  Non-thermal X-ray emission in some supernova remnants originates from
synchrotron radiation of ultra-relativistic particles in turbulent magnetic
fields. We address the effect of a random magnetic field on synchrotron
emission images and spectra. A random magnetic field is simulated to construct
synchrotron emission maps of a source with a steady distribution of
ultra-relativistic electrons. Non-steady localized structures (dots, clumps and
filaments), in which the magnetic field reaches exceptionally high values,
typically arise in the random field sample. These magnetic field concentrations
dominate the synchrotron emission (integrated along the line of sight) from the
highest energy electrons in the cut-off regime of the distribution, resulting
in an evolving, intermittent, clumpy appearance. The simulated structures
resemble those observed in X-ray images of some young supernova remnants. The
lifetime of X-ray clumps can be short enough to be consistent with that
observed even in the case of a steady particle distribution. The efficiency of
synchrotron radiation from the cut-off regime in the electron spectrum is
strongly enhanced in a turbulent field compared to emission from a uniform
field of the same magnitude.
