Author ORCID Identifier

https://orcid.org/0000-0001-6964-6625

Date Available

7-17-2023

Year of Publication

2023

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Chemical and Materials Engineering

First Advisor

Dr. Thomas John Balk

Abstract

A dispenser cathode’s ability to thermionically emit electrons is highly dependent on its material properties, especially those of the surface. Understanding the relationship between surface properties and electron emission, therefore, is vital to reach the next generation of the many vacuum electron devices (VEDs) that rely on the physics of electron emission. In the past century, many techniques have been developed to characterize material surfaces and quantify thermionic emission. These techniques are based on a wide range of different physical phenomena, including measuring photoemission via the photoelectric effect, measuring the electrostatic potential between metals in electrical contact, and current collection via positively biased anodes in a diode configuration. They do not necessarily have one-to-one correlation with each other and they are often incapable of studying cathodes in their operational conditions of high temperatures and in a vacuum. An investigation into the correlation between surface properties and electron emission in such an environment is needed to move the field forward. As such, the Cathode Characterization Chamber (CCC) has been assembled at the University of Kentucky to function as one testing space to utilize many diverse surface and emissions characterization techniques simultaneously. In this work, multiple methods of improved implementations of the aforementioned techniques are described, including lesser-known applications such as measurement of contact potential difference at high temperatures and the collection of electron emission using a Kelvin probe in an Ultra-High Vacuum (UHV). Additionally, an investigation into dispenser cathode design using this knowledge is described here, wherein a multi-element alloy cathode coating is explored as a candidate for improved emission performance when compared to current standard cathode coatings. A key parameter for evaluating thermionic emission performance that will receive significant attention throughout here is the work function. And the full testing capabilities of the CCC are shown to be a valuable toolset for evaluating the work function under many environmental conditions that would not be possible without this unique system. Ultimately, the results show a path toward multiple improved implementations of cathode characterization and the use of those methods to propose improved cathode design.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.283

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