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東大CNSにおけるGEMの基本動
作特性の研究
Measurement of basic properties
of GEM at CNS, Univ. of Tokyo
Yorito Yamaguchi
CNS, Univ. of Tokyo
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
2/18
Outline
•Introduction
•Setup for Measurements
•Basic properties of Standard-GEM
−P/T dependence, Gain Stability, VGEM dependence
•Development of 150mm-GEM
−Feature of 150mm-GEM
−Electric field, Gain, Multiplication factor, Gain Stability
•Summary
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
3/18
Introduction
A new type of GEM was successfully developed using a
dry etching technique.
Etching
technique
CERN
SciEnergy Co., Ltd
wet etching
dry etching
The cross
section of
a hole
Hole shape
Bi-conical
Cylindrical
Basic properties were measured to evaluate the performance of
SciEnergy-GEM.
•P/T dependence, Gain Stability ,VGEM dependence.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
4/18
Setup for Measurements
• ED = 0.5kV/cm
• ET = EI
• DVT = DVI = DVGEM
•Moisture % < 10ppm
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
5/18
Measurement of basic properties
−P/T dependence of Gain
−Gain Stability
−VGEM dependence of Gain
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
P/T Dependence of Gain ①
6/18
Longitudinal axis : Gain
Horizontal axis : P/T [Torr/K]
Range : 2.50~2.65
Ar/CH4
Ar/CO2
It was observed that
Gain decreases
exponentially as P/T
increases.
A change of 1% in
P/T value causes a
gain variation of 9%
(Ar/CH4) and of 11%
(Ar/CO2).
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
P/T Dependence of Gain ②
7/18
Base point in Gain
•P=760.0Torr
•T=300.0K
→P/T=2.533 [Torr/K]
Both results of
SciEnergy-GEM
and CERN-GEM
are in good
agreement with the


P
 unique exponential
P

RAr/CH  exp  3.749    2.533  RAr/CO  exp  4.553    2.533
T
 function.
T



The results with different P/T can be normalized to the same
condition using the obtained function.
4
01/26/2007
2
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
Gain Stability ①
Known problem in gain stability
It was reported that gain of CERN-GEM increases
(or decreases) as a function of illumination time.
A. Orthen et al., NIM A 512 (2003) 476
Possible reason
1. Due to shape of a GEM hole
• Charge up of the insulator surface
inside the hole.
2. Due to nature of insulator
3. Due to surface conditions
Measurement condition
•VGEM is kept constant during the measurement.
•Rate of signals is 3Hz for all measurements.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
8/18
9/18
Gain Stability ②
All results are normalized to the condition of P/T=2.533 [Torr/K]
using the obtained relation between Gain and P/T.
Gain variation
•SciEnergy-GEM
•within 0.5%
(both case)
Without charge-up
•CERN-GEM
•Increase 15%
(Ar/CH4)
•Increase 45%
(Ar/CO2)
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
10/18
Gain Stability ③
SciEnergy-GEM has a much better gain stability than CERNGEM.
Electric field inside a GEM hole
10mm from hole edge Drift direction
of electron
CERN-GEM
SciEnergy-GEM
The electric field near the hole edge is
distorted due to a bulge of a insulator for
CERN-GEM.
VGEM=350V
01/26/2007
E [V/cm]
→Probability of charging-up is higher
for CERN-GEM than SciEnergy-GEM.
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
11/18
VGEM Dependence of Gain
SciEnergy-GEM can
attain 20% (Ar/CH4)
and 50% (Ar/CO2)
higher gain than
CERN-GEM at the
same VGEM.
→SciEnergy-GEM
has larger effective
area in multiplication
than CERN-GEM.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
12/18
Development of 150mm-GEM
−Feature of 150mm-GEM
−Electric field of 150mm-GEM
−Gain of 150mm-GEM
−Multiplication factor
−Gain Stability
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
13/18
Feature of 150mm-GEM
The dry etching technique can allow to fabricate a thicker GEM
(Thick-GEM) than Standard-GEM (insulator thickness:50mm).
−150mm-GEM is comparable to a triple layer structure of
Standard-GEM with respect to the total length of a hole.
Advantage of 150mm-GEM
150mm-GEM is expected
•Larger effective path length
to multiply electrons
for multiplication
more effectively than
triple layer structure of
•Less effect of transmission
Standard-GEM.
efficiency
Structure of 150mm-GEM
• Cu(8mm) + LCP(150mm) + Cu(8mm)
140mm
150mm
• f = 70mm
*LCP:Liquid Crystal Polymer
• hole pitch = 140mm
70mm
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
14/18
Electric Field of 150mm-GEM
Electric field through the hole center
VGEM/50mm=250V/50mm
● 150mm-GEM
VGEM=750V
● 100mm-GEM
VGEM=500V
● Standard-GEM (50mm)
VGEM=250V
The electric field of Thick-GEM
is much stronger than that of
Standard-GEM.
a>0
→Especially, 150mm-GEM
reaches plateau for about 50mm.
150mm-GEM should have a better multiplication ability
than Standard-GEM.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
15/18
Gain of 150mm-GEM
Gain for Standard-GEM is obtained
by triple GEM structure.
Tamagawa-san’s result
→(Gain100mm-GEM)3/2
•150mm-GEM had a
continuous discharge at
270V/50mm.(Gain~4000)
Ar(70%)/CO2(30%)
Gain
at 300V/50mm
Magnification
Ratio
Standard-GEM
30
1.0
100mm-GEM
1.0 x103
3.6 x102
150mm-GEM
3.9 x104
1.3 x103
150mm-GEM can attain much higher Gain than StandardGEM at the same VGEM/50mm.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
16/18
Multiplication Factor
Gain  M   T   M 
n
Gain1/ n
T
M : Multiplica tion factor
 T : Transmissi on efficiency
n : Number of layers
Simulation results of the
transmission efficiency is used.
■150mm-GEM (M150):T150=0.17
■100mm-GEM (M1003/2):T100=0.34
■Standard-GEM (M503):T50=0.24
EI is stronger than for StandardGEM and 150mm-GEM.
As expected from the electric field inside a hole, 150mm-GEM
has the highest multiplication factor.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
17/18
Gain Stability of 150mm-GEM
•The rate of signals = 2.5Hz
•VGEM=230V
Ar(90%)/CH4(10%)
Gain of 150mm-GEM is stable within 1.0% for 9 hours.
→150mm-GEM has a good gain stability as well as
Standard-GEM
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
18/18
Summary
•The basic properties have been measured to evaluate the
performance of SciEnergy-GEM.
−Gain decreases exponentially as P/T increases.
•A change of 1% in P/T value causes a gain variation of 9% (Ar/CH4) and
of 11% (Ar/CO2).
−SciEnergy-GEM has a much better gain stability than CERN-GEM.
•Probability of charging-up is higher for CERN-GEM because of a
distortion of electric field near the hole edge.
−SciEnergy-GEM can attain higher gain than CERN-GEM at the same VGEM.
•150mm-GEM has been fabricated successfully using dry etching.
−Electric field of 150mm-GEM is much stronger than that of Standard-GEM.
−150mm-GEM has much higher gain and multiplication ability with a good gain
stability than a triple layer structure of Standard-GEM.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
19/18
Back up
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
20/18
Applications
We are developing some detectors using GEMs.
•GEM-TPC
→S.X. Oda et al., NIM A 566 (2006) 312
•Photon detector
•Hadron Blind Detector (HBD) installed in PHENIX@RHIC.
→Please hear Ozawa-san’s talk (15:15~ in tomorrow session).
•Neutron Counter
→Development is now on going.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
21/18
Relation between Gain and P/T
a : First Townsend coefficien t
ion : Mean free path for ionization
From the equation of state,
N A : Avogadro' s number
NA P
N

R T
a
1
ion
N : Particle number density
 : Cross section for ionization
R : Gas constant
P : Pressure
NA P
P
 N  ( N , E) 
   ( , E )T : Temperatur e
R T
T


P
 NA P

Gain  exp  a ( x)dx  exp 
   ( , x)dx 
T
 R T

The expected relation between Gain and P/T should be exponential.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
22/18
Simulation of GEM structure
Aim of study
•To understand the behavior of
electrons inside a GEM hole
qualitatively and quantitatively.
•To search for optimum GEM
structure.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
23/18
Potential Distribution of GEM hole
The electric field inside the GEM hole was calculated
using Maxwell 3D.
VGEM=350V
The calculation was carried
out for two type of GEM.
•Bi-conical (CERN-like)
•Cylindrical (SciEnergy-like)
Bi-conical
Cylindrical
Potential distributions are very similar in both cases.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
24/18
Electric Field inside GEM hole
Hole center
10mm from hole edge
Drift direction
of electron
Although there is little difference between them at hole
center, the electric field of Bi-conical near the hole edge is
distorted due to a bulge of a insulator.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
25/18
Simulation of Avalanche
The avalanche inside a GEM hole was simulated using Garfield.
•The calculation results from Maxwell 3D are the inputs to Garfield.
•Avalanche simulation ware carried out with two methods.
•True path integration
•Projected path integration
•Ar/CO2 (70:30) was used at P=760.0Torr, T=300.0K.
ions
Gain can be defined as a
following equation.
Gain  M   T 
n
M : Multiplica tion factor
electrons
 T : Transmissi on efficiency
n : Number of layers
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
26/18
Behavior of Electrons
Created point of electron
Number of created electron
Lost point of electron
GEM
Gain
•There is a significant difference in multiplication near the hole edge.
•SciEnergy-GEM has better multiplication ability than CERN-GEM.
•More than 70% of secondary electrons are absorbed by the lower
electrode of GEM.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
27/18
Gain
Gainsingle  Gaintriple 
1
3
Most of electrons created near
the hole edge are absorbed by
electrode.
→There is not a big difference
in gain as seen in multiplication
factor.
Simulation results are
qualitatively consistent with
measured result, but they are
quantitatively inconsistent.
It is needed to improve the calculation method
in multiplication inside a GEM hole.
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
28/18
Setup for Measurements of 150mm-GEM
• ED = 0.5kV/cm
• DVI = DVGEM/3
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
Gain of 150mm-GEM (Ar/CH4)
01/26/2007
MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)
29/18