Gas desorption and electron emission from 1MeV potassium ion bombardment of stainless steel

Gas desorption and electron emission coefficients were measured for 1 MeV potassium ions incident on stainless steel at grazing angles (between 80degrees and 88degrees from normal incidence) using a new gas-electron source diagnostic (GESD). Issues addressed in design and commissioning of the GESD include effects from backscattering of ions at the surface, space-charge limited emission current, and reproducibility of desorption measurements. We find that electron emission coefficients gamma(e) scale as 1/cos(theta) up to angles of 86degrees, where gamma(e) = 90. Nearer grazing incidence, gamma(e) is reduced below the 1/cos(theta) scaling by nuclear scattering of ions through large angles, reaching gamma(e) = 135 at 88degrees. Electrons were emitted with a measured temperature of similar to 30 eV. Gas desorption coefficients gamma(0) were much larger, of order gamma(0) = 10(4). They also varied with angle, but much more slowly than 1/cos(theta). From this we conclude that the desorption was not entirely from adsorbed layers of gas on the surface. Two mitigation techniques were investigated: rough surfaces reduced electron emission by a factor of 10 and gas desorption by a factor of 2; a mild bake to similar to220degrees had no effect on electron emission, but decreased gas desorption by 15% near grazing incidence. We propose that gas desorption is due to electronic sputtering.