Surface morphology and deuterium retention of tungsten after low- and high-flux deuterium plasma exposure

Abstract

Abstract.The surface morphology and deuterium retention were investigated of polycrystalline tungsten targets that were exposed to deuterium plasmas at widely varying conditions. By changing only one parameter at a time, the isolated effects of flux, time and pre-damaging on surface modifications and deuterium retention were studied. The sample exposed to low-flux plasma (10 20 m −2 s −1 ) is mostly smooth with only a few areas containing very large blisters (50 -500 µm). The samples exposed to high-flux plasmas (10 24 m −2 s −1 ) show large numbers of smaller blisters (1 -10 µm) and in addition even smaller protrusions (<750 nm). The size of the blisters and their density strongly increase with fluence. Pre-damaging tungsten with MeV ions leads to less blisters but to more protrusions. In addition to these (sub-)micrometer-sized structures, all samples show formation of nanostructures. Comparison of a low-flux and high-flux sample exposed to similar fluence showed that the variation in morphology is dominated by the flux differences. It is shown that the blisters and protrusions originate in inter-and intra-granular cavities, respectively. The depth of the cavities underneath the surface correlates well with the depth distributions of the retained deuterium. Trapping of significant amounts of deuterium therefore seems to take place in and/or close to these cavities and gives rise to an additional peak in the thermal desorption spectrum at 700 K.PACS numbers: 28.52.Fa, 28.52. Nh, 52.40.Hf, 52.77.Dq, 61.80.Jh, Submitted to: Nuclear Fusion Surface morphology and deuterium retention at high-flux deuterium plasmas 2

Deuterium retention and morphological modifications of the surface in five grades of tungsten after deuterium plasma exposure

“…Equivalent specimens to WP-R, rc-WP-R, WJ, and rc-WJ -same material and treatment -were studied in [7][8][9][10]25,26], [7,8], [11,15], and [12][13][14][15][16][17], respectively. All equivalent specimens of rolled Plansee material originate from a single sintering batch to ensure the same initial microstructure and chemical composition.…”

“…This NRA D inventory is obtained by summing up the deuterium over the full range analysed by NRA of nearly 12 µm, which is the maximum depth accessible by the 3 He beam with the highest used energy of 6.0 MeV. For comparison, some literature data [7,11,12,19,25,34] for the same W grades but slightly different exposure conditions are also included in Fig. 1(a).…”

“…It is proposed that the D oversaturation in the W lattice during the exposure, i.e., D concentration above the thermo-dynamical solubility limit, is responsible for this damaging [see e.g. 7,13,39]. These defects can be termed as hydrogen loading-induced damage.…”

“…The second aim is to provide data belonging to a series of experiments dedicated to study the influence of the ion flux during plasma exposure on surface morphology and deuterium retention. This joint action covers a flux range of about 4 [25], where accumulating the same fluence takes only ~100 seconds.…”

Quantitative Microstructure and Defect Density Analysis of Polycrystalline Tungsten Reference Samples after Different Heat Treatments

“…First results using exactly this material with the same surface finish and heat treatments, but with a less detailed characterisation, were already published [5,6,7,8].…”