Numerical Simulation Of The Influence On Ionosphere By High-Altitude Nuclear Explosion

A high-altitude nuclear explosion releases large quantities of energetic particles and electromagnetic radiation capable of producing ionization in the atmosphere. The ionized regions can affect electromagnetic signals whose transmission paths propagate through these regions. In this dissertation, numerical simulation methods for ionospheric effects of nuclear explosion above 100km are developed, and then it was used to calculate the temporal and spatial distribution of additional electron density. Based on this distribution, the influence on short-wave communication is analyzed. The main contributions from the dissertation can be outlined as follows.1. The Monte Carlo method is used to simulate atmosperic ionization effects of the prompt radiation from high altitude nuclear explosion. Simulation presents the instantaneous spatial distributions of the electron density in the atmosphere. The atmosphere is a kind of non-uniform media, whose density drops rapidly with the increase of height. Therefore, a method, which samples the mass distance to replace the step length of the particle, is used to considerably increase the computing speed. The MCATNP, which is a special code to simulate the transport of neutron and photon in atmosphere, was designed to compute the spatial distributions of the electron density from the ionization of prompt radiation.2. Delayed gamma rays and beta particles are produced during the radioactive decay of the fission debris. This continuing radiation produces ionization characterized by a production rate of ion pairs per unit volume per unit time. The MCATNP code can also be used to simulate atomsperic ionization by delayed gamma rays with a body source. A equivalent surface source model is developed to simulate ionization by beta particles, whose ion-pair production rate is computed as a function of the mass of gas traversed in the direction of a magnetic field line. The number densities of electrons and ions at a specific time after explosion was abtained from the solution of a system of three diffetential equations which describe the time rate of change in each particle density. The initial condition of equations are specified by the ionization of prompt radiation, and source terms given by the ionization of delayed radiation.3. By using these models and methods above, the additional ionization distribution produced by 1Mt nuclear burst at an altitude of 100km was calculated as an example. The results give the instantaneous spatial distribution of X-rays and initial nuclear radiation, present the ion-pair production rate distribution of delayed radiation, and the temporal and spatial distribution of electron density in additional ionization regions. Based on these, the absorption of radio wave is computed when the wave passes through the additional ionization regions without bending. A quantitative method was developed in terms of the relation between the absorption value and the influence grades of nuclear effect, that can be used to analyze short-wave communication effects of nuclear explosion. Finally, this method was used to investigate short-wave communication effects of 1Mt and 1kt nuclear explosion.