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Title: A theoretical and computational study of the ion beam explosive instability
Author: Hand, Raymond Peter
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1974
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This thesis contains an account of a theoretical study of the nonlinear interaction of three waves in a plasma. Kinetic equations are derived, which describe the interaction for a plasma obeying the fluid equations of magnetohydrodynamics, and for a plasma obeying the Vlasov-Poisson equations. In the magnetohydrodynamic case we find that energy is transferred back and forth between the three waves in a periodic manner. We study a Vlasov plasma with a diffuse ion beam propagating through it, and find that one wave, a Landau unstable ion sound wave propagating on the beam, behaves as though its energy were negative. The kinetic equations predict that as it transfers energy to two other waves, it grows in amplitude, and that all three waves reach an infinite amplitude in a finite time. This phenomenon is known as an 'explosive instability', and the mechanisms governing the interaction are analysed in order to find stabilisation processes. We show that the unstable oscillations cause a heating of the beam ions, a reduction in beam velocity and a distortion of the beam distribution function, all of which contribute to stabilising the Interaction. We find that the heating Is the dominant process, causing heavy Landau damping of the unstable waves. Two computer programs are described which were used to simulate the beamed plasma configuration in order to test the theory. The results show that heating is the dominant beam effect, and that wave growth saturates as the heating becomes significant. Some of the computational techniques developed during the implementation of the programs are described, and a critical survey is made of the programs themselves.
Supervisor: Not available Sponsor: Culham Laboratory
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics