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Standard Single GEM: transport properties

Standard Single GEM: transport properties. Matteo Alfonsi & Gabriele Croci GDD Meeting September, the 30 th 2008. V drift < 0. I drift. 8.9 keV X-Rays. E drift. V TopGEM  Keithley. I top. E GEM. I bottom. V BottomGEM > 0. Not measured. V anode = 0.

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Standard Single GEM: transport properties

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  1. Standard Single GEM: transport properties MatteoAlfonsi & Gabriele Croci GDD Meeting September, the 30th 2008

  2. Vdrift< 0 Idrift 8.9 keV X-Rays Edrift VTopGEM Keithley Itop EGEM Ibottom VBottomGEM > 0 Not measured Vanode= 0 N.B.: Induction field always reversed, so the charge is collected on bottom “Inverted Ei Setup” Case 1) Electron drift in GEM holes Case 2) Ions : Vdrift> 0 and VBottomGEM < 0 !!!!!!!

  3. Electrons Drift Scans

  4. Electrons Drift Scans for higher GEM voltages

  5. Ions Drift Scans

  6. Electrons – Ions Comparison @ 20V

  7. Electron GEM Voltage Scan Edrift = 1 kV/cm

  8. Ions GEM Voltage Scan Edrift = 1 kV/cm

  9. Vdrift< VTopGEM Idrift 8.9 keV X-Rays Edrift VTopGEM< - 600 V Itop EGEM Ibottom VBottomGEM = - 600 V “StandardSetup” Ianode Anode  Keithley

  10. Ions Drift Scan in Std Setup (Low ΔVGEM)

  11. Ions Drift Scan in Std Setup (High ΔVGEM)  Still reasonable @ ΔVGEM = 300V Ions ionization current But @ ΔVGEM = 500V we discovered that few photons (about 1 every 2400 if you assume G = 600) are converted in the holes(this is our hypothesis..) Electrons ionization current

  12. Comparison Ions Electrons in Std Setup (Low ΔVGEM) Electrons Ions

  13. Possible explanation Cu X-Rays Ions produced in the drift gap far from the GEM foil are more likely focused in the centre of the hole and pass through, because they are characterized by a lower diffusion GEM Electric Field with high potential difference on GEM electrodes

  14. Comparison Ions Electrons in Std Setup ( ΔVGEM = 500V) Electrons Ions

  15. Comparison of “Inverted Ei Setup” with the “Standard Setup” with Induction field at 3 kV/cm

  16. Electron Drift Scans Comparison (no Gain)

  17. Ions Drift Scans Comparison (no Gain)

  18. Ions Drift Scans Comparison (300 V)

  19. Charging up problems

  20. At the same time Itop goes from 7.1 nA to 5.8 nA

  21. Time Scans, Edrift = 1kV/cm, ΔVGEM =50V, Einduction = 3 kV/cm 2) Ions and On Before 1) On Before Electrons Current Variation ~ 30% Ions Current Variation ~ Few % 4) Ions,Electrons, Ions and On Before Ions Current 3) Electrons, Ions and On Before Electrons Current

  22. Simulations

  23. Ions Drift simulation:ED = 1kV/cm , VGEM = 20V , inverted EI = -0.1kV/cm 1000 events generated Ions starting from a track passing above the hole, along the diameter of it. NO IONS SHOULD PASS FROM MEASUREMENTS Ions starting points shown. Z-start = 90 µm Color represents the ending place Ions ending place (%) Anode  0.8 % Bottom GEM  29.3 % Kapton 0.8 % Top GEM  68.5 % Other  0.6 %

  24. Spare Slides

  25. Drift Scan comparison (500V) VGEM= 500 V Einduction = 3 kV/cm VGEM= 500 V Einduction = - 2.5 kV/cm

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