A stream of electrons enters plasma like a jet of water hitting a calm pond. The jet disturbs the surface, giving rise to waves that grow quickly and mix the water. In plasma, this process is called the Buneman instability: the electron beam excites oscillations that then scatter its energy. This phenomenon is important for understanding anomalous resistance — when plasma resists current more strongly than ordinary theory predicts.

In the new work, scientists considered how the thermal motion of ions and electrons affects the growth of the instability. It turned out that in warm plasma, the growth rate differs markedly from predictions of simple models that treat particles as cold. The maximum growth rate still depends on the electron-to-ion mass ratio, but not on their temperature ratio. This is an unexpected result that refines previous understanding.

When going from cold to warm plasma, ion inhomogeneity decreases, and the generation of sidebands, additional oscillations, weakens. As a result, energy transfer from the beam to the plasma becomes less efficient. This mechanism links microscopic density fluctuations to macroscopic heating, which may be important for laboratory experiments and astrophysical processes involving charged particle beams.