TY - GEN
T1 - Hydrogen Retention in Lithium and Lithium Compounds
AU - Buzi, L.
AU - Yang, Y.
AU - Nelson, A. O.
AU - Koel, B. E.
N1 - Funding Information:
Lithium (Li) conditioning of plasma facing components (PFCs) in magnetic fusion devices has improved plasma performance and lowered hydrogen (H) recycling partially due to the efficiency of Li in binding H isotopes. In current fusion experiments [1], the presence of impurities inevitably creates Li-O and Li-C-O compounds. Unraveling the fundamental mechanisms for H retention, its post-exposure time dependence, and sputtering for these Li compounds is crucial for the application of Li as a PFC. The present experiments were performed under ultrahigh vacuum (UHV) conditions on thin Li films deposited on a Ni(110) substrate to avoid effects due to grain boundaries, intrinsic defects, and impurities diffusing to the surface. A H2+ beam was generated in a differentially pumped ion gun in the energy range of 400-1200 eV. Temperature programmed desorption (TPD) and Auger electron spectroscopy (AES) were used to measure H retention and sputtering rates under different conditions. Li-O and Li-C-O compounds were formed by dosing background gas molecules on pure Li films at various surface temperatures. Experiments showed that upon oxidation, Li thermal stability increased by 350 K. A drop of 60% in total H retention as the temperature varied from 90 to 520 K was observed in both pure Li and Li2O and confirmed by molecular dynamics (MD) simulations. Additionally, H retention measurements in Li and Li2O films showed that they retain similar H amounts [2]. These findings support the possibility that low H recycling can be achieved if Li2O is formed under fusion reactor conditions. Preliminary sputtering experiments showed that after irradiating Li2O with 500 eV H+ ions, the oxide layer remained chemically unaltered after 6 min (7×1019 H2+/m2). The oxide layer, however, was fully removed after one hour of H2+ irradiation (7×1020 H2+/m2). Dosing carbon monoxide (CO) on a pure Li layer led to the formation of a Li-C-O surface that demonstrated increased Li thermal stability by 150 K. Preliminary TPD results indicate that clean Li retains H primarily as LiH. The amount of H retained in clean Li and Li-O films is constant for post-H exposure times up to 1 hour, but decreases to one-half of the original amount after 16 hours for both films. Further experiments are currently in progress to investigate H retention as a function of post-H exposure time for other Li compounds. [1] M.J. Lucia et al., J. Nucl. Materials 463 (2015) 907. [2] L. Buzi et al., J. Nucl. Materials 502 (2018) 161. _____________________________ *This material is based upon work supported by the U.S. Department of Energy, Office of Science/Fusion Energy Sciences under Award Number DE-SC0012890 and USDOE Contract DE-AC02-09CH11466.
Publisher Copyright:
© 2018 IEEE.
PY - 2018/6/24
Y1 - 2018/6/24
N2 - Lithium (Li) conditioning of plasma facing components (PFCs) in magnetic fusion devices has improved plasma performance and lowered hydrogen (H) recycling partially due to the efficiency of Li in binding H isotopes. In current fusion experiments [1], the presence of impurities inevitably creates Li-O and Li-C-O compounds. Unraveling the fundamental mechanisms for H retention, its post-exposure time dependence, and sputtering for these Li compounds is crucial for the application of Li as a PFC.
AB - Lithium (Li) conditioning of plasma facing components (PFCs) in magnetic fusion devices has improved plasma performance and lowered hydrogen (H) recycling partially due to the efficiency of Li in binding H isotopes. In current fusion experiments [1], the presence of impurities inevitably creates Li-O and Li-C-O compounds. Unraveling the fundamental mechanisms for H retention, its post-exposure time dependence, and sputtering for these Li compounds is crucial for the application of Li as a PFC.
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U2 - 10.1109/ICOPS35962.2018.9575196
DO - 10.1109/ICOPS35962.2018.9575196
M3 - Conference contribution
AN - SCOPUS:85118926327
T3 - IEEE International Conference on Plasma Science
BT - ICOPS 2018 - 45th IEEE International Conference on Plasma Science
PB - Institute of Electrical and Electronics Engineers Inc.
T2 - 45th IEEE International Conference on Plasma Science, ICOPS 2018
Y2 - 24 June 2018 through 28 June 2018
ER -