Collapse—The Shock Heating of a Plasma

There have been numerous independent suggestions to use high speed shocks to heat deuterium gas to thermonuclear temperature (E. Teller, R. R. Wilson, H. Grad, W. Marshall), and extensive experimental work in this field is being carried on by, e.g., Kolb, and Janes. Our own work in this field has been directed towards a fundamental understanding of the strong shock process, in the limit of no particle collision, to find out if, within this limit, the ion heating following the passage of the shock is large enough to give rise to a thermonuclear reaction. The reason for the emphasis on the limit of no particle collision (within the dimensions of the system) is that for practical magnetic field strengths sufficient to contain plasma at a thermonuclear temperature of say 10 kev, the density of plasma is so low that the collision mean free path becomes many times greater than the dimensions of the system. Under these conditions it is generally agreed» ~ that the dominant length in the shock transition process is determined by the cyclotron radius of the ions or electrons in the magnetic field, and that the forces of charge separation dominate the process of momentum change of ions. The more exact theories treat the case where the magnetic field energy density Я/8тг behind the shock dominates the partial pressure of plasma oscillatory or thermal motion. In the case where magnetic field pressure is dominant, the oscillatory or thermal energy density behind the shock resides primarily in the ions. One of us e has discussed the probable consequences of extremely strong shocks (in the limit of no particle collision), for the case where the magnetic pressure behind the shock does not dominate plasma energy density. It is tentatively concluded that in this limit the energy density will reside in electron plasma oscillations which relax into an electron temperature before the ions are heated. It is hoped that the experimental program will eventually test these theories. In shock-heating a body of plasma, the basic procedure is to apply a large pressure that rises in a time short compared to the transit time of sound across a plasma dimension. A large fraction of the energy input into a shock will produce irreversible heating, and this large and sudden heating is the objective. In the experiment to be described, the geometry used is