Theoretical Study of a Spherical Plasma Focus

A theoretical model is developed for two concentric electrodes spherical plasma focus device in order to investigate the plasma sheath dynamics, radiative emission, and the ion properties. The work focuses on the model development of the plasma sheath dynamics and its validation, followed by studying of the radiation effects and the beam-ion properties in such unique geometry as a pulsed source for neutrons, soft and hard x-rays, and electron and ion beams.;Chapter 1 is an introduction on fusion systems including plasma focus. Chapter 2 is an extensive literature survey on plasma focus modeling and experiments including the various radiations and their mechanism. Chapter 3 details modeling and validation of the plasma sheath dynamics model with comparison between hydrogen, deuterium, tritium and deuterium-tritium mixture for the production of pulsed neutrons. Chapter 4 is a study of the radiative phase, in which neutron yield is investigated, as well as the predicted beam-ion properties. Chapter 5 summarizes and discusses the results. Chapter 6 provides concluding remarks and proposed future works.;The phases of the developed model are the rundown phase I, rundown phase II, the reflected phase and a radiative phase. The rundown phase I starts immediately after the completion of the gas breakdown and ends when the current sheath reaches the equator point of the spherical shape. Then immediately followed by rundown phase II to start and it ends when the shock front hits the axis, which is the beginning of the reflected shock phase. Reflected shock front moves towards the incoming current sheath and meets it which is both the end of the reflected shock phase and the beginning of the radiative phase. After the reflected shock front and the current sheath meet, the current sheath continues to move radially inward by compressing the produced plasma column until it reaches the axis. Since the discharge current contains important information about the plasma dynamic, electrodynamics, thermodynamics, and radiations emitted from the plasma focus, the discharge current wave form has been used to validate the model. A good agreement has been achieved between theoretical calculation and the experimental measurement of a similar spherical plasma focus device. The snowplow model with the help of the shock wave equations coupled to the circuit equations is used to predict the plasma and shock wave parameters by using the momentum and magnetic force equations. While these equations are used in the phases of the rundown phase I and II, the reflected shock phase with the necessary modification of the magnetic field calculation, and the constant reflected shock front velocity; the radiative phase additionally includes the effect of the radiations emitted from the plasma column (Bremsstrahlung, line and radiative recombination), and the joule heating with the plasma resistance. Neutron yield and the ion properties are calculated in the radiative phase.;The parameters for the spherical plasma focus are 8.0 and 14.5 cm inner and outer electrode radii, respectively, 432 muF capacitor bank, 25 kV charging voltage, and 14.5 Torr DT gas pressure. A high discharge current of about 1.5 MA, a high neutron yield of 1.13 x 1013 neutrons, and a high plasma column-ion density of 1.61 x 1024 m --3 are achieved with the given parameters. The developed model is also used to investigate the effect of the gas pressure, discharge voltage, and the molecular mass of the gas on the maximum plasma temperature and pinch start time. It is found that the maximum plasma temperature can be obtained with a relatively shorter pinch start time using a relatively heavier gas with lower gas pressure and higher discharge voltage.