Energetic neutral atom Energetic neutral atom Energetic neutral atom (ENA) imaging, often described as "seeing with atoms", is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere, even to its outer boundary. This constitutes the far-flung edge of the solar system. The solar wind consists of ripped-apart atoms (called plasma) flying out of the Sun. This is mostly hydrogen, that is, bare electrons and protons, with a little bit of other kinds of nuclei, mostly helium. The space between solar systems is similar, but they come from other stars in our galaxy.
Two-stream instability in various limiting cases as beam-plasma instability, beam instability, or bump-on-tail instability. Consider a cold, uniform, and unmagnetized plasma, where ions are stationary and the electrons have velocity formula_1, that is, the reference frame is moving with the ion stream. Let the electrostatic waves be of the form: formula_2 Applying linearization techniques to the equation of motions for both species, to the equation of continuity, and Poisson's equation, and introducing the spatial and temporal harmonic operators formula_3, formula_4 we can get the following expression: formula_5 which represents the dispersion relation for longitudinal waves, and represents a quartic equation in formula_6.