SPATS

1
SPATS a South Pole Acoustic Test Setup

• 1st International ARENA Workshop
• Zeuthen
• May 2005

2
Overview

• Motivation
• Experimental Targets
• Absorption and Scattering
• Speed of sound and refraction
• Background noise and transient events
• Setup
• In-ice components
• Data acquisition
• Networking and synchronisation
• Organization
• Collaboration
• Project schedule
• Summary

3
Motivation
In-Ice neutrino detection In-Ice neutrino detection In-Ice neutrino detection In-Ice neutrino detection
optical radio acoustic
Absorption length km 0.1 1 10 ?
Energy threshold eV 109 1015 1018
Ice properties well studied first data unknown
Experimental status working array small test array RD

• Hybrid Optical-Radio-Acoustic array
• ? a most powerful neutrino observatory
• Relevant acoustic properties of south polar ice
  are unknown
• ? Dedicated setup to determine acoustic properties

4
Experimental Targets

• Aim measure all relevant parameters needed for
  an acoustic detector proposal
• Absorption length
• ? sensor density and possible detector volume
• Velocity of sound and refraction
• ? signal shape and vertical sensor spacing
• Ambient noise
• ? energy threshold
• Transient background events
• ? signal-to-noise event ratio

5
Scattering
B. Price, University Berkeley

• Dominant process
• Rayleigh scattering at crystal boundaries
• ? crystal size
• ? frequency
• ?s ? a3 f4
• Theoretical values
• ?s (10 kHz) 800 km
• ?s (100 kHz) 0.2 km
• ? can (probably) be neglected

6
Absorption

• Dominant process
• molecular reorientation
• ? energy loss in relaxation
• temperature dependant
• crystal size dependant
• Theoretical calculation
• ?a (-51?) 7.1 km
• ? largest in upper ice layers

B. Price, University Berkeley
J. Vandenbroucke, University Berkeley
7
Speed of sound

• Speed of sound
• weak temperature dependance
• strong density dependance
• ? very distinct kink profile
• ? refraction of surface noise
• Measurement
• In same layer
• Inter-layer ? improved precision

J. Vandenbroucke, University Berkeley
?t1vs(d1)x
?t2vs(d2)x
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Background noise and transient events

• Problem
• even in multi-km3 detector? probably few events
  per year
• ? need either
• low noise rate
• good background suppression
• ? long term measurement
• Possible sources
• anthropogenic (at the surface)
• ? refraction
• ? absorbed ? crystal size vs. air bubbles
• micro cracks as in salt mines
• glacial flow ? slip-stick motion
• artificial EMR sources
• No data above 100 Hz !

• For comparison Water
• Wind and waves
• Anthropogenic (ships, oil drills)
• Animals (dolphins, wales)
• Single sensor threshold
• 100 m, 3-100 kHz, PAskaryan (90 deg)

Eth 18 EeV Eth 2 EeV
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The IceCube project

• Aim
• 1 km3 neutrino telescope
• IceCube
• 70 holes _at_ 125 m spacing
• 60 optical modules per hole
• 50 cm diameter, hot water drilled
• depth 2500 m
• instrumented depth 1400 2400 m
• ? use free space above for test of acoustic ice
  parameters

10
Setup

• Use IceCube holes
• 3 distant holes
• down to 400 m
• 7 levels per hole
• sensors
• transmitters
• auxiliary
• Surface digitization
• String PCs
• DAQ
• Power
• Fiber LAN

TV-Tower Berlin
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Acoustic stage

• In all three holes
• at the same height? do measurement in same layer
• sensor and transmitter at each stage? reduce
  systematic error in redundant setup
• Sensor module and transmitter module
• close together ? check with low signals
• standard pressure housing
• 10 cm diameter steel tube
• end caps with commercial penetrators
• String support
• own kevlar cable
• avoid sensor in shadow off IceCube cable? need
  spacer
• Auxiliary devices
• temperature or pressure sensors
• commercial hydrophones

12
Acoustic stage sensor

• Sensor module
• based on existing design
• PZT5 piezoceramics plus amplifier? directly
  coupled to steel tube
• three channels per module? local coincidences?
  azimuthal coverage? directional information ?
• Power supply
• cable losses? use larger supply voltage
• ? 5V generated in module

13
Acoustic stage transmitter

• Active element
• piezoceramic transducer? signals 1000 V
  possible
• no orientation possible? ring-shaped ceramic
• ? azimuthal symmetry
• broad resonance? large pressure amplitude
• directly coupled to the ice? calculable system
• HV Signals
• Problem cable capacitance? down in the ice
• use LC-circuits? only short pulses

14
String PC

• Limitations
• cable costs
• cable losses
• ? DAQ at top of each string
• String PC
• DAQ board(s) (software trigger)
• Power supply
• Network connections
• only used for triggeringand data handling? slow
  CPU, small Flash-RAM
• buried in snow? insulated container

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DAQ options

• Problem
• low temperatures
• ? must survive power failures
• power consumption
• Industrial Microcontroller (e.g. PC104 /
  CompactRIO)
• specified for -40? to 80?
• low power 15 Watts
• smaller choice of components
• bound to specific software / OS
• Standard PC
• large choice of components
• free choice of software / OS
• needs temperature control
• larger power 100 Watts

16
Networking

• Communication requirements
• data rates ? 50 MB / day (over satellite)
• long distance from string to counting house
• long freeze-in time after pole station closing
• ? remote access from north via satellite ( 56
  kbps)
• String-to-Master PC
• Ethernet on electrical cables
• ? too large distances
• Ethernet on fiber-optical cables
• DSL on electrical cables
• Time synchronisation
• velocity of sound measurement, triggering, source
  position reconstruction
• ? sub-millisecond timing
• ?t 0.1 ms ? ?x 40 cm / 400 m ??vs 0.1
• network time distribution? typical few
  millisecond
• GPS receiver at each string
• separate clock distributed

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Collaboration

• University Berkeley
• B. Price
• ? data acquisition and software
• University Stockholm
• P.O. Hulth
• ? communication and networking
• University Uppsala
• A. Hallgren
• ? deployment and surface installation
• DESY, Zeuthen
• R. Nahnhauer
• ? in-ice components

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Project schedule 2005
April April April May May May May June June June June June July July July July August August August August August September September September September October October October October
WK 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Sensor finalization Sensor finalization Sensor finalization Sensor finalization Sensor finalization Sensor finalization
Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building Sensor and transmitter building
Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Sensor and transmitter calibration Setup whole system Setup whole system Setup whole system
Build DAQ system Build DAQ system Build DAQ system Build DAQ system Build DAQ system Build DAQ system Setup whole system Setup whole system Setup whole system Test system in lake Test system in lake Test system in lake Test system in lake
DAQ software development DAQ software development DAQ software development DAQ software development DAQ software development DAQ software development DAQ software development DAQ software development Software testing Software testing Software testing Software testing Software testing
Order parts Order parts Order parts Parts arrive Parts arrive Ship to pole Ship to pole
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Polar season 2005/2006
November November November December December December December January January January January January February February February February March March March March March April April April April June June June June
WK 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings Ice Cube strings
String 1 Refreezing String 1 Refreezing String 1 Refreezing String 1 Refreezing String 3 Refreezing String 3 Refreezing String 3 Refreezing String 3 Refreezing
String 2 Refreezing String 2 Refreezing String 2 Refreezing String 2 Refreezing
DAQ setup DAQ setup DAQ setup DAQ setup commis-sioning commis-sioning commis-sioning
DAQ test DAQ test DAQ test Test data Test data Absorption Refraction Absorption Refraction Absorption Refraction Absorption Refraction Background monitoring Background monitoring Background monitoring Background monitoring Background monitoring Background monitoring Background monitoring Background monitoring
Surface cables Surface cables Surface cables Station closes Station closes
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Summary

• Development of acoustic detection in ice behind
  optical and radio
• ? SPATS dedicated setup at south pole
• resolves important parameters
• deployment in next polar season
• first data expected spring next year