Radial compression and inward transport of positron plasmas using a rotating electric field

It has recently been demonstrated that positron plasmas confined in a Penning-Malmberg trap can be compressed radially by applying a rotating electric field [Phys. Rev. Lett. 85, 1883 (2000)]. A more complete description of the original experiments is presented, together with the results of new measurements. Good coupling of the rotating electric field is observed over a broad range of frequencies. The heating caused by the rotating field is counteracted by cooling using a polyatomic gas. Rapid compression rates $\text{ṅ/n∼15\hspace{0.5em}}{\mathrm{s}}^{\text{−1}}$ can be achieved, with central density increases of a factor of 20 or more. The good coupling and high compression rates can be explained in terms of excitation of heavily damped Trivelpiece–Gould modes, or alternatively as coupling directly to particle bounce resonances. Potential improvements and applications are discussed, including the production of high-density positron plasmas and brightness-enhanced positron beams.