Study of a charge distribution on a readout board with a triple GEM chamber

MPGD group T. Uchida, M. Sekimoto, T. Murakami, M. Tanaka, S. Tanaka,

N. Ujiie, and K. Nakayoshi (KEK)K. Kadomatsu and A. Sugiyama (Saga University )

E. Nakano and S. Nakagawa (Osaka City University) 　

Shoji Uno (KEK)KEK Detector Technology Project　

October 31st , 2006

Contents

• GEM foils made by Japanese company

• Effective Gas gain as a function of various parameters

• VGEM, ED, ET,EI, gI

• Gas mixture: Ar-CH4(90/10) (P10)

Ar-CO2(70/30)

• Charge distribution on a readout board

GEM foils made by Japanese company• New method (plasma etching) was tried in a

few years ago. – Not chemical etching (CERN) – M. Inuzuka, et al.,

NIM A 525(2004) 529-534 • Plasma + Laser

– To reduce sparks • It is convenient for us to make new types of

GEM foils.– Fine pitch/small hole : 50m/30m– Thicker/thinner : 100(150)m/ 25m – Other activities in Japan

• Univ. of Tokyo• RIKEN • etc

• Today, I will report on results with standard GEM foils.– 50m thick – 140m pitch 70m diameter

10cm

10cm

Scienergy Co., Ltd. (Japanese company)http://www.scienergy.jp/

Chamber Structure

gI(1 mm)

gD ( 4 mm)

GEM1

GEM2

GEM3gT2(2 mm)

gT1(2 mm)

55Fe (5.9 keV X-ray)

Cathode

Strip

0.5kV/cm

1.75kV/cm

1.75kV/cm

3.5kV/cm

Drift region

Transfer1 region

Transfer2 region

Induction region

Ar-CO2

ΔVGEM ＝ 370V

P10ΔVGEM ＝ 330V

Effective gas gain vs ΔVGEM

Ar-CO2

P10

Gas gain vs various parameters

P10

Ar-CO2

Ar-CO2

Ar-CO2

P10

P10

Ar-CO2

EDEI

ETEI

Readout strip

• Readout strip

– Strip pitch ： 200 m

– width 　　　 ： 100 m 　– gap 　 ： 100 m 　– length : 50mm

– Number of strips = 64

Zoom up view100m

100m

200m

　 Read out system

RPN220× ４

ADC 2249W× ６

CCNET

GATE

GATE

BUSY

Fanin Fanout

Gate Gen.

GATE

GATE

120 μsdelay

VETO

Disc.

RPN220

Belle-CDCPre-amp. ×4

Belle-CDCPre-amp.

30 m

0.5 m

Strip

Foil

Pulse Trans.

CAMACSystem

　 One 　 Event 　 Display

Channel

AD

C

0 63

AD

C

0 63Channel

ΔVGEM＝ 370V

Ed= 0.5 kV/cm

Et=2.59kV/cmEi=5.18 kV/cm

ΔVGEM＝ 370V

Ed= 0.5 kV/cm

Et=2.59kV/cmEi=5.18 kV/cm

= 181.2± 0.3 m = 181.2± 0.3 m

Ar-CO2(70/30)

Charge distribution

-1 0 1

Triple GEM gD, gT1, gT2, gI=1.5, 1, 1, 1mm

dX （ each strip － COG) ｍｍ

= 359.7±0.4 m = 359.7±0.4 m

P10

ΔVGEM＝ 330V

Ed= 0.5 kV/cm

Et=1.65 kV/cmEi= 3.3 kV/cm

ΔVGEM＝ 330V

Ed= 0.5 kV/cm

Et=1.65 kV/cmEi= 3.3 kV/cm

ADC

SUMADC

-1 0 1

Measurement results for a gauss fit in a charge distribution Unit : mm

GEM structure Total gap P10 Ar-CO2

Triple gD,gT1,gT2,gI = 4, 2, 2, 1 7 0.465

gD,gT1,gT2,gI = 1.5, 2, 2, 1 5.75 0.417 0.207

gD,gT1,gT2,gI = 1.5, 1, 1, 2 4.75 0.390 0.203

gD,gT1,gT2,gI = 1.5, 1, 1, 1 3.75 0.343 0.181

Double gD,gT1,gI= 1.5, 2, 1 3.75 0.340 0.173

gD,gT1,gI = 1.5, 1, 1 2.75 0.157

Total gap : gD/2 + (gT1+ gT2 ) + gI

Charge spread

y = 0.2979x + 0.0016

y = 0.0668x + 0.0062

y = 0.3416x - 0.0078

y = 0.0441x + 0.00230

0.05

0.1

0.15

0.2

0.25

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Total depth(cm)

σ2 (

mm

2)

P10P10

Ar-CO2Ar-CO2

Data

MagBoltz

2 (m

m2 )

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 1 2 3 4

/ cm)電場（ｋｖ

σ2 (m

m2 )MagBoltz 　 vs. 　 Measurement

Data

P10P10

Ar-CO2Ar-CO2

Data

MagBoltz

Electric field in transfer region (kV/cm)

Summary• Japanese company can produce GEM foils with

new methods ( Plasma or (and) Laser ).

• GEM chamber has been constructed and tested.

• Effective gas gain was measured for various parameters.

• Charge distribution was measured. It is consistent with naive estimation from diffusion without GEM structure.