Self consistent analysis for the ion-beam generation in the pinch phase of dense plasma focus
Abstract
The dense plasma focus (DPF) device has been garnering interest for a myriad of applications ranging from ion-beam surface treatment, x-ray lithography and radioisotope generation to space propulsion. The DPF is a coaxial plasma device which produces x-rays, ion beams, and neutrons. Empirical development has allowed DPF performance to satisfy minimal operating requirements in the aforementioned applications. However, a thorough physics based understanding or the device can allow possible order of magnitude increases in performance. A new theory on the development of ion beams in DPF is advanced in this thesis. The theory involves the seeding and growth of a nonlinear magnetic Rayleigh-Taylor (MRT) instability which forms a bubble of trapped magnetic field during pinch. Subsequent compression of the magnetic bubble induces strong transient electric fields of the order of 20 megavolts per meter. Resistive magnetohydrodynamic (RMHD) calculations are carried out to track the evolution of the plasma sheath from liftoff to rundown to pinch phases. The seed perturbation of the MRT instability is caused by hydromagnetic effects as the plasma sheath transits the inner corner of a hollow anode. This behavior can also be extended to a solid anode type device. Original one-dimensional conformal grid electromagnetic algorithms are constructed to calculate the axial electric field produced by the collapsing magnetic cavity. Implementation of a simple particle acceleration model using the calculated electric fields produced particles with energies in the 100 keV range. Verification of the results against measured experimental ion-beam spectra validate the theory as a significant contribution to DPF research.
Degree
Ph.D.
Advisors
Choi, Purdue University.
Subject Area
Fluid dynamics|Gases|Nuclear physics
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