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Measurement of acoustic properties of glacial ice at the South Pole

Measurement of acoustic properties of glacial ice at the South Pole. Rolf Nahnhauer , DESY. The Vision. Build a > 100 km 3 detector to d o physics with extremely high energy cosmic neutrinos *) - astrophysics - E > 10 16 eV :

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Measurement of acoustic properties of glacial ice at the South Pole

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  1. Measurement of acoustic properties of glacial ice at the South Pole Rolf Nahnhauer, DESY XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  2. The Vision Build a > 100 km3detector to do physics with extremelyhigh energy cosmic neutrinos*) - astrophysics - E > 1016eV : study origin of cosmic rays - (AGN’s, black holes, GZK cutoff, …) - particle physics - E > 1018eV : study neutrino cross section (sphalerons, mini BH, strong,…) - cosmology - E > 1021eV : study relic neutrino background radiation (UHE absorption at CBR ) UHE neutrino detection techniques: *) see e.g. R. Nahnhauer ,ARENA 2010 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  3. air dense medium acoustic“pancake” v-induced cascade coherentradio signal opticalCherenkov signal Best solution : hybrid detector in ice   • Multiple detection of same signal possible in several materials (best in ice) • - Extend energy range of sensitivity and enlarge volume (bigger spacing?)- Calibrate Radio with Optical and cross-calibrate Acoustic & Radio - Improve energy and direction reconstruction- Reject background more efficiently Trust your signal ! XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  4. Measure acoustic properties of ice at the South Pole Use upper 500 m of holes drilled forthe IceCube observatory acoustic strings deployed 01/2007 deployed 12/2007 completed in December 2010 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  5. The South Pole Acoustic Test Setup - SPATS Y. Abdou et al., Nucl. Instr. Meth. A 683 (2012) 78 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  6. The Movable Pinger 07/08 08/09 – 09/10 Three campaigns: 07/08  measure sound speed 08/09  measure attenuation length  09/10  measure frequencydependenceof  measure sound speed on inclined tracks XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  7. The Four SPATS Goals Get information about: 1.)Sound speed:what is the sound speed value? is it depth dependent (= refraction?)2.)Transient events:are there transients events? what are their features (rate, sources)? could they be a significant source of background? 3.)Noise: what is the noise level? which  energy threshold does it correspond to? 4.)Attenuation coefficient: never measured up to know, only models are known is it depth dependent? is it frequency dependent? Needs time information Needs amplitudeinformation XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  8. Sound Speed • from pinger data 2007/08 •  swinging sound source in water filled hole vp = (387812) m/s vs = (1976 8) m/s at 375 m no refraction observed below 200m depth ! • two combinations at 125 m distance - accuracy better than 1% - first in situ measurements for P and S waves at South Pole R.Abbasi et al., Astropart.Phys. 33 (2010) 277 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  9. Attenuation length I From pinger data 2008/09  = 1/ ≈ 300  60 m No significant evidence for depth or frequency dependence, but not excluded R.Abbasi et al., Astropart.Phys. 34 (2011)382 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  10. Attenuation length II P.B.Price, Journal of Geophysical Research 111 (2006)B02201 Attenuation length predicted much larger: bscat= 1/scat  d3 f4 What about scattering? Y. Abdou et al., Proccedings of 32nd ICRC, V3 (2011) 68 From pinger data 2009/10: pulses @ 30, 45, 60 kHz No or very weak frequency dependence:  certainly not f 4 Attenuation seems not to be dominated by scattering XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  11. Steady Noise Conditions Monitoring data for > 4 years available  noise is Gaussian and stable over long time  noise level ~14 mPa in deep ice estimated (main uncertainty is sensitivity)  in-situ calibration desirable and under study R.Abbasi et al., Astropart.Phys. 35 (2012)312 XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  12. Transient Acoustic Signals R.Abbasi et al., Astropart.Phys. 35 (2012)312 - ~4 years continuous data taking- only human in-ice sources from IceCube hole drilling and Rod-Wells - monitor hole-re-freezing- source location precision better than 5 m before end of IceCubeconstruction after end of IceCubeconstruction reconstructed 4 string acoustic event vertices in x-y plane XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  13. Acoustic neutrino flux limits No original SPATS goal R.Abbasi et al., Astropart.Phys. 35 (2012)312 zero events triggered below 200 m outside IceCubein a ½ year quite period ACORNE SPATS SAUND2 1km3 1020 eV x x XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  14. 100km2 20 km 400 km2 20 km A possible hybrid neutrino detector concept 1km2 on same string:  optical modules (?)  radio antennas between 200-400m depth  acoustic antennas between 200-(400-1000m) depth 30km2 rely strongly on correlated hits from all technologies per event 500m x 500m sensor spacing shown ! XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  15. Detector deployment requirements - string area 100 - 10000 km2 - string distance 300 - 1500 m - string depth 200 - 1200 m - hole diameter 4 - 8 inch - x00 – x000 strings - in about 5 years (with only a 3-6 month per year available) Science Fiction ? robotic drilling + deployment scheme needed XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  16. Look to neighboring fields for fresh ideas B. Dachwald, Faculty of Aerospace Engineering, FH Aachen University of Applied Sciences, Aachen IceMole and the EnceladusExplorer Project this conference , session 29 Development and testing of a maneuverable subsurface probe that can navigate autonomously through deep ice Next test: Demonstrate the recoverability of IceMole and payloads by digging a “vertical U” Location: Hofsjökull, Iceland, Sep 2012 Distance: ≈40m Melting velocity: ≈1m/h Mass:≈30kg  Forward motion with combined melting head and ice screw  Maneuverability in ice by differential heating of the melting head payload XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  17. Can the IceMole concept solve drilling problems for large scale hybrid detectors ? Too early to answer, needs to be adapted to the problem first  get less ambitious , drill only straight downward holes  get considerably faster  get water out of hole (?) Present design can however easily be modified for module field testingdeploying corresponding payloads Ideas under discussion between groups of + XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  18. Summary The South Pole Acoustic Test Setup has measured prominent acoustic properties of glacial ice down to 500 m:  the speed of sound for P-waves is found to be vp (375m)= (387812) m/s  the speed of sound for S-waves is found to bevs(375m)= (1976 8) m/s  no refraction observed below 200m depth  the sound attenuation length has been measured as 30060 m in contrast to the expectation of several kilometers  scattering could be excluded as dominant source for this attenuation  the steady noise level has been found Gaussian and stable during four years  the estimated noise level below 200 m amounts to 14 mPa  in-situ sensor calibration is desirable to consolidate this value  transient acoustic event sources could be attributed to present or former human activities for optical neutrino telescopes  the SPATS transient data have been used to derive a neutrino flux limit at ultra-high energies XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  19. Outlook •  a large scale hybrid ultra-high energy neutrino detector in Antarctic ice using two or moretechnologies (includingacoustics) seemspossible •  robotic drilling and deployment schemes have to be developed in this context to get more than 100 strings per season in the ice • the IceMole concept is a first scenario pointing in this direction •  first ideas about possible modifications for a realistic application are under discussion XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

  20. Thank you ! XXXII SCAR Open Science Conference - Astronomy & Astrophysics from Antarctica

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