Hydrogen-vacancy interaction in molybdenum

Keriem, M.S. Abd El; Werf, D. P. van der; Pleiter, F.

doi:10.1088/0953-8984/5/12/008

Cited by 6 publications

(2 citation statements)

References 8 publications

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“…Additionally, it was assumed that the recombination rate coefficient was infinite (like that of tungsten [6]). Many researchers have examined the trapping of hydrogen isotopes in implanted molybdenum [7][8][9][10], and an energy of 1.4 eV most accurately represents a consensus of those studies. Using this set of parameters, it was not possible to duplicate either the retention or release data.…”

Section: Resultsmentioning

confidence: 99%

Deuterium retention and release from molybdenum exposed to a Penning discharge

Causey

Kunz

Cowgill

2005

Journal of Nuclear Materials

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Section: Resultsmentioning

confidence: 99%

Deuterium retention and release from molybdenum exposed to a Penning discharge

Causey

Kunz

Cowgill

2005

Journal of Nuclear Materials

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“…For a sheath corresponding to T e =20 eV the B +3 energy approaches 200eV and a vacancy creation rate of 1 vacancy per incident B +3 ion. In one modelling study [58] the number of hydrogen atoms that can be accommodated in one vacancy is in the range of 2-3, while in another study, potentially more than 6 H atoms can be stored [59]. A concern with such an explanation is that the boron levels in the plasma during the pre-boronization period 1 are lower by a factor of 5 than in period 3.…”

Section: Processes That Might Explain the Disparity Between C-mod Andmentioning

confidence: 99%

Hydrogenic retention with high-Z plasma facing surfaces in Alcator C-Mod

et al. 2009

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Abstract. The retention of deuterium (D) fuel in the Alcator C-Mod tokamak is studied using a new 'static' gas balance method. C-Mod solely employs high-Z molybdenum (Mo) and tungsten (W) for its plasma-facing materials, with intermittent application of thin boron (B) films. The primarily Mo surfaces are found to retain large fractions, ~20-50%, of the D 2 gas fuelled per quiescent discharge, regardless if the Mo surfaces are cleaned of, or partially covered by, B films. Several experiments and calculations show that it is improbable that B is retaining significant fractions of the fuel. Rather, the retention is occurring in Mo and W surfaces through ion bombardment, implantation and diffusion to trap sites. Roughly 1% D of incident ion fluence, D , to surfaces is retained, and with no indication of the retention rate decreasing after 25 s of integrated plasma exposure. The magnitude of retention is significantly larger than extrapolated from the results of laboratory studies for either Mo or W. The high levels of D/Mo in the near surface, measured directly post-campaign (~ .01) in tiles and inferred from gas balance, are consistent with trapping sites for fuel retention in the Mo being created, or expanded, by high D atom densities in the near surface which arise as a result of high incident ion fluxes. Differences between C-Mod and laboratory retention results may be due to such factors as the multiply-ionized B ions incident on the surface directly creating traps, the condition of the Mo (impurities, annealing), and the high flux densities in the C-Mod divertor which are similar to ITER, but 10-100x those used in laboratory studies. Disruptions produce rapid heating of the surfaces, releasing the trapped hydrogenic species into the vessel for recovery. The measurements of the large amount of gas released in disruptions are consistent with the analysis of tiles removed from the vessel post-campaign -the campaign-integrated retention is very low, of order 1000x less than observed in a single, non-disruptive discharge.

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