Mariner 10 radiation. The plasma experiment's goal was to study the ionized gases (plasma) of the solar wind, the temperature and density of its electrons, and how the planets affected the velocity of the plasma stream. The experiment contained two components, facing in opposite directions. The Scanning Electrostatic Analyzer was aimed toward the Sun, and could detect positive ions and electrons, which were separated by a set of three concentric hemispherical plates. The Scanning Electron Spectrometer was aimed away from the Sun, and detected only electrons, using just one hemispherical plate. The instruments could be rotated about 60 degrees to either side.
Degree of ionization plasma is in a "Coulomb-collision dominated regime", i.e. when formula_9, which can correspond to a degree of ionization as low as 0.01%. A "partially" or "weakly ionized gas" means the plasma is not dominated by Coulomb collisions, i.e. when formula_10. A particular case of fully ionizes gases are very hot thermonuclear plasmas, such as plasmas artificially produced in nuclear explosions or naturally formed in our Sun and all stars in the universe. Stars contain largely hydrogen and helium gases, that are "fully ionized" into electrons, protons (H) and helium ions (He). Equations to characterize such very hot, fully ionized thermonuclear