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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)

QuickTime™ and aTIFF (LZW) decompressor

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Program to develop general expertise for LAr Dark Matter:20 kg device at Princeton

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

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

AcrylicSteel 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

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39Ar Ion chamber vessel