Dissertation Defense: Cesar Whesly Segura Del Rio

Title: Modulated Injected Current Cathode Experiment in a Linear Crossed-Field Amplifier using Gated Field Emitter Arrays

Program: Electrical and Computer Engineering PhD

Committee Chair: Jim Browning

Committee: Jim Browning, Kris A. Campbell, Karthik Srinivasan, Jennifer Houle

Abstract: Crossed-Field Amplifiers (CF

As) belong to a broader group of electron devices that use thermionic cathodes as electron sources for high-power and high-frequency RF sources and amplifiers. Gated Field Emitter Arrays (GFE

As) are proposed as an alternative electron source for CF

As because of their small size and ability to modulate electrons. A voltage applied between the GFEA gate and emitter produces an electric-field enhancement near the sharp emitter tips that causes electrons to tunnel from the emitter tips into the vacuum. The purpose of this research is to study modulated electrons emitted from 9M emitter-tip GFE

As by superimposing a 10 V peak-amplitude sinusoidal voltage of 561 MHz frequency on the gate-to-emitter DC voltage and apply GFEA phase control in CF

As.

Particle-In-Cell (PIC) simulations used Fowler–Nordheim (FN) coefficients extracted from current–voltage (I–V) measurements of a 9M emitter-tip GFEA to implement a modulated-emission function. A prior CFA experiment, which achieved a ~5.5 dB measured gain, was simulated using a modulated cathode and microstrip meander-line circuit with RT/duroid® 5880 dielectric. The simulated CFA anode-to-sole distance was reduced to 1 cm. The CFA operated at an anode-to-sole voltage of 1.5 kV, a cathode-to-sole voltage of 475 V, a magnetic field of 0.0154 T, an RF input power of 1 W, a frequency of 561 MHz, an average current of 95 mA, and a peak current of 630 mA supplied by eight GFE

As. Without accounting circuit losses, the simulation predicted 4.1 dB gain with continuous current and 11.1 dB gain with modulated current in phase with the RF signal.

A similar CFA was simulated using a microstrip meander-line circuit with PTFE dielectric at an anode-to-sole voltage of 1.8 kV and cathode-to-sole voltage of 600 V, while the other operating conditions remained unchanged. The phase between the modulated current and RF signal was swept from 0 to 360°. The simulation predicted 9.2 dB gain for in-phase modulation with the RF signal and -2.2 dB attenuation for out-of-phase modulation with the RF signal.

Additional simulations studied modulated electron emission, power coupling, and electron collection replacing the RT/duroid® 5880 circuit with a smooth anode under the same operating conditions. Gaussian noise with a mean of zero and standard deviation of three was introduced into the modulated-emission function to evaluate CFA performance.

To experimentally demonstrate modulated electron emission, a circuit was developed for a single GFEA by superimposing a 10 V peak-amplitude sinusoidal voltage of 561 MHz frequency on a 46 V gate-to-emitter bias. A zinc oxide (ZnO) phosphor screen located ~1 cm above the modulat