Semi-analytic model of a carbon fiber thermal-field emitter
Abstract
Carbon fibers passing current are subject to resistive heating. When failure occurs, this is related to their local temperature. The failure temperature and its location are estimated. The temperature variation is calculated using analytical models for electrical and thermal conductivities based on the temperature dependent electron–phonon relaxation time. In the absence of radiative heat loss, an analytic expression of temperature along the fiber is given from which a maximum possible emission current is derived and is governed by a single introduced parameter ωo. A method of treating the radiative heat loss is developed and is governed by a second parameter γ, which allows a rapid numerical means to calculate the correction to the analytic form. Heat variation along a thick carbon fiber is contrasted to that along a multi-walled carbon nanotube (MWNT): it is shown that the relative magnitude of ωo compared to γ determines that the analytical formula is a good approximation for MWNTs but requires numerical correction for fibers. Furthermore, it is shown that the analytical form of ωo specified a maximum current beyond which the carbon emitter fails due to thermal runaway. The theoretical models are used to interpret observed behavior of field emission from carbon fibers and the resulting damage they endure when the extracted field-emission current is high. Results from implementing the developed temperature variation model into the MICHELLE beam optics simulation code are presented, with an example application predicting the conditions for stable equilibrium operation as well as for the onset of fiber failure.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 05, 2021
- Source ID
- 10.1063/5.0044800
Entities
People
- Aaron J. Jensen
- Daniel Puentes
- G. Tripathi
- J. R. Harris
- Jacob Sanchez-roddy
- John H. Burke
- John Petillo
- Jonathan Ludwick
- Joseph Connelly
- Kevin L. Jensen
- M. Cahay
- Serguei Ovtchinnikov
Organizations
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- Leidos
- Office of Naval Research
- United States Naval Research Laboratory
- University of Cincinnati
- West Virginia University