“We noticed the similarity of the discharge structures. (…) Langmuir pointed out the importance and probable wide bearing of this fact. We struggled to find a name for it. For all members of the team realized that the credit for a discovery goes not to the man who makes it, but to the man who names it. Witness the name of our continent. We tossed around names like ‘uniform discharge’, ‘homogeneous discharge’, ‘equilibrium discharge’; and for the dark or light regions surrounding electrodes, names like ‘auras’, haloes’, and so forth. But one day Langmuir came in triumphantly and said he had it. He pointed out that the ‘equilibrium’ part of the discharge acted as a sort of sub-stratum carrying particles of special kinds, like high-velocity electrons from thermionic filaments, molecules and ions of gas impurities. This reminds him of the way blood plasma carries around red and white corpuscles and germs. So he proposed to call our ‘uniform discharge’ a ‘plasma’. Of course we all agreed.But then we were in for it. For a long time we were pestered by requests from medical journals for reprints of our articles.”

In a letter to Nature Vol 233 (1971) page 219, Harold M. Mott-Smith recollects how Irving Langmuir started using the word “plasma” in about 1927

U.S. scientist Irving Langmuir won the Nobel Prize in Chemistry in 1932 for discoveries and investigations in surface chemistry. Amongst other things, his research into molecular adsorption provided insight into the physics of vacuum pumping. Without this knowledge, nobody would be able to build today’s tokamak vessels that provide vacuum conditions needed for fusion. Irving Langmuir also invented, and used, a very simple but effective diagnostic to measure electron temperatures and densities of low temperature plasmas, which today we call the “Langmuir probe“. At JET there are tens of Langmuir probes installed in the carbon tiles (i.e. in the plasma-facing wall), used to characterise JET plasmas at their very edge; within current JET enhancements, 45 new probes will be installed. Indeed, the importance of “plasma-wall interactions” studies has escallated as we contemplate future fusion reactors like ITER. And this is just one of the reasons why today’s plasma science plays an inspirational role for further research into surface chemistry. Perhaps this is the best recompense to Irving Langmuir for his merit in giving plasma its name.

Picture of the Month

Langmuir probes in an early divertor tile structure of JET

Langmuir probes in an early divertor tile structure of JET