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We have used a radio frequency quadrupole decelerator to decelerate antiprotons emerging from the CERN Antiproton Decelerator from MeV-to keV-scale energy, and collected five decelerated pulses in a multiring trap. Some 5 10 6 antiprotons were stacked in this way. Cooling of the trapped antiprotons by a simultaneously trapped electron plasma was studied nondestructively via shifts in plasma mode frequencies. We have also demonstrated the first step in extracting a 10 -500 eV antiproton beam from the trap.

A new positron accumulation scheme compatible with ultrahigh vacuum conditions has been developed, which is realized by preparing a high density electron plasma as high as approximately 10(11) cm(-3) and an ion cloud as energy absorbers. The present accumulation rate normalized by the intensity of 22Na positron source is (3.6+/-0.3)x10(2)e(+)/s/mCi, which is more than one and a half orders of magnitude higher than other ultrahigh vacuum compatible schemes so far reported.

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