Nuclear Fusion Reaction Kinetics and Ignition Processes in Z Pinches

摘要

This thesis presents work on two topics related to nuclear fusion in plasmas.udThe first topic is the energy spectrum of products of fusion reactions in plasmas,udcalled the production spectrum. The second is an investigation of the fusion reactionudprocesses in high energy density Z pinch plasmas and the feasibility of ignition ofudsuch plasmas.udA method is presented for the derivation of production spectra for plasmas withudvarious distributions of ion velocities. The method is exact, requiring the solution ofuda 5 dimensional integral and is suitable for both isotropic and anisotropic distributions.udIt is shown that many of the integrals can be solved analytically. The solutionsudare used to study the spectra of neutron energies produced by deuterium-deuteriumudand deuterium-tritium reactions. It is found that for maxwellian distributions of ionsudthe neutron spectrum is asymmetric with a longer high energy tail when comparedudwith gaussian approximations of the spectrum.udDeuterium and deuterium-tritium Z pinch plasmas are studied computationallyudusing a hybrid code in which the fuel is modelled as a magnetohydrodynamic (MHD)udfluid and fast ions are modelled as discrete particle-in-cell (PIC) particles. Usinguda Z pinch model in which the magnetic and thermal pressures are in equilibriumudit is found that significant energy gain can be achieved for currents greater thanud50MA. Deuterium gas puff experiments with a 15MA current are also analysedudcomputationally in order to determine the reaction mechanism. The results of MHDudsimulations in 3 dimensions are post-processed with a PIC code to model reactionsudoccurring due to the acceleration of deuterium ions by large electric fields. It isudfound that reactions due to this beam-target mechanism represent a small fractionud(0.0001) of the number of thermonuclear reactions.