Effects of Thermal-Barrier Potentials on the Central-Cell Electron Energy Confinement

Abstract

The effects of the thermal-barrier potentials ɸb on the central-cell electron energy confinement are theoretically and experimentally investigated in the GAMMA 10 tandem mirror. In particular, the scaling of the central-cell electron temperatures Te with “the central-cell electron-confining potentials” ɸb is studied on the basis of the electron energy-balance equation and the generalized Pastukhov theory. The obtained theoretical scaling of Te with ɸb is then compared with the experimentally observed relation between these two parameters. In GAMMA 10, the main tandem-mirror operations are characterized in terms of(i) a high-potential mode having kV-order plasma-confining potentials, and (ii) a hot-ion mode yielding fusion neutrons with 10-20 keV bulk-ion temperatures. In this report, the scaling of Te with ɸb covering over these two representative operational modes is investigated, since the scalings of Te or the dominant parameters which determine Te have been remained for a long time as an unresolved important issue for tandem-mirror plasmas. It is found that the data in the two representative operational modes of the high-potential and hot-ion modes in the GAMMA 10 tandem mirror are in good agreement with the theoretically derived scaling formula, though the heating-source parameter dependence in the electron energy-balance equation is quite different in the two modes.