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

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Presentation on theme: "INFN Trieste, October 2008 Summary of measurements on: CsI coated ThGEM triple CERN."— Presentation transcript:

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

2 Single ThGEM M1 with CsI the currents at anode, bottom and top are read out by the picoammeters two induction fields (4kV/cm, 6 kV/cm),  V drift = 0 Scan in  V: 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 Photocurrent, f(  V drift) only the cathode is read-out

3 Single ThGEM C4 with CsI preliminary measurements Photocurrent at the cathode  V scan, no filters only the anode read-out

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

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 CsI single photoelectron spectra With autogateWith external gate  V2 & induction  fixed  V1 & transfer scans

7 Triple ThGEM CERN We measured essentially the double ThGEM (the top two ThGEM), keeping the anode and bottom GND, and using as “anode” the top 3. The currents are read out by the picoammeters. The signal source is a 164 Hz 55 Fe. Drift scan: for E drift > 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  V 1 is low, the field lines from cathode to TOP 1 are stronger and more electrons go to TOP 1

8 Triple ThGEM CERN  V1 and  V2 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 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 CERN 55 Fe 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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