2-STREAM AND GRAVITATIONAL INSTABILITIES IN A GRAIN PLASMA

If the massive component of a two-component plasma consists of weakly charged solid grains, electrostatic and gravitational instabilities can operate on similar spatial and temporal scales. In particular, when the grain charge-to-mass ratio is of the order of the square root of the gravitational constant, the electrostatic two-stream (or Buneman) instability can seed the Jeans gravitational instability, selecting a scale for the resulting condensation. Using particle-in-cell simulations, we verify the behavior of each of these instabilities acting alone in the appropriate limits, and show that when both act in concert a grand equipartition among all available stores of energy is achieved.