Laser-cooled positron source

We examine, theoretically, the feasibility of producing a sample of cold (⩽4 K), high-density (≈10¹⁰/cm³) positrons in a Penning trap. We assume⁹Be⁺ ions are first loaded into the trap and laser-cooled to approximately 10 mK where they form a uniform density column centered on the trap axis. Positrons from a moderator are then injected into the trap along the direction of the magnetic field through an aperture in one endcap of the trap so that they intersect the⁹Be⁺ column. Positron/⁹Be⁺ Coulomb collisions extract axial energy from the positrons and prevent them from escaping back out the entrance aperture. Cooling provided by cyclotron radiation and sympathetic cooling with the laser-cooled⁹Be⁺ ions causes the positrons to eventually coalesce into a cold column along the trap axis. We present estimates of the efficiency for capture of the positrons and estimates of densities and temperatures of the resulting positron column. Positrons trapped in this way may be interesting as a source for antihydrogen production, as an example of a quantum plasma, and as a possible means to produce a bright beam of positrons by leaking them out along the axis of the trap. Contribution of the National Institute of Standards and Technology; not subject to US copyright.