An in-situ technique to measure erosion and deposition in fusion devices

David N. Ruzic, Glenn A. Gerdin

Research output: Contribution to journalArticlepeer-review

Abstract

Erosion or deposition of sub-micron layers of graphite or other materials can be measured by bombarding a sub-surface layer of 10B or 6Li with thermal neutrons and observing with a surface-barrier detector the energy loss of the prompt alphas or tritons produced. To demonstrate the feasibility of this technique, a (5250 ± 250) Å layer of boron and a (1.25 ± 0.05) μm layer of Li2B4O7 were electron-beam evaporated onto graphite substrates and exposed to a thermal neutron flux of (8.0 ± 0.5) × 105 cm-2 s-1. The (n,α) reactions of the 10B produce a 1.78 MeV α, a 1.48 MeV α, and a 0.848 MeV 7Li. The reactions of 6Li produce a 2.73 MeV 3H and a 2.05 MeV α. Carbon coatings of (600 ± 25) Å, (8250 ± 500) Å, (2.0 ± 0.2) μm, and (4.0 ± 0.4) μm were placed between the active layers and a surface barrier detector in vacuuo. The thinner layers shifted the 1.48 MeV α peak by (31.7 ± 4.5) keV and (431 ± 43) keV respectively. The thicker layers shifted the 2.73 MeV 3H peak by (206 ± 15) keV and (346 ± 20) keV respectfully. Therefore, utilizing boron implants, 100 Å to 1 μm of graphite erosion or redeposition can be determined. Utilizing lithium implants, thicknesses in the range of 1 μm to 10 μm can be determined. Theoretical energy shifts, thermal diffusion, and the feasibility of this technique as a between shot diagnostic for limiters, divertor plates, and/or first-wall armor are discussed.

Original languageEnglish (US)
Pages (from-to)453-457
Number of pages5
JournalJournal of Nuclear Materials
Volume145-147
Issue numberC
DOIs
StatePublished - Feb 2 1987

Keywords

  • carbon
  • erosion probe measurements
  • erosion rate
  • limiter/divertor plates
  • wall erosion

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Materials Science(all)
  • Nuclear Energy and Engineering

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