It is shown that plasma waves need not have an asymmetric spectrum in order to produce an electric current in a plasma embedded in a curved magnetic field. For instance, in a toroidal plasma, up–down asymmetric electron–cyclotron heating drives a toroidal current even if there is no net wave–particle momentum transfer and the wave field does not interact preferentially with electrons travelling in any one direction. The resulting current drive efficiency is calculated and is found to be smaller than that of the conventional current drive mechanism in the banana regime, but not insignificant in the plateau regime.
