  Based on 1) a conjecture about the mean free path for particle scattering in
perpendicular shock geometries, and 2) a model for Wolf Rayet star winds, we
argue that explosions of Wolf Rayet stars can lead through diffusive particle
acceleration to particle energies up to 3 10^9 GeV. As a test we first
demonstrate that the magnetic fields implied by this argument are compatible
with the dynamo limit applied to the convective interior of the main sequence
stars which are predecessors of Wolf Rayet stars; second we show that this
implies the same strength of the magnetic fields as is suggested by the
magnetically driven wind theory. Third, we use data from radio supernovae to
check the spectrum, luminosity and time dependence which suggest that the
magnetic fields again have to be as high as suggested by the magnetically
driven wind theory. This constitutes evidence for the magnetic field strengths
required to accelerate particles to 3 10^9 GeV. Fourth, we demonstrate that
within our picture the nonthermal radio emission from OB and Wolf Rayet stars
can reproduce the proper radio spectra, time variability and radio
luminosities. Fifth, the comparison of Wolf Rayet stars and radio supernovae
suggests that electron injection into the acceleration process is a step
function of efficiency with the shock speed as the independent parameter.
