1. Nanobeacon: A low cost calibration instrument for KM3NeT
David Calvo and Diego Real
IFIC (CSIC – Universidad de Valencia)
VLVNT-2013

2. KM3NeT: ARTIST IMPRESSION
640 strings
20 DOM/string
12800 DOMs
Volume: ~5 km3
12,800 DOMs in the deep sea at 3-5 km depth
with point-to-point connection to shore

3. KM3NeT DIGITAL OPTICAL MODULE (DOM)
Lower Hemisphere
19 PMTs
Upper Hemisphere
12 PMTs
PMT Base:
High Voltage Supply
Analog Front-End
Central Logic Board
(CLB)

4. KM3NeT TIME CALIBRATION REQUIREMENTS
The angular resolution is critical in a NT. A good angular resolution provides the needed point spread function to resolve cosmic neutrino sources from the atmospheric background.
The angular resolution relies on a good positioning and time calibration.
Working within the specifications the attainable angular resolution of KM3NeT is better than 0.1º for E > 100 TeV.
The absolute time resolution depends on:
OM time offsets (2n order effect).
Detector electronic paths (dominant effect).
In order to obtain correlations with the physics phenomena (e.g. GRB) an accuracy of 1 ms is required in the absolute timing.
Relative time resolution (between OMs) depends on:
OM transit time spread (TTS), typically σ~1-1.5 ns.
Optical properties of the sea water: light scattering + chromatic dispersion (σ~1-1.5 ns) for light coming from a distance of 50 m.
Electronics (σ<0.5 ns).
Therefore, an overall unavoidable uncertainty of ~2 ns will always be present.
The determination of the calibration constants with a σ~1 ns fulfils the requirements for relative time resolution.

5. KM3NeT TIME CALIBRATION PROPOSAL
Experience has shown that a system of external light sources with a well-known emission time is very useful to ensure the time calibration of the detector and measure water optical parameters
The main use of this system is to measure PMT time relative with LED beacons along the same detector line (intra-line calibration).
Inter-line calibration with LEDs is also possible but is more challenging due to movement of the lines. In this case the use of lasers could be an alternative to LED beacons.
Synchronizing time offsets between beacon elements is cumbersome and time consuming. An
d time consuming
Providing trigger signals introduces unwanted electrical noise to system 5

6. KM3NeT TIME CALIBRATION PROPOSAL
Decoupling within the same D.U. (intra- D.U.) and between D.U. (inter-D.U.) calibration systems
INTRA D.U. Calibration:
One Nanobeacon per DOM.
Less expensive and high redundancy
Not triggered by the clock to avoid electronic noise
Frequency of several kHz
Avoid cumbersome synchronization process, only one LED per Nanobeacon
INTER D.U. Calibration: (See Diego’s talk)
Laser 532 nm
Higher in intensity and shorter pulses < 1 ns
No synchronization needed
More expensive but less redundancy required
Tunable by Liquid Crystal Optical attenuator
Collimated beam -> Diffusion device needed 6

7. KM3NeT NANOBEACON - ELECTRONICS
Two electronic components:
Control Board:
Selects the trigger (external or internally generated in the control board).
Selects the internally generated trigger frequency.
Selects the LED intensity of flashing.
Provides a trigger and intensity signals to the pulser board.
Pulser:
It contains the LED and make it flash with the Control Board signals
The nanobeacon control board, currently a daugther board, is going to be integrated on Central Logic Board 7

8. KM3Net NANOBEACON - ELECTRONICS
NCB: Nanobeacon Control Board.
Selects the LED intensity of flashing (Booster 2.5 V V)
Selects the trigger (external or auto-trigger)
Provides an external trigger signal
Selects the frequency of the internal trigger (0 Hz – 8 KHz) 8

9. KM3Net NANOBEACON - ELECTRONICS
Pulser Board
Pulser:
Auto-triggered – External clock not needed
Controlled by a DC Voltage:
- LED intensity and frequency non-correlated 9

10. KM3NeT LED STUDIES
9 different LED models (470 nm) have been evaluated :
Light Intensity
Pulse Rise time and Width (SPE)
Angular distribution H H
FILTERS
PULSER + LED
DARK BOX
OSCILOSCOPE
LECROY Δt

11. KM3NeT NANOBEACON - PRESELECTED LEDS
LED STUDIES
5 LED Models preselected according to:
Timing characteristics
Angular distribution
MODEL
FWHM (º)
Intensity(pJ)
Rise time (ns)
FWHM (ns)
CB26
23º
150
2.4
4.6
CB30
28º 90
2.2
4.3
NSPB500S
20º
170
3.2
6.1
CB15
15 º
4.8
AB87
51º
130
Taking advantage of the redeployment of ANTARES line 12, a special LED Optical Beacon (“KM3NeT” Beacon) with the five preselected models built for in-situ validation.

12. KM3NeT NANOBEACON – PRESELECTED LEDS
The preselected model is the Avago HLMP-CB1A (replacing CB15)
Similar characteristics than CB15 but low power consumption
The circuit works at a nominal 24 V.
Nanobeacon property
Performance
Optical rise-time
~ 2.5 ns
Optical FWHM
~ 4.8 ns
Wavelength
470 nm (blue)
Angular distribution
15º
Intensity
~150 pJ
Power consumption
< 0.12 W
Reference signal w.r.t. OM signal
RMS ~ 1 ns

13. KM3NeT NANOBEACON STATUS - PPM
Nanobeacon included in the 3 DOMs of the PPM DU 13

14. KM3NeT NANOBEACON STATUS - PPM
Nanobeacons currently integrated on the PPM DU
CONTROL BOARD
PULSER BOARD 14

15. KM3NeT NANOBEACON STATUS – NEMO PHASE II
8 upwards-orientated LED Nanobeacons of different wavelengths have been integrated
2 LEDs of 470 nm were mounted on the first floor from the bottom.
2 LEDs of 470 nm on the second floor
2 LEDs of 440 nm on the third floor
and 2 LEDs of 400 nm on the fourth floor 15

16. CONCLUSIONS KM3Net Nanobeacon: Only intra D.U. calibration
Time calibration less subject to positioning and DU rotation
Scattering + attenuation corrections not so critical
Sphere not needed - Integrated in the OM spheres
Electronics and Mechanics very simple
Preliminary test OK
Inexpensive ~ 50 € / Nanobeacon
3 Nanobeacons integrated on the KM3NeT PPM DU
8 Nanobeacons of different wavelengths nm) have been integrated in “Nemo Tower Phase II”

17. THANKS FOR YOUR ATTENTION!17