Effect of the radial electric field on the fluctuation-produced transport in the H-1 heliac

Highly coherent low-frequency fluctuations are studied experimentally in th e low electron temperature plasma in the H-1 toroidal heliac. The fluctuati ons, presumably pressure-gradient-driven resistive MHD modes, produce consi derable radial particle transport. A build-up of strong sheared radial elec tric field leads to dramatic modifications in the fluctuation-driven transp ort. These modifications correlate with sudden changes in the plasma confin ement, resembling low-to-high transitions in other machines. Strong negativ e shear in the radial electric field eventually leads to the suppression of the fluctuations, while the onset of the strong positive shear correlates with the reversal of the fluctuation-driven particle flux, leading to the i nward-directed pinch. It is concluded that the radial electric field modifi es radial profiles of the fluctuation propagation velocity due to the Doppl er shift, and it is this velocity shear which is important for the transpor t modifications.