ELECTROSTATIC MODES AS A DIAGNOSTIC IN PENNING-TRAP EXPERIMENTS

A subset of the electrostatic modes of a cold cloud of electrons, a no n-neutral electron plasma, trapped in a Penning trap has been observed and identified using a recent theoretical model. The detection of the se modes is accomplished using electronic techniques which could apply to any ion species. The modes are observed in the low-density, low-ro tation limit of the cloud where the cloud approaches a two-dimensional charged disk. We observe both axially symmetric and asymmetric drumhe ad modes. The shape, rotation frequency, and density of the cloud are found in a real-time nondestructive manner by measuring the frequency of these modes. In addition, it is found that radio-frequency sideband cooling compresses the cloud, increasing its density. The ability to measure and control the density of a trapped ion cloud might be useful for experiments on low-temperature ion-neutral-atom collisions, recom bination rates, and studies of the confinement properties of non-neutr al plasmas.