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

2 Thomas K Hemmick May 17 th, Outline 1.GEM Basics 2.GEM applications: 1.Charged Tracks 2.X-rays 3.UV-Photons 3.Performance characterization 4.Stony Brook Production Facility maps.

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

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

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

6 Thomas K Hemmick May 17 th, Watch the Magic (Reverse Bias)… 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!!! HV We have a detector sensitive to UV and blind to ionizing particles! ~150 μ m

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 : Grad Lab 14 C MARIACHI Winder Det R&D

9 BNL Large Winder 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 Large footprint: 5m x 5m

10 Facility Overview (Life Cycle of the HBD) Entrance Foyer “Class” of Clean Room evaporator GEM storage vessel laminar flow hood (“Class”: number of ≤0.5 μm particles/m 3 ) glove box

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.