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Measurement of MPGD-TPC resolution with charge dispersion in a beam test in a magnet
Madhu Dixit TRIUMF/ Carleton University
Canada A.Bellerive, K.Boudjemline, J.Miyamato, Carleton UniversityE.Neuheimer, E.Rollin, K.Sachs, Y.Shin & S. TurnbullJ.-P. Martin University of Montreal
France D.Burke, P.Colas, A.Giganon & I.Giomataris DAPNIA CEA Saclay V.Lepeltier & Th.Zerguerras LAL Orsay
Germany R. Settles MPI (Munich)
Japan H.Kuroiwa & T.Takahashi Hiroshima UniversityK.Fujii, M.Kobayashi, T.Matsuda & H.Yamaoka KEK/IPNSY.Kato Kinnki UniversityT.Watanabe Kogakuin UniversityT.Araki, H.Fujishima, T.Higashi, , K.Kodomatsu, Saga UniversityA.Sugiyama, T.Yamamoto & Y.TanakaA.Yamaguchi Tsukuba UniversityM.Habu, S.Matsushita, K.Nakamura & O.Nito Tokyo University of
Agriculture &Technology
Vancouver Linear Collider Workshop 19-22 July 2006
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VLCW06 M. Dixit
Motivation & overview• ILC tracker goal (1/pT) ≤ 5.10-5 (GeV/c)-1
=> MPGD-TPC ∆(1/pT) ≤ 1.5 x 10-4 (GeV/c)-1
• TDR TPC: 200 pads; Tr ~ 100 m ( 2 m drift), pad size 2 x 6 mm2 => Total TPC pad count ~1.5 x 106
• R&D shows 2 mm too wide for 100 m resolution with normal readout.Ways to improve the MPGD-TPC resolution:
Under consideration - narrower 1 mm x 6 mm pads (3 x 106 total). R&D issues: High density electronics, larger heat load, TPC endcap mass etc.
Alternative: Disperse avalanche charge to improve resolution for 2 mm wide pads. Development of a TPC readout with charge dispersion in MPGDs with a resistive anode. Charge dispersion demonstrated in cosmic ray TPC tests with no magnet.
B = 1 T 4 GeV/c beam test at KEK PS in October 2005. Two TPCs: MP TPC (MPI Munich, Saclay, SAGA, KEK) with GEMs & Micromegas & Canadian TPC with Saclay Micromegas. Update of results reported at LCWS 2006 Bangalore. Progress in simulation. Summary & outlook.
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VLCW06 M. Dixit
•Modified MPGD anode with a high resistivity film bonded to a readout plane with an insulating spacer.•2-dimensional continuous RC network defined by material properties & geometry.•Point charge at r = 0 & t = 0 disperses with time.•Time dependent anode charge density sampled by readout pads.
t
1
RC
2r2
1
r
r
(r, t) RC
2t
r 2RC
4 te
(r,t) integral over pads
(r) Q
r / mmmm ns
Charge dispersion in a MPGD with a resistive anode
Equation for surface charge density function on the 2-dim. continuous RC network:
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VLCW06 M. Dixit
50 m pillars
Drift Gap
MESHAmplification Gap
Al-Si Cermet on mylar
Micromegas with a resistive anode for the charge dispersion readout
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VLCW06 M. Dixit
The two beam test TPCs
- Micromegas 10 x10 cm2
- Drift distance: 16 cm
- 126 pads, 2 x 6 mm2 each in 7 rows-ALEPH preamps + 200 MHz FADCs rebinned to 25 MHz
-Micromegas & GEMs 10 x10 cm2
-Drift distance 25.9 cm
- 384 pads 2.3 x 6.3 mm2 each in 16 rows-ALEPH preamps + 11 MHz AlephTime Projection Digitizers
Carleton TPC MP TPC
Charge dispersion readout endplate
Micromegas
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VLCW06 M. Dixit
•4 GeV/c hadrons (mostly πs)
•0.5 & 1 GeV/c electrons
•Super conducting 1.2 T magnet without return yoke
•Inner diameter : 850 mm
•Effective length: 1 m
KEK PS 2 test beam set up with Carleton & MP TPCs Beam data taken both in & outside the magnet for the two TPCs
Carleton TPC in the beam outside the magnet
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VLCW06 M. Dixit
Track display - Ar+5%iC4H10 Micromegas 2 x 6 mm2 pads B = 1 T
Zdrift = 15.3 cm
main pulse7
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VLCW06 M. Dixit
The pad response function (PRF) - a measure of pad signal as a function of track position
Khalil Boudjemline CAP Congress 2006
rela
tive
am
plit
ude
15.7 cm
6 < z < 7cm
8 < z < 9cm
10< z < 11cm
12 < z < 13cm
14 < z < 15cm
4 < z < 5cm
2 < z < 3cm
0 < z < 1cm
xpad-xtrack / mm
TPC
44
22
44
22
1
1],,),(,[
xbxb
xaxabazxPRF
Ar/iC4H10 95/5
•PRF determined empirically from self consistency of track data.
•PRF parameterized in terms of FWHM & base width
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VLCW06 M. Dixit
Track fit using the PRF
Determine x0 & by minimizing
for the entire event
2 mm
6 mm
Track at: xtrack= x0+ tan() yrow
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2
2
rows padsi i
ii
A
PRFA
Definitions:
- residual: xrow-xtrack
- bias: mean of xrow-xtrack = f(xtrack)
- resolution: of the residuals
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VLCW06 M. Dixit
Bias for central rows / Ar+5%iC4H10 B = 1 T
xtrack / mm (± 14 mm)
Res
idua
l / m
m (
± 0.
15 m
m)
bias before bias remaining
± 20 m
correction
row 4
row 5
row 6
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VLCW06 M. Dixit
Extrapolate to B = 4TUse DTr = 25 µm/cm
Resolution (2x6 mm2 pads) Tr 100 m (2.5 m drift)
Transverse spatial resolution Ar+5%iC4H10 E=70V/cm DTr = 125 µm/cm (Magboltz) @ B= 1T
x 02
Cd2 z
Neff
4 GeV/c + beam = 0°, = 0°
0= (53±3) m Neff = 211 (stat.)
Micromegas+Carleton TPC 2 x 6 mm2 pads
•Strong suppression of transverse diffusion at 4 T.Examples:DTr~ 25 m/cm (P10)
~ 20 m/cm (Ar/CF4 97/3)
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VLCW06 M. Dixit
Ar+5%iC4H10 4 GeV/c + beam B = 1 T
0=175 m, Nef=22
pad plane
=0°=10°
track
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Is extrapolating high-gain 0 Ar/C4H10 data to ILC-TPC operating conditions credible? Effect of track angles & gain on resolution
Gain for Ar/C4H10 was ~ 2 times larger than for ArCO2
Significantly worse 0 for 10° tracks for Ar/C4H10 than 0°
0= 53 m Neff = 21<> ~ 16°, -5°< <5° 0= 70 m, Neff = 28
Ar+10%CO2, Cosmics, B = 0 T
2 x 6 mm2 pads Gain ~ 8000 2 x 6 mm2 pads, Gain ~ 3500
0°
10°
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VLCW06 M. Dixit
Track angle effect is mostly due to clusteringtrack = 0°
clusters
6 mm
2 mm
track = 10°
x
y
-For angled tracks, y centroid wanders due to ionization clustering. -y centroid movement affects x centroid position.
00
clusters
cclusters
cc NeNexx /
x centroid
x / mm
= 120 m
Ar/iC4H10 95/5B = 1 T
Clustering only
= 124 m
Ar/iC4H10 95/5B = 1 T
Clustering only
Clustering+ gain
fluctuation
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To the track angle effect, one must add 0 50 m for noise & systematics
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VLCW06 M. Dixit
Re-analyze Ar/CO2 90/10 cosmic ray data for track angles
2 x 6 mm2 pads, DTr =223 m/cm B = 0 T
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For < 1.5° 0= 50 m! Gain ~ 2 times lower than Ar/C4H10
Track angle effect similar to that observed for Ar/C4H10
range
pad plane
track
< 1.5° < 1.5°
1.5° < < 5.0° <
1.5°
1.5° < < 5.0°
5.0° < < 8.0°
< 1.5°
1.5° < < 5.0°
5.0° < < 8.0°
8.0° < < 11.0°
< 1.5°
1.5° < < 5.0°
5.0° < < 8.0°
8.0° < < 11.0°
11.0° < < 14.0°
Cosmics
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VLCW06 M. Dixit
Track angle effect will be smaller for shorter pads
clusters
cclusters
cc NeNexx /
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For longer pads, this can be accomplished effectively by segmenting the cathode into ~ 2 mm width strips in y.
clusters
2 mm
2 mm
track = 10°
x
y
00
clusters
4 mm
2 mm
track = 10°
x
y
00
clusters
6 mm
2 mm
track = 10°
x
y
00
2 mm = 54 m2 mm = 54 m
4 mm = 89 m
2 mm = 54 m
4 mm = 89 m
6 mm = 120 m
clusters
8 mm
2 mm
track = 10°
x
y
00
2 mm = 54 m
4 mm = 89 m
6 mm = 120 m
8 mm = 145 m
x / mm
Ar/iC4H10 95/5B = 1 T
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VLCW06 M. Dixit
First principles TPC simulation (stand alone) Cosmic track with charge dispersion - GEM TPC
(track Z drift distance ~ 67 mm, Ar/CO2 90/10 gas)Detailed model simulation including clustering, longitudinal & transverse diffusion, gas gain, GEM pulse formation, charge dispersion & preamp rise & fall time effects.
Centre pad amplitude used for normalization - no other free parameters.
2x6 mm2 pads
Simulation
Data
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VLCW06 M. Dixit
Micromegas -TPC track PRF (histogram) versus PRF determined experimentally ( lines)
Resistivity = 1000 k/, Dielectric spacer thickness = 50 m, K = 4Intrinsic Micromegas pulse risetime = 50 ns Aleph preamp rise time = 37 ns, Fall time = 1980 ns
PRF for 5 mm drift PRF for 145 mm drift
Ar/CO2 90/10 Vdrift = 22.8 m/ns DTr=223 m/cm DL=263 m/cm
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VLCW06 M. Dixit
Summary & outlook• Successful demonstration of charge dispersion readout concept for the
MPGD-TPC in a magnetic field in a beam test. 0~ 50 m in Ar/C4H10 95/5 with 2x6 mm2 pads at B=1 T for 4 GeV/c
pions. • No loss of performance for Ar/CO2 90/10 for cosmic rays at
B = 0 T at lower gain.• Track angle effect ~ 20 m for 100 mR tracks possible with cathode
segmentation in y as 2 mm wide strips.• Extrapolation of Ar/C4H10 results to ILC-TPC should be valid.• Charge dispersion works with GEMs and Micromegas both. The ILC-
TPC resolution goal of ~100 m with 2 mm x 6 mm pads for all tracks appears feasible.
• Charge dispersion phenomena well understood. Stand alone simulation will be incorporated into GEANT4 framework.
• 4 T cosmic tests at DESY this year. Two track resolution tests at Fermilab planned for next year.
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VLCW06 M. Dixit19
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VLCW06 M. Dixit
Additional slides
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VLCW06 M. Dixit
ExB cancels track angle effect
TPC wire/pad readout
100 µm
Average Aleph resolution ~ 150 µm.Resolution ~ 100 µm even for 2 m drift.Limit from diffusion (10 cm drift) ~ 15 µm; (2 m drift) ~ 60 µm.
When there is no ExB effect, the wire/pad TPC resolution approaches the diffusion limit for the Aleph TPC
E not parallel to Bnear anodes
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VLCW06 M. Dixit
The GEM-TPC resolution was first measured with conventional direct charge TPC readout.
The resolution was next measured with a charge dispersion resistive anode readout with a double-GEM & with a Micromegas endcap.
Cosmic ray resolution of a MPGD-TPC•15 cm drift length with GEM or Micromegas readout •B=0•Ar:CO2/90:10 chosen to simulate low transverse diffusion in a magnetic field.•Aleph charge preamps. Rise= 40 ns, Fall = 2 s. •200 MHz FADCs rebinned to digitization effectively at 25 MHz.•60 tracking pads (2 x 6 mm2) + 2 trigger pads (24 x 6 mm2).
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VLCW06 M. Dixit
Measured TPC transverse resolution for Ar:CO2 (90:10) R.K.Carnegie et.al., NIM A538 (2005) 372
R.K.Carnegie et.al., to be published
Unpublished
Compared to conventional readout, resistive readout gives better resolution for the GEM and the Micromegas readout. The z dependence follows the expectations from transverse diffusion & electron statistics.
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