Microscopic theory of electron absorption by plasma-facing surfaces

TL;DR

This paper introduces a microscopic method to calculate electron absorption probabilities at plasma-facing surfaces, considering surface potentials and scattering, challenging the perfect absorber assumption.

Contribution

It presents a novel invariant embedding approach to accurately model electron absorption, incorporating surface potential transmission and internal backscattering effects.

Findings

Absorption probabilities are significantly less than unity.

The model aligns with electron-beam scattering data.

Contradicts the perfect absorber assumption.

Abstract

We describe a method for calculating the probability with which the wall of a plasma absorbs an electron at low energy. The method, based on an invariant embedding principle, expresses the electron absorption probability as the probability for transmission through the wall's long-range surface potential times the probability to stay inside the wall despite of internal backscattering. To illustrate the approach we apply it to a \SiOTwo\ surface. Besides emission of optical phonons inside the wall we take elastic scattering at imperfections of the plasma-wall interface into account and obtain absorption probabilities significantly less than unity in accordance with available electron-beam scattering data but in disagreement with the widely used perfect absorber model.