David Attié P. Colas, E. Delagnes, Y. Giomataris, M. Campbell, X. Llopart,

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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 Gas pixel detector

for x-ray for x-ray

observationobservation

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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

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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 polarimetry 2 e- from double beta decay, nuclear recoils in WIMP

or 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

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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 m

55 m

14111 m

1612

0 m

1408

0 m

(pi

xel a

rray

)

Pixel

11 22 33

44

55

55

μ m

55 μ m

Pre

am

p/

shap

er

TH

L dis

c. Con

fig

ura

tion

la

tch

es

Interface

Counter

Syn

chro

niz

ati

on L

ogic

12345

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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

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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

~ 8

0 k

V/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-

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• 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

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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 c

m

• Micro-TPC with a 6 cm height field cage

• Size : 4 cm × 5 cm × 8 cm

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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

NbF

RMS

12

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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

θβ

φθυhcm

αZrΩdσd e

2

4

2227

2452

0

cos

cos1

cossin24

BAB

NNN

P

2

minmax

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

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Prototype TPC polarimeter using TimePix/Micromegas


• 55Fe source

• Ne/Iso (90:10)

• TOT mode

• z < 5 mm

• Vmesh = -450 V

• tshutter = 0.2 s

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• 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

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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)

Counts

2O mm

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Conclusions

• TimePix chip/Micromegas + SiProt: demonstrator for the digital TPC useful 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 capability How 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

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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

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Backup slides

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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:

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TimePix chip architecture

IO

Logic

LVDS

In

LVDS

Out32-bit CMOS Output

256-bit Fast Shift Register

3584

-bit

Pix

el C

olum

n-0

3584

-bit

Pix

el C

olum

n-0

Bandgap + 13 DACs16

120

m

14111 m35

84-b

it P

ixel

Col

umn

-135

84-b

it P

ixel

Col

umn

-1

3584

-bit

Pix

el C

olum

n-2

5535

84-b

it P

ixel

Col

umn

-255

1408

0 m

(pix

el a

rray

)

• 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

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TimePix chip schematic

Preamp

Disc

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

P0

P1

Shutter

Ovf Control

Clk_Read

Shutter_int

For each pixel

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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

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Ar

CO

2 7

0/3

0H

e C

O2 7

0/3

0TimePix & 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

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• 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

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• 90Sr source

• Ar He

• Time mode

• z ~ 40 mm

• Vmesh = -340 V


spark-proof !

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• 90Sr source

• Ar/Iso (95:5)

• Time mode

• z ~ 40 mm

• Vmesh = -340 V


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Gas mixture containing Neon

http://www-cxro.lbl.gov

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Simulated quality factor

Bellazzini et al., NIMA 572 (2007) 167

Documents

David Attié P. Colas, E. Delagnes, Y. Giomataris, M. Campbell, X. Llopart,