[hal-00779760] Nonstationary shocks and basic sources of "macro-turbulence" (micro-instabilities excluded)

Stationary shocks (Part 1) represent a first (simplified) approach of collisionless shocks. In fact, the behavior of shocks is more intricated since the balance between the three effects (nonlinear effects versus dispersive/dissipative effects) which characterize the shock itself (to see Part 1) leads to non stationary behavior of the front itself. Indeed, the shock front is self-adapting its own dynamics in space and time, according to the local need for energy partition. Both numerical simulations and in situ measurements of shocks evidence clearly that the shock front is nonstationary and not homogeneous. The crossing of a same given shock by several real (or virtual) probes of space missions provide quite different signatures of local electric/magnetic fields, density, temperature, pressure and of local particle distribution functions too. These mechanisms will be presented and shown to coexist and compete each other. In this second course, we will focus on nonstationarity processes based on large fluctuations of the main macroscopic fields at the shock front, where these fluctuations are generated by local large scale dissipative and nonlinear dispersive effects. In this approach, these processes exclude any plasma instabilities. One key consequence is that these nonstationarity effects do have a strong impact on the formation of energetic particles (both electrons and ions). These open a way to new possibilities of particle energisation not accessible or described by presently existing theories or by models based on stationary shocks only. This impact will be illustrated in recent results obtained on electron/ion dynamics by a self-consistent approach.



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