Plasma Applications

Abstract

The effect of plasmas had been noticed as early as 1901, when Marconi found that radio waves could cross the Atlantic in spite of the curvature of the earth. We now know that the waves were reflected by the ionosphere. The study of plasmas probably began with Irving Langmuir's experiments on sheaths in 1928, and it was he who coined the name plasma in a blood-free context. Practical use of plasmas began in the late 1940s with E.O. Lawrence's invention of the calutron (named for the University of California) for the separation of U 235 from U 238 for use in atomic bombs. It was the effort to tame the H-bomb into a steady source of electricity—hydrogen fusion—that spawned modern plasma physics. More on that later. Today, many objects used in everyday life are made or treated with plasmas. These are not the fully ionized plasmas needed for fusion but are partially ionized plasmas with electron temperatures below about 4 eV, the so-called low-tempera-ture plasmas. About 12 % of electricity generated in the U.S. is used for lighting, and over 60 % of lamps involve low-temperature plasmas. Fluorescent lights use an argon or neon plasma containing mercury to generate invisible ultraviolet light, which then excites a phosphor coating that glows visibly. Fluorescents are being replaced by more efficient LEDs (light-emitting diodes), which contain solid-state plasmas in p-n junctions. The latter are also at the heart of solar cells. Semicon-ductors in electronic devices are made with the use of plasma etching and deposi-tion. Plastic sheets are made hydrophylic or hydrophobic depending on whether they are to be printed on, such as in food packaging. The pixels in our TVs and computer screens are etched with plasmas. Windows are glazed with plasmas to transmit or reflect specific wavelengths. Heat barriers in jet engines are made with plasma deposition. Thrusters in spacecraft are plasma ejectors (Sect. 10.4). In medicine, plasmas are used for sterilization and for hardening or knee implants by ion implantation, for instance. The subject of plasma chemistry has been © Springer International Publishing Switzerland 2016 F.F. Chen, Introduction to Plasma Physics and Controlled Fusion, DOI 10.1007/978-3-319-22309-4_10 355 developed for these applications. All lasers contain plasmas, ranging from the huge megajoule lasers at Livermore in the U.S., in Osaka in Japan, and at Bordeaux in France, to the laser pointers used in lectures. Many phenomena in basic physics either involve plasmas or may involve plasmas when finally solved. Lightning strikes are gas discharges between charged clouds or between a cloud and ground. Ball lightning is a glowing sphere of plasma that is on the ground and lasts many seconds. Because of its unpredictability, it is unexplained. The geodynamo inside the earth that creates its magnetic field involves motions of liquids, but probably not gaseous plasmas. The BICEP2 experiment (Background Imaging of Cosmic Extragalactic Polarization) seeks to find evidence of primordial gravitational waves from the Big Bang in the cosmic microwave background. Dust is believed to be involved. Dusty plasmas have been added to this edition.