Download Recent Analysis Results from MicroMegas

D. Attié, P. Colas, M. Dixit, M. Riallot, YunHa Shin, S. Turnbull, W. Wang
and all the LC-TPC collaboration
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Wenxin.Wang_IWLC meeting 2010
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The EUDET facility at DESY Hamburg
See K.Dehmelt’s talk
 PCMAG: KEK
superconducting
magnet, 1.2 T
• e- test beam @DESY
(1GeV/c<p<6GeV/c)
SiPM Cosmic
Trigger Setup
Saclay
Moving frame
DESY
LP : part of a
TPC endplate
Cornell
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Micromegas TPC
From December 2008 to
March 2010 we tested 5
panels. One module was
installed in the centre of
the Large Prototype each
time
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Read out by T2K electronics
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5 Micromegas Modules for TPC
Module 4&5
2 Resistive Kapton
~3 MΩ/□
Resistive Kapton
Standard
~5 MΩ/□
Module 2
Resistive ink
~3 MΩ/□
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Bulk technology (à la T2K)

The mesh is held by the pillars on the whole
surface. There is not need for frame. Very robust.


A T2K ND280
TPC event (in
operation since
1 year
9 m² of bulk
Micromegas
Resistive bulk :
continuous RC circuit
to spread the charge
to improve resolution
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Test schedule

December 2009: tested modules 4 and
5 without magnetic field.

March 2010: tested modules 2 (ink) and
3 (kapton) with 1T magnetic field.

June-July 2010: data taken in a high
intensity hadron beam at CERN.
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Data analysis results (B=0T)
Vd (cm/μs)
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Drift Velocity in T2K gas
compared to Magboltz
simulations for
- P=1035 hPa
- T=19°C
- 35 ppm H20
( T2K gas: Ar:CF4:iso=95:3:2)
8
7
6
5
4
3
Simulations (Magboltz)
2
Measurements
1
0
0
100
200
300
400
Ed (V/cm)
Vdrift = 7.698 +- 0.040 cm/µs at E=230 V/cm
(Magboltz : 7.583+-0.025(gas comp.))
The difference is 1.5+-0.6 %
B=0 data : Drift velocity measurements
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Data analysis results
PRF : Pad Response Function
A measure of signal size as a function of track position relative to the
centre of the pad
The PRF:
→ is not Gaussian.
→ can be characterized by its
FWHM (z) & base Width (z),
plus another shape parameter.


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Data analysis results
Γ ~ 4 mm
δ ~ 14 mm
Γ ~ 2.6 mm
δ ~ 10 mm
B=1T data : comparison of resistive ink and Carbon-loaded Kapton
PRF(Pad Response Functions) fits, z ~ 5 cm
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Bias
Bias after
±50µm
±50µm
Bias before
Bias due to non-uniformity can be easily corrected.
(module 3 CLK, B=1T)
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Residuals
Position residuals xrow-xtrack
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Uniformity
MEAN RESIDUAL vs ROW
number
Z=5cm
Z-independent distortions
Distortions up to 50 microns
for resistive ink (blue points)
Z=35cm
Rms 7 microns for CLK film
(red points)
Z=50cm
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Uniformity
Very Preliminary
Average charge by row using 5GeV e- beam (B = 1T)
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Uniformity (B = 0T)
Very Preliminary
Using cosmic-ray
Average charge by row using cosmic-ray events
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Data analysis results (B = 0T & 1T)
Carbon-loaded kapton resistive foil
  0
2
Cd2  z

N eff
B=0 T Cd = 315.1 µm/√cm (Magboltz)
Module 4
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χ2 : 10.6
Ndf: 10
B=1 T Cd = 94.2 µm/√cm (Magboltz)
Module 3
χ2 :
Ndf:
Wenxin.Wang_IWLC meeting 2010
29.1
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Neff measurement with Micromegas
Averaging B=0T and B=1T data
(excluding ink module):
• Neff = 38.0±0.2(stat) ±0.8 (Cd syst)
• σ0= 59 ± 3 µm
• Assuming Polya distribution, =3.2±
0.7. Consistent with M. Lupberger’s
thesis.
See Michael Lupberger’s talk
in EUDET meeting in Hamburg
Note that 1/<1/N> = 47.1 from Heed for 5 Gev electrons on 6.84 mm long pads.
This demonstrates that gain fluctuations are not exponential (Neff would be 23)
but smaller.
1/<1/N> = 34.9 for 5.4 mm pads (GEM case).
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Test in a high intensity beam
Top
Bottom
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
Test at CERN (July 2010) at 180 kHz (5 x 2 cm² beam)
showed no charging up and stable operation

Peaking time of 200 ns is enough to obtain the best
resolution -> 300 ns suffice to distinguish 2 tracks on
the same pad
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Conclusions

A lot of experience has been gained in building and operating
Micromegas TPC panels

The uniformity of the detector is excellent, with no distortions
nor edge effects, and very small dead areas

The measured resolution meets LC needs : 60 microns at zero
drift distance with 3 mm wide pads

The effective number of electrons per row is measured to be 38

The detector peformed perfectly normally in high intensity
beam

Next step is to equip the whole endplate with full integration
of the electronics flat behind the panels
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Thank you
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