Diffusion of alkali species in porous tungsten substrates used in contact ionization sources

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Contact ionization (doped) sources used in current Heavy Ion Fusion experiments consist of a porous tungsten substrate doped with an alkali carbonate. In the early stages of the heating cycle (T - 600 C), the carbonate breaks down and releases the alkali atoms that then diffuse through the substrate. At the emitter surface there is a balance between the fast desorption rate of the alkali atoms (mostly as neutrals) and the slower replenishment rate from the substrate by diffusion. Time-resolved measurements of neutral particle evaporation rates at the emitter surface have been used to estimate the effective diffusion coefficient (D) ... continued below

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1 p.

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Chacon-Golcher, E. (Edwin); Kwan, J. (Joe) & Morse, E. C. (Edward C.) January 1, 2002.

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Contact ionization (doped) sources used in current Heavy Ion Fusion experiments consist of a porous tungsten substrate doped with an alkali carbonate. In the early stages of the heating cycle (T - 600 C), the carbonate breaks down and releases the alkali atoms that then diffuse through the substrate. At the emitter surface there is a balance between the fast desorption rate of the alkali atoms (mostly as neutrals) and the slower replenishment rate from the substrate by diffusion. Time-resolved measurements of neutral particle evaporation rates at the emitter surface have been used to estimate the effective diffusion coefficient (D) that characterizes the migration of alkali species in the substrate. These estimates are consistent with the observed source lifetimes (tens of hrs.) and establish the alkali migration in the bulk as a diffusion-limited process. The measurements suggest that the faster migration rates (D {approx} 10{sup -5} - 10{sup -6} cm2/s) occur early during the heating cycle when the dominant species are the neutral alkali atoms. At operating temperatures there is a slower migration rate (D x 10-7cm2/sd) ue to the dominance of ions, which difise by a slower surface diffusion process.

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1 p.

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  • Submitted to: 2003 Particle Conference, May 12-16, 2003, Portland, OR

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  • Report No.: LA-UR-02-7481
  • Grant Number: none
  • Office of Scientific & Technical Information Report Number: 976476
  • Archival Resource Key: ark:/67531/metadc930310

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • January 1, 2002

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 12, 2016, 3:39 p.m.

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Chacon-Golcher, E. (Edwin); Kwan, J. (Joe) & Morse, E. C. (Edward C.). Diffusion of alkali species in porous tungsten substrates used in contact ionization sources, article, January 1, 2002; United States. (digital.library.unt.edu/ark:/67531/metadc930310/: accessed April 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.