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ADC channel

ADC channel. R&D for the next generation of gaseous photon detectors for Imaging Cherenkov Counters. Jarda Polak ( INFN Trieste ). Today’s generation of gaseous PD, their limitations and the way out The R&D lab studies Our plans for future.

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ADC channel

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  1. Fulvio TESSAROTTO ADC channel

  2. R&D for the next generation of gaseous photon detectors for Imaging Cherenkov Counters Jarda Polak (INFNTrieste) Today’s generation of gaseous PD, their limitations and the way out The R&D lab studies Our plans for future Today’s generation of gaseous PD, their limitations and the way out Fulvio TESSAROTTO

  3. Fulvio TESSAROTTO

  4. Fulvio TESSAROTTO

  5. Tests with double (and triple) THGEM th. 0.4, Ø 0.4, p. 0.8, 10 μm rim Gain (with ~600 Hz Fe source): Single ~ 3000 Double ~ 20000 (preliminary) Triple ~ 80000 (very preliminary) drift Edrift THGEM 1 Etransfer THGEM 2 Einduction anode Fulvio TESSAROTTO ADC channel

  6. Triple THGEM: th. 0.4, Ø 0.4, p. 0.8, 10 μm rim Fulvio TESSAROTTO

  7. Triple THGEM: th. 0.4, Ø 0.4, p. 0.8, 10 μm rim Fulvio TESSAROTTO

  8. Triple THGEM: th. 0.4, Ø 0.4, p. 0.8, 10 μm rim Fulvio TESSAROTTO

  9. Tests in COMPASS experimental area THGEM prototypes tested with digital r/o: double 30 x 30 mm2, 16 ch. th. 0.4, Ø 0.4, p. 0.8, 10 μm rim double 100 x 100 mm2, 256 ch. th. 0.2, Ø 0.2, p. 0.4, 10 μm rim Prot. 30x30 DAQ Prot. 100 x 100 Excellent stability of double THGEM with 100 fC signals Catch r/o Trigger: esternal (scintillators) or internal (signals from bottom of THGEM) Registering currents, amplitudes (CREMAT or ORTEC), timing (CMAD – DREISAM – CATCH - DAQ) Fulvio TESSAROTTO

  10. range of the fit Double THGEM with CsI 4.5 mm THGEM 1: th. 0.4, Ø 0.4, p. 0.8, no rim THGEM 2: th. 0.4, Ø 0.4, p. 0.8, no rim CsI 2.5 mm drift 0 V/cm ΔV1 1250 V Etransfer 2400 V/cm ΔV2 1325 V Einduction 2400 V/cm 2.5 mm drift Edrift THGEM 1 Etransfer THGEM 2 Einduction anode ln(counts) Signal amplitude distribution average signal amplitude: 7.3 fC corresponding to a gain of ~ 45600 fC ADC channel Fulvio TESSAROTTO

  11. Double THGEM with CsI drift 0 V ΔV1 1300 V Etransfer 2800 V/cm ΔV2 1300 V Einduction 2400 V/cm ln(counts) average signal amplitude: 10. fC corresponding to a gain of ~ 62000 fC Fulvio TESSAROTTO

  12. Single photon amplitude (trigger = bottom 2) Distribution cut by trigger condition: 4.4 fC on bottom 2 drift 0 V/cm ΔV1 1300 V Etransfer 3200 V/cm ΔV2 1275 V Einduction 3200 V/cm Average charge: 9.2 fC Fulvio TESSAROTTO

  13. Fulvio TESSAROTTO

  14. First observations on CsI-coated ThGEM in Trieste- ADDENDUM - presented by Gabriele Giacomini phone meeting 20/08/2008

  15. In these preliminary measurements we used a deuterium lamp (AVALIGHT-DHS produced by AVANTES) to extract electrons from a CsI layer, coating the “top” surface of the ThGEM (type “C4”). This irradiation produces a DC current, which is measured by picoammeters ( Keithley and home-made) . The amount of irradiation is not accurately known (since the lamp is not perfectly calibrated), then information about the gain cannot be extracted from these measurements. Irradiation level is chosen to avoid a fast ageing of the CsI layer, known to lose its quantum efficiency after a collected charge of ~ mC/cm2. Fulvio TESSAROTTO

  16. The chamber PicoAmmeter KEITHLEY HV in High quality quartz window (HERAUS Suprasil II) Ar/CO2 (70/30) In (N2 while idle) Ar/CO2 out (N2 while idle) THGEM top, coated with CsI Cathode wires (almost invisible) Fulvio TESSAROTTO

  17. The set-up AVALIGHT-DHS Deuterium lamp Optic fiber and its holder. The beam out of the fiber diverges and irradiates the whole quartz window. The anode pads are covered by an Aluminum box, a BNC carries out the signal/current Fulvio TESSAROTTO

  18. Just a sketch … Beam out from optic fiber Quartz window hn Cathode wires - HV e- 7 mm Top: CsI coated - HV 0.4 mm Bottom - HV 5 mm Anode pads gas in gas out 1 MW signal/current Fulvio TESSAROTTO

  19. Measurement of the photocurrent (no gain on THGEM) collection efficiency • Photoelectrons collected by cathode (grounded by Keithley picoammeter) and • DV = -100 V, so electrons drift only towards cathode wires. • anode  GND • Scan in Vtop (then in E drift), • keeping fixed DV • 1000 V  ~ 1kV/cm Ar/CO2 1 atm • e- extraction efficiency from CsI depends on drift/diffusion inside CsI itself • Potential barrier between CsI and “vacuum” depends on the Fields • higher fields decrease the detrimental effect of electron backscattering on gas atoms/ molecules, accounting for a charge loosing • Some gain at the cathode wires? Fulvio TESSAROTTO

  20. DV scan (gain from ThGEM) • In this set-up: • Electrons collected by anode • Edrift (fixed) = 0 V/cm • (but we measured Ianode to be insensitive • to E drift ) • Einduction (fixed) = 4000 V/cm • Scan in DV, until multiplication occurs The currents reported are read immediately after the opening of the shutter, the currents then decrease with time, due to the well known polarization effects. • The graph shows three regions: • DV < 250 : partial collection of electrons inside the holes • 250 V < DV < 1000 V : enhanced collection inside holes but gain still ~ 1 • DV > 1000 V : multiplication (we gain a factor 2 every 80 V) In the last points the currents are huge (and time dependent) so we don’t stay for long times. - In this range, environment light too provides high current Fulvio TESSAROTTO

  21. Wavelength response To study the response of CsI to a specific wavelength, we filtered the D2 light source with several narrow bandpass filters (450, 390, 340, 289, 239 nm). We measure again the anode current and we operate the THGEM while it multiplies: DV > 1000V The beam spot irradiates the filter, while the environment light is blocked by the black paper sheet, covering the quartz window. The chamber is blind at 450, 390 and 340 nm (as expected from CsI) but shows significant sensitivity at 289 and, more, at 239 nm. Fulvio TESSAROTTO

  22. Induction scans for different DV (i.e. gains) • Keeping fix the DV (the gain), • we are interested to the ratio : • Ianode / Ianode+bottom • e.g., to decide the voltages in order to get: • a good signal from the anode • a trigger from the bottom. • This ratio is a monotonicfunction of the induction field and saturates at quite high induction fields. DV = 1400 V DV = 1550 V DV = 1480 V Increasing the gain, for a given induction field, more and more electrons go to bottom: the fringe of the hole field competes with the induction field in the electron collection, lowering the ratio of the electrons reaching the anode. Fulvio TESSAROTTO

  23. DV scan - II c4 With the 240 nm filter, we do again the DV scan – for two different Vinduction – reading the currents from anode, bottom, top and drift. (Einduction=6kV/cm) (Einduction=4kV/cm) Vdrift = 3000 V Vdrift = 4000 V Idrift is ~ 0, altough Edrift has a sign for which the cathode competes with the holes in collecting the electrons (Vdrift is constant). Increasing the gain, more electrons to BOTTOM Fulvio TESSAROTTO

  24. Fulvio TESSAROTTO

  25. range of the fit Double THGEM with CsI 4.5 mm THGEM 1: th. 0.4, Ø 0.4, p. 0.8, no rim THGEM 2: th. 0.4, Ø 0.4, p. 0.8, no rim CsI 2.5 mm drift 0 V/cm ΔV1 1250 V Etransfer 2400 V/cm ΔV2 1325 V Einduction 2400 V/cm 2.5 mm drift Edrift THGEM 1 Etransfer THGEM 2 Einduction anode ln(counts) Signal amplitude distribution average signal amplitude: 7.3 fC corresponding to a gain of ~ 45600 fC ADC channel Fulvio TESSAROTTO

  26. Fulvio TESSAROTTO

  27. Toward larger areas: Prototypes: Small, active area 30 x 30 mm2 Medium, active area 100 x 100 mm2 Large, active area 576 x 576 mm2 Next step: many engeneering problems to be faced  build a first tentative prototype box for addressing one by one the problems; start with a large THGEM with “standard” parameters 0.6, 0.4, 0.8 Fulvio TESSAROTTO

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  41. Possible structureof a full sizedetector Anode pads Al frame THGEMs Stesalite frames 600 mm 1500 mm 600 mm Fulvio TESSAROTTO

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