Measuring Δ′ from electron temperature fluctuations in the Tokamak Fusion Test Reactor

A method is developed for determining directly from experimental data the classical tearing mode stability parameter Δ′. Specifically, an analytical fit function is derived for the electron temperature fluctuations (T̃e) in the vicinity of a magnetic island. Values of Δ′ determined from the fit function parameters for m/n=2/1, 3/2 and 4/3 modes (m and n are poloidal and toroidal mode numbers) are obtained using the high resolution T̃e profile data from major radius shift (“jog”) experiments on the Tokamak Fusion Test Reactor (TFTR) [D. Meade et al., Proceedings of the International Conference on Plasma Physics and Controlled Nuclear Fusion. Washington, District of Columbia, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. I, pp. 9–24]. It is found that the n⩾2 modes have Δ′<0.