We report a successful quantitative account of the experimentally determined electron thermal conductivity ${\chi }_e$ in a beam-heated $H$ mode plasma by the magnetic fluctuations from microtearing instabilities. The calculated ${\chi }_e$ based on existing nonlinear theory agrees with the result from transport analysis of the experimental data. Without using any adjustable parameter, the good agreement spans the entire region where there is a steep electron temperature gradient to drive the instability.

• Received 21 May 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.135003