flat-panel in milanopessina.mib.infn.it/biblio/lhcb/rich-upgrade meeting... · 2009. 8. 26. ·...
TRANSCRIPT
RICH-UPG, 26/08/09 1
Flat-Panel in Milano
INFN-Milano-Bicocca
RICH-UPG, 26/08/09 2
Summary
New approach in PMT characterization;
New PMT soon available.
RICH-UPG, 26/08/09 3
HAMAMATSU H9500
H9500 is a 16 x 16 pixels (256 in total) having about 3 x 3 mm2 active area per pixel.
Electrical connections are on the back of the PMT. 4 Samtec (QTE‐040‐03‐F‐T‐A) connectors with 80 contacts in 2 rows are present (16 GND + 64 anodes)
RICH-UPG, 26/08/09 4
Cross-talk study with Flat-Panel: a step forward
INFN-Milano-BicoccaSyracuse University
Summary from the last meeting:
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Front-End from Syracuse (I)The readout chip and the acquisition system are from Syracuse, originally intended for BTeV.
The main features of the VA64MaPMTv0r6 are:
• 64 channels, 0.35-CMOS from Syracuse Uni. - Ideas;
• 0.32 V/Mel gain with about 70 ns CR-RC shaping time;
• Adjustable trigger threshold level, minimum at 10 fC (62 Kel);
• Noise maximum at 2200 el.
The output is digital
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Front-End from Syracuse (II)
X 64Glue board and PS
Mezzanine
board and
PTA
Acquisition system
Signal is analog at its start and ends digital at the DAQ.
The only way we have to study the signal is through the setting of the threshold, that is common within each chip and to the 4 chips of the board.
External Threshold level adj. added
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Measurement set-up for cross-talk study (III)
CF
Cj
Cj+5
Cj+5k
Pixelj+1
Pixelj+n
Zi
Zi
Zi
Pixelj
Connections well separated
We connected one channel every 5 suppressing completely the cross‐talk from the small, necessary, short flat cable.
RICH-UPG, 26/08/09 8
Measurement set-up for cross-talk study (III)
Connections of the pixels to the electronics has been made with mini‐coaxial cable or twisted cables. In both cases well distant and separated.
Flat‐Panel
To the Electronic
Coaxial connecting cables well apart
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Flat Panel (I)
Here 2 examples of a pair of standard, plastic fibers optic on 2 pixels, all the other darkened.
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Flat Panel (II)
The fiber optics has been illuminated with a commercial blue‐led at 470 nm wave length.
1KΩLed diodes
Pulser
LEDs has been biased just around threshold and tiny coupled to the optical fiber in order to send to the pixel, at random, a photon every second.
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Cross-talk interpretation (I)
‐‐
‐‐ ‐‐‐‐
‐‐ ‐‐‐ ‐
‐‐ ‐
‐‐ ‐‐‐‐ ‐‐
Many input Photons
Many electrons atThe first dynode
5 % Probability= 5 % of electrons leak
5 % signal Amplitude at the anode. A cross‐talk signal is always present.
Almost unaffected signal at the anode
‐‐ ‐‐‐
Single‐Photons input
Few el generated, 4 – 5.
5 % Probability of 1 el to leak
A few number of signals, but with large fraction of the original signal.
When cross‐talk happens the signal at the anode undergoes to 20 % ‐30 % of amplitude reduction.
Signal generated from many photons Signal generated by a single photon.
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Cross-talk interpretation (II)
Histogram example from the BA0828:
Cross‐talk measured when the threshold was at 50 % of the maximum for cluster at larger gain
CROSS‐TALK threshold (well above ±3 σ) was found:
•BA0808: 0.75 Mel (signal at 2.1 Mel);
•BA0828: 1.1 Mel (cluster with signal at 2.15 Mel);
•BA0828: 0.55 Mel (cluster with signal at 1.3 Mel).
HV: ‐900 V
Results confirmed the expectations:
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Simulation of cross-talk from single-photon signal (I)
At 110 V of drop‐out at the first dynode the cross talk signal drops to 20 – 25 %.
0 100 200 300 400 500 6000
200
400
600
800
1000
1200
Electron Numbers after 3 dynodes to single photon response
Num
ber o
f Hits
Central pixelDrop-out at the first Dynode= 110 V
0 20 40 60 80 100 1200
100
200
300
400
500
Number of cross-talk Electrons
Num
ber o
f Hits
Side pixelDrop-out at the first Dynode= 110 V
Simulation interpreted data:
RICH-UPG, 26/08/09 14
New set-up
We are now working on a new set‐up in view of the design and implementation of the front‐end.
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Toward a new front-end (I)
LP
LP CP LP
LP NM
NMNM
NM
We are still concentrate on the study of the single pixel response and the coincidence signal from the cluster of close pixel for cross‐talk evaluation.
NM=not measured;LP=Lateral pixel;CP=central pixel
The first step in signal amplification and analysis was trough a classical scheme based on the Charge Sensitive Preamplifier, CSP.
Signal acquisition and analysis was the first step to solve since multichannel and coincidence from more than one channel are needed.
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Toward a new front-end (II)
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
+
-1 pF
60 KΩ
C T=1
pF
50 Ω
+
-1 pF
60 KΩ
CT=1 pF
50 Ω60 KΩ
1 pF
60 KΩ
CT =1 pF
50 Ω
+
-1 pF
60 KΩ
CT=1 pF
50 Ω
+ -
1 pF
CT =1 pF
50 Ω
Test Signal
RICH-UPG, 26/08/09 17
Toward a new front-end (III)
The Op Am is a commercial AD9631 featuring about 300 MHz gain bandwidth product.
At the moment the CSPs have been simply bred‐boarded.
+
-1 pF
60 KΩ
CT=1 pF
50 ΩTest Signal
The test signal is very important for the calibration of the pixel response.
RICH-UPG, 26/08/09 18
Signal Acquisition (I)
Signal acquisition has been done exploiting the capability of the new generation of oscilloscopes.
The Tek DPO7254 has a memory depth of 40 MB. The memory can be split among its 4 channels, 10 MB/channel.
The very important characteristic is that the memory can be sectored in slots with settled time resolution.
The signal in every slot is stored only if the trigger threshold is fired.
This way thousand of signals from the 4 channels can be acquired, stored and downloaded for off‐line analysis.
Coincidence is easily studied.
RICH-UPG, 26/08/09 19
Signal Acquisition (II)
Matteo at work…
ns
Signal analysis permitted to verify that we inject a single photon with a high degree of confidence: in the off‐line study no pileup has been observed on the tail of the signals.
The rate of photon injection was less than 3 KHz.
Signals were interpolated with a double exponential, as expected:
We tested the processing capability of the oscilloscope. We inject a test signal to one CSP.
Up to a rate of 350 KHz we did not see any loss of data.
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Signal Acquisition (III)
Mel
The calibration was done for the studied pixels by illuminating, individually, each of them with a single fiber.
This was done at 3 different biasing voltages: 850 V, 950 V and 1050 V.
It was observed that the uniformity is good, although greater collecting statistic is needed.
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
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Signal Acquisition (IV)
Coincidence of signals from different channels is easily recovered from the data downloaded.
ns
Central, inducingpixel
Cross‐talk signal in coincidence
Cross‐talk signal in coincidence
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Signal Analysis: very preliminary (I)
Cross‐talk study has confirmed the results obtained with the set‐up from Syracuse.
In addition, additional features has been further raised.
The first important result is that it seems that we are able to discriminate between the cross‐talk coming from the first and second dynode in the chain.
Spectra of the 4 pixels
Spectra of cross‐talked pixels in coincidence with central pixel
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
Spectra of cross‐talked pixels in ratio of the inducing signal
850 V Biasing,Pixel 59 and neighbored
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First Dynode
Second Dynode
Signal Analysis: very preliminary (II)
The ratio of the 2 peaks is almost a factor of 4, just what expected from the gain at those stages.
At the same time the cross‐talk level for the single photo‐electron is close to 40 % of the inducing signal.
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
850 V Biasing,Pixel 59 and neighbored
RICH-UPG, 26/08/09 24
Signal Analysis: very preliminary (III)
The level of cross‐talk at this bias voltage is smaller and close to 30 %.
Spectra of the 4 pixels
Spectra of cross‐talked pixels in coincidence with central pixel
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
Spectra of cross‐talked pixels in ratio of the inducing signal
950 V Biasing,Pixel 59 and neighbored
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Signal Analysis: very preliminary (IV)
The level of cross‐talk improves slightly with respect to 950 V bias.
Spectra of the 4 pixels
Spectra of cross‐talked pixels in coincidence with central pixel
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
Spectra of cross‐talked pixels in ratio of the inducing signal
1050 V Biasing,Pixel 59 and neighbored
RICH-UPG, 26/08/09 26
Signal Analysis: very preliminary (V)
Similar behavior has been observed with another pixel, the 63.
Spectra of the 4 pixels
Spectra of cross‐talked pixels in coincidence with central pixel
LP 47
LP 62 CP 63 LP 64
NM NM
NMNM
NM
Spectra of cross‐talked pixels in ratio of the inducing signal
1050 V Biasing,Pixel 63 and neighbored
RICH-UPG, 26/08/09 27
Signal Analysis: very preliminary (VI)
An open question is the presence of the split of thepeak.
It seems in the ratio of a cross‐talk signal generated from N or N+1 electrons at the first dynode, namely 1/(N‐1) or 1/(N).
Looking at the spread of the spectrum it turns out that the S/N is not good enough to justify such a result.
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
Peak split
RICH-UPG, 26/08/09 28
Signal Analysis: very preliminary (VII)
A last observation, that needs further statistic to be proved, is the asymmetry of the cross‐talk.
Pixels along one direction seem more prone to be fired with respect to the other.
LP 43
LP 58 CP 59 LP 60
LP 75 NM
NMNM
NM
LP 47
LP 62 CP 63 LP 64
NM NM
NMNM
NM
RICH-UPG, 26/08/09 29
Near future (I)
Available soon: small inactive border: R7600 upgrade.
PMT in order: arriving in the first half of September.
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Near future (II)
Tentative features:
1.15 x 1.15 mm2 pixel area;
8 x 8 channels;
3 x 105 gain;
cross‐talk for large input photons < 2 %.
The bias circuit is not embedded in the device.
This way it will be possible to set the bias of the dynode chain with adjustable ratio, for the study of the cross‐talk as a function of the voltage level at the first dynode.
RICH-UPG, 26/08/09 31
Conclusions
• A New front‐end set‐up for the Flat panel characterization has been tested.
• A R7600 flat panel, optimized for single‐photon event and small cross‐talk, is coming.