Runaway Electrons in the Small Shell-Less Tokamak Device NOVA-I

The mechanisms of the production and confinement of runaway electrons in the tokamak device NOVA-I were studied by experimentally measuring the energies of these electrons examining how their behavior depended on the discharge parameters. Numerical calculations were also made on their drift orbits. From a comparison of the experimental and numerical analyses, it is concluded that: (1) neutral particles obstruct the production of runaway electrons during the breakdown phase of the discharge, while the densities of electrons having energies of the order of 10 eV build up; (2) electrons then begin to run away in the hot central region of the plasma, since the density of neutral particles decreases with ionization; (3) the orbits of the runaway electrons shift outward while spreading radially as the energy of the runaway electrons increases with time, until the orbits intersect the outer limiter or the torus wall.