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Lulin Background Measurement and Detector Issues
NuTel project
NTU, Taiwan
K.Ueno
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Outline
Schedule of 2002 Design of detector/electronics LuLin test Calibration Detector thought Conclusion
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Schedule of 2002 May – July: design and fabrication of
electronics, detector and software. Most was made from scratch.
August – September: debugging full telescope system.
October: LuLin observatory test in moonless nights.
October – December: data analysis and calibration.
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Design of detector/electronics
Main task of this design – create a simple equipment for the measurement of background light from a mountain.
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Preamplifier schematics
+-
FromPMT
+-
FromPMT
First version(current -> voltage)
Second version(charge -> voltage)Gain~100mV/1p.e
RC=500ns
Power supply (16-channels preamplifier):380mA on +/- 5V (3.8W, 240mW/channel)
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Preamplifier test with test pulse Q~3*10^7 e (~10 photons)
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Hamamatsu PMT testUniformity from different channels
NTU
0
10
20
30
40
50
60
70
80
90
100
0 8 16 24 32 40 48 56 64
系列1
系列2
系列3
系列4
系列5
系列6
系列7
系列8
系列9
系列10
系列11
系列12
HAMAMATSU
0
10
20
30
40
50
60
70
80
90
100
0 8 16 24 32 40 48 56 64
系列1
系列2
系列3
系列4
系列5
系列6
系列7
系列8
系列9
系列10
系列11
系列12
Measured at NTU Data from Hamamatsu
Broken PMT
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Design of detector/electronics
Receiver parameters:• Gain: 1 (~100mV/pe)• Noise: ~5mV rms• There is a small problem: an overshoot in the tail.
+-
Shaper
ComparatorLVDS
transmitter
To Trigger
From
preamp.
100 nSDelay line
ToADC
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Design of detector/electronics
Trigger: using our TTM2 module made for BELLE experiment (in VME + FPGA based) changing firmware code – one week only!• Use this LVDS-level connector
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Design of detector/electronics
Trigger: from TTM2 to NuTel Trigger• Change 3 IC (transmitters onto receivers)
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Design of detector/electronics
ADC – use industrial one (Acromag ADC):• Inputs: differential 32 channels for simultaneous
conversion• Dead time: ~10 s (8 s – from data sheet!)• Operation clock: 8MHz (there is a jitter 125ns)• Range: +/- 10V (14 bit, 1.25 mV/bin)• Noise: ~1mV (from data sheet)
Problem: a real dead time is a bit larger than from data sheet, so we have low ADC readout rate (most time DAQ resets ADC module due problems in ADC) in case of big event rate (large photon flux), so a most information is from Trigger's counter, which operates with 60MHz clock)
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Design of detector/electronics
DAQ:• use VME connected with PC via SBS system• Code: Visual C++, Windows
ADC SBS PCWindows,
Visual C++
ADCdata
On linetrigger
Buffer RAMHarddisc
HistogramsHarddisc
Triggerdata
Trigger
VME
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Design of detector/electronics
DAQ: some print-screens from software
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Design of detector/electronics
Main task of this design – create a simple equipment for the measurement of background light from a mountain
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LuLin test Some pictures from LuLin observatory
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LuLin test Some pictures from LuLin observatory
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LuLin test Some pictures from night shifts
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Sirius seen by prototype at Lulin
Study:• Effective field of
view• Lens transmittance
as function of off-axis angle.
In the future, • Calibrate the
pointing accuracy• Monitoring telescope
health
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Lulin Set-up
Lens: 15cm radius
Total PMT area 1.75cm x 1.75 cm
Neutral density
BG3
PMT Plate
Focal length 30 cm
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How to calculate the photon flux
R *[T2Q(d photon flux [ s –1 cm -2 sr -1]
A : lens area (15cm * 15 cm * 3.14)
solid angle span by total PMTs (1.75cm/30cm)^2
Neutral density factor
lens transmittance
T2: BG3 transmittance (optional)
Q : PMT quantum efficiency
R: trigger rate
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Transmittance of BG3, PMT, and Lens
transmittance & Quantum efficiency
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
200 250 300 350 400 450 500 550 600 650
wavelength (nm)
trans
mitt
ance
& Q
uant
um e
ffici
ency
Lens
BG3
PMT
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Trigger-rate in different experiments
trigger rate
0
100
200
300
400
500
600
700
800
900
experiments with and without BG3
trigg
er ra
te (K
)
3deg +BG3 3deg
7deg +BG3
7deg 15deg + BG3
15deg
Before Sirius
sirius
After Sirius
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Photon flux in different experiments
photon flux
0
100000
200000
300000
400000
500000
600000
700000
800000
experiments with and without BG3
phot
on fl
ux (K
) [c
m -2
, s -1
, sr -
1 ]
3deg+BG3 3deg7deg + BG3
7deg
15deg+BG3 15deg
Befire Sirius
Sirius
After Sirius
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Summary table Trigger –rate (mean) +- RMS (K)
Photon-flux [K cm –2, sr-1 s-1]
3deg+BG3 33.72+- 2.31
11892.64
3deg 87.332+- 3.94
13850.17
7deg +BG3 97.706+-1.93
34459.74
7deg 237.6+-3.13
37681.51
15deg+BG3 209+-14.9 73711.82
15deg 980+-17.23 155420.4
Before Sirius
364+-6.74 128378.5
Sirius 1937+-3.091
683156.9
After Sirius 274.9+-38.9
96953.96
All Sirius data are BG3 included
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From LuLin test to
Calibration Setting thresholds on LuLin:
• Minimal threshold when noise data (pedestal) are never read from ADC + ~ 1 rotation of variable resistor (~ 50 mV)
• Thresholds during calibration: same as on LuLin
Dark current rate from 16 channels:
• ~ 10-20 Hz after keeping more then one hour at black box
• ~ 100 - 200 Hz on LuLin and at black box after operating with LED light
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Calibration Electronics test with test pulse:
• Sensitivity: ~100mV/3.3*10^6 e (1 photoelectron)
ADC data with optimized timing. A most noise is due jitter in ADC
ADC data with non-optimized timing. Strobe to ADC is delayed on 100 nS from optional timing
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Calibration Electronics test with test pulse:
• Cross-talk due electronics: very small
We observed a change in pedestals in some channels ~0.3 mV when a signal on neighboring one is ~1.5 V (0.02% !!! cross-talk)
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Calibration Electronics test with pulse to LED + fiber + PMT:
• Cross-talk due PMT: ~1% (from data sheet)
Cross-talk ~ 0.6%
Cross-talk ~ 0.2%
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Pedestals varies from channel to channel in range from –10mV to +4mV
Calibration
Typical pedestal distribution
A noise (r.m.s.) of pedestal distribution varies from 0.6 mV (minimum) to 2.5 mV (maximum).
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Pedestal Dark current Light Limit (overflow)
Calibration Test using LED pulse 100 ns x 1kHz:
– Typical histogram in case of big photon flux
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Preamp
Current amp. or charge amp.? If charge amp., should have a small time
constant to avoid a dead time. Large dynamic range of energy is needed. 10**14~10**18 eV and a light amount
depends on a detector-shower distance. Multi-gain or logarithmic gain or both? Space per channel for 8X8 MAPMT is
already tight.
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Timing measurement
Need to cover a large coincidence time window of 1 us or more a pipeline DAQ.
What clock rate? Normally 40 MHz. If we can assume a simple and uniform
shape, the time resolution can be much smaller than the clock period in offline.
If a pulse shape is complex and not simple depending on a direct Cerenkov or a fluorescence, the rate should be higher.
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Trigger
A simple coincidence among detectors may have too many fake triggers.
Time info. must be associated w. the pixel angular info. to reduce the fakes.
The association can be best done in hardware. Possible?
If not, must be done in a higher-level software trigger. Longer time to decide.
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TT
TT
Det1Det1
Det2Det2
θ
Shower
Det1Det1Det2Det2
Δt12
A candidate combination of Det1 & 2 signals issearched for in a time window.A trigger accepts a correct combination of t and .
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Monitor and control
Ideally a physics event or constant should be used as a monitor. But looks difficult.
Environmental parameters such as temperatures etc. must be monitored.
HV/LV monitor and remote control.
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Alignment and calibration
Reflected lights of a laser beam can simulate EAS and can be used for alignment.
Need a GPS system for a detector position and a time stamp.
Need a good scheme to synchronize sub-detectors over a long distance.
Is there a ‘gold-plated’ event available for alignment and calibration?
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Need to worry many more
MDAQ
SDAQ
SDAQ
SDAQ
Optics
Optics
Optics
PMT/PA Wire/Wireless
How to get power.Make SDAQ low-power.SDAQ-MDAQ communication.MAPMT maintenance.Hostile environment.etc. ………..
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Conclusion
A telescope (a detector and its electronics) were made in a short time to gain some experience.
Clear signals for a background and Sirius were observed, for demonstration, at Lulin observatory in October moonless nights.
A BG trigger rate was 130 photons/m**2 sr ns at 1 p.e. threshold.
Calibration is still under way. A new design of a telescope will be made based
on the experience.