1. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Time calibration in NEMO M. Circella, INFN Bari Time calibration The NEMO Phase 1&2 towers Time calibration in NEMO Phase 1: approach, implementation, results Time calibration in NEMO Phase 2

2. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 NEMO Phase 1 mini-tower FCM Symmetric systems offshore and onshore Dense Wavelength Division Multiplexing (DWDM) based on passive Add&Drop Synchronous Protocol FCM onshore  offshore Clock recovered offshore from data flow OM Front End (FE) and time- stamping in OM Analog signals sampled at fixed rate (200 MHz) Data recording triggered when signal exceeds a remotely-set threshold The clock recovered by FCM is sent to OM Synchronous Protocol FCM  OM 800 Mbps Synchronous protocol Junction Box DWDM Add&Drop Optical Module (OM & FE) Synchronous protocol Floor Control Module (FCM) 220 m 100 m 40 m

3. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Clock Shore Station TDC 25ps sensitive GPS receiver (+/-30 ns RMS) GPS Antenna (now on the roof ot the onshore station) Control PC Modular Crate with FPGA board by National Instr. Clock recovery from GPS receiver Data and time recovery from GPS by IRIG-B format Clock Fan-out toward onshore-FCMs UTC data flow sent to onshore FCMs in synchronous protocol Go-and-Back time measurements between each pair of onshore/offshore FCMs by TDC Network Time Protocol (NTP) server for synchronization of PCs by ethernet GPS Receiver TDC Connecting Board Clock 10MHzIRIG-B 4 X LVDS Clock 4MHz 4 X LVDS Time Data 4Mbit/s FPGA Stop x Start x RS232 GPS Antenna SCSI PC NTP

4. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Time measurements in NEMO Even two identical clocks which measure time differences exactly in the same way are not guaranteed to show the same time… Same problem for all neutrino telescopes ? Time stamping is made by means of a 16-bit counter incremented at 100 MHz inside each OM PMT waveforms are sampled at 200 MHz All offshore clocks are synchronized to the onshore (GPS- syncronized) clock Time is measured in units of 125  s Each OM can be considered as a clock which measures time correctly but with a fixed delay wrt to the onshore clock

5. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Time measurements in NEMO Time stamping is made by means of a 16-bit counter incremented at 100 MHz inside each OM PMT waveforms are sampled at 200 MHz All offshore clocks are synchronized to the onshore (GPS- syncronized) clock Time is measured in units of 125  s Each OM can be considered as a clock which measures time correctly but with a fixed delay w.r.t. to the onshore clock

6. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Time measurements in NEMO (and time calibration) Each OM can be considered as a clock which measures time correctly but with a fixed delay w.r.t. to the onshore clock Such delay depends on: - length of cables (fixed once the integration is finished) - onshore and offshore electronics (fixed but… ageing may matter?) - PMT transit time (it depends on the operating conditions and may change with ageing) We need a system able to illuminate the PMTs at known times

7. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Time calibration system of NEMO Phase 1 I floor II floor III floor IV floor Optical module Optical fibre (in connection cables) Electro-optical connector pulser splitting box Approach: network of optical fibres to illuminate groups of PMTs by means of fast optical pulsers

8. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Why an optical fibre network for time calibration (in Phase 1)? We decided not to use optical beacons in the water, because of: Large spacing (and peculiar orientation) of the PMTs on the NEMO tower Decoupling from positioning system and water characteristics (e.g.: attenuation, scattering) With a proper design of the fibre network, the PTMs can be illuminated at comparable levels of light Interesting possibility for the implementation of very large detectors

9. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 The optical fibre The search has been made with attention to the best optical properties (attenuation, chromatic and multimodal dispersion) The fibre was then characterized for the effects on operating conditions (temperature, pressure) Selected fiber: Thorlabs AFS50/125 Multimode 0.22 NA Core 50  m Monomodal and multimodal fibres tested Optimal fibre features: multimodal low chromatic dispersion at visible wavelengths large numerical aperture large core

10. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Testing/characterizing the fibre Hyperbaric tests: no performance variation up to 200 bar Oven tests: negligible temperature correction needed for our fibre lengths

11. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 The optical network Electro-optical connector Splitter 10/90 1x2 Splitter 50/50 1x2 Splitter 50/50 2x2 Commercial components (cheap and easily available) used for splitter box assembly

12. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 The optical pulser Pulser LED + fibre interface Power conditioning Intensity control Control connector Power connector LED Agilent HLMP CB15 InGaN Blue Central wavelength 472 nm Low power consumption (+5V e +12V) Small and compact board Evolved from an old design by Kapustinski et al. Response time jitter less than 100 ps Coarse and fine control of the pulse intensity Pulse intensity may be changed from 1-2 to about 10 photoelectrons No performance degradation after (equivalent) usage of >5 years

13. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Optical interfaces I We need effective and robust coupling A collimator is used on the pulser board for LED/optical fibre coupling

14. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Optical interfaces II 10° We need effective and robust coupling A collimator is used on the pulser board for LED/optical fibre coupling The light is injected into the PMT from its neck

15. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Putting all things together… 160 cm 70 cm Floor Control Module (internal view) Floor Control Module (external view)

16. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Putting all things together…(II) Various phases of FCM integration

17. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Low-resolution calibration pulse times (Raw) signals from the optical pulsers Example: the pulser from plane 2 illuminates the OMs on planes 1, 2 and 3 OM0 and OM3 on plane 1 OM0 and OM3 on plane 3 The four OMs on plane 2

18. OFFSET INTERFACE OFFSET INTERFACE Control Panel Result Panel

19. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Offset calculations Time in 125µs time window High-resolution correction Offset i = 125  s – t peak,i + pre-calibration i

20. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 From Phase 1 to Phase 2 System worked smoothly in NEMO Phase 1, but… -pre-calibration was a hard task -cabling layout was complicated (and integration of FCM painful) -fibres increase cable costs No calibration fibres in NEMO Phase 2 cables Optical pulsers moved into the optical modules

21. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 2 pairs 1 pair FCM clock outin TimCal TimCtrl TimCal: - it generates the calibration pulses - it controls the pulse intensity - it generates ‘echo’ signals TimCtrl: - it communicates with the shore station - it takes control of TimCal operations - it performs TDC measurements of the echo signals from TimCal Power of TimCal transferred from TimCtrl Power of TimCtrl & TimCal: +12V Upper floor Lower floor The NEMO Phase 2 time cal. system FCM 1 pair Requirements: - TimCal stable for an adequate lifetime - Cable delays are known (or measurable)

22. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 2 pairs 1 pair FCM clock outin TimCal TimCtrl TimCal: equipped with an Altera MAX-II CPLD for all logic operations 2 DACs used or LED voltage set (coarse/fine resolution) ADC for voltage check LED support redesigned Upper floor Lower floor The NEMO Phase 2 time cal. system FCM 1 pair TimCal board (prel.)

23. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 The NEMO Phase 2 time cal. system The pulser will be mounted directly on the front-end board The light will be injected into the PMT by means of an optical fibre using the same interface used in Phase 1

24. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 2 pairs 1 pair FCM clock outin TimCal TimCtrl TimCtrl: Commercial board (featuring Altera Cyclone III FPGA) + connection board TDC implemented inside FPGA (resolution ~0.5 ns) Upper floor Lower floor The NEMO Phase 2 time cal. system FCM 1 pair Connection board (prel.) TimCtrl board

25. M. Circella, INFN Bari Time-calibration in NEMO VLVnT08 Conclusions Time calibration system of NEMO Phase 1 up and running… Time calibration system of NEMO Phase 2 under implementation Both systems may be useful developments for very large detectors