Micromegas TPC
Large Prototype
beam tests
David Attié
— on behalf of the LC-TPC Collaboration —
TILC09 – Tsukuba – April 17-21, 2009
[email protected]
Astrophysics Detector Workshop – Nice – November 18th, 2008
1
Outline
• 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
[email protected]
TILC09 – Tsukuba – April 18th, 2009
2
How to improve the spatial resolution?
• 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
 sz=0 > 250 μm amplification avalanche over one pad
• Spatial resolution σxy:
limited by the pad size (s0 ~ width/√12)
charge distribution narrow (RMSavalanche ~ 15 μm)
Simulation for the ILC-TPC
 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
[email protected]
TILC09 – Tsukuba – April 18th, 2009
55 mm
1. Pixels
2. Resistive anode
3
Micromegas
Best technology for gaseous detector readout: Micro Pattern Gaseous Detector
• more robust than wires
• fast signal & high gain
• better ageing properties
• no E×B effect
• low ion backdrift
• easier to manufacture
Micromegas
• MICROMEsh GAseous Structure
Y. Giomataris et al., NIM A 376 (1996) 29
• metallic micromesh (typical pitch 50μm)
• sustained by 50-100 μm pillars
cathode
~50 µm
~1 kV/cm
~50 kV/cm
• simplicity
• single stage of amplification
• fast and natural ion collection
• discharges non destructive
[email protected]
TILC09 – Tsukuba – April 18th, 2009
4
Resistive anode
• One way to make charge sharing is to make
a resistive anode
(r)
Q(t)
M.S.Dixit et.al., NIM A518 (2004) 721
• Equivalent to adding a continuous RC circuit
on top of the pad plane.
(r,t) integrate
over pads
• Charge density ρ(r,t) obeys 2D telegraph
equation:
 ρ (r ,t ) 
RC
e
2t
r 2RC
4t
Current generators
R
R
C
R
C
R
R
C
C
Signal pickup pads
Rp
Rp
R
C
R
R
C
C
Resistive foil
∂
ρ
1  ∂2 ρ 1 ∂
ρ


∂
t RC  ∂
r2 r ∂
r 
t (ns)
r (mm)
Rp
Pad amplifiers
[email protected]
TILC09 – Tsukuba – April 18th, 2009
5
Resistive anode
2 x 6 mm2 pads
(r)
Q(t)
(r,t) integrate
over pads
r (mm)
t (ns)
M.S.Dixit and A. Rankin NIM A566 (2006) 281
Simulation
Data
[email protected]
TILC09 – Tsukuba – April 18th, 2009
6
Micromegas with resistive anode
• 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 mm²
15 cm drift space
mesh
Resistive foil
Glue
pads
• 25 µm mylar with Cermet (Al-Si) of 1 MW/□
glued onto the pads with 50 µm thick dry adhesive
PCB
Micromegas
TPC COSMo
[email protected]
Resistive anode
5 T magnet at DESY + TPC COSMo
TILC09 – Tsukuba – April 18th, 2009
7
Spatial resolution at 0.5T
Cd2  z
• B = 0.5T, resolution fitted by s x  s 0 
N eff
2
where N eff  1 / 1 / N
2
• Resolution s0 (s at z = 0) ~ 50 µm still good at low gain (will minimize ion feedback)
• Mean of Neff = 27 (value measured before ~ 22)

[email protected]
 s0 = 1/40 of pad pitch
Gain = 4700
Gain = 2500
Neff=25.2±2.1
Neff=28.8±2.2
TILC09 – Tsukuba – April 18th, 2009
8
Spatial resolution at 5T
tofit
B = 4T with T2K gas for 2x6 mm2 pads:
• Analysis: -Extrapolate
Curved track
Tr = 23.3 μm/cm,
- EP < •2DGeV
 s ~ 50 µm independent of the drift distance
•
N
~
27,
eff (~3°)
- |f| < 0.05
• 2 m drift distance,
 Resolution of sTr  80 mm will be possible !!!
Ar Iso (95:5)
B = 5T
50 mm
[email protected]
TILC09 – Tsukuba – April 18th, 2009
9
ILC-TPC Large Prototype
• 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
[email protected]
TILC09 – Tsukuba – April 18th, 2009
10
ILC-TPC Large Prototype
• Endplate ø = 80 cm of 7 interchangeable panels of 23 cm:
– Micromegas
– GEMs
– Pixels (TimePix + GEM or Microgemgas)
24 rows x 72 columns
<pad size> ~ 3x7 mm2
[email protected]
80 cm
TILC09 – Tsukuba – April 18th, 2009
11
Bulk Micromegas panels tested at DESY
• 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
[email protected]
Carbon loaded kapton Micromegas module
TILC09 – Tsukuba – April 18th, 2009
12
Beam test conditions
• Bulk Micromegas detector: 1726 (24x72) pads of ~3x7 mm²
• AFTER-based electronics (72 channels/chip):
– frequency tunable from 1 to 100 MHz
(most data at 25 MHz)
– 12 bit ADC (rms pedestals 4 to 6 channels)
– 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.
100000
Most of the data taken
at Vmesh = 380 V  gain ~ 2800
Gain
10000
1000
128 μm gap bulk Micromegas
100
280
330
380
430
Vmesh (V)
[email protected]
TILC09 – Tsukuba – April 18th, 2009
13
ILC-TPC Large Prototype
[email protected]
TILC09 – Tsukuba – April 18th, 2009
14
5 GeV e- beam data in T2K gas
• B = 1T
• T2K gas: Ar/CF4/iso-C4H10 (95:5:3)
[email protected]
• Frequency sampling: 25 MHz
TILC09 – Tsukuba – April 18th, 2009
• Peaking time: 500 ns
15
Pad signals: beam data sample
• RUN 284
• B = 1T
• T2K gas
• Peaking time: 100 ns
• Frequency: 25 MHz
[email protected]
TILC09 – Tsukuba – April 18th, 2009
16
Pad signals: cosmic-ray data sample
• RUN 294
• B = 1T
• T2K gas
• Peaking time: 1 μs
• Frequency: 100 MHz
[email protected]
TILC09 – Tsukuba – April 18th, 2009
17
Displacement / vertical straight line (μm)
Systematics
200
B = 0T
150
100
50
0
-50
-100
-150
-200
0
4
8
12
 rms displacement: ~9 microns
[email protected]
TILC09 – Tsukuba – April 18th, 2009
16
20
24
Pad line number
18
Drift velocity measurement
• 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
[email protected]
TILC09 – Tsukuba – April 18th, 2009
19
Drift Velocity vs. Peaking Time
• B=1T data
• For several peaking time settings: 200 ns, 500 ns, 1 µs, 2µs
 Edrift = 140 V/cm
 VdMagboltz = 76 mm/ns
 VdMagboltz = 59 mm/ns
Time bins
Time bins
 Edrift = 220 V/cm
Z (cm)
[email protected]
TILC09 – Tsukuba – April 18th, 2009
Z (cm)
20
Determination of the Pad Response Function
• Fraction of the row charge
on a pad vs xpad – xtrack
(normalized to central pad charge)
 Pad pitch 
Clearly shows charge spreading
over 2-3 pads
(use data with 500 ns shaping)
• Then fit x(cluster) using this
shape with a χ² fit,
and fit simultaneously all lines
to a circle in the xy plane
xpad – xtrack (mm)
[email protected]
TILC09 – Tsukuba – April 18th, 2009
21
Residuals (z=10 cm)
row 5
row 6
row 7
row 8
row 9
row 10
• Lines 0-4 and 19-23 removed for the time being
(non gaussian residuals, magnetic field inhomogeneous for some z positions?)
[email protected]
TILC09 – Tsukuba – April 18th, 2009
22
Residuals (z=10 cm)
row 6
• There is a residual bias of
up to 50 micron, with a
periodicity of about 3mm.
• Unknown origin:
row 7
– Effect of the analysis?
– Or detector effect:
 pillars?
 Inhomogeneity of RC?
row 8
[email protected]
TILC09 – Tsukuba – April 18th, 2009
23
Spatial resolution at 1T
• 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
σx  σ0
[email protected]
TILC09 – Tsukuba – April 18th, 2009
2
Cd2  z

Neff
24
Resitive technology choice
Further tests for Micromegas
In 2009 with 7 detector modules.
Compact the electronics with
possibility to bypass shaping
In 2008 with one detector module
[email protected]
TILC09 – Tsukuba – April 18th, 2009
Front End-Mezzanine4 chips
Wire bonded
25
Conclusions
• 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
[email protected]
TILC09 – Tsukuba – April 18th, 2009
26
Backup slides
[email protected]
TILC09 – Tsukuba – April 18th, 2009
27