  A filter system for removing electronegative impurities from liquid argon is
described. The active components of the filter are adsorbing molecular sieve
and activated-copper-coated alumina granules. The system is capable of
purifying liquid argon to an oxygen-equivalent impurity concentration of better
than 30 parts per trillion, corresponding to an electron drift lifetime of at
least 10 ms. Reduction reactions that occur at about 250 degrees Celsius allow
the filter material to be regenerated in-situ through a simple procedure. In
the following work we describe the filter design, performance, and regeneration
process.
