Dependence of energy confinement time on column cross-section ellipticity in T-8

The dependence of the energy confinement time tausub(E) on the plasma cross-section ellipticity is measured in the T-8 finger-ring tokamak, the ellipticity being varied from 1.3 to 1.6. Ellipticity variation is achieved by properly directed quadrupole magnetic fields so that the plasma column is compressed or stretched, the plasma column axis being fixed by a feedback system. Measurements of poloidal-magnetic-field distributions, diamagnetic fluxes and electron temperature near the column axis have shown that the plasma current density distribution over the magnetic surfaces does not change with ellipticity nor does the mean electron temperature, which is only a function of the plasma density. The mean electron temperature derived from conductivity is also independent of ellipticity if plasma current and radial plasma dimension are fixed. These results suggest that an increase in ellipticity leads to an increase in tausub(E) that is approximately proportional to k2. A possible reason for this increase in tausub(E) is discussed. (author)