Abstract
Stable MHD modes have been externally excited by electrode exciters placed at the edge of the CHS heliotron/torsatron plasma. The excited modes are related to the rational surface m = 3/n = 2 (m, n: poloidal and toroidal mode number, respectively) near the edge. These stability margins can be estimated based on the plasma response to externally applied small magnetic field perturbations. This experiment suggests a possibility that the stability margin of MHD modes can be investigated by applying small magnetic field perturbations externally.
