OBSERVATION OF SPHERICAL FOCUS IN AN ELECTRON PENNING TRAP

We produce simultaneously dense and well-confined nonneutral plasmas b y spherical focusing. A small (3 mm radius) Penning trap has low-energ y electrons injected at a single pole of the sphere. Precisely when th e trap parameters art adjusted to produce a spherical well, the system self-organizes into a spherical state through a bootstrapping mechani sm which produces 3 hysteresis. Additional confirmation of the dense s pherical focus is provided by electrons scattered by the central core. Core densities up to 35 times the Brillouin density have been inferre d from the data.