SPATS a South Pole Acoustic Test Setup

SPATS – a South Pole Acoustic Test Setup Sebastian Böser sboeser@ifh. de 1 st International ARENA Workshop Zeuthen May 2005

Overview Motivation Experimental Targets l Absorption and Scattering l Speed of sound and refraction l Background noise and transient events Setup l In-ice components l Data acquisition l Networking and synchronisation Organization l Collaboration l Project schedule Summary South Pole Acoustic Test Setup – 2 sboeser@ifh. de

Motivation In-Ice neutrino detection: optical radio acoustic Absorption length [km] ~ 0. 1 ~1 ~ 10 ? Energy threshold [e. V] ~ 109 ~ 1015 ~ 1018 well studied first data unknown working array small test array R&D Ice properties Experimental status l Hybrid Optical-Radio-Acoustic array a most powerful neutrino observatory l Relevant acoustic properties of south polar ice are unknown Dedicated setup to determine acoustic properties South Pole Acoustic Test Setup – 3 sboeser@ifh. de

Experimental Targets Aim: measure all relevant parameters needed for an acoustic detector proposal l Absorption length sensor density and possible detector volume l Velocity of sound and refraction signal shape and vertical sensor spacing l Ambient noise energy threshold l Transient background events signal-to-noise event ratio South Pole Acoustic Test Setup – 4 sboeser@ifh. de

Scattering B. Price, University Berkeley Dominant process: l Rayleigh scattering at crystal boundaries crystal size frequency λs ∝ a 3 × f 4 Theoretical values l λs (10 k. Hz) ≈ 800 km l λs (100 k. Hz) ≈ 0. 2 km can (probably) be neglected South Pole Acoustic Test Setup – 5 sboeser@ifh. de

Absorption B. Price, University Berkeley Dominant process: l molecular reorientation energy loss in relaxation l temperature dependant l crystal size dependant Theoretical calculation: λa (-51℃) ≈ 7. 1 km largest in upper ice layers J. Vandenbroucke, University Berkeley South Pole Acoustic Test Setup – 6 sboeser@ifh. de

Speed of sound l weak temperature dependance l strong density dependance very distinct kink profile refraction of surface noise Measurement: l In same layer l Inter-layer improved precision South Pole Acoustic Test Setup – 7 J. Vandenbroucke, University Berkeley Δt 1=vs(d 1)x Δt 2=vs(d 2)x sboeser@ifh. de

Background noise and transient events Problem: l even in multi-km 3 detector probably few events per year need either l low noise rate l good background suppression long term measurement Possible sources: l anthropogenic (at the surface) refraction absorbed ? crystal size vs. air bubbles l micro cracks as in salt mines l glacial flow slip-stick motion l artificial EMR sources For comparison: Water l Wind and waves l Anthropogenic (ships, oil drills) l Animals (dolphins, wales) Single sensor threshold: l 100 m, 3 -100 k. Hz, PAskar’yan (90 deg) Eth = 18 Ee. V Eth = 2 Ee. V No data above 100 Hz ! South Pole Acoustic Test Setup – 8 sboeser@ifh. de

The Ice. Cube project Aim: l ~ 1 km 3 neutrino telescope Ice. Cube: l 70 holes @ 125 m spacing l 60 optical modules per hole l 50 cm diameter, hot water drilled l depth: ~2500 m l instrumented depth: 1400 – 2400 m use free space above for test of acoustic ice parameters South Pole Acoustic Test Setup – 9 sboeser@ifh. de

Setup Use Ice. Cube holes l 3 distant holes l down to 400 m 7 levels per hole l sensors l transmitters l auxiliary TV-Tower Berlin South Pole Acoustic Test Setup – 10 Surface digitization l String PCs l DAQ l Power l Fiber LAN sboeser@ifh. de

Acoustic stage In all three holes l at the same height do measurement in same layer l sensor and transmitter at each stage reduce systematic error in redundant setup Sensor module and transmitter module l close together check with low signals l standard pressure housing l 10 cm diameter steel tube l end caps with commercial penetrators String support l own kevlar cable l avoid sensor in shadow off Ice. Cube cable need spacer Auxiliary devices l temperature or pressure sensors l commercial hydrophones South Pole Acoustic Test Setup – 11 sboeser@ifh. de

Acoustic stage: sensor Sensor module l based on existing design l PZT 5 piezoceramics plus amplifier directly coupled to steel tube l three channels per module local coincidences azimuthal coverage directional information ? Power supply l cable losses use larger supply voltage ± 5 V generated in module South Pole Acoustic Test Setup – 12 sboeser@ifh. de

Acoustic stage: transmitter Active element l piezoceramic transducer signals ≥ 1000 V possible l no orientation possible ring-shaped ceramic azimuthal symmetry l broad resonance large pressure amplitude l directly coupled to the ice calculable system HV Signals l Problem: cable capacitance down in the ice l use LC-circuits only short pulses South Pole Acoustic Test Setup – 13 sboeser@ifh. de

String PC Limitations l cable costs l cable losses DAQ at top of each string String PC l DAQ board(s) (software trigger) l Power supply l Network connections l only used for triggering and data handling slow CPU, small Flash-RAM l buried in snow insulated container South Pole Acoustic Test Setup – 14 sboeser@ifh. de

DAQ options Problem: l low temperatures must survive power failures l power consumption Industrial Microcontroller (e. g. PC 104 / Compact. RIO): Ì specified for -40℃ to +80℃ Ì low power: 15 Watts ━ smaller choice of components ━ bound to specific software / OS Standard PC: Ì large choice of components Ì free choice of software / OS ━ needs temperature control ━ larger power: 100 Watts South Pole Acoustic Test Setup – 15 sboeser@ifh. de

Networking Communication requirements: l data rates: ≳ 50 MB / day (over satellite) l long distance from string to counting house l long freeze-in time after pole station closing remote access from north via satellite (≈ 56 kbps) String-to-Master PC Ñ Ethernet on electrical cables too large distances ü Ethernet on fiber-optical cables ü DSL on electrical cables Time synchronisation l velocity of sound measurement, triggering, source position reconstruction sub-millisecond timing Δt = 0. 1 ms Δx ≈ 40 cm / 400 m Δvs ≈ 0. 1 % Ñ network time distribution typical few millisecond P GPS receiver at each string P separate clock distributed South Pole Acoustic Test Setup – 16 sboeser@ifh. de

Collaboration l University Berkeley B. Price data acquisition and software l University Stockholm P. O. Hulth communication and networking l University Uppsala A. Hallgren deployment and surface installation l DESY, Zeuthen R. Nahnhauer in-ice components South Pole Acoustic Test Setup – 17 sboeser@ifh. de

Project schedule 2005 April W K May June July August September October 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 and transmitter building Sensor and transmitter calibration Build DAQ system DAQ software development Order parts Parts arrive South Pole Acoustic Test Setup – 18 Setup whole system Test system in lake Software testing Ship to pole sboeser@ifh. de

Polar season 2005/2006 Novemb December er WK 46 January 47 48 49 50 51 52 1 2 3 4 February 5 6 7 8 March April June 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Ice Cube strings String #1 Refreezing String #3 Refreezing String #2 Refreezing DAQ setup commissioning DAQ test Surface cables South Pole Acoustic Test Setup – 19 Test data Absorption Refraction Background monitoring Station closes sboeser@ifh. de

Summary Development of acoustic detection in ice behind optical and radio SPATS: dedicated setup at south pole Presolves important parameters Pdeployment in next polar season Pfirst data expected spring next year South Pole Acoustic Test Setup – 20 sboeser@ifh. de