Harold Ralph Lewis, Jr., (7 June 1931 - 25 March 2002) was an American physicist, researcher at the Los Alamos National Laboratory, and professor at Dartmouth College.
[4] After completing his graduate studies, Lewis was a postdoctoral research associate at Heidelberg University from 1958 to 1960.
[4] In 1963, Lewis pivoted his research focus to plasma physics, and joined the Los Alamos National Laboratory (LANL) as a staff scientist.
[1] From 1975 to 1976, Lewis took a yearlong leave from LANL and served as a visiting professor at the University of Wisconsin-Madison.
Other research contributions have included: "the study of explicitly time-dependent invariants of time-dependent Hamiltonian systems, description of solutions of the initial-value problem for the small-signal response of collisionless plasmas, use of Hamilton's principle to generate algorithms for the numerical simulation of the equations of collisionless plasmas and other Hamiltonian systems; and the application of time-dependent operator invariants in the description of quantum systems.
"[4] Lewis' research in this direction led him to rediscover the Ermakov-Lewis invariant, a quantity conserved during Hamiltonian evolution of a harmonic oscillator system.
[5] While at Dartmouth, Lewis published on plasma physics of nonideal magnetohydrodynamic steady states in fusion devices and on some nonlinear mechanics problems.