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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
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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)
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.
60 keV X-rays (241-Am) in 8.5 Bar Argon 220 electrons rms noise 39-Ar spectrum flat to 560 keV 560 keV ~ 20,000 electrons Ion Chamber in lead shield at Fermilab Counting Lab.
High Pressure Ion Chamber (Copper body,Titanium bolts) Lead Shield for Ion Chamber
Program to develop general expertise for LAr Dark Matter: 20 kg device at Princeton 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)
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.
3-D Study of Electrostatic Asymmetries Dielectric Constant Argon Gas Steel Bolt Anode Acrylic Luminescence Region Grid in liquid Field Cage Field Lines from liquid surface Argon Liquid Cryostat Walls at Ground C.J.Martoff