The role of defects, deuterium, and surface morphology on the optical response of beryllium

Abstract

The knowledge of optical properties of beryllium is of crucial importance in fields such as nuclear fusion and aerospace applications. The optical properties of pure beryllium are known in the visible and infrared domains. Nevertheless, the role of different physico-chemical parameters such as composition and surface roughness, that is often neglected in first approximation, deserves dedicated comprehensive studies. In this work we have studied the optical properties of bulk beryllium and magnetron sputtering codeposited beryllium layers in the 500–2000 nm spectral range. Experimental measurements show that beryllium reflectivity strongly depends both on bulk fabrication procedure and on surface preparation. Different models allow us to perform a quantitative interpretation of reflectivity results and to study the influence of different parameters: i) a multi-reflection interference model to understand the role of oxyde layer, ii) a Lorentz-Drude model for the bulk composition effect, iii) scattering models for the surface roughness, and iv) the Maxwell-Garnett model for the surface porosity. The calculated relative permittivity of the studied samples is used to evaluate the emissivity in the visible and infrared domain. Such evaluation, giving indications of possible evolution of optical properties of beryllium in a plasma environment, can provide a useful tool for thermography studies of tokamak walls.

Optical Properties of Tungsten: A Parametric Study to Characterize the Role of Roughness, Surface Composition and Temperature

“…A possible reason could be that the previous relation is valid only in the case that surface irregularities are much smaller compared to the used wavelength σ λ [18]. More accurate scattering models, considering the bidirectional reflection distribution function and, thus, overcoming the previous limitation, could provide a more accurate agreement between theoretical and experimental results [19], as shown in Minissale et al [20] in the case of beryllium samples.…”

Raman microscopy to characterize plasma-wall interaction materials: from carbon era to metallic walls

“…For carbon, the PDOS signature is mainly hidden because of resonance bands and cannot be used easily, which is not the case for Be for which there is no such resonance. Up to now, in addition to the Raman allowed band at 450 cm −1 and the PDOS in the range 300-700 cm −1 , all the spectra recorded on Be in air [49,68,73,90,91] display two extra signatures: a broad signature which roughly displays the same shape as the PDOS but at the double wavenumbers, and a few structured sharp bands. Both broad and sharp signatures fall in the range 700-1300 cm −1 .…”

Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications

“…Finally, it should be noted that the total hemispherical emissivity, at least for low temperatures, has a strong dependence on the surface roughness, microstructural details and impurity concentrations [120,121]. As a result, an insitu assessment of the Be emissivity is recommended especially for IR thermography studies [122,123] and our recommended total hemispherical emissivity expression should only be employed when such an option is not available.…”