1. Measurements of Stability of Gas Electron Multiplier (GEM)
Y.L. Yamaguchi, H. Hamagaki,
K. Ozawa, S.X. Oda, M. Inuzukaa, S.Sanob
CNS,Univ. of Tokyo, National Research Institute for Cultural Properties Tokyoa, Waseda Univ.b
9/21/2005
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Contents
Introduction
Gas Electron Multiplier (GEM)
Characteristics of CNS-GEM and CERN-GEM
Aim of the study
Experimental setup for measurements
Results
P/T dependence of gain
Gain stability
CNS-GEM and CERN-GEM
Ar-CH4 and Ar-CO2
Summary
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3. DNP/JPS meeting in Hawaii
Gas Electron Multiplier (GEM)
GEM is originally invented by
Structure
A metalized polymer foil with holes
(Cu:5mm + Kapton:50mm + Cu:5mm )
Hole :
f @ 50mm
A photograph of GEM
Insulator
Mechanism of signal amplification
A micrograph of GEM
VGEM is applied between the metal layers.
When an electron passes through the hole on GEM, strong electric field inside the hole induces the cascade of electrons.
VGEM
50mm
100mm
GEM can be an upgrade for a wire chamber.
Electric field inside holes
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Characteristics of CNS-GEM and CERN-GEM
We succeeded in fabricating a new type of GEM (CNS-GEM) using a dry etching method.
CERN-GEM
CNS-GEM
Etching method
wet etching
dry etching
The cross section of a hole
A hole with double-conical shape
A hole with cylindrical shape
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Aim of the study
Measure basic properties of CNS-GEM.
Gain
P/T dependence
Stability
Known problem on gain stability
It has been reported that gas gain of CERN-GEM increases (or decreases) as a function of illumination time.
A. Orthen et al.,NIM A 512 (2003) 476
Possible reason
Due to shape of holes of GEM
Charge up of the Kapton surface inside the holes.
CERN-GEM
CNS-GEM
CNS-GEM is expected to have better stability than CERN-GEM.
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Experimental setup for the measurements
55Fe(X-ray,5.9 keV)
HV1
Mesh
P/T dependence of gain
Gain stability
CNS-GEM,CERN-GEM
Ar-CH4
(Ar : CH4 = 90 : 10)
Ar-CO2
(Ar : CO2 = 70 : 30)
HV2
3mm
1MΩ
10MW
GEM 3
10MW
1MΩ
2mm
1MΩ
10MW
GEM 2
1MΩ
10MW
1MΩ
2mm
GEM 1
10MW
2mm
10MW
1MΩ
PAD
VME ADC
PreAmp
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P/T dependence of gain (CERN-GEM)
Gain is measured as a function of P/T.
Pressure is manually changed during the measurement.
Correlation function is evaluated as the formula below.
CERN-GEM
Ar-CH4
Assumed correlation function is good agreement with the measurements.
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P/T dependence of gain (CNS-GEM)
0.1% fluctuation of P/T causes about 1% fluctuation of gain.
The effect of P/T on gain is less than 1%.
P/T is stable within 0.1% during our measurements.
Ar-CH4
Ar-CO2
CNS-GEM
CNS-GEM
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9. Gain stability of CERN-GEM
Gain stability of CERN-GEM is measured as a baseline.
Increasing of gain as a function of illumination time is clearly seen.
A difference of gain stability between Ar-CO2 and Ar-CH4 is observed. Further study is underway.
9/21/2005
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Gain stability of CNS-GEM (Ar-CH4)
CNS-GEM shows very good stability!!
CNS-GEM is stable within error of the measurement.
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Gain stability of CNS-GEM (Ar-CO2)
The case of Ar-CO2 is similar to that of Ar-CH4.
The gain stability of CNS-GEM is better than that of CERN-GEM.
The shape of holes in GEM significantly affect gain stability.
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Summary
P/T dependence and stability of gain have been measured.
Assumed correlation function between gain and P/T is good agreement with the measurements.
A difference of gain stability between Ar-CO2 and Ar-CH4 is observed.
Further study is underway.
The gain stability of CNS-GEM is better than that of CERN-GEM.
The shape of holes in GEM significantly affect gain stability.
9/21/2005
DNP/JPS meeting in Hawaii