1/18 01/26/2007mpgd workshop in saga (yorito yamaguchi, cns, univ. of tokyo) 東大 cns における...

01/26/2007

1/18

MPGD Workshop in Saga (Yorito Yamaguchi, CNS, Univ. of Tokyo)

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 Outline

•Introduction

•Setup for Measurements

•Basic properties of Standard-GEM

−P/T dependence, Gain Stability, VGEM dependence

•Development of 150m-GEM

−Feature of 150m-GEM

−Electric field, Gain, Multiplication factor, Gain Stability

•Summary


3/18

Introduction Introduction A new type of GEM was successfully developed using a dry etching technique.

CERN

wetwet etching

Bi-conicalBi-conical

SciEnergy Co., Ltd

drydry etching

CylindricalCylindrical

Etching technique

The cross section of a hole

Hole shape

Basic properties were measured to evaluate the performance of SciEnergy-GEM.

•P/T dependence, Gain Stability ,VGEM dependence.


4/18

Setup for MeasurementsSetup for Measurements

• ED = 0.5kV/cm

• ET = EI

• VT = VI = VGEM

•Moisture % < 10ppm


5/18

Measurement of basic properties−P/T dependence of Gain

−Gain Stability

−VGEM dependence of Gain


6/18

Ar/CO2

Longitudinal axis : Gain

Horizontal axis : P/T [Torr/K]

Range : 2.50~2.65

It was observed that Gain decreases exponentially as P/T increases.

A change of A change of 1%1% in in P/T value causes a P/T value causes a gain variation of gain variation of 9%9% (Ar/CH(Ar/CH44) and of ) and of 11%11%

(Ar/CO(Ar/CO22).).

P/T Dependence of Gain ①P/T Dependence of Gain ①

Ar/CH4


7/18

533.2749.3exp

4Ar/CH T

PR

533.2553.4exp

2Ar/CO T

PR

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 unique exponential function.

The results with different P/T can be normalized to the same condition using the obtained function.

P/T Dependence of Gain ②P/T Dependence of Gain ②


8/18

Gain Stability ①Gain Stability ①

It was reported that gain of CERN-GEMCERN-GEM increases (or decreases) as a function of illumination time.

A. Orthen et al., NIM A 512 (2003) 476

Known problem in gain stability

1. Due to shape of a GEM hole• Charge up of the insulator surface

inside the hole.2. Due to nature of insulator3. Due to surface conditions

Possible reason Possible reason

Measurement condition

•VGEM is kept constant during the measurement.

•Rate of signals is 3Hz for all measurements.


9/18

Gain Stability ②Gain Stability ②All 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)

•CERN-GEM

•Increase 15% (Ar/CH4)

•Increase 45% (Ar/CO2)

Without charge-up


10/18

Gain Stability ③Gain Stability ③SciEnergy-GEM has a much better gain stability than CERN-GEM.

10m from hole edge

SciEnergy-GEMCERN-GEM

The electric field near the hole edge is distorted due to a bulge of a insulator for CERN-GEM.

→Probability of charging-up is higher for CERN-GEM than SciEnergy-GEM.

Drift direction of electron

E [V/cm]

Electric field inside a GEM hole

VGEM=350V


11/18

VVGEMGEM Dependence of Gain Dependence of GainSciEnergy-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.


12/18

Development of 150m-GEM−Feature of 150m-GEM

−Electric field of 150m-GEM

−Gain of 150m-GEM

−Multiplication factor

−Gain Stability


13/18

Feature of 150Feature of 150m-GEMm-GEMThe dry etching technique can allow to fabricate a thicker GEM (Thick-GEM) than Standard-GEM (insulator thickness:50m).−150m-GEM is comparable to a triple layer structure of Standard-GEM with respect to the total length of a hole.

•Larger effective path length for multiplication

•Less effect of transmission efficiency

Advantage of 150m-GEM 150150m-GEM is expected m-GEM is expected to multiply electrons to multiply electrons more effectively than more effectively than triple layer structure of triple layer structure of Standard-GEM.Standard-GEM.

150m

70m

140m

• Cu(8m) + LCP(150m) + Cu(8m)

• = 70m

• hole pitch = 140m

Structure of 150m-GEM

*LCP:Liquid Crystal Polymer


14/18

Electric Field of 150Electric Field of 150m-GEMm-GEMVGEM/50m=250V/50m

>0

The electric field of Thick-GEM is much stronger than that of Standard-GEM.

→Especially, 150m-GEM reaches plateau for about 50m.150150m-GEM should have a better multiplication ability m-GEM should have a better multiplication ability

than Standard-GEM.than Standard-GEM.

● 150m-GEM VGEM=750V

● 100m-GEM VGEM=500V

● Standard-GEM (50m) VGEM=250V

Electric field through the hole center


15/18

Gain of 150Gain of 150m-GEM m-GEM

Standard-GEM

100m-GEM

150m-GEM

Gainat 300V/50m

Magnification Ratio

3.9 x104

1.0 x103

30

3.6 x102

1.3 x103

1.0

→(Gain100m-GEM)3/2

Tamagawa-san’s result

•150m-GEM had a continuous discharge at 270V/50m.(Gain~4000)

150150m-GEM can attain much higher Gain than m-GEM can attain much higher Gain than Standard-GEM at the same VStandard-GEM at the same VGEMGEM/50/50m.m.

Gain for Standard-GEM is obtained by triple GEM structure.

Ar(70%)/CO2(30%)


16/18

Multiplication FactorMultiplication Factor

layers ofNumber :

efficiencyon Transmissi:

factortion Multiplica:

/1

n

M

GainMMGain

T

T

nn

T

Simulation results of the transmission efficiency is used.

■150m-GEM (M150):T150=0.17

■100m-GEM (M1003/2):T100=0.34

■Standard-GEM (M503):T50=0.24

As expected from the electric field inside a hole, 150As expected from the electric field inside a hole, 150m-GEM m-GEM has the highest multiplication factor.has the highest multiplication factor.

EI is stronger than for Standard-GEM and 150m-GEM.


17/18

Gain Stability of 150Gain Stability of 150m-GEMm-GEM

Ar(90%)/CH4(10%)

•The rate of signals = 2.5Hz

•VGEM=230V

Gain of 150Gain of 150m-GEM is stable within 1.0% for 9 hours.m-GEM is stable within 1.0% for 9 hours.→150150m-GEM has a good gain stability as well as m-GEM has a good gain stability as well as Standard-GEMStandard-GEM


18/18

SummarySummary•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.

•150m-GEM has been fabricated successfully using dry etching.

−Electric field of 150m-GEM is much stronger than that of Standard-GEM.

−150m-GEM has much higher gain and multiplication ability with a good gain

stability than a triple layer structure of Standard-GEM.


19/18

Back up


20/18

Applications 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.


21/18

),(),(1

ion

ET

P

T

P

R

NENN A

dxx

T

P

T

P

R

NdxxGain A ),(exp)(exp

From the equation of state,

T

P

R

NN A

eTemperatur:

Pressure:

constant Gas:

ionizationfor section Cross:

number sAvogadro':

densitynumber Particle:

ionizationfor path freeMean :

tcoefficien TownsendFirst :

ion

T

P

R

N

N

A

The expected relation between Gain and P/T should be exponential.

Relation between Gain and P/TRelation between Gain and P/T


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.


23/18

Potential Distribution of GEM holePotential Distribution of GEM holeThe electric field inside the GEM hole was calculated using Maxwell 3D.

Potential distributions are very similar in both cases.

The calculation was carried out for two type of GEM.

•Bi-conical (CERN-like)

•Cylindrical (SciEnergy-like)

VGEM=350V

Bi-conical Cylindrical


24/18

Electric Field inside GEM holeElectric Field inside GEM holeHole center 10m from hole edge

Drift direction of electron

Although there is little difference between them at hole Although there is little difference between them at hole center, the electric field of Bi-conical near the hole edge is center, the electric field of Bi-conical near the hole edge is distorted due to a bulge of a insulator.distorted due to a bulge of a insulator.


25/18

Simulation of AvalancheSimulation of AvalancheThe 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

electrons

Gain can be defined as a following equation.

layers ofNumber :

efficiencyon Transmissi:

factortion Multiplica:

n

M

MGain

T

nT


26/18

Behavior of ElectronsBehavior of ElectronsCreated point of electron Number of created electron Lost point of electron

GEM

•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.

Gain


27/18

Gain Gain

Simulation results are qualitatively consistent with measured result, but they are quantitatively inconsistent.

3

1

triplesingle GainGain

It is needed to improve the calculation method It is needed to improve the calculation method in multiplication inside a GEM hole.in multiplication inside a GEM hole.

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.


28/18

Setup for Measurements of 150Setup for Measurements of 150m-GEMm-GEM

• ED = 0.5kV/cm

• VI = VGEM/3


29/18

Gain of 150Gain of 150m-GEM (Ar/CHm-GEM (Ar/CH44))

1/18 01/26/2007mpgd workshop in saga (yorito yamaguchi, cns, univ. of tokyo) 東大 cns における...

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