Thers et al. 15 GeVπ 4 µm Nickel grid 2.45 mm conversion gap (Ar+11%iC4H10) 4 µm Nickel grid 100 µm amplif. gap 400 µm Epoxy 7 µm Copper strips → Physicslist: QGSC_BERT → Integration of Edep in 300x300 µm² → Production threshold: 300 µm Requires large simulation (rare processes, ~10-6 ) Spark rate simulations CT review, 12/02/2009 S.Procureur

  6. Secondary particles production Manydifferent types of secondaryparticlescanbeproduced: → smallprobability to produceHIPs P [MeV] Spark rate simulations CT review, 12/02/2009 S.Procureur

  7. Origin of the HIPs Origin of particlesleavingat least 0.2 MeV in 300x300 µm² : → 42% from the drift electrode → 22% from the gas → 10% from the micro-mesh → 23% from the strips drift mesh strips Spark rate simulations CT review, 12/02/2009 S.Procureur

  8. Deposited energy distribution → Energyabove 1 MeV can bedeposited! (~2000 times more than a MIP) Wewill assume that : → the number of primaryelectronsisproportional to Edep (Np=Edep/wi) → if a depositedenergy of 1 MeV produces a sparkat a gain equals to unity (normalization), then a 500 keVdepositwillproduce a sparkwith a gain of 2 Spark rate simulations CT review, 12/02/2009 S.Procureur

  9. Spark rate estimate → Power lawdependenceisclearly observed, as in the data How to relate the « normalized » gain (from simulation) to the real one? 1) Make use of the Raether’slimit (spark if NpxG ~ 2x107) 2) Relate the spark rate with a α source and depositedenergy Spark rate simulations CT review, 12/02/2009 S.Procureur

  10. Comparison with data • Correct order of magnitude • Similarslope Spark rate simulations CT review, 12/02/2009 S.Procureur

  11. Some systematics Production threshold Integration size → Dependenceonly on the integration size (shouldbe close to transverse diffusion size) Spark rate simulations CT review, 12/02/2009 S.Procureur

  12. Spark rate predictions 1) Bulk (woven, thickmesh) vs non bulk (electroformed, thingrid): → Expectsimilarspark rate for the 2 types of detectors Spark rate simulations CT review, 12/02/2009 S.Procureur

  13. Spark rate predictions 2) Aluminizedmylar vs woven Inox drift electrode: → Spark rate ~2 times largerwith the Inox drift Spark rate simulations CT review, 12/02/2009 S.Procureur

  14. CERN tests (150 GeV) → Bulk~non bulk; Inox drift>~ mylar drift (but large dispersion) Spark rate simulations CT review, 12/02/2009 S.Procureur

  15. 1st comparison with simulation → Preliminarycomparison (usingRaether’slimit) shows nice agreement betweenmeasurements and simulation Spark rate simulations CT review, 12/02/2009 S.Procureur

  16. Towards a SR estimate for CLAS12 → Looks suspiciously stable down to 300 MeV It would be really useful to experimentally investigate the SR at energies below 2 GeV (JLab? CERN? …) Spark rate simulations CT review, 12/02/2009 S.Procureur

  17. Conclusion • Better understanding of sparks (HIPs production) • Simulation can give a correct estimate of the spark rate  Can use it to optimize the detector design (material, mesh segmentation) • Still doubts on the reliability of the simulation at CLAS12 energies  The simulation will never replace an experimental measurement! Spark rate simulations CT review, 12/02/2009 S.Procureur

  18. Central Tracking Effect of the number of Silicons in the tracking • More multiple scattering, but limited effect Spark rate simulations CT review, 12/02/2009 S.Procureur

  19. Backup Micromegas simulations JLab review, 05/07/2009 S.Procureur

  20. Reconstruction (Socrat) - Forward • Comparison between FST and FMT performance (with DC) • Very similar performance  large improvement of vertex determination wrt DC Micromegas simulations JLab review, 05/07/2009 S.Procureur

  21. Reconstruction (Socrat) - Forward • Comparison between FST and FMT performance (with DC) Micromegas simulations JLab review, 05/07/2009 S.Procureur

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