Electron emission physics simulations
Abstract
The proposed research has the following goals- To investigate whether parametrisation of highfidelity MD models of electron emission and propagation can be used to generate reduced order models that can serve as a basis for proper boundary conditions for PIC-codes; to understand the effects of near cathode ionization on electron emission and propagation; and to better understand space-charge and discrete particle effects on strong-field emission.Emission and propagation of electrons in the immediate neighborhood of the cathode must be properly understood when modelling electron sources. If one considers a cathode surface, with some characteristic length scale, L, describing it surface structure (e.g. crystal grain size or pitch between emitters in an array), it turns out that discrete particle effects are important in a cell that extends to a distance above the cathode surface comparable to L. In this region the potential energy between electrons may be much higher than their kinetic energy and emission from a point can be strongly affected by the electric field created by the surrounding electrons. In this is region of strong interaction between individual electrons, we observe rapid thermalization and emittance growth through electron-electron scattering, and granular space-charge effects on emission.The high-fidelity approach of molecular dynamics has proven to be very useful for modelling the physics of the region immediately around the cathode surface. Nonetheless, it is a computationally costly method and prohibitive to use directly with design of vacuum electronic devices. We propose to derive the electron distribution near the cathode using machine learning methodology, based on a sufficiently large number of MD simulations that are fed into reduced order models.It is also near to the cathode that ionization of background gas is most likely to occur, as the ionization cross section is typically highest when the electron energy is from 10 s of eV to 200 eV and the density of desorbed gas is also likely to be highest near the cathode surface. Ions can have a strong affect on the electric field at the surface of the cathode, thereby affecting field emission and electron propagation, and should be properly accounted for.We propose to study how best to implement advanced and physically correct model components for ionization and strong-field emission into the MD code. We will then use the MD code to better understand fundamental processes regarding ionization and strong-field emission, and also use the detailed results from the MD simulations to construct a practical parametrized model suitable for use in design codes. The work is primarily academic in nature, but will likely have considerable practical value.Short pulse electron bursts are of considerable interest. In particular, emission from sharp tips driven by ultrafast lasers is an intriguing method of generating coherent electron bunches of high brightness.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 22, 2024
- Source ID
- FA86552317003
Entities
People
- Á. Valfells
Organizations
- Air Force Office of Scientific Research
- Reykjavík University
- United States Air Force