Gas Desorption and Electron Emission from 1 MeV 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 80 and 88 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}{sub e} scale as 1/cos({theta}) up to angles of 86, where {gamma}{sub e} = 90. Nearer grazing incidence, {gamma}{sub e} is reduced below the 1/cos({theta}) scaling by nuclear scattering of ions through large angles, reaching {gamma}{sub e} = 135 at 88. Electrons were emitted with a measured temperature of {approx}30 eV. Gas desorption coefficients {gamma}{sub sigma} were much larger, of order {gamma}{sub sigma} = 104. 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 ten and gas desorption by a factor of two; a mild bake to 230 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.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15014471
- Report Number(s):
- UCRL-JRNL-205347; TRN: US0802581
- Journal Information:
- Published in: Physical Review Special Topics-Accelerators and Beams, vol. 7, n/a, September 17, 2004, pp. 093202-1-- 093202-16, Vol. 7
- Country of Publication:
- United States
- Language:
- English
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