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ALCPG, Cornell University July 14-16 th. 2003 Scintillator Readout w/ Geiger Avalanche Photodiodes - update since Arlington David Warner, Robert J. Wilson.

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Presentation on theme: "ALCPG, Cornell University July 14-16 th. 2003 Scintillator Readout w/ Geiger Avalanche Photodiodes - update since Arlington David Warner, Robert J. Wilson."— Presentation transcript:

1 ALCPG, Cornell University July 14-16 th. 2003 Scintillator Readout w/ Geiger Avalanche Photodiodes - update since Arlington David Warner, Robert J. Wilson Department of Physics Colorado State University Stefan Vasile aPeak 63 Albert Road, Newton, MA 02466-1303

2 R.J.Wilson, Colorado State University Motivation Scintillating fiber, or WLS readout of scintillator strips basic component of several existing detectors (MINOS, CMS-HCAL); option for LCD Standard photodetector – photomultiplier tubes, great devices but… –“ Expensive ” (including electronics etc.), –Bulky, magnetic field sensitive… –Multi-anode PMTs a great step forward. Geiger-mode Avalanche photodiodes (GPDs) –Large pulse (~volt); high quantum efficiency; relatively fast; small pixels (10-150 microns); Con: high dark count rate. –Compact; low mass; low voltage operation (~10s volts) – modest physical plant; magnetic field insensitive; compatible with CMOS - cheap? New funds available to the developer, aPeak (Newton, Mass.) –Small p.o. from SLAC/CSU –A Phase I DoE SBIR recently approved w/ subcontract to CSU

3 R.J.Wilson, Colorado State University Status at Arlington (01/10/03) Encouraging device characteristics measurements on small diameter GPDs (at aPeak) “Old” unpackaged 50  m GPDs showed substantially increased dark count rate making them unusable for our studies; aPeak has designed new GPDs in a shared IR&D run using a technology less sensitive to moisture problems. HEP will likely use sealed package in any case. Active quenching circuitry provides 1  s - 0.1  s pulse widths. Tapered optical couplers fabricated. Cosmic ray test setup with MINOS-style scintillator/fiber from SLAC. Calibrated with 1” pmts. Larger, 150  m devices by early February, 2003. Applying for funds to continue the work.

4 R.J.Wilson, Colorado State University Since Arlington New 50 and 150  m GPDs received by aPeak February, 2003; characterized with a pulsed, green LED source by aPeak. Only available for our studies for a short time. CSU cosmics apparatus taken to aPeak (Warner); data taken by Warner & Vasile over few days. aPeak received SBIR Phase I award with sub-contract to CSU; includes funds for devices at CSU (finally!)

5 R.J.Wilson, Colorado State University All characterization measurements were performed at aPeak. Configuration: Green (550 nm) LED, 150 ns pulse@10 kHz Avg. ~10 photons/pulse Fixed bias GPD, 14.5 V Active quench circuit (< 1  sec output pulse width) Measurements: Dark Count Rate, DCR Detection Efficiency, DE = (Illuminated Rate - Dark Rate)/10 kHz Temperature dependence Device Characterization

6 R.J.Wilson, Colorado State University 50  m  150  m  DE DCR DE DCR DE DCR DE DCR Temperature Dependence New devices characteristics (1) DE=Detection Efficiency, DCR= Dark Count Rate

7 R.J.Wilson, Colorado State University Interpreting Detection Efficiency # photons detected, n d = QE * A * N  where N  is the number photons incident on the photodetector and QE*A is an effective single photon detection efficiency. From Poisson statistics, the probability for n d to fluctuate to 0 is given by: So the we define a Detection Efficiency, For 150 micron GPD at 20 o C, DE~0.50 for ~10 => QE*A ~ 0.069

8 R.J.Wilson, Colorado State University Dark Count Rate: Breakdown voltage, temperature New devices characteristics (2) 50  m  150  m  Volts above breakdown DCR GPDs with passive quenching used for these measurements Range doesn’t extend to operating region of the cosmic ray test configuration (solid lines shouldn’t be used for extrapolation)

9 R.J.Wilson, Colorado State University New devices characteristics (3) Breakdown voltage; Detection Efficiency 150  m  50  m  slope = 13 mV/  C Temperature,  C Breakdown, V Bias voltage, V R 1.00 0.50 11 photons/pulse average ~room temp. Detection Efficiency Breakdown voltage vs. Temp.Detection Eff. vs. Bias voltage 13.6513.7013.7513.8013.8513.90 Breakdown voltage relatively insensitive to temperature Detection efficiency plateaus well (need to see behavior for higher values of V R )

10 R.J.Wilson, Colorado State University GPD Scintillating Fiber Test Bed For these measurements only a single fiber was instrumented with GPD readout.

11 R.J.Wilson, Colorado State University GPD Scintillating Fiber Test Bed Disc. Ch. T Disc. Ch. B 2-Fold Coinc. Cosmic Ray Trigger (To Scalar Ch. 1 and GPD Coincidence) Disc. Y-11 Readout Coinc. 2-Fold GPD/PMT Coincidence GPD Noise RateMonitor From GPD Active QuenchAmp. Scope Trigger Scintillators Test Bar HV (From PMT) MINOS-style scintillator bar w/ Y11 WLS readout – courtesy of SLAC

12 R.J.Wilson, Colorado State University

13 Cosmics detection efficiency No ADC/DAQ available at aPeak so … Estimate average number of photons/event at the end of spliced Y11 fiber using digital scope traces from the reference pmt (average pulse height and pulse width into 50-ohm load). For 1 mm diameter Y11 cores and 0.15 mm GPDs: Using QE*A=0.069 estimated for 150 micron GPD at 20 o C, predict DE = (1-exp(-0.069*4) = 0.24 This neglects additional losses, such as Fresnel reflection at the Y11-GPD interface.

14 R.J.Wilson, Colorado State University GPD Efficiency Procedure We compare the triple coincidence of two hodoscope scintillators and the GPD readout of the test bar with that of the hodoscope alone after correcting the triple rate for accidentals due to the GPD dark count rate (375 kHz). Low statistics signal runs (4-8 hours) were taken for three configurations with the hodoscope positioned to provide essentially full coverage of the test bar. These signal runs were interspersed with background runs for which the hodoscope was moved to give essentially zero overlap with the test bar. These background data were compared to the expected accidental rate from the measured GPD dark count rate. For configurations 1 and 2, there was a press-fit air interface between the Y11 fiber and the GPD; for configuration 3, optical grease was used to improve the coupling. For configurations 2 and 3, the GPD discriminator output and trigger gate widths were reduced, halving the probability for accidental coincidences.

15 R.J.Wilson, Colorado State University Very Preliminary Data

16 R.J.Wilson, Colorado State University Comments  These preliminary data were taken under less than ideal circumstances, so one should beware of drawing firm quantitative conclusions. With that caveat…  It is the first demonstration of WLS fiber readout with the aPeak GPDs  The measured detection efficiency with the Y11 readout of 21±5(stat.)±??(sys.)% is consistent with that predicted using the LED measurements  Doubling the number of incident photons (perhaps with a tapered optical coupling) should roughly double the detection efficiency  Lowering the GPD operating temperature to –30ºC potentially will more than double the detection efficiency as well as reduce the dark count rate

17 R.J.Wilson, Colorado State University Future Plans aPeak SBIR Work plan: Fabricate 2 runs of GPD arrays using two layout design concepts Development of active quenching circuits for hybrid integration Electro-optical evaluation of the GPD array and active quenching circuitry array performance, including reliability testing Continue to improve the layout design for increased detection efficiency, lower dark count rate and GPD array re-configuration on-the-fly Evaluation of GPD prototypes for detection efficiency, false counts, and timing performance on a cosmic ray setup – at CSU Investigate potential for use in LCD Muon/Calorimeter readout. Review multi-pixel/fiber readout scheme (c.f. B. Dolgoshein, Silicon Photomultiplier)

18 R.J.Wilson, Colorado State University aPeak Advertisement


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