Confinement Studies with ECH Plasmas in ATF

Electron cyclotron heating (ECH) experiments in the Advanced Toroidal Facility (ATF) torsatron exploit unique capabilities for external control of the magnetic configuration and long‐pulse operation. The ECH power deposition profile is determined from the change of the electron temperature profiles during ECH power turn‐off and from power modulation. The measured dependence of absorbed power on the magnetic field agrees well with that obtained from ray tracing calculations for first‐pass and multiple‐bounce absorption. In ATF, parameters of basic physics interest (magnetic shear, magnetic well/hill, and contained trapped particle fraction) have been varied dynamically during a single long‐pulse (up to 20‐s) discharge (dynamic configuration control). Varying a single physics parameter while keeping others fixed elucidates the parameter’s influence on plasma behavior. Modulation of the magnetic well significantly affects the plasma stored energy. This may be related to the observed electron density fluctuat...