[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 1
David Attié
P. Colas, E. Delagnes, Y. Giomataris,M. Campbell, X. Llopart,
M. Chefdeville, H. van der Graaf, J. Timmermans, J. Visschers
Gas pixel detector
for x-ray observation
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 2
Outline
Introduction: motivations for a gas pixel detector
1. The TimePix readout chip• Description• Architecture and schematic
2. Micro Pattern Gaseous Detector TPC• Description of Micromegas• Micro-TPC
3. Application for x-ray observations• Measurement of primary statistics in gas• TPC based polarimeter
Conclusion
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 3
Motivations for pixelized gaseous detector
• Gaseous detector advantages:– 2D/3D imaging– Low occupancy and low radiation length X0
mean free path could be important
• Spatial resolution:– σxy limited by the pad size (pitch/√12)– narrow charge distribution (RMS ~15 μm)
• High granularity:– δ-ray recognition/suppression in TPC– possibility to count primary clusters & electrons– direction & energy of tracks:
low-energy e- for X-ray polarimetry2 e- from double beta decay, nuclear recoils in WIMPor neutrino interactions for dark matter search
Digital TPC as a tracking detector with very high spatial resolution for astrophysics & high energy physics experiments
ALICE TPC simulations
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 4
Llopart et al., NIMA 581 (2007) 361
• Chip (CMOS ASIC) upgraded in the EUDET framework from the Medipix2 chip developed first for medical applications
• IBM technology 0.25 μm on 6 layers
• Characteristics:– surface: 1.4 x 1.6 cm2
– matrix of 256 x 256– pixel size: 55 x 55 μm2
• For each pixel:– preamp/shaper– threshold discriminator– register for configuration– TimePix synchronization logic– 14-bit counter
• Noise: ~ 650 e-– 70 e- per pixel, Cin ~ 15 fF
Description of the TimePix chip
55 μm
55 μm
14111 μm
1612
0 μm
1408
0 μm
(pix
el a
rray
)
Pixel
11 22 33
44
55
55μ m
55 μm
Prea
mp/
shap
er
THL
disc
.
Conf
igur
atio
n la
tche
s
Interface
Counter
Sync
hron
izat
ion
Logi
c
12345
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 5
Medipix ModeTOT Mode Timepix Mode
TimePix Synchronization Logic Control
DACs values
Mask P1 P0 Mode
0 0 0 Masked
0 0 1 Masked
0 1 0 Masked
0 1 1 Masked
1 0 0 Medipix
1 0 1 TOT
1 1 0 Timepix-1hit
1 1 1 Timepix
100 MHz
Analog Signal
Internal Shutter
Shutter
Internal Clock
Digital Signal
not detected
detected
• Each pixel can be configured independently in 5 different modes
• Internal clock up to 100 MHz
Summed charge
10 ns
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 6
Detectors using TimePix chip
+-
+-
+-
Medipix2/TimePix chip TimePix chip
X-ray source
Ionizing
particle
Flip-chip bump bondingconnections
Semiconductorsensor
Gas volume
Amplification System (MPGD)
Drift cathode grid
Solid detector Gas detectorx, y, F(x, y) 2D x, y, z(t), E(x,y) 3D
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InGrid: Integrated Micromegas Grid
• Integrate Micromegas detector directly on a CMOS chip by post-processing
Resistive layer for protection of a-Si:H
~ 80 kV/cm
NIKHEF(MESA+,
Univ. Twente)
IMT Neuchatel
• Micromegas is a Micro Pattern Gaseous Detector formed by a metallic micromesh (hole pitch 70 μm) sustained by 50 μm pillars above the anode
• Multiplication between anode and mesh
• Gain up to 105
~ 1 kV/cm
PCBpad
e-
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 8
• Energy resolution depends on thegrid geometry
• Grids can be very flat– best energy resolution achieved:
13.6 % with 55Fe source in P10
– removal of Kβ 6.5 keV line:11.7 % @ 5.9 keV in P10
• Hole pitch down to 14 μmwith various diameters
• Different gaps (35-75 μm)
• Until now: grid is 1 μm of Albut can also be increased to 5 μmby electrolysis to be more robust
Escape peak Kα
Escape peak Kβ
13.6 % FWHM
Kβ-filtered spectrum with Cr foil
11.7% FWHM
Gap: 50 μm; Hole picth: 32 μm,Ø: 14 μm
InGrid: energy resolution
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 9
Micro-TPC using TimePix/Micromegas
Field cage
Cover
Micromegasmesh
TimePix chip
Windows for X-ray sources
Windows for β sources
• Gas mixture at atmospheric pressure
6 cm
• Micro-TPC with a 6 cm height field cage
• Size : 4 cm × 5 cm × 8 cm
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 10
Micro-TPC TimePix/Micromegas
• TimePix chip+ SiProt 20 μm+ Micromegas
• 55Fe source
• Ar/Iso (95:5)
• Time mode
• z = 25 mm
• Vmesh = -340 V
• tshutter = 283 μs
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Measurements of primary statistics in gases
• Diffusion σt should be big enough to separate electrons: e- per pixel ~ 1• Study of primary electrons and Fano factor F using RMS• Spectrum of number of electrons for 2000 events:
Sensitive to Kα & Kβ lines
FWHM = 9,5 %
5.9 keV line at ~ 226 e-
TimePix+Ingrid+ 15 μm SiProt Argon + 5% Isobutane
F: Fano factor√b: single e- gain distribution rms (%)ε: detection efficiencyN: number of primary e-
Nεε
NbFRMS −
+−
=12
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 12
Polarimetry using photoelectric absorption
• Differential photoelectron cross-section emittedfrom the atomic s-orbital in non relativist limit:
• θ polar angle, φ azimutal angle
• Emission angles are modulated by the polarization P
( )
φΩdσd
θβφθ
υhcmαZr
Ωdσd e
2
4
2227
2452
0
cos
cos1cossin24
∝
−⎟⎟⎠
⎞⎜⎜⎝
⎛=
BAB
NNNP
+=
−=
2minmax
Auger electron
X-ray
Photoelectron
E
φ
θ
)(cos)( 2polφφBAφN −+=
maximum in the plane ⊥ γ direction
• Ideal polarimeter is a track imager with:resolution elements < mean free path of photoelectron
Nmax
Nmin
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 13
Prototype TPC polarimeter using TimePix/Micromegas
• TimePix chip+ SiProt 20 μm+ Micromegas
• 55Fe source
• Ne/Iso (90:10)
• TOT mode
• z < 5 mm
• Vmesh = -450 V
• tshutter = 0.2 s
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 14
• TimePix chip+ SiProt 20 μm+ Micromegas
• 55Fe source
• Ne/Iso (90:10)
• TOT mode
• z < 5 mm
• Vmesh = -450 V
• tshutter = 0.2 s
Prototype TPC polarimeter using TimePix/Micromegas
• Determination of the polarization
Barycentre
Principal axis
φ
• Identify the cluster
• Low Ek-edge of Neon eauger areisotropically emitted with a smallfraction of the photon energy
• In low Z gas mixture tracks arelonger so angular reconstruction is easier
φ photoemission angle
Reconstructed absorption point
Reconstructed photoemission direction with identificationof the absorption point and theremoval of the final part of the track
Photoelection + eauger track in Neon+10 Isobutane
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 15
Example of TPC for x-ray polarimeter
Black et al. NIMA 581, 2007, 755
Unpolarized
5.9 keV photons
Polarized 6.4 keV photons
90o45o0o
GEM like Readout Strips130 μm pitch
X-ray
Drift Electrode
Digitized Waveforms
Differentiated Waveforms Image
Gas mixture: Neon/DME 50:50 at 0,6 atm
Triggerx
y
z
x(t)
y
Photoelectron
e- Drift
• Uniform response• Modulation (P ~50 %)• No false modulation• An encouraging start
Photoemission electron angle (degree)
Coun
ts
2O mm
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 16
Conclusions
• TimePix chip/Micromegas + SiProt: demonstrator for the digital TPCuseful tool for x-ray observations
• Ultimate resolution for a TPC thanks to the single electron sensibilityMicro-TPC is an excellent tool to characterize photon absorption in gas mixtures
- statistics of primary electrons and clusters- Fano factor (gain fluctuation)
• Identification of the photoelectron angle by imaging the photoelectron trackis very promising for soft x-ray polarimetry ( 2 keV < Eγ < 50 keV)
• Still some technologic issues: Self triggering capabilityHow to improve the readout of the chips (speed and larger surface) ?- through Si connectivity: avoiding bonding wires- fast readout technology (~5 Gb/s)
Sealed detector
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 17
The TimePix collaboration
Thank you for your attention
• NIKHEF Harry van der GraafMartin FransenJan TimmermansJan VisschersSipho van der PuttenArno Aarts
• Saclay CEA/DAPNIA David AttiéPaul ColasEsther Ferrer-RibasArnaud GiganonYannis GiomatarisMarc Riallot
• Univ. Twente/Mesa+ Jurriaan SchmitzVictor Blanco CarballoCora SalmSander Smits
• FREIBURG A. BambergerK. DeschU. RenzM. TitovN. VlasovA. ZwergerP. Wienemann
• CERN Erik HeijneXavier LlopartMedipix Consortium
β- from 90Sr source in He/Isobutane 80:20
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 18
Backup slides
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 19
Readout system for Medipix2/TimePix chip
• MUROSv2.1:– Serial readout– VHDCI cable of length <3m– read 8 chips in mosaic– tunable clock [30-200MHz]– ~40fps @160MHz
http://www.nikhef.nl/pub/experiments/medipix/muros.html
• USB:– Serial readout– ~5 fps@20MHz
http://www.utef.cvut.cz/medipix/usb/usb.html
• Mosaic achitecture:
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 20
TimePix chip architecture
• 36×106 transistors on 6 layers(~550 transistors/pixel 13.5 μW)
• Reference clock per pixel up to 100 MHz
• Characteristics:– analog power: 440 mW– digital power (Ref_Clk = 80 MHz): 450 mW– serial readout (@ 100 MHz): 9.17 ms– parallel readout (@ 100 MHz): 287 μs
• Pixel modes:– masked– counting mode (Medipix, Timepix-1h)– Time-Over-Threshold “charge” info– Common stop “time” info
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 21
TimePix chip schematic
PreampDisc
THR14 bitsShift
Register
Input
Ctest
Testbit
Test Input
Mask
4 bits thr Adj
Mux
Mux
Clk_Read
Previous Pixel
Next Pixel
Conf
8 bits configuration
Polarity
Analogic part Digital part
Ref_Clk
Timepix Synchronization
Logic
Ref_Clkb
P0P1
Shutter
Ovf Control
Clk_Read
Shutter_int
For each pixel
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 22
1 516
516
1X (column number)
Y
1 45.75 90.5 135.3 180
1
First TimePix Quad
Llopart & Campbell, CERN
• First Timepix quad
+ 300 μm Si crystal
1. Medipix mode counting- 55Fe source
- tshutter =40 s
2. Time mode- 90Sr source
- tshutter = 237 μs
3. Time-Over-Threshold mode- 241Am source
- tshutter = 5 s
1 516
516
1X (column number)
Y
0 2953 5905 8858 1.181e+004
2
1 516
516
1X (column number)
Y
1 250.8 500.5 750.3 1000
3
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 23
Ar
CO2
70/3
0H
e CO
270
/30
TimePix & GEMs
Freiburg (+Bonn)
• Cartes de 181x181 en mode Time & et en TOT
• Fournit les informations charge & temps en même temps
• Fort potentiel pour la séparation de traces
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 24
• Timepix chip + Micromegas on frame:
• Timepix chip + SiProt + Ingrid:
Moiré effects+ pillars
“Uniform”
MESA+
IMT Neuchatel “counting” mode
TimePix using Micromegas
Resistive layer for protection
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 25
Micro-TPC TimePix/Micromegas
• TimePix chip+ SiProt 20 μm+ Micromegas
• 90Sr source
• Ar He
• Time mode
• z ~ 40 mm
• Vmesh = -340 V
• tshutter = 180 μs
spark-proof !
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 26
Micro-TPC TimePix/Micromegas
• TimePix chip+ SiProt 20 μm+ Micromegas
• 90Sr source
• Ar/Iso (95:5)
• Time mode
• z ~ 40 mm
• Vmesh = -340 V
• tshutter = 180 μs
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 27
Gas mixture containing Neon
http://www-cxro.lbl.gov
[email protected] NDIP08 – Aix-les-Bains – June 19th, 2008 28
Simulated quality factorBellazzini et al., NIMA 572 (2007) 167
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