How to diagnose something hotter than 100 million degrees

The basic concept behind any Controlled Thermonuclear Fusion approach is to bring a plasma to very high temperatures and to keep it confined for a time sufficiently long to allow a number of fusion reactions to take place. The easiest of these reactions are those between deuterium and tritium, two isotopes of hydrogen. Deuterium is universally available in large quantities since about 1 part in 5000 of hydrogen in seawater is deuterium.

As a potential fuel of a fusion reactor, a liter of seawater could produce as much energy as 300 liters of oil. On the contrary, there is no sizable natural source of tritium because of its short radioactive half-life. Fortunately it can be obtained with breeding from lithium, which can also be extracted from seawater where its average concentration is 0.17 ppm. Thus, deuterium and lithium could provide an effectively inexhaustible source of energy, lasting for more than a million years.

The science of hot plasmas covers a wide variety of topics, from classical and relativistic electrodynamics to quantum mechanics. During the last sixty years of research, our initial primitive understanding of plasma physics has made impressive progress thanks to a variety of experiments – from tabletop devices with plasma temperatures of a few thousands of degrees and confinement times of less than 100 microseconds, to large tokamaks with plasma temperatures of up to five hundred million degrees and confinement times approaching one second. We discovered that plasma confinement is impaired by a variety of instabilities leading to turbulent processes with scales ranging from the plasma size to a few millimeters. Understanding these phenomena, which are what has slowed down progress towards a fusion reactor, has required the use of very sophisticated diagnostic tools, many of them employing electromagnetic waves.

The primary objective of the book is to discuss the fundamental physics upon which the application of electromagnetic waves to the study of confined plasmas is based.

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