Status of acoustic activities

1
Status of acoustic activities

• AMANDA/IceCube collaboration meeting
• Uppsala
• October 2004

2
Overview

• 2nd proton beam run (preliminary)
• sensitivity
• beam parameters
• temperature variation
• Self noise investigations
• amplifier self noise
• environmental EM noise
• Proposal for an acoustic test array at south pole
• desired ice parameters
• test array proposal
• DAQ and costs

3
2nd proton beam run
University Uppsala, University Erlangen, DESY
Zeuthen

• Synchrocyclotron at theThé Svedberg Laboratoriet
• 177 MeV protons
• 30 ms extraction time
• EBunch 10 PeV to 800 PeV
• ? one order below 1st proton beam run
• Two different setups
• Ice Block 1 UppsalaIron Ball and (old) Epoxy
  Sensors
• Ice Block 2 ZeuthenGlas Ball and (new) Epoxy
  Sensors
• Temperature Sensors PT100

Preliminary analysis by Jutta Stegmaier
4
Signal shapes

• Different sensor types
• resonant sensorGlass ball, Iron ball
• non-resonant sensorsEpoxy sensor
• But Signal shape mostly determined by
  reflections !!!

Iron ball sensor
Epoxy sensor
DtRef
5
Measurements

• Variation of different parameters
• Beam intensity? Sensitivity
• Geometry (beam position)? Speed of sound, sound
  / pressure field
• Beam profile? Signal shape
• Ice temperature? Sensitivity, noise level, speed
  of sound

6
Beam intensity

• Thermoacoustic generation
• Signal travels with vsound
• Signal shape constant
• Signal amplitude linear to input energy

• Sensitivity
• S 10-2?0.5 V / PeV _at_ 1 m
• Problem
• Piezoceramic properties
• Ice quality
• Temperature

7
Geometry (beam position)

• Vary beam entrance
• Superposition of
• cylindrical wave
• spherical wave
• ? combination of 1/r and 1/r2

8
Beam profile

• Beam profiles
• from evalution of fluorescence screen
• nearly circular
• diameters 0.3, 0.5 and 0.8 cm
• BUT
• beam spreading in ice to 3 cm
• ? no change in signal shape

9
Temperature variation

• Temperature dependent
• volume expansion coeffiecient a
• speed of sound
• ? thermoacoustic signal
• ? vibrational modes
• piezoceramic response
• electronic noise level (should increase with
  temperature)
• ? not observed
• ? dominated by acoustic or EM noise ?
• BUT Signal increasing with lower temperatures !

r 0.92 g/cm3
r 0.89 g/cm3
r lt 0.89 g/cm3
10
2nd proton beam run summary

• Preliminary analysis
• nothing unexpected
• BUT lots of data available
• ? lacking manpower for detailed analysis
• Preliminary conclusion
• new sensors more sensitive
• low temperature increases signal
• resonance mode detectors as trigger

diploma thesis http//www.ifh.de/sboeser/ThesisJ
utta.pdf
11
Self noise investigations

• Either acoustic or electronic self noise will
  limit the energy threshold!
• Investigation of electronic self noise
• sensors in air
• ? bad impedance matching
• ? no coupling to acoustic signals in air
• Tested with vacuum chamber
• acoustic signal should decreasewith lower
  pressure
• noise level nearly constant
• ? mostly electronic noise

12
Self noise investigations

• Noise contributions
• thermal activity in piezo ceramics
• ? neglegible
• amplifier self noise
• ? low noise amplifier
• ? low noise power supply
• coupling of environmental EM noise
• ? better shielding
• ? input impedance adapted for long cable
• Frequency filtering possible with known signal
  power spectrum

13
Acoustic test setup at south pole

• An acoustic detector proposal or simulation needs
  detailed knowledge about ice properties
• ? build a specialized array at south pole
• Measurements
• absorption length
• ? sensor density and possible detector volume
• refraction, speed of sound
• ? signal geometry and vertical sensor spacing
• noise level
• ? energy threshold
• background event scanning
• ? fake events e.g. microcracks, slip-stick motion

14
Absorption length
J. Vandenbroucke, B.Price

• Experimental requirements
• measure amplitude of the same signal at various
  distances
• ? at least 3 holes(distances of at least 750 m)
• ? calibrated high-power transmitter
• Possible transmitters
• piezoceramics
• ? up to 1000 V / mm
• powerfull laser and mirror
• ? conflicts with IceCube ?

15
Speed of sound vs. depth

• Speed of sound
• temperature profile
• density profile
• No precise measurements available for south pole
  for our depth
• How to measure
• send signals through different depth levels
• measure arrival time
• Refraction
• ? deformation of signal
• lower peak amplitude
• needs less vertical module density

16
Noise level

• Acoustic or self noise level will determine
  detector threshold
• Contributions
• Thermal noise
• Acoustic noise
• Electronic self noise
• Needs well known glaciophone
• ? frequency response
• ? absolute calibration
• Do upper layers absorbsurface sounds
• grain size labs ?
• low density / air bubbles labs ?
• ? upper meters of special interest

• Calibration - two modes
• single shot
• send sharp peak? compare Fourier Transform of
  input and output
• ? signal overlaid with reflections
• single frequency
• amplitude and phase? influenced by detector
  shape
• ? need larger calibration volume(e.g. lake ?)

17
Background events

• How to measure
• coincidences
• long term operation mode
• Possible rejection parameters
• geometry
• signal shape
• arrival direction

• Problem
• even a large detector will have a low event rate
• ? very low background rate
• ? very good background reduction
• Possible sources
• Microcracks due to (thermal) tension
• Slip-stick motion of ice
• artificial EM sources

18
Acoustic test setup at south pole

• Setup proposal
• 3 holes
• diameter 13 cm
• depth 400 m
• 8 sensors per hole
• large variation of ice properties at the surface
• ? non-equal spacing
• 8 transmitters per hole
• no possibility for transmitter allingment
• ? omnidirectional

19
Data aquistion

• Data aquisiton
• low data rates
• low sampling rates
• ? use of-the-shelf digitization
• Surface vs. in-ice digitization
• easier
• cheaper
• low-frequency signal
• ? no dispersion in cables
• ? no need for in-ice digitization

• String PCs
• shielded cables very expensive
• ? one PC directly at each string
• insulated box burried in snow
• communication via fiber LAN
• Example NI-DAQ 6070E
• analog input12 bit, 16 Channel, 1.25 MHz
• analog output12 bit, 2048 byte FIFO, 1.0 MHz
• stability 20 ppm / ºC

20
Costs
21
Summary

• Aim proper evaluation of the feasability of an
  acoustic detector
• Software
• signal generation
• signal propagation
• DAQ software
• Theory
• calculation of event rates
• theoretical ice properties

• Hardware
• data aquisition
• sensitive and cheap sensors
• powerfull transmitters
• Experimental data
• verification of thermoacoustic model
• sensor/transmitter calibration
• ice parameters