  The problem of the cosmic ray origin is discussed in connection with their
acceleration in supernova remnant shocks. The diffusive shock acceleration
mechanism is reviewed and its potential to accelerate particles to the maximum
energy of (presumably) galactic cosmic rays ($10^{18}eV $) is considered. It is
argued that to reach such energies, a strong magnetic field at scales larger
than the particle gyroradius must be created as a result of the acceleration
process, itself. One specific mechanism suggested here is based on the
generation of Alfven wave at the gyroradius scale with a subsequent transfer to
longer scales via interaction with strong acoustic turbulence in the shock
precursor. The acoustic turbulence in turn, may be generated by Drury
instability or by parametric instability of the Alfven waves.
