  The self-organization of magnetospheric plasma is brought about by inward
diffusion of magnetized particles. Not only creating a density gradient toward
the center of a dipole magnetic field, the inward diffusion also accelerates
particles and provides a planetary radiation belt with high energy particles.
Here, we report the first experimental observation of a 'laboratory radiation
belt' created in the Ring Trap 1 (RT-1) device. By spectroscopic measurement,
we found an appreciable anisotropy in the ion temperature, proving the betatron
acceleration mechanism which heats particles in the perpendicular direction
with respect to the magnetic field when particles move inward. The energy
balance model including the heating mechanism explains the observed ion
temperature profile.
