Particle transport studies with applied resonant fields on TEXT

Externally applied resonant magnetic fields have been used on TEXT to modify the particle flux and the radial electric field near the plasma edge. Magnetic fields with primary mode numbers m/n = 7/3 and 7/2, and an average radial field amplitude ⟨|br|/Bϕ⟩ ≃ 0.1% have been employed. This perturbation produces mixed islands and stochastic regions at the plasma edge (r/a ≥ 0.8) without affecting the interior. Working particle transport is shown to be increased by typically 30% only in the presence of (computed) magnetic islands. The effect is diminished at high perturbing field strength when the islands become stochastic. A novel transport mechanism due to × convection is proposed to explain this. Outward impurity transport is increased as well.