Hiroyuki Sekiya Oct. 4th 2007 Hamamatsu, JAPAN NNN07

Development of Gaseous Photomultiplierwith GEM/μ PIC Hiroyuki Sekiya ICRR, University of Tokyo

E-mail: sekiya@icrr.u-tokyo.ac.jp

Abstract: We are developing a new photon detector with gas amplification devices. The transmissive CsI photocathode is combined with 10cm×10cm GEM/μPIC for the first prototype which is aimed to apply to the large liquid Xe detectors. Using Ar+C2H6(10%) gas, we achieved the gas gain of 105 which is enough to detect single photoelectron. We, then, irradiate UV photons with the Excimer Xe lamp to the prototype detector and we successfully detected the UV photons.

1.MotivationRecently, large area micro pattern gaseous detectors such as GEM, Micromegas, and μPIC have been developed and successfully operated. 30cmGEM30cmμ-PIC

These devices with photocathode can realize a gaseous photomultiplier for future large volume detectors.

Possible features Large areaLow costSmall volume

Position resolutionLow background

Handling the bialkali photocathodes requires special equipments, therefore, we use the CsI for the first step. In particular, the quantum efficiency of the CsI matches the liquid/gas Xe scintillators; thus, dark matter and neutrino experiments are the targets of this photon detector.

2.Prototype Detector

Window/photocathode

•MgF2 54Φ×5t•Al electrode (edge10mm)

•CsI evaporated by HPK

GEM

μPIC

10cmGEM

10cmμ-PIC

•Advanced MSGC•PCB technology (Toshiba, DNP)•10cm×10cm•256×256 strips　 merged to 4×4

Structure of μ-PIC

400μm

anode

cathode

•SMASH (plasma etched GEM)

(SciEnergy Co., Ltd.)•100μm Liquid Crystal Polymer•10cm×10cm•140μm pitch, 70μm Φ

2GEMs + μPIC System for suppression ion/photon feedback high gain operationGas: Ar ＋ C2H6 （ 90 ： 10 ） 1atm

3.Gas Gain Measurement In the beginning, the gas gain of the detector was examined.

10 MΩ

20 MΩ

1MΩ

100pF

500MΩ

20μmAl

6mm

2mm

6mm

12mm-HV

20 MΩ

20 MΩ

+HV

-HV

100pF

5.9keV Xrays of 55Fe were irradiated

Signals 　　 Charge amplifiers were used. CP581(11V/pC) for GEM2 CP515-1(5V/pC) for μPIC

0.3kV/cm

0.3kV/cm

400V@GEMs gas gain =6000V@μPIC

400V@GEMs gas gain =600170V@μPIC

GEM2 GEM2

μPICcathode

μPICcathode

ResultsGEM HV dependence μPIC HV dependence

0V@μPIC 400V@GEMs

Although the signals were saturated, 400V was successfully applied to the μPIC without any discharges → 　 Stable operation with the gain of 105.

Output of the amplifierwas saturated.Can still apply higher HV.

4.Light DetectionThe UV light test was conducted with a Xe2 ∗ Eximer Lamp .(Ushio H0016)

1mmΦcollimaterlow gas gain(=600) operation without charge amplifiers

GEM2

μPICcathode

2mV100μs

137Cs 662keV irradiation

Air leak to the path

Light OFF

10mV100μs

10mV100μs

Light ON!

GEM2

μPICcathode

18kHz Oscillation was observed! Light attenuation was confirmed.

Amplitude

became 1/4

•λmean =172nm •50mW @35.5Φwindow•18kHz dielectric disharge

Too strong intensity

Ion feedback

5.Conclusions and Prospects

References[μPIC] A.Takada et al., Nucl. Instr. and Meth A. 573 (2007) 195[GEM/SMASH] SciEnergy Co., Ltd. http://www.scienergy.jp[This detector] H.Sekiya, Proc. of the International Workshop on new Photon-Detectors, Proceedings of Science, PoS(PD07)028

The gas gain of 105 with the suppression of ion feedback flow is achieved, which enable the detection of single photo-electron.The UV light was successfully detected. → A milestone in the realization of 10cm-size gas PMTsMany additional tests such as the uniformity, the longtime stability, the detection efficiency should be conducted.10cm size transmissive/reflective photocathodes will be tested.Bialkali photocathodes for visible light will be developed.

25μm Mylar ® tape window (only for this measurement)