Several years ago, it was proposed that a dense non-neutral plasma cou
ld be produced in a Penning trap. Nonneutral plasmas have excellent co
nfinement, and such a dense plasma might produce simultaneously high d
ensity and good confinement. Recently, this theoretical conjecture has
been demonstrated in a small (3 mm radius) electron experiment, PFX (
Penning Fusion Experiment). Densities up to 35 times the Brillouin den
sity (limiting number density in a static trap) have been inferred fro
m the observed strong (100:1) spherical focusing. Electrons are inject
ed at low energy from a single pole of the sphere. A surprising observ
ation is the self-organization of the system into a spherical state, w
hich occurs precisely when the trap parameters are adjusted to produce
a spherical well. This organization is caused by a bootstrapping mech
anism which produces a hysteresis. Observations of energy-scattered el
ectrons confirm the existence of a dense spherical focus. (C) 1997 Ame
rican Institute of Physics.