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Development of M ulti- P ixel P hoton C ounters and readout electronics. Makoto Taguchi. High Energy Group. Contents. T2K experiment M ulti- P ixel P hoton C ounters ( MPPC )

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## Makoto Taguchi

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**Development of**Multi-Pixel Photon Counters and readout electronics Makoto Taguchi High Energy Group**Contents**• T2K experiment • Multi-Pixel Photon Counters (MPPC) • Basic performance • Laser test • Readout electronics of MPPC • Conclusion**T2K experiment**main goals • search for appearance • precise measurement of disappearance J-PARC SK**# of channels ~ 60,000 and space is limited**compact & low cost under 0.2T environment tolerance to magnetic field efficiency for the detection of particles large light yield Photosensor for T2K T2K near detectors Magnet 0.2T magnet use scintillator+wave length shifting fiber for the near detectors target requirements to photosensor MPPC is chosen as the photosensor for T2K that satisfies these requirements**Multi-Pixel Photon Counter(MPPC)**• New(~2years ago) photosensor produced by Hamamatsu Photonics • 100 or 400 avalanche photodiode(APD) pixels in 1mm2 • Each pixel works in Geiger mode above breakdown voltage output from each pixel is independent of # of created p.e. within the pixel • The output from MPPC is a sum of output charge from all APD pixels output from MPPC is proportional to the # of fired pixels ~5mm photon • high (~106) gain Geiger mode • insensitive to magnetic field semiconductor • compact, low cost (~2000Yen?) • excellent photon counting attractive feature Geiger-APD pixels 100um**Measurement of basic performance of MPPC**Motivation • Test samples ・・・latest (Oct. 2006) 100 and 400 pixel samples • Test items ・・・raw signal gain noise rate Photon detection efficiency crosstalk-rate Linearity recovery time MPPC is a new photodetector Basic performance of MPPC satisfies the T2K requirement? presented here**Raw signal**blue LED MPPC output charge oscilloscope or ADC photon pedestal pedestal 1p.e. 1p.e. 2p.e. 3p.e. 2p.e. gate 3p.e. Excellent photon counting capability!**15deg.**Gain 20deg. 25deg. ADC distribution pedestal 1p.e. Q Gain = Q/e bias voltage C : capacitance V: bias voltage Vbd : breakdown voltage • Gain = 1.0x106 ~ 3.0x106 and increases with lower temperature • linear dependence on bias voltage, G = C (V-Vbd)**Noise rate**• MPPC emits thermal noise without external light • count the rate above thresholds of 0.5p.e. and 1.5p.e. (kHz) • noise rate at 0.5p.e. th. <500kHz and becomes higher with higher temperature • noise rate at 1.5p.e. th. <100kHz and becomes higher with lower temperature • cross-talk effect 0.5p.e. th. 1.5p.e. th. 15deg. 20deg. 25deg. bias voltage**Cross-talk**• “photons generated during an avalanche trigger another avalanche in neighboring pixel” crosstalk rate = fobserved 1- 15deg. festimated • Crosstalk rate 0.2 ~ 0.4 and increases with lower temperature 20deg. festimated : estimated fraction of 1p.e. events from that of pedestal events assuming Poisson fobserved : observed fraction of 1p.e. events 25deg. ADC dist. bias voltage**Photon Detection Efficiency(PDE)**x QE x • PDE = Geiger probability (V,T) ~90% geometrical efficiency ~70% quantum efficiency of APD ~70% PDE(MPPC)/QE(PMT) • PDE of MPPC is 2~3 higher than that of PMT and increases with lower temperature setup PMT blue LED WLS fiber 15deg. 20deg. 25deg. p.e.(MPPC) MPPC 1mmφslit p.e.(PMT) V**Summary of basic performance**@20deg. Performance of MPPC satisfies the requirements for T2K!**Motivation**Laser test for the old samples, • gain in the edge of pixel is higher than that in the center of pixel • breakdown voltage is different in each pixel check the response within one pixel /of each pixel for the new samples • test items ・・・ gain, efficiency, cross-talk presented here efficiency = setup # of events > 0.5p.e. # of total events green laser • pixel-to-pixel uniformity • uniformity within one pixel MPPC 10um movable stage**uniformity within one pixel**pixel-to-pixel uniformity gain gain RMS/mean=2.0% Response within one pixel/of each pixel is well uniform! RMS/mean=3.3% efficiency efficiency RMS/mean=2.0% RMS/mean=2.5%**use ~60,000 MPPCs in T2K and compact&multi-channel**electronics is necessary establishment of test system for mass production of MPPC is also needed we have developed the readout electronics with Trip-t ASIC produced at Fermilab 32 channel inputs for negative charge 1) serialized analog output corresponding to the amplitude of input charge 2) serialized analog output corresponding to the timing of input charge 3) discriminated output for each channel Readout electronics of MPPC with “Trip-t” chip Motivation Trip-t 14mm 14mm # of readout channels 321**ch2**A_OUT (charge) ch1 ch3 Trip-t input charge ch1 analog multiplexer charge Pipeline front end ch2 timing T_OUT (timing) analog multiplexer ch3 Pipeline digital Digital multiplexer D_OUT(digital) • amplifier (gain is adjustable) • generate digital signals store signals before readout (depth 1~48) serialize 32ch signals**Readout of MPPC with Trip-t**test board(4ch) output from Trip-t 3p.e. 2p.e. 1p.e. LED AD conversion by flash ADC 4MPPC readout 4 MPPCs simultaneously succeed in developing the multi-channel readout electronics of MPPC! 400pixel 100pixel 400pixel 400pixel**Dynamic range of Trip-t**ADC count • Dynamic range ~40p.e. with the lowest gain of Trip-t, assuming MPPC gain of 7.5x105 • OK for test of large number of MPPCs • not OK for T2K (requires ~100p.e.) saturation Trip-t can be used for the readout electronics of MPPC in T2K Trip-t gain > > high/low gain method for real type elec. charge(-pC) 100pF high gain channel MPPC • high gain channel ・・determine gain w/ photopeaks • low gain channel・・accommodate large signal low gain channel 10pF**Conclusion**• MPPC is a new photodetector produced by Hamamatsu Photonics and chosen as the photosensor for T2K • Basic performance of MPPC satisfies the requirements for T2K • Response within one pixel/of each pixel is well uniform • Trip-t which was produced at Fermilab can be used for the readout electronics of MPPC in T2K • future development ・・test of large number of MPPCs with 32ch Trip-t board • Our study is an important step not only for T2K but also for wide use of MPPC**Principle of APD**• high reverse bias voltage applied to a pn junction • multiplication region, where created e- -e+ pairs cause an avalanche multiplication • Normal mode - operate below the breakdown voltage(Vbd) - gain < ~ 100 - have linear output to # of injected photons reverse bias • Geiger mode - operate above the breakdown voltage(Vbd) • - gain ~106 - does not have linear output to # of injected photons E**Gain**15deg. 20deg. 25deg. 100pixel 400pixel bias bias**15deg.**gain(2) ΔV =V-Vbd 20deg. 25deg. 400pixel 100pixel ΔV ΔV Gain is a function of only ΔV**Device-by-device gain variation**• 400pixel #1 #1 #2 #2 #3 #3 bias V ΔV =V-Vbd Device-by-device gain variation comes from the device-by-device variation of Vbd**15deg.**Noise rate 20deg. 25deg. 100pixel 400pixel (kHz) (kHz) 0.5p.e. th. 0.5p.e. th. 1.5p.e. th. 1.5p.e. th. bias bias**Device-by-device variation of noise rate at 0.5p.e. th.**• 400pixel (kHz) (kHz) #1 #1 #2 #2 #3 #3 ΔV =V-Vbd bias V Device-by-device variation of noise rate comes from the device-by-device variation of Vbd**15deg.**Cross-talk rate 20deg. 25deg. 100pixel 400pixel bias bias**15deg.**Cross-talk rate(2) ΔV =V-Vbd 20deg. 25deg. 400pixel 100pixel ΔV ΔV cross-talk rate is a function of only ΔV**Device-by-device variation of cross-talk rate**• 400pixel #1 #1 #2 #2 #3 #3 ΔV = V-Vbd bias V Device-by-device variation of cross-talk rate comes from the device-by-device variation of Vbd**15deg.**PDE(MPPC)/QE(PMT) 20deg. 25deg. 400pixel 100pixel bias bias**15deg.**PDE(MPPC)/QE(PMT)(2) 20deg. 25deg. ΔV =V-Vbd 100pixel 400pixel ΔV ΔV PDE is a function of only ΔV**Device-by-device variation of PDE**• 400pixel #1 #1 #2 #2 #3 #3 bias V ΔV = V-Vbd Device-by-device variation of PDE comes from the device-by-device variation of Vbd**Vbd vs T**Vbd Vbd 400pixel 100pixel degree degree Vbd is proportional to the temperature**Comparison of latest and old samples (gain)**100pixel 400pixel latest old latest old ΔV ΔV**Comparison of latest and old samples (noise rate)**100pixel 400pixel (kHz) (kHz) latest latest old old ΔV ΔV noise rate of latest sample is lower**Comparison of latest and old samples (cross-talk rate)**100pixel 400pixel latest latest old old ΔV ΔV cross-talk rate of latest sample is higher increase of geometrical efficiency**Comparison of latest and old samples (PDE)**100pixel 400pixel latest latest old old ΔV ΔV PDE of latest sample is higher increase of geometrical efficiency**Linearity**setup • # of injected p.e. to MPPC is estimated by the p.e. detected by a monitor PMT • expected response: paper MPPC LED Nfired : # of fired pixels N0 : # of pixels c : Cross-talk rate x : # of injected p.e. PMT**(Data-exp.)/Data(%)**# of fired pixel +10% 100pixel Data -10% injected p.e. expectation injected p.e. (Data-exp.)/Data(%) # of fired pixel +20% 400pixel Data expectation -10% injected p.e. injected p.e.**Linearity(3)**(Data-Fit)/Data(%) (Data-Fit)/Data(%) 400pixel 100pixel -20% -20% # of injected p.e. # of injected p.e.**Recovery time**• “time to quench an avalanche and then reset the applied voltage to its initial value” • fire all pixels by the light from LED1 and check the response to the light from another LED(LED2) with changing the time difference between the LED1 and LED2**Recovery time(2)**• 100 pixel • 400 pixel All pixels are recovered 100ns after all pixels are fired Recovery time < 100ns**uniformity of cross-talk rate within one pixel**# of events > 1.5p.e. cross-talk rate = # of events > 0.5p.e. 100pixel 400pixel**Pixel-to-pixel uniformity of cross-talk rate**400pixel 100pixel**Measurement of active area inside one pixel**efficiency 400pixel 100pixel efficiency =58% =72% 38um 85um 50um 100um um um laser spot scan**Correction of MPPC signal**Motivation Gain, PDE, crosstalk of MPPC are all sensitive to the temperature and bias voltage 1 MPPC Signal ∝ Gain(T,V) x PDE(T,V) x 1-crosstalk(T,V) T : temperature V : bias voltage It is necessary to correct the variation of gain, PDE,crosstalk when temperature or bias voltage changes I have studied two correction methods**put scintillators in four layers**inserted fibers are connected by four MPPCs(two are 400 pixel and two are 100pixel) change temperature intentionally between 20 and 25 degree The same bias voltage is applied to four MPPCs two triggers(cosmic,LED) Set up cosmic-ray blue LED MPPC1(100) MPPC2(100) 1/2inch PMT MPPC3(400) MPPC4(400) scintillator 1mm φfiber temperature chamber With this setup we have traced the variation of light yield for cosmic-ray

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