GEM R&D Efforts at CNS

GEM R&D Efforts at CNS

Hideki Hamagaki

Center for Nuclear StudyUniversity of Tokyo

2007/03/23 GEM workshop with Sauli@RIKEN 2

Contents• Recollection of Early Days

– Motivation– Getting started– Making GEMs

• GEM application– GEM-TPC– HBD

• GEM characteristics and performances– Gain variation– Gain dependence on P/T– Ion feedback– Making it thicker

• Summary and outlook


What was the Motivation?

•PHENIX Upgrade of Inner Detectors– Discussions started in 2001– HBD/TPC hybrid using CF4 gas & GEM


Requirements from Physics

• Low-mass e+e- pairs– better rejection power for e+e- pairs from Dalitz decay and photon

external conversions– low-mass vector mesons -> chiral symmetry restoration– thermal pairs

• Better tracking capability


Effort Has Begun in 2002

•M. Inuzuka joined my group– A main player of GEM development for 3 years until he

got a permanent research position at Department of Conservation Science, National Research Institute for Cultural Properties, Tokyo ( 東京文化財研究所・保存科学部 )

• Intimate collaboration with Toru Tamagawa•Having started with CERN-GEM

– learn what is GEM– purchase GEMs from CERN– building test setup


First Try with CERN-GEM

• July 2002: Gas chamber & July 2002: Gas chamber & readout pad designreadout pad design

• Aug. 2002: fabricationAug. 2002: fabrication• Sep. 2002: test with a RI Sep. 2002: test with a RI

sourcesource

Drift Plane

GEM 2

GEM 1

2mm

2mm

3mm

1MΩ

1MΩ

1MΩ

1MΩ

HV 1 (-1.5~-2.2kV)

HV 2 (-1.4~-1.6kV)


Signal Amplification• In the fall of 2002; the first signal from CERN-

GEM ever seen in Japan

VGEM=400V (HV2=-1600V), HV1=-2200VVGEM=390V (HV2=-1560V), HV1=-2160V


ADC Distributions•Double-GEM

• Tripple-GEM

P10VGEM=395VEd=2kV/cm

ArCO2

VGEM=445VEd=2kV/cm

P10VGEM=335VEd=2kV/cm

ArCO2

VGEM=380VEd=2kV/cm

CF4VGEM=535VEd=0.3kV/cm


Gain vs. VGEM

● 3-GEM, P10 ▲ 2-GEM, P10● 3-GEM, ArCO2 ▲ 2-GEM, ArCO2

● 3-GEM, CF4

S.Bachmann et al. Nucl. Instr. and Meth.A438(1999)376

Weizmann Institute of Science; December, 2002


Making GEM with a Dry Etching Method

• Need to make GEM in Japan– convenience for further studies– variations & optimization

• Look for a capable company– Found a company in the fall of 2002– Fuchigami Micro (now SciEnergy) ha

s expertise on the dry etching technologies

– ended up with a method different from CERN

• Some results by the spring of 2003

– (NIM A525, 529, 2004)

CERN

Fuchigami Micro

70μm

70μm


Characterstics of Early CNS-GEM•Comparable gain to

CERN-GEM

•Many have problems –Low resistance or sparks at low HV

–Lower breakdown point than CERN-GEM


Improvement of CNS-GEM

•Efforts to improve resistance and to reduce sparks at initial HV-on– cleaning & desmear process– desmear; not needed in wet etching,

but crucial in dry etching

•Breakdown voltage– Over-hung of Copper edges– Reduction of over-hung by the spring

of 2004

CERN-GEM

CNS-GEM


Test of Gain Variation

• Gain measurement with Fe55 source

• Gain of CNS-GEM seems to stabilize in shorter time

• Difference may be due to the difference in the hole shape?

• Many possibilities– hole shape– insulation material/surface

Blue : CERN-GEMCERN-GEM （（ Gas : Gas : flowflow））

Black: CNS-GEMCNS-GEM （（ Gas : noflowGas : noflow ））

Red:Red: CNS-GEM(Gas: flow) CNS-GEM(Gas: flow)


Development of GEM-TPC• Normal TPC uses MWPC for electron multiplication• Use GEM (Gas Electron Multiplier) instead of

MWPC


Advantage of GEM-TPC• Ion Feedback to drift region can be smaller

– Requirement to gating grid is less demanding

• Signals can be shorter because of no tail from ions• E x B effect is less because of uniform E field

parallel to B expect in a tiny region near GEM holes

• Flexible arrangement of readout pads is possible

-> Better position resolution & two-particle separation 　　　　

• R&D for ILC is under way (talk by A. Sugiyama)


Building GEM-TPC prototype• Original TPC with MWPC was developed

by T. Isobe & K. Ozawa in 2002 ~ 2003 (NIM A564, 190, 2006)

• Modified by S.X. Oda to use GEM in 2003 ~ 2004 (NIM A566, 312, 2006)

• Two types of readout pads– rectangular & chevron type– 1.09 mm x 12 mm

• Charge-sensitive pre-amp– 1 s time-constant

• Readout with 100 MHz FADC


FEE & DAQ development• Charge sensitive Pre-amp

– 1pF feedback capacitance– 100 difference drive

• FADC( 林栄精器 RPV-160)– 100MHz sampling rate– 8bit dynamic range

• Original DAQ System (By T. Isobe)– CES RIO3 module to control VME bus

• PowerPC on board CPU• 100 MBytes/s bandwidth on VME

– Linux base VMEDAQ

TPC Pre-amp


Typical signals from GEM-TPC

Time (6.4s=640bin, 1bin=10ns)

With 100 MHz FADCGas = Ar-C2H6 Drift length = 85mm Rectangular padBeam = 1 GeV/c electron from KEK-PS in May 2004

Track


Performance of GEM-TPC (I)

•Position resolution– x direction– z direction– resolution gets worse with

increase of drift length•diffusion effect •magnitude depends on gas

species

CF4

Ar+C2H6(30%)

P10

R : P10 chevronB : P10 rect.Y : Ar+C2H6 rect.G : CF4 chevron

Electric field

(V/cm)

Drift velocity(cm/s)

Diffusion(T)@1cm

(m)

Diffusion(L)@1cm

(m)

Ar(90%)+CH4(10%)

130 5.5 570 360

Ar(70%)+C2H6(30%)

390 5.0 320 190

CF4 570 8.9 110 80


Performance of GEM-TPC (II)

•Energy loss measurement– P10: (55Fe;5.9 keV) = 11 %

•Ne(primary) ~ 222 for 5.9keV X-ray in P10 ~1.7 times larger than statistical estimate

– obtained energy loss is as expected for various particles with different momentum

•Beam rate effect– no change up to 5000 cps/cm2– good enough for HI applications– further studies may be needed

Z direction

R : P10 chevronB : P10 rectangular

36 mm of P10 gasdrift length = 85mm


UV Photon Detection• Effort was started in the fall of 2

003, by M. Inuzuka, and was succeeded by Y. Aramaki, backed up by Yokkaichi & Ozawa (2005 ~ 2006)

• CsI photo-cathode• CF4 gas

– Cherenkov radiator• large index of refraction• transparent down to low

– Electron multiplication– no window in between; transmissio

n, material

• Ne(Cherenkov) > Ne(ionization)


CsI Photo-cathode•Nickel and Gold are plated

on to Copper, before CsI evaporation– prevent CsI + Cu chemical r

eaction

•Development of Al-GEM– tried a few times– no success so far (spring of

2007)


Additional Complications

•Absorption of UV photons ( ~ 120 ~ 200 nm) by oxygen and water– oxygen < 10 ppm; water < 15ppm for transmission of

more than 95 % for L = 36 cm

•Care for deliquescence of CsI– water contamination in radiator gas– handling procedure of GEM setup– reserve of CsI


QE Measurement of CsI

Cut off CO2 ~ 7.2 eV CH4 ~ 8.5 eV CF4 ~ 11.5 eV

• Reasonable QE() obtained by Y. Aramaki


Understanding Characteristics and Performance of GEM

•Y. Yamagachi; 2004 ~ 2006– long-term gain variation– p/T dependence– thick GEM– simulation

•S. Maki; 2005– ion feedback

•S. Sano; 2005 ~ 2006– simulation


p/T Dependence of Gain• Electron multiplication in gas

– a function of E/p, or more precisely E/n ~ ER(T/p)

• M ~ Aexp[aE/n] = Aexp[(aE/n0)(1 – n)]; n = n0 + n

T

PrGain 395.01555.10exp

T

PrGain 395.01478.16exp


Measuring Ion Feedback

Ion feedback factor: F =Ic/Ia

HV1<HV2

50mm

chamber

drift region

Pad(anode)GEM1

GEM2

GEM3

Mesh(cathode)

Shield

3mm

2mm

2mm

2mm

3mm

R

Xrays (~17keV)

Typical values: HV1=-2200V, HV2=-2100V,VGEM =350V

Mesh Current

HV1

HV2

A

A

• What to measure:– pad current: Ia– mesh current: Ic

• Parameters– VGEM ： voltage applied to e

ach GEM (V)– Ed ： electric field in the dri

ft region (kV/cm)– Et ： electric field in the tra

sfer region (kV/cm)– number of GEMs ： 1,2 or

3

Ia

Ic

Ed

ArCH4　

Pad Current


Experimental Configurations

• Voltage configuration • 3 GEM configurations

3mm 3mm3mm

2mm

2mm2mm

2mm 2mm

Triple Double Single

•Et and Ei changes together with VGEM.

•Measure F as functions ofVGEM, Ed, and Et/Ei

HV1

HV2Ed= （ HV1-HV2 ）/0.3　　　　　　　　 [kV/cm]

VGEM

　　=HV2/6[V]R

R

R

R

R

R

Eｔ

Ei

Eｔ


Dependence of Ia and Ic onVGEM

1

10

100

1000

10000

290 300 310 320 330 340 350 360

VGEM(V)

Ia,

Ic

(nA)

電流

値

- Ia(Triple)- Ia(Double)- Ia(Single)- Ic(Triple)- I (Double)ｃ- I (Single)ｃ

Ed =0.33(kV/cm)

•　 Both Ia and Ic increase exponentially with VGEM

Gain is ~700 (Triple) at VGEM =320V


Dependence of F on VGEM

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

290 300 310 320 330 340 350 360

VGEM(V)

ion

feed

back

FF(Triple)F(Double)F(Single)

Ed =0.33(kV/cm)

• F decreases with increase of VGEM

• F for triple-GEM is large compared to single- and double-GEM

• At large VGEM, F value for triple-GEM approaches those of single- and double-GEM


Dependence of F on Ed

0

0.05

0.1

0.15

0.2

0.25

0.3

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Ed(kV/ cm)

ion

feed

back

F

F(Triple)F(Double)F(Single)

VGEM =320(V)• F increases with increase of Ed

• Ion feedback is less than 5% with small Ed

• Evaluation is needed for performance at low Ed

• Pad current Ia is constant, while mesh current Ic is changing with Ed

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Ed(kV/ cm)

ion

feed

back

F

- Ia(nA)- Ic(nA)


Making it Thicker•Motivation

– Larger gain compared to using multiple thin-GEMs for the same voltage per GEM thickness

– Smaller diffusion compared to the multiple-GEMs•diffusion in the transfer region between the GEMs

Electric field along the center of a GEM hole

● 150m-GEM VGEM=750V

● 100m-GEM VGEM=500V

● Standard-GEM (50m) VGEM=250V


Making of 150m-GEM• Structure of 150m-GEM

– Cu(8 m) + LCP(150 m) + Cu(8 m)– hole pitch = 140 m, = 70 m

• Large gain as expected• Sparks at low voltage

•investigation is under way• LCP? Overhung?• limit for charge density?

• On thick-GEM, Toru Tamagawa’s talk in this afternoon


Summary and Outlook•GEM development at CNS in the last 5 years was

summed up– motivation– making GEM– R&D for applications; TPC and HBD– Basic characteristics

• long term gain variation, p/T dependence, ion feedback•making it thicker

•Development in near future– Gain variation vs material choice and hole shape– Improvement of thick-GEM performance– Coarse-grained 2D readout (1~2mm pixel)

Documents

GEM R&D Efforts at CNS