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Summary of CsI Coated ThGEM Measurements at CERN/INFN Trieste

Detailed summary of measurements on CsI-coated ThGEM and triple ThGEM conducted at CERN/INFN Trieste in October 2008. Includes single ThGEM M1 and C4 measurements with CsI, behavior of charge sharing at different gains, preliminary measurements, and double ThGEM M1 studies. Explore the effects of different light sources and acquisition methods on single and double ThGEMs. Triple ThGEM C7 measurements at CERN highlight charge sharing and stability issues at high gains.

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Summary of CsI Coated ThGEM Measurements at CERN/INFN Trieste

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  1. Summary of measurements on: • CsI coated ThGEM • triple ThGEM @ CERN INFN Trieste, October 2008

  2. Single ThGEM M1 with CsI the currents at anode, bottom and top are read out by the picoammeters Photocurrent, f(DV drift) only the cathode is read-out two induction fields (4kV/cm, 6 kV/cm), DV drift = 0 Scan in DV: the light has been chosen to enhance the gain = 1 plateau • Different behavior of the charge sharing between anode and bottom • at different gains: • HIGH gains, increasing the gain: • more and more to the bottom • LOW gains, increasing the gain: • more and more to the anode

  3. Single ThGEM C4 with CsIpreliminary measurements DV scan, no filters only the anode read-out Photocurrent at the cathode

  4. Single ThGEM C4 with CsIanode, bottom & top read-out DV scans : two induction fields of 4kV/cm and 6 kV/cm With 239 nm passband filter!!

  5. Double ThGEM M1 with CsI On compass01, jarda /var/www/html/jarda/THGEMs - Trieste LAB activity/IV DOUBLE GEM • The double ThGEM M1 with CsI can’t stand the current produced by the D2 lamps, even the ORIEL at its minimum yield. • So, the only measurement possible is the single electron spectrum. • The light sources are two: • environment UV (the quartz window is uncovered) • D2 lamp filtered with the two band pass filters of 239 nm and 289 nm. • The acquisition are of two kinds: • with autogate (series UV#)  a large pedestal is observed • with external gate produced by the bottom signal (because of some spurious signals running the threshold is a bit high: ~ 4fC and this explains why we can’t reach the lower part of the spectra)

  6. Double ThGEM M1 with CsIsingle photoelectron spectra With autogate With external gate • DV2 & induction  fixed • DV1 & transfer scans

  7. Triple ThGEM C7 @ CERN We measured essentially the double ThGEM (the top two ThGEM), keeping the anode and bottom 3 @ GND, and using as “anode” the top 3. The currents are read out by the picoammeters. The signal source is a 164 Hz 55Fe. Drift scan: for Edrift > 1kV/cm, practically all the charge is collected inside the holes of the first ThGEM: all measurements performed with a drift field of 1kV/cm (500V).\ Note that, when the DV1 is low, the field lines from cathode to TOP1 are stronger and more electrons go to TOP1

  8. Triple ThGEM C7 @ CERNDV1 and DV2 scans The currents of all electrodes are measured: because of the non ideality of the picoammeters, just non negligible currents can be measured. Then drift, top1, bottom1 currents are readable just for high gains and, when it happens, all currents sum to zero!! scans done for two induction fields: 3kV/cm (480 V) and 2kV/cm (320 V).

  9. Triple ThGEM C7 @ CERN charge sharing between “last bottom” and “anode”induction scans Drift = 1kV/cm (fixed) – transfer = 2kV/cm (fixed) DV 1 fixed = 1300 V, so the same amount of charge arrive at the second ThGEM, the sharing is in this case independent of the gain… DV 2 fixed = 1300 V, so different amount of currents arrive at second ThGEM: more current comes, more goes to the anode

  10. Triple ThGEM C7 @ CERN • 55Fe spectra acquired with the maximum gain: • charge ~300 fC • Gain = 8.5k for both double and triple ThGEM. the triple ThGEM is not stable! At this high gain…

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