Investigations of Novel Configurations for High Power Microwave Generation.

Abstract

This thesis concerns high power microwave generation. Included are simulation studies of a new class of magnetron, the Recirculating-Planar-Magnetron (RPM), with advantages in fast startup, large cathode and anode area, and compact extraction geometry. Various configurations are simulated. The fast startup was triggered by the unusual “negative mass” effect, which is also studied thoroughly here. We also explore, via both experiments and simulation, radio frequency (RF) sources generated by nonlinear transmission lines (NLTL’s). Further, the application of intense pulsed electric fields on biological cells are examined. Electrons rotating under a uniform axial magnetic field and a radial electric field exhibit an effective mass that may be negative, positive, or infinite, in response to an azimuthal electric field. Simulation results show instability or stability when the effective mass is negative or positive, respectively, depending on the magnitude and orientation of the radial electric field. Thus, the inverted magnetron and the RPM would have a much faster startup than the conventional magnetron. This attractive feature is fully implemented in the novel RPM configuration. NLTL’s are promising solid-state microwave sources. A series of experiments on a low voltage NLTL’s constructed using nonlinear capacitance in a L-C ladder circuit has been performed. The waveforms generated on the line have an oscillatory characteristic and are extracted into a load. The results are confirmed using circuit simulations. Other NLTL experiments have been performed using nonlinear inductance at MW power levels. Pulse sharpening of input pulses was observed in addition to oscillations at the characteristic L-C frequency. These results suggest two general criteria for the frequency of oscillation and the risetime necessary to generate oscillations. Experiments and simulations were performed to determine the difference between capacitive coupling and conductive connection for the ns-pulse electroporation of cells. We found that for the capacitively coupled case the bipolar pulse experienced by the cells leads to no net cell-membrane charging. The conductive connection case is different. The pulse remains unipolar and it leaves the cells with a net polarization after the pulse is applied. Experimentally, only cells subjected to the ns-pulse with conductive connection demonstrated electroporation with the drug Bleomycin.