Kolympari, Crete, June 16, 20091 Study of avalanche fluctuations and energy resolution with an InGrid-TimePix detector P. Colas Progress report, based

Kolympari, Crete, June 16, 2009Kolympari, Crete, June 16, 2009 11

Study of avalanche Study of avalanche fluctuations and energy fluctuations and energy

resolution with an InGrid-resolution with an InGrid-TimePix detectorTimePix detector

P. ColasP. Colas

Progress report, based on PC, IEEE Dresden 2008, Max Chefdeville’s thesis 2009, and more recent

analysis

Paul Colas, CEA/Irfu Paul Colas, CEA/Irfu SaclaySaclay

Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009

22

Gain fluctuationsGain fluctuationsAn old problem : Wejsman 1949, Legler 1955, 1961, Riegler 2003,…

With a renewed interest: space resolution of an MPGD tracker (gain fluctuations lower by a factor (1+)/(2+) the number of effective electrons, D. Arrogancia et al., NIM A 602 (2009) 403

threshold

Efficiency for single-electron detection

And with new means of investigation : Microbulk, InGrid + TimePix

G/<G>

Avalanche size distribution

P. ColasP. Colas

Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 33

Gain fluctuationsGain fluctuationsThough there is no clear justification for this, we use Polya to parameterize the gain distribution.

For =0, the distribution is an exponential (Furry model)

Alternative convention is parameter m=1+

P. ColasP. Colas


New experimental handlesNew experimental handles

P. ColasP. Colas

Many measurements have been carried out (see T. Zerguerras’s Many measurements have been carried out (see T. Zerguerras’s talk). talk). New detectors provide new handles:New detectors provide new handles:

•Electron counting with InGrid on TimePix provides a direct Electron counting with InGrid on TimePix provides a direct measurement of Fano fluctuations, giving access to the measurement of Fano fluctuations, giving access to the contribution of gain fluctuations to the width of the observed contribution of gain fluctuations to the width of the observed 5555Fe peak (itself measured by InGrids or Microbulks).Fe peak (itself measured by InGrids or Microbulks).

•Time-over-threshold on single pixels give the charge Time-over-threshold on single pixels give the charge distribution of single electron avalanchesdistribution of single electron avalanches

•Study of electron counting vs gain gives a sensitivity to Study of electron counting vs gain gives a sensitivity to


TimePix chip

Idea : take a medical imaging chip (Medipix 2), add a clock to each pixel, replace ‘grey levels’ by ‘clock ticks’

(Michael Campbell, Xavi Lloppart, CERN)

65000 pixels, 14-bit counter, 100 MHz tunable clock frequency -> more voxels than the ALEPH TPC, but tiny!

55 m

55 m

PixelPixel

14111 m

1612

0 m

1408

0 m

(pi

xel a

rray

)

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

P. ColasP. Colas


See electrons from an X-ray conversion one by one and count them, study their fluctuations

(Nikhef-Saclay)

P. ColasP. Colas


Micromegas + Micromegas + TimePixTimePix

TimePixREADOUTREADOUT

MICROMESHMICROMESH

DRIFTDRIFT

DRIFTDRIFT

SPACESPACE

EEDD ~ 1 kV/cm ~ 1 kV/cm

EEAA ~ 80 kV/cm ~ 80 kV/cm

InGrid (Nikhef-Twente)

55Fe

Cr filter

Micromegas detector

5.9 keV Xrays giving 220 elec. in argon with rms sqrt(F/220)

Peak width: contribution from primary (Fano) fluctuations and gain fluctuations (assuming high detection efficiency)

Width=√(F+B)/N

P. ColasP. Colas


Chromium K-edge (Center for X-Ray Optics)

Microbulk detectorKEK, january 2007

P. ColasP. Colas


Result : 5.6% r.m.s. resolution

(Broken record)

Noise very small thanks to adequate filter on the mesh

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5% rms resolution

InGrid measurements

P. ColasP. Colas

Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 1111P. ColasP. Colas


rms resolution

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0 2 4 6 8 10 12theta

= 2

For F=0.20

Resolu

tion

(r

ms)

Theta parameter

P. ColasP. Colas


In the gain fluctuations, the avalanche statistics and the effect of the field configuration in the hole cannot be disentangled.

A full simulation shows how the resolution depends on the detector geometry.

P. ColasP. Colas


Energy resolution & collectionEnergy resolution & collection The collection efficiency varies with the field The collection efficiency varies with the field

ratioratio

Record Record 5555Fe spectra at various field ratiosFe spectra at various field ratios Peak position VS field ratioPeak position VS field ratio

Assume peak maximum is full collectionAssume peak maximum is full collection


Study efficiency vs gain

SiProt on chips: spreads the charge over 2-3 pads: count clusters

Use the rms size of the x-ray spot to select contained events

Use the time distribution to remove noise

P. ColasP. Colas


Measured spectra at -330 VMeasured spectra at -330 V Timepix #1Timepix #1 Timepix #2Timepix #2

5.9 and 6.5 keV escape events (event ratio ~ 7:1)

5.9 and 6.5 keV escape events (event ratio ~ 50:1)

Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 P. ColasP. Colas 1717

Single electron detection efficiency and Single electron detection efficiency and gaingain

Trend depends on:Trend depends on: the threshold the threshold tt, the gas gain , the gas gain G G and and mm

(TimePix) threshold

Single electron Single electron detection efficiency detection efficiency

and gainand gain Number of detected electrons at given Number of detected electrons at given

voltage determined byvoltage determined by Adjusting 2 gaussians on escape peakAdjusting 2 gaussians on escape peak KKbetabeta parameters constrained by K parameters constrained by Kalphaalpha ones ones 3 free parameters3 free parameters

Number of detected electrons and Number of detected electrons and voltagevoltage

Use common gain parametrizationUse common gain parametrization Fix pFix p22 (slope of the gain curve) (slope of the gain curve) 2 free parameters: t/A and 2 free parameters: t/A and ηηNN

Single electron detection efficiency Single electron detection efficiency and gainand gain

m rms (%)

1 100 39.432 71 3.083 58 1.164 50 1.415 45 1.60

Best fit for m = 3 (=2)Yields √ b = 1/√m ~ 58 %

• Also, ηN = 115 e- Upper limit on W(Ar5iso) < 25 eV• Correcting for un-efficiency: Upper limit on F(Ar5iso) < 0.3

Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 P. ColasP. Colas 2020

m= +1

RESULT OF THE FIT

= 2.2 -0.6 +1.3


W and F in Ar/iso 95/5 at 2.9 W and F in Ar/iso 95/5 at 2.9 keVkeV

Assume full collection efficiency of detector #1

Np = Nc = 115 ± 2 e-

W = 25.2 ± 0.5 eV

Peak width measured with detector #2 corrected for detection and collection eff. (87 %)

RMS(Np) ~ 4.3 %

F = 0.21 ± 0.06

Extrapolation to 5.9 keV photo-peak straightforward

Np = 230 ± 4 e-

Consistent with, and more precise than previous measurements

Consistent with measured values and theoretical estimate 0.17 for pure Ar

P. ColasP. Colas


ConclusionsConclusions New ‘almost perfect’ detectors give New ‘almost perfect’ detectors give

gain gain fluctuations wich can be parametrized fluctuations wich can be parametrized by polya with by polya with ~ 2. ~ 2. from e-counting vs Vfrom e-counting vs Vmeshmesh : : =2.2=2.2+1.5+1.5

-0.6-0.6

Fano fluctuations are now accessible by Fano fluctuations are now accessible by electron counting. electron counting.

Best resolution understood as sqrt((F+B)/N ), Best resolution understood as sqrt((F+B)/N ), with F=0.2 and B=0.3 for Micromegaswith F=0.2 and B=0.3 for Micromegas

More systematic measurements with best More systematic measurements with best possible InGrids+TimePix to be madepossible InGrids+TimePix to be made

P. ColasP. Colas

Thanks toThanks to


D. ATTIÉD. ATTIÉ1)1), M. CAMPBELL, M. CAMPBELL2 )2 ), M. CHEFDEVILLE, M. CHEFDEVILLE3)3) , E. , E. DELAGNESDELAGNES1)1) , K. FUJII , K. FUJII33)) , Y.GIOMATARIS , Y.GIOMATARIS1)1) , H. VAN , H. VAN

DER GRAAFDER GRAAF44) ) , X. LLOPART, X. LLOPART2)2) , J. SCHMITZ , J. SCHMITZ5)5), J. , J. TIMMERMANSTIMMERMANS44))

1) 1) Irfu,CEA Saclay; 2) CERN ; 3) KEK, 4) Nikhef; 5) TwenteIrfu,CEA Saclay; 2) CERN ; 3) KEK, 4) Nikhef; 5) Twente

Most of the work presented here was carried out by Max Chefdeville for his PhD

thesis.

P. ColasP. Colas

Documents

Kolympari, Crete, June 16, 20091 Study of avalanche fluctuations and energy resolution with an InGrid-TimePix detector P. Colas Progress report, based