Date of Award

Fall 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical and Computer Engineering

Committee Director

Ravindra P. Joshi

Committee Member

Linda Vahala

Committee Member

Michel Audette

Call Number for Print

Special Collections LD4331.E55 J85 2014

Abstract

The magnetron became a major component in radar systems around the time of the World War II. More recent radar techniques require short microwave pulses (with nanosecond pulse-widths for ultra wideband operations) and high peak power in the Giga-Watt range. In order to achieve these specifications for the military, the magnetron needs to have both a fast start and the rapid growth rate of oscillations in order to serve as a microwave source for the short-pulse applications. These two factors depend on the geometry of the cathode. Other requirements include high conversion efficiency and low leakage current (in order to avoid damage and enhance device reliability).

This thesis focuses on computer simulations as a proof of concept and provides quantitative predictions of output performance parameters such as efficiency, output power, operating frequency, and leakage currents. The magnetron perfonnance results of both the solid and the transparent cathode are compared. The transparent cathode was invented at the University of New Mexico to improve the start time and achieve fast build-up of oscillations in short-pulse relativistic magnetrons. From a solid cathode, longitudinal snips are removed to construct the transparent cathode. The number of strips is chosen to match the number of anode blocks and equals six for the A6 magnetron.

In addition, the role of secondary electron emission (SEE) on the output power is evaluated in this thesis research through particle-in-cell simulations. The simulation results seem to indicate that SEE would be detrimental to the power output from the A6 relativistic magnetron. This is linked to deviations in the starting trajectories of secondary electrons following their generation and the lowered fraction with a synchronized rotational velocity for the cluster. A peak power output of about 1.33GW is predicted at a magnetic field of 0.65 T. A higher reduction in output power has been predicted for repeated secondary emissions through electron cascading. Finally, the role of end-caps on the cathode for potentially reducing the leakage current has been probed. The central goal is to conduct a parameter study that comprehensively incorporates performance enhancing features such as the use of endcaps and cathode extensions. The numerical simulation results demonstrate peak output power in excess of I GW, with leakage currents below 50 Amperes and efficiencies on the order of 66% for B-field in the 0.4 T- 0.42 T range.

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DOI

10.25776/pc53-v989

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