D retention and material defects probed using Raman microscopy in JET limiter samples and beryllium-based synthesized samples

Abstract

We report on the detection by means of Raman spectroscopy of amorphous beryllium deuteride, BeD2, in magnetron sputtered deposits synthesized in two different laboratories and containing about 20 at% of deuterium. In contrast, this signature has not been found for the JET limiter samples studied coming from the inner, outer or upper limiters, even when coming from a deposition zone of the limiters. We give a way to disentangle that BeD2 signature from other signatures falling in the same spectroscopic range and mainly related to other phenomena. We also analyze the Raman characteristics of the JET sample defects. These results could help in the interpretation of D thermal desorption spectra and in future analyses of JET thick Be deposit divertor tiles.

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

“…Using magnetron sputtering, and creating samples with a D content as high as 20 at.%, we have found that a broad signature could lie close to 1000 cm −1 , in agreement with previous references plus a narrower band close to 1200 cm −1 [68]. These two bands have been seen only on a very limited number of samples [68]. We believe that this is due to four reasons: (1) they fall at the same position as the intense 2PDOS signature.…”

“…This is, unfortunately, in the range where the 2PDOS lies. Using magnetron sputtering, and creating samples with a D content as high as 20 at.%, we have found that a broad signature could lie close to 1000 cm −1 , in agreement with previous references plus a narrower band close to 1200 cm −1 [68]. These two bands have been seen only on a very limited number of samples [68].…”

“…Other combinations are theoretically possible, but would require single-crystalline samples to be investigated. The area under the 2PDOS curve is in general found to be between 0.1 and 1 compared to PDOS but can be up to 3 times larger in some cases [68]. The area related to the 2E 2G , E 2G +B 1G and 2B 1G sharp related signatures are weak.…”

“…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 .…”

“…The presence of beryllium deuteride is also something not yet established. In most publications, only frequencies of the hydride isotope are provided, that has to be multiplied by a correction factor taking into account a reduced mass involving deuterium (see details in [68]). Spectroscopic signatures are supposed to be lower than 1500 cm −1 for bulk phases, as shown by their PDOS [63][64][65].…”