Twenty years of physics: Plasmas

TWENTY YEARS AGO the study of plasmas occupied a relatively minor role in physics: The wide variety of plasma phenomena remained unexplored. The field had its origin early in this century in the study of the gas discharge, a relatively dense, slightly ionized plasma regime where the dominant effects are ionization, excitation, recombination and other atomic collision processes. Irving Langmuir initiated modern plasma physics through his discovery of plasma electrostatic oscillations and his realization that this was an aspect of collective particle motion. It is these collective motions which, generating and interacting with electric and magnetic fields, are responsible for the wealth of physical phenomena that take place in a plasma and make it so different from ordinary fluids.