We report sympathetic cooling and compression of a few thousand positrons by laser-cooled 9 Be ϩ ions in a Penning ion trap. The observed centrifugal separation of the two species implies approximate rigid rotation of the positrons and 9 Be ϩ ions, and a positron density comparable to the 9 Be ϩ ion density of տ4ϫ10 9 cm Ϫ3 . We use the sharpness of the separation to place a 5-K upper limit on the positron temperature of motion parallel to the magnetic field. The positron lifetime is greater than two weeks in our room-temperature Penning trap.

We have simulated the trapping and cooling of moderated positrons in a Penning trap in which the positrons lose energy through collisions with a simultaneously stored laser-cooled 9 Be ϩ plasma. Once the positrons are trapped, they cool through sympathetic cooling with the 9 Be ϩ plasma. After the positrons cool, their motion parallel to the magnetic field reaches a state of thermal equilibrium with the 9 Be ϩ ions and they rotate about the trap axis at the same frequency as the 9 Be ϩ ions. Therefore, a centrifugal separation will occur, forcing the positrons to coalesce into a cold column along the trap axis. A simulation which, in part, utilizes Monte Carlo techniques, indicates a capture efficiency of as high as 0.3% for 300 K moderated positrons passing through a 9 Be ϩ plasma with a density of 10 10 atoms cm Ϫ3 and a column length of 1 cm. This capture efficiency leads to the positron capture rate of ϳ1000 positrons per second, assuming a 100 mCi positron source and 10 Ϫ3 for the efficiency for moderating positrons from the source. The resulting dense reservoirs of cold positrons may be useful for antihydrogen production and for reaching a plasma state in which the mode dynamics must be treated quantum mechanically.

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We present results on trapping and cooling of positrons in a Penning trap. Positrons from a 2 mCi 22 Na source travel along the axis of a 6 T magnet and through the trap after which they strike a Cu reflection moderator crystal. Up to a few thousand positrons are trapped and lose energy through Coulomb collisions (sympathetic cooling) with laser-cooled 9 Be + . By imaging the 9 Be + laser-induced fluorescence, we observe centrifugal separation of the 9 Be + ions and positrons, with the positrons coalescing into a column along the trap axis. This indicates the positrons have the same rotation frequency and comparable density ( 4 × 10 9 cm −3 ) as the 9 Be + ions, and places an upper limit of approximately 5 K on the positron temperature of motion parallel to the magnetic field. We estimate the number of trapped positrons from the volume of this column and from the annihilation radiation when the positrons are ejected from the trap. The measured positron lifetime is > 8 days in our room temperature vacuum of 10 −8 Pa.

Abstract. We present results on trapping and cooling of positrons in a Penning trap. Up to a few thousand positrons are trapped and sympathetically cooled through Coulomb collisions (sympathetic cooling) with laser-cooled 9 Be+ ions. By imaging the 9Be+ laser-induced fluorescence, we observe centrifugal separation of the 9Be+ ions and the positrons, with the positrons coalescing into a column along the trap axis. This indicates the positrons have the same rotation frequency and comparable density (-4 x 109 cm-3 ) as the 9 Be+ ions, and places an upper limit of approximately 5 K on the positron temperature of motion parallel to the magnetic field. The measured positron lifetime is > 8 days in our room temperature vacuum of 10-8 Pa.