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FIRST TEST RESULTS FROM A MICROMEGAS LARGE TPC
PROTOTYPEP. Colas (CEA Saclay), on behalf of the LC-TPC collaboration
Micromegas with resistive anode: previous resultsThe Large PrototypeMicromegas panelsDataDrift velocity measurementPad response functionResolution
12/03/2009, Tsukuba 1P. Colas, Micromegas TPC tests
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Introduction : resistive anode
12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 2
D. Arogancia, K. Fujii et al., to appear in NIM A
LC-TPC goal is 200 measurement points on a track, with <130 micron resolution
With Micromegas, signal spread is equal to the avalanche size, 12-14 microns : not enough charge sha-ring at low diffusion even with 1mm pads.Need to share the charge between neighbouring pads to make a barycentre possible and improve resolution.
Also charge sharing saves number of channels ($, W, X°)
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Introduction : resistive anode (2)
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One way to make charge sharing is to make a resistive anode (M.S.Dixit et.al., NIM A518 (2004) 721.) This corresponds to adding a continuous RC circuit on top of the pad plane. Charge density obeys 2D telegraph equation
t
1
RC
2r2
1
r
r
(r, t)RC2t
r2RC4 te
M.S.Dixit and A. Rankin NIM A566 (2006) 281
SIMULATION
MEASUREMENT
Res. foil also provides anti-spark protection
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Previous testsMicromegas TPC endplates have been tested in the past1) Berkeley-Orsay-Saclay in cosmics, 2T, 1000 channels (2002-2004)2) MP-TPC at KEK, 1T, 380 channels (June 2005)3) Carleton-Saclay chamber at KEK, 1T, 128 channels with resistive anode
(10/05)
4) Carleton-Saclay chamber at DESY 5T in cosmics, 128 channels with r.a. Now test 1 panel in 1 T at DESY, 1726 channels (T2K electronics)
12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 4
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Previous results with resistive anodes
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KEK beam test, 2005 DESY 5T cosmic test, 2007
50 micron resolution at short drift distance, with 2mm pads
(was obtained with an AlSi cermet-coated mylar)
eff
dx N
zC
220
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The EUDET setupat DESY
See talk by K. Dehmelt
PCMag magnet from KEKCosmic trigger hodoscope from Saclay-KEK-INRBeam trigger from NikhefDummy modules from BonnField cage, gas from DESYEndplate from Cornell
12/03/2009, Tsukuba 6P. Colas, Micromegas TPC tests
Test one Micromegas module at a time
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12/03/2009, Tsukuba P. Colas, Micromegas TPC tests
Two panels have been tested at DESY
Both in ‘bulk’ technology
One with standard pads, one with resistive anode (Carbon-loaded kapton)
Improved resistive anode 75 micron kapton + 25 micron C-loaded kapton (CERN)
Other 2 ready/ in preparation : resistive ink and thin-layer deposit (N. Wyrsch, Neuchatel)
RESULTS
7
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Detector and electronics
- 24x72 pads of 3x7 mm²- AFTER-based electronics : low-noise (700 e-) pre-amplifier-
shaper, 100 ns to 2 µs tunable peaking time, full wave sampling by SCA, frequency tunable from 1 to 100 MHz (most data at 25 MHz), 12 bit ADC (rms pedestals 4 to 6 channels)
- Beam data (5 GeV electrons) were taken at several z values by sliding the TPC in the magnet. Beam size was 4mm rms.
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1012/03/2009, Tsukuba P. Colas, Micromegas TPC tests10
• Peaking time: 1 μs• Frequency sampling: 100 MHz
Cosmic ray data sample
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0
1
2
3
4
5
6
7
8
0 100 200 300 400 500 600
Z (mm) arbitrary origin
Drif
t tim
e (µ
s)
Measured drift velocity (Edrift = 230 V/cm, 1002 mbar) : 7.56 ± 0.02 cm/µs
Magboltz : 7.548 ± 0.003 pour Ar:CF4:isobutane:H2O/95:3:2:100ppm
B=0 data
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DESY - 8 déc. 2009 TPC Analysis 12
y = 13,884x - 165,42
-200
-150
-100
-50
0
50
100
150
200
0 4 8 12 16 20 24Dis
plac
emen
t w
rt v
ertic
al s
trai
ght
line
(mic
rons
)
Pad line numberRms displacement: 9 microns
B=0 data
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13
Magboltz 59 m/nsMagboltz 76 m/ns
12/03/2009, Tsukuba P. Colas, Micromegas TPC tests
B=1T data for several peaking time settings200 ns, 500 ns, 1 µs, 2µs
Edrift = 220 V/cm Edrift = 140 V/cm
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Determination of the Pad Response Function
Fraction of the row charge on a pad vs xpad – xtrack
(normalized to central pad charge)
Clearly shows charge spreading over 2-3 pads(use data with 500 ns shaping)
Then fit x(cluster) using this shape with a ² fit, and fit simultaneously all lines to a circle in the xy plane
xpad – xtrack (mm)
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RESIDUALS (z=10 cm)
Do not use lines 0-4 and 19-23 for the time being (non gaussian residuals, magnetic field inhomogeneous for some z positions?)
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There is a residual bias of up to 50 micron, with a periodicity of about 3mm.
Effect of the analysis?Or detector effect : pillars? Inhomogeneity of RC?
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12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 17
Resolution 46±6 microns with 2.7-3.2 mm padsEffective number of electrons 23.3±3.0 consistent with expectations
eff
dx N
zC 2
20
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CONCLUSION• Excellent start for the Micromegas
TPC tests within the EUDET facility. Smooth data taking
• First analysis results confirm excellent resolution at small distance:
50 microns for 3mm pads• Expect even better results with new
(bypassed shaper) AFTER chips• Plans are to test several resistive
layer fabrication, then go to 7 modules with integrated electronics
12/03/2009, Tsukuba P. Colas, Micromegas TPC tests 18