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Liquid Argon Dark Matter:
Synergies with R&D for Neutrino Detectors:
Chemically clean Argon for drifting electrons and light output (Oxygen and H20 relevant for both, N2 relevant for light only)
TPC construction and HV feedthroughs
Light detection - waveshifting, cryogenic PMTs and Bases
Effects of detector materials on Argon purity (H20 and O2)
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Liquid Argon R & D specific to Dark Matter Search
Context is collaboration with Princeton, Temple et al.,
Approach is to treat general issues:
Ar39 background - 1 Bq/kilogram (560 keV max beta)•Source of Depleted Argon from Gas Wells in US (~1 kg/day now) •Depletion measurements (Bern) limited at x25 below atmosphere•Building High Pressure (2500 psi) Ion Chamber at FNAL, with muon veto and low-activity-lead shield to go in NuMI tunnel.
We’ve been practicing on a chamber we made, using a shield in the Radiation Counting Lab at Fermilab => electronics noise level is acceptable.
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Ion Chamber in lead shield at Fermilab Counting Lab.
220 electrons rms noise
39-Ar spectrum flat to 560 keV560 keV ~ 20,000 electrons
60 keV X-rays (241-Am) in 8.5 Bar Argon
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Lead Shield for Ion Chamber High Pressure Ion Chamber (Copper body,Titanium bolts)
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Program to develop general expertise for LAr Dark Matter:20 kg device at Princeton
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Device to develop light-collection, TPC design,PMTs (from Hamamatsu), bases, and electronics readout.
Fermilab supplying PMT bases, HV feedthroughs,electrostatics design (C.J. Martoff, guest)
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Argon Liquid
Argon Gas
Acrylic
Steel Bolt
Luminescence RegionGrid inliquid
Anode
Field Lines fromliquid surface
3-D Study of Electrostatic AsymmetriesDielectric Constant
Cryostat Walls at Ground
FieldCage
C.J.Martoff
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Next three years:
Complete and study 20 kg device.
Investigate wave-shifter technology
- base materials, WLS chemicals and application techniques
Investigate effects of materials on light output and detection
- longevity of coatings, effects of impurities in Argon
Develop prototype scale (1 meter distances) device
Complete Argon system with atmospheric Argon, full size TPC (including HV and light reflectors); partial readout coverage to pursue development of: light sensors, read-out electronics and DAQ.
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Extras ..
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QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Argon Liquid
Argon Gas
Acrylic
Steel Bolt
Luminescence RegionGrid in liquid
Anode
Field Lines from liquid surface
3-D Study of Electrostatic AsymmetriesDielectric Constant
Cryostat Walls at Ground
Field Cage
C.J.Martoff
9
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39Ar Ion chamber vessel
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