Acoustic Sensors for the ANTARES Experiment supported by

Acoustic Sensors for the ANTARES Experiment supported by the BMBF Christopher Naumann, Physikalisches Institut IV Universität Erlangen-Nürnberg ARENA Workshop, Zeuthen, 2005

Acoustic Particle Detection – Sound Production Neutrino creates hadronic shower in water energy is deposited heats water up local expansion+relaxation pressure signal (bipolar) other marine sources of sound: wind, waves, ships, animals ARENA, 2005 sound range in water: O(km) (3. 1 km for 10 k. Hz, 135 m for 100 k. Hz) Christopher Naumann

Signal and Noise Spectrum in the Sea • noise depends on wind speed • at high frequencies dominated by thermal noise • Expected signal (green, arbitrary units): maximum between 10 and 50 k. Hz, where noise is minimal (at sea state zero) look for signal in frequency band ~10 to ~50 k. Hz ARENA, 2005 try to look for neutrinos in the deep sea ! Christopher Naumann

The ANTARES Neutrino Telescope Antares-Design: 12 Strings x 25 Storeys x 3 optical modules for the optical detection of neutrinos from 100 Ge. V up to 1 Pe. V Additional goal: use ANTARES as test infrastructure for acoustic detection ! ARENA, 2005 Christopher Naumann

Aim: Acoustic Storeys • Equip several ANTARES storeys for acoustic particle detection… 1. ) remove optical components (photomultipliers, etc. ) ? 2. ) replace with acoustic sensors "Eyes of ANTARES" "Ears" Unfortunately, it's not as easy as that… ARENA, 2005 Christopher Naumann

ANTARES Acoustics: Requirements • ANTARES site 2400|m below the sea: – must be pressure resistant (>250|bar) and able to survive hostile environment (sea water at ~13°C) • expected pressure signals from neutrino events (Askaryan): ~10 m. Pa peak-to-peak for 1018 e. V in 400 m distance require very sensitive sensors (µPa – m. Pa) • high acoustic background in the sea (~2. 5 m. Pa between 10 -100 k. Hz at no wind) need sophisticated background suppression (filters, coincidence triggers) • future acoustic detector needs at least O(103) sensors (probably more) cost of single sensors should be as low as possible ARENA, 2005 Christopher Naumann

Concept One: Single Hydrophones easiest method: build an „array“ of hydrophones, which are attached to the optical module frame alternative: customised hydrophones from ITEP ARENA, 2005 guaranteed waterproof and pressure-resistant already calibrated electronics idea: buy commercial hydrophones commercial hydrophone (here: HTI) hydrophones are used by the navy and for fishing not optimised for neutrinos ! Difficult to change specifications ! currently sensitivity too poor ( <<1 V/Pa) possible design for „acoustic storey“ with 6 hydrophones Christopher Naumann

Self-Made Hydrophones alternative: build our own hydrophones from scratch 5 cm piezo tube pre-amp+cable polyurethane coating against water and pressure can build to our own specifications (piezo, amplifier, coating, directional characteristics) probably much cheaper (<200€ ? ) R&D necessary ! ARENA, 2005 2 cm small hydrophone prototype for test in pressure tank Christopher Naumann

Second Concept: “Acoustic Modules“ • basic idea: equip glass spheres of optical modules (OM) with acoustics hardware instead of photomultipliers 17" (42 cm) OM "AM" Photomultiplier ARENA, 2005 acoustic sensors and electronics (schematic) Christopher Naumann

Sensors - Layout piezo ceramics (eg. PZT-5 A or PZT 7 A), glued to glass sphere pre-amplifiers (70 d. B), band pass filters (3. 4 – 72 k. Hz) 2. 5 cm use an array of several sensors per sphere for background suppression via correlation sensor array for sphere must be able to calibrate and study sensors… ARENA, 2005 Christopher Naumann

Signal Measurement and Sensor Calibration calibrated transducer "Fish Tank" external or internal preamplifier (HTI) calibration signal sensor response compare sent and received signals calibration ARENA, 2005 Christopher Naumann

Comparison of Signals - Examples hydrophone / sensor response to bipolar pressure signal from calibrated transducer (vertical scale identical) commercial hydrophone self-made hydrophone sensor in glass sphere 200µs signal shapes influenced by coating, glass sphere and pre-amplifier • limited amplifier bandwidth to reduce noise => signal distorted • have to find events in background => must understand signal shape To understand signal shape, must know sensitivity spectrum. . . ARENA, 2005 Christopher Naumann

Device Calibration Chain: 1. Cross-calibrate transducers using identical pair 2. Use this calibration to calculate receiver sensitivity can get complete spectrum from only one measurement per sensor device Sensitivity of Piezo+Pre-Amp piezo resonances “plateau” at -120 d. Bre(V/µPa) can calibrate self-made sensors and sensor arrays in our laboratory no need for complicated calibration source ! Use calibrated transducer only relative calibration need at least one absolute calibration source as reference (laser ? ) or fit transducer calibration curve to values given by manufacturer amplifier cut-off 10 k. Hz 100 k. Hz but lab measurements alone are not enough… ARENA, 2005 Christopher Naumann

Test Experiment: AMADEUS • important for signal analysis: good knowledge of the acoustic situation at the ANTARES site and the performance of sensors in deep sea conditions. . . Basic Idea: test acoustic sensors and data acquisition + study acoustic background in situ using an autonomous acoustic system on an ANTARES test line Situation: ANTARES test string "Line Zero" successfully deployed in March - together with. . . AMADEUS = Autonomous Module for the Acoustic DEtection Under the Sea ARENA, 2005 Christopher Naumann

AMADEUS (Architecture) hardware for data taking and storage 5 acoustic sensors on walls and top 60 cm top view batteries for >75 hours continuous data taking titanium cylinder 158 mm ARENA, 2005 Christopher Naumann

Data Taking and Storage Hardware • ADC-Board (PCI Card) (500 k. Hz, 16 bit, 2. 5/10 V) single or multiple channels, controlled via run script • autonomous PC-Board (small, low power consumption) • read from 1 to 5 sensors (at 500 k. Hz total) • write to CF card (silent !) when flash card full: • stop data taking • Buffer and Storage: – mass storage: 80 GB HDD – buffer: 1 GB compact flash card • dump card to disk (noisy !) • clear flash card • Timer to start data taking after set time (hours to weeks) repeat until hard disk full or data taking run completed ARENA, 2005 Christopher Naumann

AMADEUS (Operation) • Deployed in March together with ANTARES test string, stayed there until the middle of May • first Data already available in March, as string was recovered and re -deployed after about a day ! • data taking successful… have first acoustic data (about 12 GByte) from the ANTARES site ! data analysis has just begun… and we hear already something ! ARENA, 2005 Christopher Naumann

amplitude (V) Sound of the Sea at the ANTARES site, have acoustic beacons for positioning time (s) can use these. . . spectral density (au) 1. as calibration source time (s) 2. to study reconstruction algorithms (“find beacons“) First result: can find and identify individual beacons acoustic beacons but what we really want is hidden between the lines. . . ARENA, 2005 Christopher Naumann

noise spectrum, only few seconds of data • only small portion of data analysed: measured noise spectrum roughly in agreement with predictions. . . but expected to get better as full data analysed 10 20 30 40 50 60 70 80 90 100 k. Hz el 0 ar y sea state zero sea state 1 can see depth dependence of noise level (during line recovery) im in SS 3 pr noise spectral density (d. B re µPa 2 / Hz) Sound of the Sea (2) – noise analysis AMADEUS = an audible success ! ARENA, 2005 Christopher Naumann

Conclusion and Outlook • Hydrophones and acoustic modules under development – first prototypes working fine • Autonomous experiment AMADEUS very successful – both sensors and data acquisition working fine – have acoustic data from the ANTARES site – next data expected soon (in May, Line Zero recovered on May 12 th) • piezo+amplifier only noise level of self-made hydrophones and sensors already comparable to sea state zero (~4 m. V RMS at – 120 d. Bre(V/µPa) 4 m. Pa RMS) • Top sectors of ANTARES strings 10 and 12 to be fitted with acoustic hardware (see Robert's talk) Thank you ! ARENA, 2005 Christopher Naumann