A Laser-Cooled, High Density Positron Plasma

摘要

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 (～ 4 x 10~9 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.