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The G as E lectron M ultiplier: GEM

Learn about GEM basics, applications for charged tracks, X-rays, UV-Photons, and performance characterization. Discover Thomas K. Hemmick's insights from Stony Brook University in 2006.

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The G as E lectron M ultiplier: GEM

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  1. The Gas Electron Multiplier: GEM Thomas K. Hemmick Stony Brook University 1 Thomas K Hemmick May 17th, 2006

  2. Outline • GEM Basics • GEM applications: • Charged Tracks • X-rays • UV-Photons • Performance characterization • Stony Brook Production Facility maps. 2 Thomas K Hemmick May 17th, 2006

  3. Gas Electron Multiplier (GEM) • The original idea by F.Sauli (mid 90s) US Patent 6,011,265 • Traditionally CHARGED PARTICLE detectors (not photons) 150μ 80μ • Two copper layers (5μm thick) separated by insulating film (50μm thick) with regular pitch of holes • HV creates very strong field such that the avalanche develops inside the holes • Just add the photocathode • added bonus: no photon feedback onto photocathode 3 Thomas K Hemmick May 17th, 2006

  4. Ways to use GEM stacks HV charged particle or photon primary ionization Forward BiasCharged Particles Forward BiasX-ray g Mesh HV Gamma Conversion Triple GEM Readout Pads Readout Pads Primary Ionization traildirected through GEM holes Point-like Ionization spotdirected through GEM holes • Lateral spread of avalanche is ~500 μm. • With “charge sharing” pad configuration 10’s of mm resolution • Single electron gain ~104 easily achieved and stable

  5. More Ways to use GEM stacks Reverse Bias (Photosensitive Mode) g Mesh primary ionization photo electron HV e- CsI layer Triple GEM VUV only untilnew gas-resistantcathode material found Readout Pads • Photosensitivity limited by: • Longest wavelength set by CsI work function (l<200 nm) • Shortest wavelength set by gas transparency (l>120 nm) • Ideal for Cherenkov Light! • Not useful for common plastic scintillators etc…

  6. Watch the Magic (Reverse Bias)… HV ~150 μm • Start with a GEM • Put a photocathode (CsI) on top • photoelectron from Cherenkov light avalanches in the high density E-field • Use more GEMs for larger signal • Pick up the signal on pads • What about ionizing particles (hadrons)? • We need a mesh with a reverse voltage on it to blow electrons away!!! • We have a detector sensitive to UV and blind to ionizing particles! 6 Thomas K Hemmick May 17th, 2006

  7. Clean tent present and future • The clean tent was used for the PHENIX drift chamber construction and most recently the PHENIX Hadron-blind detector. • The operation of this tent is independent of the linac and will continue. • We shall receive the Brookhaven Large Winding Machine on permanent loan and expand ten operations.

  8. Future Lab Layout: MARIACHI 14C Grad Lab Det R&D Winder

  9. BNL Large Winder Large footprint:5m x 5m • Extremely useful in general. • NECESSARY for PHENIX maintenance. • Must be removed from BNL • Use linac vault to bring it to SB • Fantastic for all varieties of large wire chambers

  10. evaporator glove box laminar flow hood GEM storage vessel Facility Overview (Life Cycle of the HBD) (“Class”: number of ≤0.5 μm particles/m3) “Class” of Clean Room Entrance Foyer

  11. Electric Lift System (2) • Where to store the lid of the gain box?? • Gain box lid is heavy. • Nowhere to set the lid during GEM insertion/extraction. • YEP!! You guessed it! …UP! • Patch Panel: • “Plug and Chug” • 56-pad gain map in 1 hour!!

  12. Gain Measurement Output • Maestro (PC-based MCA software) • GUI for gain tests (easy to use, flexible!!). • Automated Gain Saturation: • One spectrum every 5 min. • Root macros to plot gain curve • Automated Gain Map: • Prompts user vocally to move cable to next signal. • Complete map (56 pads) in 1 hour.

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