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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 MatteoAlfonsi & Gabriele Croci GDD Meeting September, the 30th 2008
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 !!!!!!!
Electron GEM Voltage Scan Edrift = 1 kV/cm
Ions GEM Voltage Scan Edrift = 1 kV/cm
Vdrift< VTopGEM Idrift 8.9 keV X-Rays Edrift VTopGEM< - 600 V Itop EGEM Ibottom VBottomGEM = - 600 V “StandardSetup” Ianode Anode Keithley
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
Comparison Ions Electrons in Std Setup (Low ΔVGEM) Electrons Ions
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
Comparison Ions Electrons in Std Setup ( ΔVGEM = 500V) Electrons Ions
Comparison of “Inverted Ei Setup” with the “Standard Setup” with Induction field at 3 kV/cm
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
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 %
Drift Scan comparison (500V) VGEM= 500 V Einduction = 3 kV/cm VGEM= 500 V Einduction = - 2.5 kV/cm