The Induction Linac System Experiment (ILSE) is a heavy-ion fusion (HIF) device that is being designed at Lawrence Berkeley Laboratory (LBL). The machine will be capable of accelerating 16 carbon ion beams, which are subsequently merged into 4 beams, to energies in the neighborhood of 10 MeV (10 million electron- volts). The purpose of the experiment will be to demonstrate the process of simultaneous acceleration and current amplification for a multiple beam accelerator configuration. If this process can be mastered, the beams produced by a machine such as ILSE would be used to implode and heat a deuterium-tritium (D-T) fuel pellet and produce a thermonuclear inertial confinement fusion (ICF) burn. This technology of achieving a fusion reaction using ion beams is referred to as Heavy-Ion Fusion (HIF) [1].

The conventional way of using a nonlinear Fabry-Perot cavity as an optical memory requires a negative pulse input to reset the state of the cavity. The possibility of using positive pulses to turn a system of nonlinear Fabry-Perot cavities on and off is studied and it was found that positive pulse switching is possible in a system of two coupled nonlinear cavities. First, Korpel and Lohmann's proposal of using polarization switching in a single nonlinear birefringent cavity was studied. After a detailed investigation of their proposal it was found that positive pulse switching in a single nonlinear Fabry-Perot cavity is not possible. One of the reasons is that the eigen-polarization states of the output of a nonlinear Fabry-Perot cavity cannot be switched independently. Although it is not possible to switch a single nonlinear Fabry-Perot cavity with positive pulses we were able to use the coupling of the eigen-polarization states to implement other kinds of optical switches which were demonstrated experimentally. The cross-talk effect in a metallic Fabry-Perot cavity was also studied. Next, a steady state model of a system of two coupled nonlinear Fabry-Perot cavities was developed and it was found that positive pulse switching is possible in such a system. The output can be turned on and off either by pulses sent into different cavities or by pulses of different magnitudes sent into one cavity. Finally, the dynamic behavior of the coupled cavities system was modeled by extending Goldstone and Garmire's model of a single cavity with one input to a system of two coupled cavities with two inputs. We verified by numerical calculations that positive pulse switching is also possible in the dynamic regime. / Ph. D.

Voltage source inverters (VSI) are popular in variable speed induction motor drive applications. Pulse width modulation (PWM) is employed to achieve variable voltage variable frequency output from a fixed DC bus voltage. The modulation method greatly influences the harmonic distortion in line current and the inverter switching loss. This thesis evaluates a few space vectorbased PWM techniques which reduce the harmonic distortion and/or the inverter switching loss, compared to conventional space vector PWM (CSVPWM), at a given average switching frequency. In space vector-based PWM, the average voltage vector applied over a sub-cycle equals the commanded reference vector, thereby maintaining voltsecond balance. The given average vector can be realized by applying the voltage vectors of the inverter in different sequences. CSVPWM employs a switching sequence in which all the phases switch once in a sub-cycle. Sequences, in which a phase is clamped, while the other two phases switch once in a sub-cycle have been reported in literature. Further, certain special switching sequences have also been reported recently. These special sequences involve switching a phase twice, while switching the second phase once and clamping the third phase in a sub-cycle. This work investigates the use of such special switching sequences to reduce line current distortion and inverter switching loss in an induction motor drive. The influence of various switching sequences on line current ripple and inverter switching loss is discussed in the thesis. Comparison of the sequences in terms of switching loss leads to a hybrid PWM technique, which deploys the best sequence to reduce switching loss under a given operating condition. This technique is referred to as minimum switching loss PWM (MSLPWM). Further, a procedure for design of hybrid PWM techniques to achieve reduced line current distortion as well as inverter switching loss is elaborated. Four such specially designed hybrid PWM techniques are discussed. Analytical methods are presented for the evaluation of total RMS harmonic distortion factor of line current and inverter switching loss corresponding to different PWM techniques. The MSLPWM and the hybrid PWM techniques are evaluated analytically in terms of harmonic distortion and switching loss. It is observed that the switching loss corresponding to MSLPWM is considerably less than that with CSVPWM over the entire range of power factor. The reduction in switching loss with MSLPWM is as high as 36% at high power factors close to unity, while it is not less than 22% at power factors close to zero. MSLPWM also reduces the harmonic distortion for power factors close to unity at high modulation indices. Compared to CSVPWM, the hybrid PWM techniques result in a maximum reduction of about 40% in the harmonic distortion at fundamental frequencies close to 50Hz, and about 30% reduction in switching loss at power factors close to unity. The various PWM techniques are tested on a constant V /f induction motor drive with a digital control platform based on ALTERA Cyclone II field programmable gate array (FPGA) device. With a 10kVA IGBT based inverter feeding a 2.2kW, 415V, 50Hz, three-phase induction motor, the total RMS harmonic distortion factor of line current (IT HD) is measured at different fundamental frequencies for the various PWM techniques. The average switching frequency is 2.44kHz. The measured values of IT HD show a reduction in distortion with the hybrid PWM techniques over CSVPWM at high speeds of the drive. The relative values of IT HD corresponding to different PWM techniques agree with the theoretical predictions. With the 10kVA IGBT based inverter feeding a 6kW, 400V, 50Hz, 4pole, three-phase induction motor, the switching losses corresponding to CSVPWM and MSLPWM are evaluated and compared. This is done by measuring the steady state temperature rise of the heat sink over the ambient for the two techniques under different conditions. The thermal measurements are carried out at different loads with power factor ranging from 0.14 to 0.77. The measurements are also carried out at different fundamental frequencies (or modulation indices). Further, to separate conduction (constant) losses and switching (variable) losses, the heat sink temperatures are measured at two different switching frequencies, namely 2.44kHz and 4.88kHz. It is observed that the temperature rise due to MSLPWM is less than that due to CSVPWM consistently under various operating conditions. The thermal measurements confirm the theoretical prediction of reduction in switching loss with MSLPWM. Measurements of heat sink temperature rise corresponding to CSVPWM, MSLPWM and the hybrid PWM techniques are carried out at a higher power factor of 0.98 (lag) with the inverter feeding an RL load (instead of an induction motor). The hybrid PWM and MSLPWM result in lower switching losses as indicated by the reduction in temperature rise.