GEM R

1
GEM RD Efforts at CNS

• Hideki Hamagaki
• Center for Nuclear Study
• University of Tokyo

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

3
What was the Motivation?

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

4
Requirements from Physics

• Low-mass ee- pairs
• better rejection power for ee- pairs from Dalitz
  decay and photon external conversions
• low-mass vector mesons -gt chiral symmetry
  restoration
• thermal pairs
• Better tracking capability

5
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
  (?????????????)
• Intimate collaboration with Toru Tamagawa
• Having started with CERN-GEM
• learn what is GEM
• purchase GEMs from CERN
• building test setup

6
First Try with CERN-GEM

• July 2002 Gas chamber readout pad design
• Aug. 2002 fabrication
• Sep. 2002 test with a RI source

7
Signal Amplification

• In the fall of 2002 the first signal from
  CERN-GEM ever seen in Japan

VGEM400V (HV2-1600V), HV1-2200V
VGEM390V (HV2-1560V), HV1-2160V
8
ADC Distributions

• Double-GEM
• Tripple-GEM

9
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
10
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) has 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
70µm
Fuchigami Micro
70µm
11
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

12
Improvement of CNS-GEM
CERN-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

CNS-GEM
13
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-GEM(Gas flow)
Black CNS-GEM(Gas noflow) Red CNS-GEM(Gas
flow)
14
Development of GEM-TPC

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

15
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
• -gt Better position resolution two-particle
  separation
• RD for ILC is under way (talk by A. Sugiyama)

16
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 ms time-constant
• Readout with 100 MHz FADC

17
FEE DAQ development

• Charge sensitive Pre-amp
• 1pF feedback capacitance
• 100W difference drive
• FADC(????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
18
Typical signals from GEM-TPC
With 100 MHz FADC Gas Ar-C2H6 Drift length
85mm Rectangular pad Beam 1 GeV/c electron
from KEK-PS in May 2004
Time (6.4ms640bin, 1bin10ns)
Track
19
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

P10
ArC2H6(30)
CF4
Electric field (V/cm) Drift velocity (cm/ms) Diffusion (T)_at_1cm (mm) Diffusion (L)_at_1cm (mm)
Ar(90)CH4(10) 130 5.5 570 360
Ar(70)C2H6(30) 390 5.0 320 190
CF4 570 8.9 110 80
R P10 chevron B P10 rect. Y ArC2H6 rect. G
CF4 chevron
20
Performance of GEM-TPC (II)
36 mm of P10 gas drift length 85mm

• Energy loss measurement
• P10 s(55Fe5.9 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

21
UV Photon Detection

• Effort was started in the fall of 2003, 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 l
• Electron multiplication
• no window in between transmission, material
• Ne(Cherenkov) gt Ne(ionization)

22
CsI Photo-cathode

• Nickel and Gold are plated on to Copper, before
  CsI evaporation
• prevent CsI Cu chemical reaction
• Development of Al-GEM
• tried a few times
• no success so far (spring of 2007)

23
Additional Complications

• Absorption of UV photons ( 120 200 nm) by
  oxygen and water
• oxygen lt 10 ppm water lt 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

24
QE Measurement of CsI

• Reasonable QE(l) obtained by Y. Aramaki

Cut off CO2 7.2 eV CH4 8.5 eV CF4 11.5
eV
25
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

26
p/T Dependence of Gain

• Electron multiplication in gas
• a function of E/p, or more precisely E/n
  ER(T/p)
• M AexpaE/n Aexp(aE/n0)(1 dn) n n0
  dn

27
Measuring Ion Feedback
Xrays (17keV)
Ion feedback factor F Ic/Ia
chamber
ArCH4
50mm
Mesh Current
Shield

• What to measure
• pad current Ia
• mesh current Ic
• Parameters
• VGEMvoltage applied to each GEM (V)
• Edelectric field in the drift region (kV/cm)
• Etelectric field in the trasfer region (kV/cm)
• number of GEMs1,2 or 3

Ic
3mm
HV1
Mesh(cathode)
drift region
3mm
Ed
HV2
GEM3
2mm
GEM2
2mm
R
GEM1
Pad(anode)
2mm
Pad Current
HV1ltHV2
Ia
Typical values HV1-2200V, HV2-2100V,VGEM 350V
28
Experimental Configurations

• 3 GEM configurations

• Voltage configuration

• Et and Ei changes together with VGEM.
• Measure F as functions ofVGEM, Ed, and Et/Ei

29
Dependence of Ia and Ic onVGEM
Ed 0.33(kV/cm)
Gain is 700 (Triple) at VGEM 320V

• Both Ia and Ic increase exponentially with VGEM

30
Dependence of F on VGEM
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

31
Dependence of F on Ed
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

32
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
• 150mm-GEM VGEM750V
• 100mm-GEM VGEM500V
• Standard-GEM (50mm) VGEM250V

33
Making of 150mm-GEM

• Structure of 150mm-GEM
• Cu(8 mm) LCP(150 mm) Cu(8 mm)
• hole pitch 140 mm, f 70 mm

• Large gain as expected
• Sparks at low voltage
• investigation is under way
• LCP? Overhung?
• limit for charge density?
• On thick-GEM, Toru Tamagawas talk in this
  afternoon

34
Summary and Outlook

• GEM development at CNS in the last 5 years was
  summed up
• motivation
• making GEM
• RD 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 (12mm pixel)