Kolympari, Crete, June 16, 20091 Study of avalanche fluctuations and energy resolution with an...
-
Upload
norma-poole -
Category
Documents
-
view
214 -
download
1
Transcript of Kolympari, Crete, June 16, 20091 Study of avalanche fluctuations and energy resolution with an...
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 44
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 55
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 66
See electrons from an X-ray conversion one by one and count them, study their fluctuations
(Nikhef-Saclay)
P. ColasP. Colas
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 77
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 88
Chromium K-edge (Center for X-Ray Optics)
Microbulk detectorKEK, january 2007
P. ColasP. Colas
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 99
Result : 5.6% r.m.s. resolution
(Broken record)
Noise very small thanks to adequate filter on the mesh
P. ColasP. Colas
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 1010
5% rms resolution
InGrid measurements
P. ColasP. Colas
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 1212
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 1313
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
Kolympari, Crete, June 16, 2009Kolympari, Crete, June 16, 2009 1414
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 1515
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
Kolympari, Crete, June 16, 2009Kolympari, Crete, June 16, 2009 1616
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 2121
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 2222
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
Kolympari, Crete, June Kolympari, Crete, June 16, 200916, 2009 2323
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