Abstract:  High-energy ion beams accelerated by shocks set up compensating (return) currents in the solar wind (e.g. upstream of the terrestrial bow shock), around supernova remnants, and in many other astrophysical environments. Plasma instabilities developing in such compensated-current systems are important for energy release and particles acceleration. I will discuss interplay between two classes of plasma instabilities in the compensated-currents systems: kinetic and reactive. Kinetic plasma instabilities critically depend on the local gradients of particles’ velocity distributions at resonant velocities. Reactive instabilities are sensitive to global characteristics of particles, such as the thermal and bulk velocities of the plasma species. A particular emphasis will be on the kinetic Alfvén instability driven directly by the beams, and reactive Alfvén instability driven by compensated currents. The reactive Alfvén instability seems to be more robust than the kinetic one and dominate in the well over-threshold regime. This instability is related to the recently discovered Bell instability. Applications to the terrestrial foreshocks and supernova remnants will be shortly discussed.