Mikhail Alexandrovich Leontovich (7.03.1903 — 30.03.1981) was a Soviet theoretical physicist and an academician (1946; corresponding member 1939). He was born in Moscow. He graduated from Moscow University (1923). In 1929—34 he worked at the Research Institute of Physics of Moscow University, and in 1934—41 and 1946—52 at the Physical Institute of the USSR Academy of Sciences. From 1951 he worked at the Kurchatov Institute of Atomic Energy. At the same time, in 1934-45 and in 1955-71, he was professor at Moscow University.
His research concerned electrodynamics, physical optics, statistical physics, thermodynamics, quantum mechanics, the theory of oscillations, acoustics, radiophysics, plasma physics and the problem of controlled thermonuclear fusion. Together with L. I. Mandelstam he constructed in 1928 the theory of the sub-barrier transition of a particle in quantum mechanics (the tunnel effect), and in 1929 he took part in creating the complete classical theory of the Raman scattering of light in crystals. In 1937, together with Mandelstam, he proposed a general method of treating dissipation in systems with a finite relaxation time, which found wide application in solid-state physics and in gas dynamics.
The “boundary conditions” proposed by Leontovich for the electromagnetic field at the surface of bodies with a large complex permittivity have proved extremely fruitful in the study of a wide range of problems in electrodynamics. He developed a method of solving the boundary-value problems of electrodynamics and of the theory of radio-wave propagation — the so-called parabolic equation method, which won general recognition and stimulated progress in many areas of mathematical physics. Together with V. A. Fock he studied in 1946 the propagation of radio waves along the surface of the Earth. He did much to lay the foundations of the theory of thin wire antennas. Together with S. M. Rytov he established the relation between the correlation of current fluctuations in a medium and its conductivity.
In 1951 he took charge of theoretical research on plasma physics and on the problem of controlled thermonuclear fusion in the USSR, initiating and taking an active part in most of the work in this field. A number of fundamental physical ideas here are his, in particular on the foundations of the theory of a promising thermonuclear reactor, the tokamak. He constructed (1953) the theory of the inertial compression of a current-carrying plasma, which underlies pulsed processes. His ideas on balancing the toroidal expansion of a current-carrying plasma by means of a conducting shell, and on stabilising the plasma loop with a strong magnetic field, underlie the Tokamak system. In 1958 he was awarded the Lenin Prize for his research on powerful pulsed discharges in a gas for producing high-temperature plasma.
Founder of schools of radiophysics and plasma physics. The A. S. Popov Gold Medal.