[en] In the regions of the Tore Supra tokamak with significant ripple it is expected that a radial electric field (E_r) ensures the ambipolarity of fluxes of thermal particles trapped in ripple wells. A neoclassical calculation (Connor and Hastie 1973 Nucl. Fusion 13 221, Stringer 1972 Nucl. Fusion 12 689) shows that E_r is related to ion temperature and density gradients. The validity of this relation is investigated in a series of Tore Supra L-mode discharges without external momentum input. Doppler reflectometry measurements of fluctuations perpendicular velocity, which is dominated by the E_r x B drift, are found to be in good agreement with the predicted neoclassical E_r. (letter)