  Non-helical hydromagnetic turbulence with an externally imposed magnetic
field is investigated using direct numerical simulations. It is shown that the
imposed magnetic field lowers the spectral magnetic energy in the inertial
range. This is explained by a suppression of the small scale dynamo. At large
scales, however, the spectral magnetic energy increases with increasing imposed
field strength for moderately strong fields, and decreases only slightly for
even stronger fields. The presence of Alfven waves is explicitly confirmed by
monitoring the evolution of magnetic field and velocity at one point. The
frequency omega agrees with vA k1, where vA is the Alfven speed and k1 is the
smallest wavenumber in the box.
