It is known that improved coating properties can be obtained by plasma action in vacuum deposition, especially by vaporisation. Substantially higher coating rates can be attained in vapour deposition, but, with high plasma densities, they result in excessive scattering of the electron beam and reduce the power density. According to the invention, a plasma source, preferably a hollow cathode arc source, is arranged in the immediate vicinity of the substrate. Between the evaporator and the substrate there is a device for generating a magnetic field so that the region of high plasma density is separated from the evaporator and the electron beam by the magnetic field. The boundary field lines of this magnetic field run along an arc curving with respect to the substrate.