John Zinn

THERMAL INITIATION OF EXPLOSIVES

Numerical solutions have been obtained for the nonlinear heat conduction equations arising in the theory of thermal explosions. Explosion times are calculated for externally heated spheres, cylinders, and slabs of several explosive materials, and the results are shown to agree with experiment.

A finite difference scheme for time-dependent spherical radiation hydrodynamics problems

Abstract This paper describes a fast and simple computational procedure for a class of time-dependent radiation transport hydrodynamics problems with spherical symmetry. Local thermodynamic equilibrium is assumed, and effects of time-of-flight retardation of photons are not considered. A two-stream assumption is used wherein the monochromatic intensity function at each given point has one value for directions falling within a prescribed cone and another value for directions outside of that cone. A use of the method is illustrated in a computation of the growth of a nuclear fireball.

Structure and luminosity of strong shock waves in air

A set of numerical computations of the thermal structure and optical luminosity of strong shock waves in air is described. The model includes radiation transport coupled with hydrodynamics under assumed conditions of steady flow. With shock velocities above 10 km/sec a thermal precursor develops ahead of the shock front, and increases in prominence with increasing shock strength. For velocities above 50 km/sec the precursor is partially opaque to visible light and the computed brightness is smaller than that of a blackbody at the shock temperature. At higher velocities the brightness decreases with increasing shock strength. Steady solutions could not be found for velocities above 80 km/sec.

On the dynamics of hot air plasmas related to lightning discharges: 1. Gas dynamics

In this paper, we first study the dynamics of hot shocks in air in cylindrical geometry coupled to multiband radiation transport and detailed air chemistry. The wide energy and length scale ranges which are covered herein includes and exceeds the ones of first and subsequent return strokes happening during lightning discharges. An emphasis is put on the NOx production and the optical power emitted by strong shocks as the ones generated by Joule heating of the air from intense current flows. The production rate of NOx, which is useful for atmospheric global modeling, is found to be between 4.5 × 1016 and 8.6 × 1016 molecules/J for all computed cases, which is in agreement with the literature. Two different radiation transport methods are used to characterize the variability of the results according to the radiation transport method. With the exact radiation solver, we show that between 15 and 40% of the energy is lost by radiation, with a percentage between 20 and 25% for averaged lightning energies. The maximal visible peak is between 7 × 108 W/m and 3 × 107 W/m obtained for, respectively, a 19 kJ/cm and a 28 J/cm energy input. The mean radiated powers in the visible range are found between 9 × 106 W/m and 2 × 105 W/m for the energies just mentioned. We discuss the agreement of these values with previous studies.

The Motion of Bomb Debris Following the Starfish Test

Theoretical computations are presented which identify some of the more important processes affecting the debris expansion following the Starfish explosion. A MHD shock wave is formed, through which the moving debris and air plasma is coupled to stationary plasma. The major component of the stationary plasma is produced by the explosion through ionization of neutral air by X rays and by collisions. The detailed behavior of a model MHD shock system with collisional effects is studied by means of a Lagrangian Computer program, and the computed results are compared with photographic data. The data and computations are in good qualitative agreement as to the behavior of the downward and east-west expansion. The upward expansion is slowed partly by the processes mentioned, but it is ultimately stopped and reversed through the action of conduction currents flowing in the F1 layer in a region connected to the moving plasma by way of the field lines.

Motion of a Newly Formed Plasma in a Magnetic Field

Analytic expressions are derived for the motion of a hypothetical collisionless plasma which is created with isotropic velocities at time t = 0 within a uniform magnetic field. The electron and ion masses are assumed to be equal. It is found that the tendency of the particle magnetic moments to cancel the original B field is counteracted by macroscopic currents induced in the plasma through the changing field. The equations for the B field variation and for the macroscopic motion resemble the magnetohydrodynamic equations, with superimposed oscillatory terms of frequency ω and (ωp2 + ω2)1/2.

Motion of Newly Created Magnetoplasma

The motion of a nonuniform collisionless plasma that is created at t = 0 in a region containing a magnetic field is considered. Approximate integrals are obtained for the electron and ion Vlasov equations coupled with Maxwells equations. The results include expressions for the E and B fields, the electron and ion velocities, and the particle densities. The expression for the E field contains a smooth part equivalent to the sum of an ambipolar field and the v × B field associated with a steadily increasing drift velocity. In addition, there are large oscillatory terms with frequencies close to the plasma frequency. The B field is, in an average sense, frozen in the expanding plasma; however, it oscillates with the E field, and the oscillations become progressively stronger with time. In the framework of the approximations used, the oscillations grow without limit, until the approximations fail.

Time-Variations of D-Region Electron Densities, and Comparisons With Model Computations

An extensive series of incoherent scatter studies of the ionospheric D-region was carried out at the Arecibo radar facility during 1978 and 1979. They included several full-day sequences of electron density measurements over a range of altitudes, and also included a sequence during the serendipitous occurrence of a large solar flare. For the solar flare event simultaneous data on solar X-ray fluxes in several wavelength bands were available from the GOES-2 and ISEE-3 satellites.In the course of development of a large ionospheric computer model at Los Alamos we have used the solar flare data as a reality check. The solar X-ray flux data were used as inputs for computing ionization rates. The model computer includes 999 chemical reactions, and also includes diffusion and transport processes. In the course of the flare studies we used the data comparisons to adjust the values of three chemical rate coefficients that were poorly known. With those adjustments the model computations fitted the data quite well.Subsequent to the flare analysis we have been using the same model with some minor updates to compute the expected diurnal variations of the ambient D-region under conditions chosen to match those existing at the times of the incoherent scatter measurements. Comparisons of the computations and the data will be shown, and the relative importance of the several separate ionization processes will be discussed. We also compare model results with experimental data on concentrations of NO.