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Development and studies of a small plasma focus

Ali, Jalil (1990) Development and studies of a small plasma focus. PhD thesis, Universiti Teknologi Malaysia, Faculty of Science.

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Abstract

With fusion devices being scaled up to inflexibly larger sizes there is a need to scale down experiments so that important principles of plasma physics and technology may still be made available experimentally to smaller laboratories. The objective of the present work is to develop and study a scaled-down plasma focus based on cost-effective physics mechanisms. The work described in this thesis is a combination of three main areas namely the numerical modelling, the development and the diagnostics of a 3.3 kJ Mather-type plasma focus. In this thesis a generalised slug model with coupled-current is developed for a focus. This model considers the focus gross dynamics in three separate phases -the axial rundown phase that crucially delays the radial focus phase followed by the slow dynamics phase. The model is then used for optimizing numerically the design of a low-cost plasma focus system called the UTM PFF (Universiti Teknologi Malaysia Plasma Fusion Facility) following the design of the UNU/ICTP PFF (United Nation University / International Centre for Theoretical Physics Plasma Fusion Facility). Numerical computation indicates that good focussing actions are obtained from the design parameters. The outcome of this design is a 3.3 kJ Mather-type plasma focus system powered by a single 15 kV, 30 ~F capacitor. The practicability of such design procedure is further confirmed by the consistency and reproducibility in the performance of the actual plasma focus device constructed from this design. The generalised slug mode1 is then used to investigate the possibi 1 i ty of focus compression enhancement. For this purpose the effect of radiation cooling and the elongating 2-pinch are examined numerically. The effect of radiation cooling is studied by considering Bremsstrahlung and the Joule heating of the focus. The former, an energy loss term, enhances compression whilst the latter, energy gain term, opposes compression. From the equations of motion developed in this work it is found that the 'focus compression is further enhanced if the current exceeds 1.6 MA for a deuterium focus. This agrees with the value of Pease-Braginski i current. Results obtained based on the mechanism of an elongating 2-pinch also indicates further enhancement and stability. On the developmental side, the numerical focus model guided by a few design criteria and the resultant engineering that went into the construction of UTM PFF is described in detail in T this thesis. A number of diagnostic tools were built and developed < . g in this laboratory. Currents, voltages and magnetic field are measured by Rogowski coils, voltage probes and magnetic probes. Rogowski coils monitor the current from the capacitor bank. The magnetic probes also monitor the current inside the focus. Voltage probes monitor voltage to the focus. Geiger-Muel ler counters with activated indium foil monitor the fusioning neutrons. The 15 kV, $3:3 kJ UTM plasma focus has been successfully operated to produce strong focussing actions over a range of pressures in air. In deuterium over a range of (0.5 - 8.0) mbar neutrons were detected. UTM PFF is optimized for neutron production in deuterium at 4 mbar. The effect of knife-edge on neutron production is also studied. Results show that the optimized operating pressure is shifted to 5 mbar. In order to visualize the dynamical behaviour of the current sheath in the focus a nitrogen shadowgraph system has been developed. This is further supplemented by results obtained using streak phot6graphy. Within the framework of UTM this is a first effort to build up and develop effective plasma including laser experimental research facilities in order to acquire practical knowledge and ski 11.

Item Type:Thesis (PhD)
Additional Information:Thesis (Ph.D.) -- Universiti Teknologi Malaysia, 1990; Supervisor I : Prof. Dr. Lee Sing; Supervisor II : Prof. Dr. Mohd. Yusof Abu Bakar; Supervisor III : Prof. Dr. Mohd. Amin Alias
Uncontrolled Keywords:dense plasma focus, plasma focus system
Subjects:Q Science > Q Science (General)
Divisions:Science
ID Code:7936
Deposited By: Ms Zalinda Shuratman
Deposited On:06 Apr 2009 00:31
Last Modified:23 Jan 2011 12:32

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