  The paper presents a relativistic mechanism that can create a poloidal
non-uniformity of a radial electric field on a magnetic surface in a tokamak
plasma. This mechanism is associated with a significant current velocity of
electrons in plasma for many experimental modes of tokamak operations. It is
important that electric fields arise without the traditional separation of
charges in plasma. The presented mechanism can explain the previously
experimentally measured poloidal non-uniformity of the C+6 carbon ion toroidal
rotation velocity in the TORE-SUPRA tokamak plasma
