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No abstract

In the past two decades, the picture of fusion plasmas has changed. Once analogous to an obscure work of abstract art, it is now more like a landscape full of comprehensible features.

With the addition of inductive poloidal current drive for current profile control in the Madison Symmetric Torus (MST) reversed field pinch, the magnetic fluctuation amplitude halves, leading to reduced energy and particle transport. A four-to five-fold increase in the energy confinement time to t E ϳ 5 ms with both decreased Ohmic input power and increased stored thermal energy coincides with record low fluctuation amplitude and record high electron temperature ϳ600 eV (for MST). b ͓ 2m o ͗p͘͞B͑a͒ 2 ͔ increases from 6% to 8%. Other improvements include reduced electrostatic edge turbulence and plasma impurity content. [S0031-9007(96)02046-7] PACS numbers: 52.55. Hc, 52.25.Fi, 52.25.Gj, 52.35.Py

New profile measurements have allowed the electron thermal diffusivity profile to be estimated from power balance in the Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The measurements show that (1) the electron energy transport is conductive not convective, (2) the measured thermal diffusivities are in good agreement with numerical simulations of stochastic transport, and (3) transport is greatly reduced near the reversal surface where magnetic diffusion is small.