A laser-cooled, high density positron plasma

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 9Be+ 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 (∼4x109 cm-3) as the 9Be+ 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