[email protected] Astrophysics Detector Workshop – Nice – November 18th, 2008
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David Attié— on behalf of the LC-TPC Collaboration —
Micromegas TPC Micromegas TPC Large Prototype Large Prototype
beam testsbeam tests
TILC09 – Tsukuba – April 17-21, 2009
Outline
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• Introduction, solutions for ILC-TPC
• Micromegas with resistive anode
– description
– previous results
• The Large Prototype (LP)
• Micromegas panels in the LP
– drift velocity
– pad response function
– resolution
• Conclusion
How to improve the spatial resolution?
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• Need for ILC: measure 200 track points with a transverse resolution ~ 100 μm
example of track separation with 1 mm x 6 mm pad size: 1,2 × 106 channels of electronics z=0 > 250 μm amplification avalanche over one pad
• Spatial resolution σxy:
limited by the pad size (0 ~ width/√12)
charge distribution narrow (RMSavalanche ~ 15 μm)
1. Decrease the pad size: narrowed strips, pixels+ single electron efficiency – need to identify the electron clusters
2. Spread charge over several pads: resistive anode+ reduce number of channels, cost and budget+ protect the electronics– limit the track separation– need offline computing – time resolution is affected 2. Resistive anode
Simulation for the ILC-TPC55 m
1. Pixels
Micromegas
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Micromegas
Best technology for gaseous detector readout: Micro Pattern Gaseous Detector
• more robust than wires
• no E×B effect
• better ageing properties
• easier to manufacture
• fast signal & high gain
• low ion backdrift
• MICROMEsh GAseous StructureY. Giomataris et al., NIM A 376 (1996) 29
• metallic micromesh (typical pitch 50μm)
• sustained by 50-100 μm pillars • simplicity
• single stage of amplification
• fast and natural ion collection
• discharges non destructive
~50 µm
~50 kV/cm
cathode
~1 kV/cm
Resistive anode
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(r,t) integrate over pads
(r)
r (mm)
Q(t)
t (ns)
M.S.Dixit et.al., NIM A518 (2004) 721
• One way to make charge sharing is to make a resistive anode
• Equivalent to adding a continuous RC circuit on top of the pad plane.
• Charge density ρ(r,t) obeys 2D telegraph equation:
rρ
rrρ
tρ
RC ∂
∂
∂
∂
∂
∂ 112
2
et
RCtrρ t
RCr4
2
2),(
R R R R R R R R
C C C C C C C
Rp RpRp
Current generators
Pad amplifiers
Signal pickup pads
Resistiv
e fo
il
Resistive anode
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M.S.Dixit and A. Rankin NIM A566 (2006) 281
2 x 6 mm2 pads
(r,t) integrate over pads
(r)
r (mm)
Q(t)
t (ns)
SimulationData
Micromegas with resistive anode
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• TPC COSMo (Carleton-Orsay-Saclay-Montreal) at DESY in 2006+ Micromegas 10 x 10 cm² (gap 50 μm)+ resistive anode used to spread charge over
126 pads (7x18) of 2x6 mm²15 cm drift space
• 25 µm mylar with Cermet (Al-Si) of 1 M/□ glued onto the pads with 50 µm thick dry adhesive
5 T magnet at DESY + TPC COSMo
Micromegas
TPC COSMo
Resistive foil
Glue
pads
PCB
mesh
Resistive anode
Spatial resolution at 0.5T
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• B = 0.5T, resolution fitted by where
• Resolution 0 ( at z = 0) ~ 50 µm still good at low gain (will minimize ion feedback)
• Mean of Neff = 27 (value measured before ~ 22)
Gain = 4700 Gain = 2500
Neff=25.2±2.1 Neff=28.8±2.2
x 02 Cd2 zNeff
0 = 1/40 of pad pitch
2
/1/1 NNeff
Spatial resolution at 5T
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• Analysis: - Curved track fit- EP < 2 GeV
- || < 0.05 (~3°)
Ar Iso (95:5)
B = 5T
Ar Iso (95:5)
B = 5T
50 m
~ 50 µm independent of the drift distance
Extrapolate to B = 4T with T2K gas for 2x6 mm2 pads:
• DTr = 23.3 μm/cm, • Neff ~ 27,• 2 m drift distance,
Resolution of Tr 80 m will be possible !!!
ILC-TPC Large Prototype
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• Built by the collaboration
• Financed by EUDET
• Sharing out :
- magnet : KEK, Japon
- field cage : DESY, Allemagne
- trigger : Saclay, France
- endplate : Cornell, USA
- Micromegas : Saclay, France
- GEM : Saga, Japon
- TimePix pixel : F, D, NLc
ILC-TPC Large Prototype
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• Endplate ø = 80 cm of 7 interchangeable panels of 23 cm:
– Micromegas – GEMs– Pixels (TimePix + GEM or Microgemgas)
80 cm
24 rows x 72 columns <pad size> ~ 3x7 mm2
Bulk Micromegas panels tested at DESY
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• Two panels were successively mounted in the Large Prototype and 1T magnet - standard anode- resistive anode (carbon loaded kapton) with a resistivity ~ 5-6 MΩ/□
• Two other resistive technology are planned to be tested:- resistive ink (~1-2 MΩ/□) ready for next beam tests in May- a-Si thin-layer deposit (N. Wyrsch, Neuchatel) in preparation
Standard bulk Micromegas module Carbon loaded kapton Micromegas module
Beam test conditions
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• Bulk Micromegas detector: 1726 (24x72) pads of ~3x7 mm²
• AFTER-based electronics (72 channels/chip): – low-noise (700 e-) pre-amplifier-shaper– 100 ns to 2 µs tunable peaking time– full wave sampling by SCA
• Beam data (5 GeV electrons) were taken at several z values by sliding the TPC in the magnet. Beam size was 4 mm rms.
– frequency tunable from 1 to 100 MHz (most data at 25 MHz)
– 12 bit ADC (rms pedestals 4 to 6 channels)
ILC-TPC Large Prototype
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5 GeV e- beam data in T2K gas
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• Frequency sampling: 25 MHz• T2K gas: Ar/CF4/iso-C4H10 (95:5:3)• B = 1T • Peaking time: 500 ns
Pad signals: beam data sample
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• RUN 284
• B = 1T
• T2K gas
• Peaking time: 100 ns
• Frequency: 25 MHz
Pad signals: cosmic-ray data sample
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• RUN 294
• B = 1T
• T2K gas
• Peaking time: 1 μs
• Frequency: 100 MHz
Systematics
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Dis
plac
emen
t / v
ertic
al s
trai
ght l
ine
(μm
)
Pad line number rms displacement: ~9
microns
B = 0T
Drift velocity measurement
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• Measured drift velocity (Edrift = 230 V/cm, 1002 mbar): 7.56 ± 0.02
cm/μs
• Magboltz: 7.548 ± 0.003 for Ar/CF4/iso-C4H10/H2O (95:3:2:100ppm)
B = 0T
Drift Velocity vs. Peaking Time
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Edrift = 220 V/cm
VdMagboltz = 76 m/ns
• B=1T data
• For several peaking time settings: 200 ns, 500 ns, 1 µs,
2µs Edrift = 140 V/cm
VdMagboltz = 59 m/ns
Z (cm)Z (cm)
Tim
e b
ins
Tim
e b
ins
Determination of the Pad Response Function
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• Fraction of the row charge on a pad vs xpad – xtrack
(normalized to central pad charge)
Clearly shows charge spreadingover 2-3 pads(use data with 500 ns shaping)
• Then fit x(cluster) using thisshape with a χ² fit, and fit simultaneously all linesto a circle in the xy plane
xpad – xtrack (mm)
Pad pitch
Residuals (z=10 cm)
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• Lines 0-4 and 19-23 removed for the time being(non gaussian residuals, magnetic field inhomogeneous for some z positions?)
row 5 row 6 row 7
row 8 row 9 row 10
Residuals (z=10 cm)
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• There is a residual bias of up to 50 micron, with a periodicity of about 3mm.
• Unknown origin:
– Effect of the analysis?
– Or detector effect:
pillars?
Inhomogeneity of RC?
row 6
row 7
row 8
Spatial resolution at 1T
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• Resolution (z=0): σ0 = 46±6 microns with 2.7-3.2 mm pads
• Effective number of electrons: Neff = 23.3±3.0 consistent with expectations
eff
2d2
0x N
zCσσ
Further tests for Micromegas
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In 2008 with one detector module In 2009 with 7 detector modules.
Com
pact
the e
lect
ron
ics
wit
hposs
ibili
ty t
o b
ypass
shapin
gR
esi
tive t
ech
nolo
gy c
hoic
e
4 chipsWire bonded
Front End-Mezzanine
Conclusions
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• Excellent start for the Micromegas TPC tests within the EUDET facility. Smooth data taking.
• First analysis results confirm excellent resolution at small distance:50 μm 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
Backup slides
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