  A significant number of confined energetic electrons have been observed
outside the Last Closed Flux Surface (LCFS) of the solenoid-free, ECRH
sustained plasmas in the EXL-50 spherical torus. Several diagnostics have been
applied, for the first time, to investigate the key characters of energetic
electrons. Experiments reveal the existence of high-temperature low density
electrons, which can carry relatively a large amount of the stored energy. The
boundary between the thermal plasma and the energetic electron fluid appears to
be clearly separated and the distance between the two boundaries can reach tens
of centimeters (around the size of the minor radius of the thermal plasma).
This implies that the Grad-Shafranov equilibrium is not suitable to describe
the equilibrium of the EXL-50 plasma and a multi-fluid model is required.
Particle dynamics simulations of full orbits show that energetic electrons can
be well confined outside the LCFS. This is consistent with the experimental
observations.
