1. 1 A proposal of new simple system for testing a large number of MPPC for 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. 2 Summary as Contents 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. 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.

3. 3 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. Motivation Num. of MPPCs Time 1k 10k 100k 10M Experiment R&D Period Now In near future, we would hopefully test a prototype with order of 100K MPPCs.

4. 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. 5 Issue of Present Method ＭＰＰＣ Control PC HV RS232C Present method uses parallel AMPs and ADCmodules. Sequential process Modules AMP Multi- plexer Module

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

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

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

9. 9 The effects of serializer on 10 samples Noise rate Noise rate due to Cross-talk Gain No relay [10^5] No relay [kHz] With relay [kHz] With relay[10^5] No relay [kHz] 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. A few %

10. 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. 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. 12 Present Measurement LED on Gain measurement LED off Threshold searching Adjusting threshold for noise rate Scaler counting for Noise rate measurement Adapting threshold for noise rate (double pulse height) Scaler counting for Noise rate measurement (double pulse height) Setting MPPC

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

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

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

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

17. 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. 18 40ns Very closing pulses

19. 19 Curious Pulses 40ns

20. 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. 21 Summary 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. 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.

22. 22 backup

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

24. 24 Our Idea of Cross-talk MPPC signal Present ideaOur idea OR 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 (c.f) normal noise

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

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

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

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