Electrical and Computer Engineering ETDs


Shawn Soh

Publication Date



Reltrons are high power electron beam microwave oscillators that do not require an external magnetic field. The University of New Mexico (UNM) has a low power educational reltron system developed during an AFOSR-sponsored FY94 Multi- University Research Initiative (MURI) program. This dissertation focuses on developing mathematical models of, and performing particle-in-cell (PIC) simulations and conducting experiments on the low power reltron. The modules in the reltron tube can be described using mathematical models. We first analyze the minimum beam potential required to self-excite the modulating cavity. We obtain the resonant modes of the modulating cavity using a circuit model. The electron beam is modeled using a relativistic ballistic current model from which we derive the optimal drift distance where the modulating current will peak. We develop a transmission line model of the single and dual extraction cavity that is used to match the cavity impedance to the beam impedance. We also model the electrostatic field distribution between the anode-cathode (A-K) gap and post acceleration gap. We compare our 1D / 2D models with 3D simulations performed using HFSS and CST. Full 3D simulations are required because the reltron is not axisymmetric. We also performed PIC simulations of the reltron using MAGIC. MAGIC is able to simulate the beam-wave interaction self-consistently. This accounts for all interactions between all modules as the beam propagates through the reltron. We optimize the reltron parameters in MAGIC and confirm the UNM reltron is able to generate microwave power in the megawatt range. We conducted experiments using the UNM low power reltron to compare our mathematical models and simulations with the performance of the actual reltron system. Experiments allow us to account for physical phenomena that are not described by models or simulations. Maximum microwave power generated by the UNM low power reltron is 116 kW for a duration of 100 ns. The low output power is accounted for by electrical breakdown in the electron beam diode's A-K gap during operation. Finally, we conclude with recommendations for future work that would resolve the difficulties encountered in the experiments.'

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Miller, R. Bruce

Second Committee Member

Gilmore, Mark

Third Committee Member

Ellison, James