2007/Feb/6 ACFA ILC Workshop ICEPP , University of Tokyo Hidetoshi OTONO

1. A proposal of new simple system for testing a large number of MPPCfor the R&D phase of GLD calorimeter 2007/Feb/6 ACFA ILC Workshop ICEPP , University of Tokyo Hidetoshi OTONO On behalf of the GLD calorimeter group

2. Summary as Contents A large number of MPPCs are made in coming years in R&D. Checking them would be required for sharing the task among many universities; thus simple, robust, cheap and precise system is preferable. • Improvement points; • -Hardware • Developed a serializer (with optical relay) in order to reduce the number of expensive devices such as amplifiers and ADCs. • -Software • Simplification of measurement method for basic properties; • A way to simultaneously evaluate the • dark noise rate • noise rate due to cross-talk (double pulse height) • gain of each MPPC . • of each MPPCs.

3. Motivation 10M In near future, we would hopefully test a prototype with order of 100K MPPCs. 100k Num. of MPPCs Now Experiment 10k R&D Period 1k Time • Several calorimeter beam tests with • increasing number of MPPCs are expected • before the real ILC experiment. • We have to check basic properties (gain, noise rate, • etc.) of brand-new MPPCs in each phase of R&D. • The simple, robust and cheap measurement method • is preferable.

4. Hardware : A development of • signal serializer in order to reduce • the number of expensive amplifiers and so on. • Present method • A proposal of new method

5. Modules AMP AMP Module AMP Multi- plexer AMP AMP Issue of Present Method Control PC RS232C Present method uses parallel AMPs and ADCmodules. HV ＭＰＰＣ ＭＰＰＣ Sequential process ＭＰＰＣ ＭＰＰＣ

6. Our Method Measurement target For this purpose We have chosen optical relay. Control PC RS232C HV DC Supply About 5$ ＭＰＰＣ relayOFF ＭＰＰＣ relayOFF relayOn ＭＰＰＣ relayOFF AMP modules ＭＰＰＣ relayOFF

7. Picture of the Circuit with Relay MPPC output after a relay AMP MPPC output before a relay Supply voltage for a relay OFF OFF OFF ON Supply voltage for a relay

8. Requirement and Choice of Relay Isolation (how well the pulse can be stopped when a relay OFF) ? High isolation is required. relayOFF Insertion loss (how well the pulse can be passed when a relay ON) ? Low insertion loss is required. relayOn Isolation Insertion loss [dB] [dB] 0.6dB 10ns Orange’s properties between 100MHz ~ 1GHz 0.3dB 10dB Insertion loss Isolation Isolation: 10dB~30dB Insertion loss: 0.3dB~0.6dB GOOD GOOD 30dB 100MHz 100MHz 1GHz 1GHz

9. The effects of serializer on 10 samples Noise rate due to Cross-talk Noise rate Gain With relay[10^5] With relay [kHz] With relay [kHz] A few % No relay [kHz] No relay [kHz] No relay [10^5] There is no effect on noise rate and Cross-talk rate. Gain measurement with a relay is shifted a few percents, because of insertion loss →Correction is needed for gain measurement. Noise rate and cross-talk rate spreads are about 10%, gain spread is 3%, due to large temperature variation.

10. Plan • The relay elements is quite effective in reducing the number of AMP and costs. • Our 4ch circuit is still noisy, we need more improvement. • We are going to make a circuit with many relays. • In parallel, we are searching another candidate for serializer.

11. Software : We applied MPPC’s photon counting capabilities to simplify and • the measurement of noise rate, cross-talk rate and gain. • Moreover we raise the precision of measurement. • Present method • A proposal of new method

12. Present Measurement Scaler counting for Noise rate measurement (double pulse height) Setting MPPC LED on Gain measurement Adapting threshold for noise rate (double pulse height) LED off Threshold searching Adjusting threshold for noise rate Scaler counting for Noise rate measurement

13. A proposal of new method Change MPPC • Using dark noise for gain measurement • Threshold is fixed for noise rate • Noise rate • Noise rate • (double pulse height) • Gain OFFLINE analysis Taking ADC histogram

14. Our Circuit For the measurement of DAQ dead-time The number of MPPCs will be increasing . Scaler Clock Coin. latch AMP MPPC AMP Disc. relayOn x 63 x 10 Output register G.G veto Dark Box latch Disc. DC Supply Charge ADC RS232C 40ns gate HV Control PC NIM CCNET CAMAC

15. Our Method Gate = 40ns GAIN Num. of event Noise rate (to be corrected for DAQ dead time) Noise rate (double pulse height) (to be corrected for DAQ dead time) THRESHOLD Channel Accidental coincidence rate of Noise is negligible. So the second peak is due to Cross-talk.

16. Results Noise rate Noise rate (double pulse hight) • OURS • HPK Noise rate [kHz] • OURS • HPK Noise rate [kHz] Bias Voltage Bias Voltage We compared our measurement with HPK data Gain • OURS • HPK Gain [10^5] • Noise rate and Gain is good correlation • with HPKdata. • Difference can be seen • for noise rate (double pulse height) • 　→We are studying now. Bias Voltage

17. The Picture of Pulses We show several pulses which we are studying now. • Very closing pulses • Curious pulses like discharge whose reason is completely unknown. We took all pictures at 78.8V which is typical voltage for MPPC uses and they can be frequently shown .

18. Very closing pulses 40ns 40ns 40ns 40ns

19. Curious Pulses 40ns 40ns 40ns 40ns

20. Plans • Our method can be use for very closing pulses, and ours is more precise than present method. • Accidental coincidence of noises is negligible at 100kHz noise rate, thus the closing pulses can’t explain the difference between measurement method. • We guess that the closing pulses are due to cross-talk, though cross-talk induces ONLY the double pulse height output by present view. we are studying now. • The origin of curious pulses is unknown, thus we are studying too.

21. Summary Improvement points; -Hardware Developed a serializer (with optical relay) in order to reduce the number of expensive device such as amplifiers and ADCs -Software Simplification of measurement method for basic properties; a way to simultaneously evaluate the dark noise rate, noise rate (double pulse height) and gain . A large number of MPPCs are made in coming years in R&D. Checking them would be required for sharing the task among many universities; thus simple, robust, cheap and precise system is preferable. Our system is suitable for this purpose.

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23. Result (cont’d) Noise rate due to cross-talk • OURS • PRESENT • HPK Comparison with the result of the same MPPC by present system at another university A significant difference can be seen . The difference is about 2 times. It’s our guess that the reason is understanding of cross-talk.

24. Our Idea of Cross-talk Present idea Our idea MPPC signal MPPC signal MPPC signal OR (c.f) normal noise MPPC outputs two types of pulse due to cross-talk; two times pulse height of normal noise and double closed normal noise The present method judges the latter as single normal noise

25. A Candidate of Difference between Measurement Methods Present measurement method MPPC signal THR Disc. out 2 noises scaler Our measurement method MPPC signal 3 noises ADC ADC date Accidental coincidence rate of Noise is negligible. These can’t perfectly explain the difference.

26. Typical Pulse DarkBlue : raw pulse LightBlue : pulse via ONrelay Pink : pulse via OFFrelay

27. Gain Measurement Method Test Measurement with light source = 2.75 (10^5) Gain We checked 10 MPPCs Measurement without light source = 2.7 + 0.07 (10^5) _ Thus we decide to use Dark noise for Gain. Gain(10^5)

28. Dependence on temperature • 30oC • 25oC • 20oC • 15oC • 10oC • 0oC • -20oC • 30 oC • 25 oC • 20 oC • 15 oC • 10 oC • 0 oC • -20 oC 1p.e rate