U of R ME : Faculty-Simon

Albert Simon
Professor Emeritus of Mechanical Engineering and of Physics
Senior Scientist in the Laboratory for Laser Energetics
Hopeman 212
Phone: (585) 275-4431, Fax: (585) 256-2509, simon@me.rochester.edu.

Ph.D., Physics, University of Rochester (1950), B.S., Physics (cum laude), City College of New York (1947)

My interests are in nuclear energy, with emphasis on nuclear fusion reactors. Since hot plasmas are central to the latter, I have studied the behavior of plasma in magnetic containers, in laser-produced pellets, and in space.

A New Model of Raman Scattering in Laser-Produced Plasma

A great deal can be learned about what is going on in the outer plasma of a laser-imploded pellet by studying the scattered laser light. Some of this light is shifted in frequency (Raman scattering). Until recently, this was interpreted as due to onset of an instability in which a plasma wave was created and a photon emitted. However, the intensity at which this effect began seemed much too low to fit the theory. There were other difficulties in interpretation.

We have now found a more plausible explanation. The onset of an entirely different instability, at a lower laser intensity and in a specific region of the plasma, has a drastic effect on the rest of the plasma. A consequence is that pulses of electrons are emitted into the surrounding plasma and develop large "wakes" while moving around. These wakes make each electron a much bigger "radar target" and greatly enhance the subsequent scattering of laser light. There is good agreement between this theory and experiments.

The Effect of Weak Collisions on Ion-Wave Damping

In the absence of collisions, ion waves will damp away slowly in a plasma with cold ions. This is Landau damping caused by those electrons moving nearly in resonance with the wave. When weak electron-ion collisions are added, there is some question about the effect. Will these collisions add to the damping rate (as one might intuitively expect) or will they decrease the damping by interrupting the resonant electron orbits? For nearly thirty years, a series of papers have concluded the latter and some even predicted the possibility of instability in equilibrium plasmas. We have now shown that the former expectation is correct. Numerical solution of the Fokker-Planck equation first pointed to this. Later, we corrected an error in a key earlier paper and also obtained an analytic solution. It is generally incorrect to solve weakly collisional problems by expanding about the collisionless solution.

Representative Publications

An Introduction to Thermonuclear Research, Pergamon, New York, 1959.
Editor (with W. B. Thompson) of Advances in Plasma Physics, Vols.I-VI, Wiley, New York.
Subsection on Nuclear Fusion in section entitled "Nuclear Energy" (with M. N. Rosenbluth),Encyclopedia Americana.
Parametric Excitation of Bernstein Modes in Laser-Produced Plasma, Phys. Plasmas 2, p.3832, 1995.