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Many wonder how the term "plasma" became applied to an ionized gas. Irving Langmuir, a researcher working to understand electric discharges, was the first to use the term in this way.
Irving Langmuir was born in Brooklyn, New York on January 31, 1881. He graduated with a B.S. in metallurgical engineering from the Columbia University School of Mines in 1903. His doctoral thesis was entitled “On the Partial Recombination of Dissolved Gases During Cooling.”
His initial contributions to science came from his study of light bulbs. He discovered that the lifetime of a tungsten filament was greatly lengthened by filling the bulb with an inert gas, such as argon. As he continued to study filaments in vacuum and different gas environments, he began to study the emission of charged particles from hot filaments (thermionic emission). He was one of the first scientists to work with plasmas and was the first to call these ionized gases by that name, because they reminded him of blood plasma.
During the 1920's Irving Langmuir was studying various types of mercury-vapor discharges, and he noticed similarities in their structure - near the boundaries as well as in the main body of the discharge. While the region immediately adjacent to a wall or electrode was already called a "sheath," there was no name for the quasi-neutral stuff filling most of the discharge space. He decided to call it plasma.
The first published use of the term was in Langmuir's "Oscillations in Ionized Gases," published in 1928 in the Proceedings of the National Academy of Sciences.