Micromegas TPC prototype results

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Micromegas TPC prototype results Electronics
Developments

• Madhu Dixit
• Carleton University TRIUMF
• On behalf of LC TPC collaboration

• ILC tracking review - Beijing 5 February, 2007

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Micro-Pattern Gas Detector development for the
ILC TPC

• ILC tracker goal ?r? 100 ?m including stiff
  90 2 m drift tracks
• Anode wire/cathode pad TPC resolution limited by
  ExB effects
• Negligible ExB effects for Micro Pattern Gas
  Detectors (MPGD)
• TESLA TPC TDR 2 mm x 6 mm pads (1,500,000
  channels) with GEMs or Micromegas
• LC TPC RD 2 mm pads too wide with conventional
  readout
• For the GEM 1 mm wide pads (3,000,000
  channels)
• Even narrower pads would be needed for the
  Micromegas
• The new MPGD readout concept of charge dispersion
  can achieve good resolution with 2 mm x 6 mm
  pads.
• RD summary - mainly on the Micromegas TPC
  readout option

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Micromegas - a parallel plate gas avalanche
detectorMicromesh supported by 50 ?m pillars
above anode
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Berkeley Orsay Saclay cosmic ray TPC tests
2 T superconducting magnet
1 mm x 10 mm pads
50 cm diameter Micromegas, 50 cm max. drift
distance 1024 read out pads, Star TPC 20 MHz 10
bit digitizers
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4 Gev/c beam tests at KEK with standard readout
(2.3 mm x 6.3 mm pads)
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MP TPC with Micromegas - standard readoutKEK PS
4 Gev/c hadron test beam (2.3 mm x 6.3 mm pads)
Resolution limited by pad width at high magnetic
fields, worst at short drift distances
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Improving MPGD resolution without using narrower
pads

• Disperse track charge after gas gain to improve
  centroid determination with wide pads.
• For the GEM, large transverse diffusion in the
  transfer induction gaps provides a natural
  mechanism to disperse the charge.
• No such mechanism for Micromegas
• The GEM readout will still need 1 mm wide pads
  to achieve 100 ?m ILC resolution goal

Charge dispersion on a resistive anode - a
mechanism to disperse the MPGD avalanche charge.
It makes position sensing insensitive to pad
width. The technique works for both the GEM and
the Micromegas
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Charge dispersion in a MPGD with a resistive anode

• 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.

Equation for surface charge density function on
the 2-dim. continuous RC network
?(r)
Q
?(r,t) integral over pads
mm
ns
M.S.Dixit et.al., Nucl. Instrum. Methods A518
(2004) 721.
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Micromegas resistive anode readout structure
Surface resistivity 1 M?/?
25 ?m Al/Si coated mylar
Drift Gap
MESH
50 ?m pillars
Amplification Gap
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Cosmic ray TPC tests with MPGD charge dispersion
readout

• 15 cm drift length with GEM or Micromegas
  readout
• B0
• Ar10 CO2 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).

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.
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Charge dispersion pulses pad response function
(PRF)

• Non-standard variable pulse shape both the rise
  time pulse amplitude depend on track position.
• The PRF is a measure of signal size as a function
  of track position relative to the pad.
• We use pulse shape information to optimize the
  PRF.
• The PRF can, in principle, be determined from
  simulation.
• However, system RC non-uniformities geometrical
  effects introduce bias in absolute position
  determination.
• The position bias can be corrected by
  calibration.
• PRF and bias determined empirically using a
  subset of data used for calibration. Remaining
  data used for resolution studies.

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GEM Micromegas track Pad Response Functions
Ar10CO2 2x6 mm2 pads
The pad response function (PRF) amplitude for
longer drift distances is lower due to Z
dependent normalization.
GEM PRFs
Micromegas PRFs
Micromegas PRF narrower due to higher resistivity
anode smaller diffusion than in GEM after
avalanche gain.
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Track PRFs with GEM Micromegas readout
The PRFs are not Gaussian. The PRF depends on
track position relative to the pad. PRF
PRF(x,z) PRF can be characterized by FWHM ?(z)
base width ?(z). PRFs determined from the data
parameterized by a ratio of two symmetric 4th
order polynomials.
a2 a4 b2 b4 can be written down in terms of ?
and ? two scale parameters a b.
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Track fit using the the PRF
Track at xtrack x0 tan(?) yrow
Determine x0 ? by minimizing ?2 for the entire
event

• Definitions
• - residual xrow-xtrack
• bias mean of xrow-xtrack f(xtrack)
• resolution standard deviation of residuals

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Bias corrections for the GEM for Micromegas
Initial bias
Initial bias
Remaining bias after correction
Remaining bias after correction
2x6 mm2 pads
2x6 mm2 pads
Micromegas
GEM
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Transverse resolution (B0) - Cosmic Rays
Ar10CO2
R.K.Carnegie et.al., NIM A538 (2005) 372
K. Boudjemline et.al., NIM A - in press
A. Bellerive et al, LCWS 2005, Stanford
Compared to conventional readout, charge
dispersion gives better resolution for the GEM
and the Micromegas.
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Track display - Ar5iC4H10 KEK 4 GeV/c hadrons
Micromegas 2 mm x 6 mm pads B 1 T
main pulse
Zdrift 15.3 cm
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Pad Response Function / Ar5iC4H10
MicromegasCarleton TPC 2 x 6 mm2 pads, B 1 T
30 z regions / 0.5 cm step
0 lt z lt 0.5 cm
0 .5 lt z lt 1 cm
1 lt z lt 1.5 cm
1.5 lt z lt 2 cm
2 lt z lt 2.5 cm
2.5 lt z lt 3 cm
3 lt z lt 3.5 cm
3.5 lt z lt 4 cm
4 lt z lt 4.5 cm
4.5 lt z lt 5 cm
5 lt z lt 5.5 cm
5.5 lt z lt 6 cm
normalized amplitude
6 lt z lt 6.5 cm
6.5 lt z lt 7 cm
7 lt z lt 7.5 cm
7.5 lt z lt 8 cm
8 lt z lt 8.5 cm
8.5 lt z lt 9 cm
xtrack xpad / mm
4 pads / 4 mm
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Pad Response Function Ar5iC4H10
9 lt z lt 9.5 cm
9.5 lt z lt 10 cm
10 lt z lt 10.5 cm
10.5 lt z lt 11 cm
11 lt z lt 11.5 cm
11.5 lt z lt 12 cm
normalized amplitude
12 lt z lt 12.5 cm
12.5 lt z lt 13 cm
13 lt z lt 13.5 cm
13.5 lt z lt 14 cm
14 lt z lt 14.5 cm
14.5 lt z lt 15 cm
xtrack xpad / mm
4 pads / 4 mm
PRF parameters

• a b 0
• ? base width 7.3 mm
• ? FWHM f(z)

The parameters depend on TPC gas operational
details
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Bias for central rows / Ar5iC4H10 B 1 T
correction
bias before
bias after
row 4
Residual / mm ( 0.15 mm)
20 mm
row 5
row 6
xtrack / mm ( 14 mm)
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KEK beam test - Transverse resolution Ar5iC4H10
E70V/cm DTr 125 µm/?cm (Magboltz) _at_ B 1T
Micromegas TPC 2 x 6 mm2 pads

• Transverse diffusion strongly suppressed at high
  B fields.
• Examples (4 T)
• DTr 25 ?m/?cm (Ar/CH4 91/9)
  Aleph TPC gas
• 20 ?m/?cm (Ar/CF4 97/3)

4 GeV/c ? beam? 0, ? 0
Extrapolate to B 4T Use DTr 25 µm/?cm
Resolution (2x6 mm2 pads) ?Tr ? 100 ?m (2.5 m
drift)
?0 (521) mm Neff 22?0 (stat.)
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5 T cosmic tests of charge dispersion at DESY
COSMo (Carleton, Orsay, Saclay, Montreal)
Micromegas TPC
DTr 19 ?m/?cm, 2 x 6 mm2 pads
50 ?m av. resolution over 15 cm (diffusion
negligible) 100 ?m over 2 meters appears feasible
Nov-Dec, 2006
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The effect of lower gain on resolution
Gain 4700
Gain 2300
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3
4
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Sample cosmic ray tracks - data taken at high
at low gains (B 0.5 T)
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COSMo TPC transverse resolution - Cosmic rays
DESY magnet
Gain 4700 B0.5 T
Gain 2300 B0.5 T
The resolution and ?0 still good at low gain
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Gain dependence on B field for Ar5C4H10
Micromegas gain constant to within 0.5 up to 5
Tesla
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Micromegas gain with a resistive anode
Argon/Isobutane 90/10
Resistive anode suppresses sparking improves
Micromegas HV stability
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Simulating the charge dispersion phenomenon
M.S.Dixit and A. Rankin, Nucl. Instrum. Methods
A566 (2006) 281.

• The charge dispersion equation describe the time
  evolution of a point like charge deposited on the
  MPGD resistive anode at t 0.
• No standard pulse shape. For improved
  understanding to compare to experiment, one
  must include the effects of
• Longitudinal transverse diffusion in the gas.
• Intrinsic rise time Trise of the detector charge
  pulse.
• The effect of preamplifier rise and fall times tr
  tf.
• And for particle tracks, the effects of primary
  ionization clustering.

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Charge dispersion signals for the GEM
readoutSimulation vs. measurement for Ar10CO2
(2 x 6 mm2 pads) Collimated 50 ?m 4.5 keV
x-ray spot on pad centre.
Difference induced signals (MPGD '99, Orsay
LCWS 2000) were not included in simulation).
Primary pulse normalization used for the
simulated secondary pulse
Simulated primary pulse is normalized to the
data.
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GEM TPC charge dispersion simulation (B0)
Cosmic ray track, Z 67 mm Ar10CO2
2x6 mm2 pads
Simulation Data
Centre pulse used for normalization - no other
free parameters.
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Micromegas gas gain measurements at Saclay
(David Attie, EUDET Meeting, Munich 18 October,
2006)
Mixtures of gases containing argon
Mesh 50 mm gap of 10x10 size
iC4H10
Gaz froids CO2, CH4
C2H6
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New development Bulk Micromegas (2004)
I. Giomataris et al., CERN-Saclay collaboration,
NIM A 560 (2006).
Bulk Micromegas obtained by lamination of a
woven grid on an anode with two photo-imageable
films. The pillars hold the mesh on the whole
surface no frame needed.
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Advantages of Bulk Micromegas

• Large surfaces at low cost (1000 for a 34cm x
  36cm detector)
• Almost no dead area
• Very robust (robust mesh held everywhere)
• Insensitive to dust (the mesh is dust-tight down
  to 30 µ)
• Good/excellent uniformity of the gap
• Can be segmented and repaired

pillar
New bulk development excellent resolution and
stability (KEK test Jan.07, 55Fe with no
collimation)
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Bulk Micromegas development for T2K
Bulk Micromegas is cut with a 2 mm border
Fully engineered project Minimum dead space
between panels 8 mm
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Large panel Micromegas for T2K TPCs

• T2K will have 3 TPCs
• 72 Micromegas modules
• Total area 9 m2
• 124416 readout channels

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Electronics

• Development for LP TPC based on ALICE TPC ALTRO
  digitizing electronics.
• TPC requirements highest flexibility in terms of
  pad geometry and shape of pad panels.
• Design for 1 x 4 mm2 pads
• Proposal 32 channels modules, where each channel
  corresponds to an area of around 4 mm2.
• 2000 channels of 40 MHz ALTRO chips available.
• Plans to acquire more channels - up to 10,000 for
  LP TPC tests.

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Front End and Readout Electronics
Alice TPC
power consumption lt 40 mW / channel
DETECTOR
Front End Card (128 CHANNELS)
drift region 88ms
Custom Backplane
Capton cable
8 CHIPS (16 CH / CHIP)
8 CHIPS (16 CH / CHIP)
ALTRO
gating grid
Digital Circuit
PASA
RCU
ADC
RAM
anode wire
CUSTOM IC (CMOS 0.35mm)
pad plane
557 568 PADS
CUSTOM IC (CMOS 0.25mm )
(3200 CH / RCU)

• LINEARIZATION
• BASELINE CORR.
• TAIL CANCELL.
• ZERO SUPPR.

CSA SEMI-GAUSS. SHAPER
1 MIP 4.8 fC S/N 30 1 DYNAMIC 30 MIP
10 BIT 10 MHz
MULTI-EVENT MEMORY
GAIN 12 mV / fC FWHM 190 ns
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PASA designed for wire chamber pulses with long
ion tails
Wire TPC charge pulse
Tail cancellation and shaping
Semi-Gaussian output pulse with 200 ns
integration produced for the digitizer. (base
width 450 ns)
0 2 4 6 8
10
Time (?s)
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PASA preamplifier-shaper not suitable for
MPGD-TPC readout

• Charge pulse rise times will be much longer for
  ILC TPC tracks (dominated by charge collection).
• Up to 500 ns to collect the charge due to
  longitudinal diffusion and track angles.
• ILC TPC resolution near statistical limit of
  diffusion.
• Must collect over 90 of electrons for best
  resolution.
• No optimum shaping time to achieve both good
  single hit and 2-track resolution
• Better to digitize charge pulse directly without
  shaping.

GEM charge pulse - point x ray source
(ns)
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New preamp design to replace PASA
Luciano Musa
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Luciano Musa
Programmable peaking decay times
Programmable gain
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Leif Jonsson Eudet meeting - Munich Nov. 2006
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Summary

• MPGD-TPC has difficulty achieving good resolution
  with wide pads
• With charge dispersion, the charge can be
  dispersed in a controlled way. Wide pads can be
  used without sacrificing resolution. Charge
  dispersion works both for the GEM and the
  Micromegas.
• At 5 T, an average 50 ?m resolution has been
  demonstrated with 2 x 6 mm2 readout pads for
  drift distances up to 15 cm.
• Electronics development on track
• The ILC-TPC resolution goal, 100 ?m for all
  tracks, appears feasible.