Lulin Background Measurement and Detector Issues

NuTel project

NTU, Taiwan

K.Ueno

Outline

Schedule of 2002 Design of detector/electronics LuLin test Calibration Detector thought Conclusion

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.

Design of detector/electronics

Main task of this design – create a simple equipment for the measurement of background light from a mountain.

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)

Preamplifier test with test pulse Q~3*10^7 e (~10 photons)

Hamamatsu PMT testUniformity from different channels

NTU

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HAMAMATSU

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Measured at NTU Data from Hamamatsu

Broken PMT

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

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

Design of detector/electronics

Trigger: from TTM2 to NuTel Trigger• Change 3 IC (transmitters onto receivers)

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)

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

Design of detector/electronics

DAQ: some print-screens from software

Design of detector/electronics

Main task of this design – create a simple equipment for the measurement of background light from a mountain

LuLin test Some pictures from LuLin observatory

LuLin test Some pictures from LuLin observatory

LuLin test Some pictures from night shifts

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

Lulin Set-up

Lens: 15cm radius

Total PMT area 1.75cm x 1.75 cm

Neutral density

BG3

PMT Plate

Focal length 30 cm

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

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

Trigger-rate in different experiments

trigger rate

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experiments with and without BG3

trigg

er ra

te (K

)

3deg +BG3 3deg

7deg +BG3

7deg 15deg + BG3

15deg

Before Sirius

sirius

After Sirius

Photon flux in different experiments

photon flux

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200000

300000

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500000

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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

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

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

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

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)

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%

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).

Pedestal Dark current Light Limit (overflow)

Calibration Test using LED pulse 100 ns x 1kHz:

– Typical histogram in case of big photon flux

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.

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.

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.

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 .

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.

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?

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. ………..

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.