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.