Study of ESD from type 304 stainless steel in relation to CTR first wall applications

Abstract

Electron stimulated desorption (ESD) of adsorbed species from type 304 stainless steel (S.S.) was studied, primarily from the standpoint of controlled thermonuclear fusion reactor ’’first wall’’ applications. H+ and F+ were, by far, the most predominant ESD ion species observed from ’’as is’’ S.S. surfaces. O+, Cl+, and other ESD ions were also observed, but normally in much smaller quantities. The origin of the ESD ion signals are attributed to adsorbed H2 and/or H2O for ESD of H+, and fluorocarbon and/or alkali halide contaminants in the case of ESD of F+. Little or no temperature effects on the H+ and F+ ESD ion signals were observed over the S.S. sample temperature range from 23° to ∠450°C. The total cross section for ESD of hydrogen was found to be ∠10−16 cm2 while that for ESD of fluorine was found to be ∠10−17 cm2. The ion energy distributions of both H+ and F+ ions were obtained and no observable changes were found over the bombarding electron energy range 300–4000 eV. The total cross section for ESD of hydrogen from S.S. was investigated as a function of bombarding electron energy over the energy range 200–4000 eV. Relative cross sections for ESD of H+ and F+ were investigated over the bombarding electron energy range 50–6000 eV. The cross-section behavior for ESD vs electron energy was found to be very similar to the behavior for electron–gas-phase molecule interaction cross sections vs electron energy. The ESD cross-section maximum was observed to occur at an electron energy of several hundred eV. Above this energy the cross section slowly decreased with increasing electron energy. The observed behavior of ESD cross section vs electron energy is attributed to the interaction of both primary and secondary electrons with the surface adsorbates.