Umberto Emanuele IFIC (CSIC-UV), Valencia (Spain)

1. Status of Time Calibration System for KM3NeT Umberto Emanuele IFIC (CSIC-UV), Valencia (Spain)

2. Main points • Opticalsystemdecoupling • Preliminary test in ANTARES • Status of PPM calibrationsystem • Status of NEMO phase II calibrationsystem

3. The KM3Net Detector Digital Optical Module (DOM) 31 PMTs/DOM - 40 DOM/Line 300 lines (in two separated groups)

4. Optical calibration for KM3NeT Decoupling Calibration systems • INTRA D.U. Calibration: Nano-Beacon Single LED housed inside OMs • Less expensive and high redundancy • INTER D.U. Calibration: Laser Beacons • High intensity ( > 20 μJ ) and short pulses (< 1 ns) • Collimated beam -> Diffusion device needed

5. Nanobeacon Pulser: Auto-triggered – External clock not needed Controlled by one (or two) DC Voltage: - LED intensity and frequency non-correlated Control Electronic board: Select the intensity of flashing Select the trigger (external or auto-trigger) Provides an external trigger signal Select the frequency of the external trigger

6. Nanobeacon: mechanics Two PVC made pieces: One piece glued to the glass sphere (fixed) The second one screwed (in) to the first one: Holds the LED + Electronics Protect the PMT from the Nano-Beacon Light Possibility of replacement

7. Nanobeacon: opening angle A 15°opening angle is sufficient to illuminate OMs above the beacon even in perpendicular arrangement including potential misalignment 40m 3m

8. Nanobeacon: Valencia proposal

9. Optical calibration for KM3NeT Decoupling Calibration systems • INTRA D.U. Calibration: Nano-Beacon Single LED housed inside OMs • Less expensive and high redundancy • INTER D.U. Calibration: Laser Beacons • High intensity ( > 20 μJ ) and short pulses (< 1 ns) • Collimated beam -> Diffusion device needed

10. Laser Beacon • Titanium Container • Attenuator • LASER • Anti-Biofouling System • Connector • Slow Control Inteface • Sequence of Commands • Photodiode Signal

11. Laser Beacon The Laser Beacon source is a diode pumped Q-switched Nd-YAG Teem Photonics laser which produces very short light pulses, ~ 400 ps (FWHM), of high intensity (~20 μJ) and at a wavelength of 532 nm (green). It is housed in a titanium container and can be fixed to numerous seafloor structures (for example secondary junction boxes or detection unit sea floor anchors)

12. Laser Beacon • A voltage controlled optical attenuator • A linear polarizer followed by a liquid-crystal retarder and a second linear polarizer. • Since the light from the Laser Beacon is linearly polarized, the attenuation can be achieved with only one linear polarizer. The laser head has a built-in photodiode that provides the exact time of the laser light emission GLASS ROD MECHANICAL FIXING TITANIUM COVER DIFFUSER LASER BEAM

13. KM3NeT detector « covering » TO BE TESTED few lasers would be enough to cover all detector

14. Preliminary test of the first Nanobeacon in ANTARES

15. Preliminary test of the first Nanobeacon in ANTARES Measured in water Measured in air How will affect the LED light to the OM PMT? It does not damage the PMT The detected light is good enough for giving the temporal reference

16. Preliminary test of the first Nanobeacon in ANTARES Trigger signal w.r.t. OM signal RMS ~ 1 ns How will affect the LED light to the OM PMT? It does not damage the PMT The detected light is good enough for giving the temporal reference

17. Preliminary test of the first Nanobeacon in ANTARES ThreeNanobeaconswereinstalled in ANTARES (L9F1). At present, someruns are underanalysis in ordertoevaluate and confrmthe LED light range, theagening of thecomponents and eventual biofoulingproblems. Codes for the “TimeSlices” data format have to be optimized for the analysis. However first information is obtained from GuiBeacon code.

18. First conclusion of the preliminaryanalysis of the first Nanobeacon in ANTARES The Nanobeacon seems not to saturate/damage the OM • The feeding voltage of the NB is well correlated wit the OM rates • At 280 – 300 meters light is • observed • Short runs (4 min) in ANTARES trigger setup give good statistic • It is confirmed? • It’s enough? Final analysis on photon and charge of the hits has to be performed • Does the higher frequency of KM3NeT strongly reduce the duration of runs (~sec)?

19. Status of PPM calibration system: Nanobeacon: The Nanobeacon prototype was successfully tested on the CEA CLB:    1.-  The I2C communication worked properly    2.-  The internal trigger worked properly    3.-  The external trigger provided through the CLB worked properly    4.- The geometry of the Nanobeacon was tested and some minor changes in the position of the holes was agreed.    5.- It was also agreed to change the trigger connector to a coaxial lemo in order to reduce the induced noise.

20. Status of NEMOtower phase II calibration system: Nanobeacon • Some Nanobeacons will be integrated in the Nemo Tower, in order to test: • the integration inside of an OM glass sphere • the computations of the range of the light as simulated using the specifications of the angular distribution of the light emitted by the LEDs and measurements • the communications between the main control board and light emitting sources • the reliability of the electronics in general

21. Status of NEMOtower phase II calibration system: Laser Beacon • The integration of a Laser Beacon in NEMO Tower is under study. • A Laser Beacon was built (with integrated the acoustic system) • High pressure tests were performed • A stand-alone rechargeable battery system was developed • Supports have been built, in order to mount the Laser Beacon on the anchor • A real setup test and corresponding validation by NEMO people is needed

22. Thankyou for yourattention

23. Time Calibration: main idea Trackreconstructionrequirestheknowledge of therelativearrival times of theCherenkovphotons at thePMTs and thereforeonlytheir time offsets. The time elapsedbetweentheincidence of a photononthephotocathode of the PMT and the time stamping of theassociatedsignalmust be determinated. Themaingoal of theclocksystemistoprovide a commonsignaltosynchronizethereadout of theOMs In situ measurementof the time offsets of alltheOMsisperformedwiththeOpticalBeacon (OB) system (twokind of complementarydevices): - LED beaconsthatemitblue light (470 nm) - Laser beaconsthatemitgreen light (532 nm)

24. Time Offsets determination (ANTARES experience) Line 2 storey 21 storey 15 storey 9 OM 0 OM 1 OM 2 LOB-ARS (ns) LOB-ARS (ns) LOB-ARS (ns) storey 2 storey storey storey Time residuals should be characterized by mean values well centered at zero However, there is a linear delay due to the combination of Early photon + Walk effect Deviations from the straight line are used for calibration 24

25. LEDsselection LED candidates have been tested in the laboratory, and four models were preselected. Following the recovery and redeployment of ANTARES line 12, these new models were incorporated in one of the LED optical beacons of the line and tested in situ. The selected LED was the NSPB500S, due to the higher range end the angular distribution. Based on these results, several NanoBeacons will be integrated in the forthcoming deployment of a pre-production KM3NeT DU