Space and Laboratory Plasma Physics

Physics has experienced several revolutions in the twentieth century that profoundly changed our understanding of nature. Quantum mechanics and (special, general) relativity are the best known and certainly the most important, but the discovery of the fourth state of matter – the state of plasma – as the most natural form of ordinary matter in the Universe, with more than 99% of visible matter being in this form, is unquestionably a revolution in physics. This discovery has led to the emergence of a new branch of physics called plasma physics.

Plasma physics describes the coupling between electromagnetic fields and ionized matter (electrons, ions). Thus, it is based upon one of the four foundations of physics: the electromagnetic interaction whose synthetic mathematical formulation was made by the Scottish physicist J. C. Maxwell who published in 1873 two heavy volumes entitled A Treatise on Electricity and Magnetism. The discovery of the electron by J.J. Thomson in 1897 and the formulation of the theory of the atom at the beginning of the twentieth century have contributed to the first development of plasma physics. It was in 1928 that the name plasma was proposed for the first time by I. Langmuir, referring to blood plasma in which one finds a variety of corpuscles in movement. Experimental studies of plasmas first focused essentially on the phenomenon of electrical discharge in gas at low pressure with, for example, the formation of an electric arc. These studies initiated during the second half of the twentieth century were extended to problems related to the reflection and transmission of radio waves in the Earth's upper atmosphere (this was how the first transatlantic link was established by Marconi in 1901), which led to the discovery of the ionosphere, an atmospheric layer beyond 60 km altitude with a thickness of several hundred kilometers. As explained by the astronomer S. Chapman (1931), the ionosphere consists of gas partially ionized by solar ultraviolet radiation; therefore, it is the presence of ionospheric plasma which explains why low-frequency waves can be reflected or absorbed depending on the frequency used.