General kinetic ion induced electron emission model for metallic walls applied to biased Z-pinch electrodes

TL;DR

This paper develops a kinetic ion-induced electron emission model for metallic surfaces, validating it across materials, and applies it to study plasma interactions in biased Z-pinch electrodes, revealing effects on plasma heating and current saturation.

Contribution

The paper introduces a comprehensive IIEE model for metallic surfaces and applies it to Z-pinch electrodes, providing new insights into plasma-material interactions and electron emission effects.

Findings

SEY varies with bias potential, decreasing then increasing at the anode.

Cathode SEY is higher and grows with bias, affecting plasma heating.

With IIEE, current continues to increase, matching experimental data.

Abstract

A kinetic ion induced electron emission (IIEE) model for general applications is developed to obtain the emitted electron energy spectrum for a distribution of ion impacts on a metallic surface. We assume an ionization cascade mechanism and use empirical models for the ion and electron stopping powers. The emission spectrum and the secondary electron yield (SEY) are validated for a variety of materials. The IIEE model is used to study the effect of IIEE on the plasma-material interactions of Z-pinch electrodes. Un-magnetized Boltzmann-Poisson simulations are performed for a Z-pinch plasma doubly bounded by two biased copper electrodes with and without IIEE at bias potentials from 0 to 9 kV. At the anode, the SEY decreases from 0 to 1 kV, but then increases at higher bias potentials. At the cathode, the SEY is much larger due to higher energy ion bombardment and grows with bias potential. As the bias potential increases, the emitted cathode electrons are accelerated to higher energies into the domain collisionally heating the plasma. Above 1 kV, the heating is strong enough to increase the plasma potential. Despite SEY greater than 1, only a classical sheath forms as opposed to a space-charge limited or inverse sheath due to the emitted electron flux not reaching the space charge current saturation limits. Furthermore, the current in the emissionless cases saturates to a value lower than experiment. With IIEE, the current does not saturate and continues to increase with the 4 kV case matching most closely with experiment.