Dimensionless scaling of confinement in ATF

The results of dimensionless-parameter modulation and configuration control experiments in the Advanced Toroidal Facility (ATF) are presented. The global energy confinement time fits gyro-Bohm scaling better than Bohm-like scaling. An additional dependence was detected by modulation of single dimensionless parameters (collisionality nu(sub *) and beta (beta)), yielding tau(sub E)/tau(sub gB) is proportional to (((nu(sub *))(sup(alpha(sub nu)))(beta(sup (alpha(sub beta)), where alpha(sub nu) = 0.18 plus or minus 0.03 and alpha(sub beta) = 0.3 plus or minus 0.1. Application of this formula to NBI and ECH data significantly improves the fit, implying that improved confinement will result from increasing the heating power. Little change in confinement occurred for wide variations in the confined trapped particle fraction at constant magnetic well radius and shear. This may be explained by reduction of the helically trapped particle loss region due to the radial electric field. Configuration modulation experiments showed that the energy confinement time improves as the magnetic well radius expands, the result expected from some stabilization of resistive interchange instabilities. This is consistent with fluctuation measurements and may explain the positive dependence of confinement on beta.