As a first order Fermi acceleration process, diffusive shock acceleration works via a combination of compression, which occurs when a particle crosses the shock, and turbulent diffusion in pitch angle, which confines particles to the vicinity of the shock and ensures acceleration via multiple crossings. The pitch angle scattering occurs via turbulence which is, in turn, generated via Cerenkov emission of Alfven waves from energetic cosmic ray particles.
The net strength of the acceleration process is proportional to the large scale magnetic field. Thus, a 'dynamo' (of sorts) is a very desirable component of any diffusive shock acceleration scheme. Here we present a model of a simple mechanism whereby a large scale magnetic field is generated through the induced diffusion of Alfven wave quanta toward larger scale by acoustic wave density perturbations. The acoustic perturbations are produced via instability of the shock front driven by the energetic particle pressure gradient (i.e. Drury-Falle instability). Thus, the system naturally tends to amplify the large scale fields, and the dynamics of this process can be described by the dynamics of this process of Alfven wave quanta density, acoustic wave quanta density and the distribution function of energetic particles. We discuss the various possible states of the system and their implications for acceleration.