TCPD test measurement 1 TCPD (TGEM CCC Photon Detector) test measurement ELTE, MTA KFKI RMKI, REGARD Group (Budapest, Hungary): Levente Kovács G. Hamar, M. Mátyás D. Varga G. Hamar, M. Mátyás D. Varga Zimányi Winter School 2011, Budapest

2 TCPD test measurement Contents Chamber structure - motvationChamber structure - motvation Measurements with beta sourceMeasurements with beta source Ion and electron dirft in the chamberIon and electron dirft in the chamber Measurements with UV LEDMeasurements with UV LED Single photoelectron (PE) charge distributionSingle photoelectron (PE) charge distribution Photoelectrons & gain vs high voltagePhotoelectrons & gain vs high voltage (TGEM, SW) SummarySummary

3 Chamber structure - motivation Optimal matching of two amplifier stages (TGEM- and CCC- ). Optimal matching of two amplifier stages (TGEM- Thick Gas Electron Multiplier and CCC- Close Cathode Chamber). TGEM acts as electron pre-amplifier (gain ). TGEM acts as electron pre-amplifier (gain ). CCC (MWPC- ) works as further amplifier (gain ). CCC (MWPC- Multi Wire Proportional Chamber) works as further amplifier (gain ). Ion currents reflect field configuration. Ion currents reflect field configuration. Principle aim: to detect a single photoelectron with the TCPD chamber! Principle aim: to detect a single photoelectron with the TCPD chamber! TCPD test measurement

4 Main sections of the chamber (chamber structure) Three sections : Between cathode and TGEM: drift region. TGEM (preamplifier). Between bottom of the TGEM and the wire plane: extraction region. Readout TCPD test measurement

Electrostatic field in the TGEM- CCC & Chamber design 5 TCPD test measurement

6 Ion and electron drift in the chamber (whit beta & UV LED sorce) Avalanches are induced by single electrons (from ionization or PE) (UV LED). Continuous current is observable from ions drifting upwards (Beta). Typical voltage setting - charges Ions potentially cause ageing on the TGEM surface.

7 TCPD test measurement Ion currents as function of the extraction field Beta source used for irradiation. Low field: all currents go to the Field Wires (red line). Higher field: currents to go the TGEM top (green), focusing effect. Very high extraction field: currents go to the TGEM bottom (blue). Cathode: always low currents (purple).

Single photoelectron charge distribution (UV LED pulses) Avalanche statistics: single electron gives exponential total charge (very high fluctuation).Avalanche statistics: single electron gives exponential total charge (very high fluctuation). Exponential fit: area gives PE count, slope proportional to total amplification.Exponential fit: area gives PE count, slope proportional to total amplification. Often the Pólya distribution is used as approximation. Often the Pólya distribution is used as approximation. The total photoelectron per event is kept low (0.1 – 0.3 / event) to obtain the real single PE response. 8 TCPD test measurement

9 Single PE charge distribution vs. TGEM voltage Shape of the curves are conformal. Increasing TGEM voltage increases efficiency (not only signal / noise ratio). Departure from exponential becomes prominent at low charges. ( fix TGEM =1100 Volts) TCPD test measurement

10 Total amplification gain vs. TGEM and CCC voltages Upper panel: Gain vs. TGEM voltage. Lower panel: Gain vs. CCC sense wire voltage. Gain is exponential as a fuction of both variables, reflecting that the gain can be balanced between the two stages. No difference between UV LED and Beta source measurements: no saturation in the high gain (single electron sensitive) mode. TCPD test measurement

11 Photoelectron yield vs TGEM and CCC voltages Expectation: the PE number does not change with the sense wire voltages (but the gain does!) Photoelectron count development as a function of TGEM voltage (lower figure) The PE count after an initial exponential increase saturates at TGEM=1000 volts. Finding (measured data): There is some shallow dependence on TGEM voltage, due to improving PE extraction from TGEM surface. No dependence within error margines on CCC sense wire voltage. TCPD test measurement

12 Summary Single photoelectron detection possibility demonstrated with high signal / noise ratio. Single photoelectron detection possibility demonstrated with high signal / noise ratio. Two stage amplification (TGEM and CCC): increased stability and gain control. Two stage amplification (TGEM and CCC): increased stability and gain control. Ion back flow follows expected trends, gives information on internal electrical field. Ion back flow follows expected trends, gives information on internal electrical field. We have detected single photoelectrons with the first TCPD chamber. We have detected single photoelectrons with the first TCPD chamber. Applicability in different gas compositions (measurements with different gas mixtures see M.Matyas’ talk). Applicability in different gas compositions (measurements with different gas mixtures see M.Matyas’ talk). TCPD test measurement

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