Plasma-material Interactions in Current Tokamaks and their Implications for Next-step Fusion Reactors

The effect of heavy sputtering and of neutron irradiation simulated by displacement damaging with of 20 MeV W 6+ ions on the optical properties of tungsten mirrors was studied. Ar + ions with 600 eV of energy were used as imitation of charge exchange atoms ejected from fusion plasma. The ion fluence dependence of the surface topography and the optical properties of polycrystalline, recrystallized tungsten (grain size 20 -100 µm) were studied by optical microscopy, interferometry, reflectrometry and ellipsometry. Furthermore, after sputtering in total a layer of 3.9 μm in thickness, the orientation and the thickness of the eroded layer of many individual grains was determined by electron backscattering diffraction and confocal laser scanning microscopy. Concluding from the obtained data the neutron irradiation, at least at the damage level would be achieved in ITER, has not to make an additional contribution in the processes developing under impact of charge exchange atoms only.

Section: Introductionmentioning

confidence: 99%

“…Thus, there is an interest to perform similar comparative experiments with tungsten, which was chosen to be one of the plasma facing materials of in-vessel components of the ITER construction [3].…”

Section: Introductionmentioning

confidence: 99%

Effect of sputtering on self-damaged recrystallized W mirror specimens

Voitsenya

Balden

Belyaeva

et al. 2013

“…It is known [1] that tungsten was chosen as the candidate material of the baffle and dome of the divertor, both will be plasma facing components of the vacuum vessel. Recently it was decided that divertor target plates will also be made of tungsten.…”

Section: Introductionmentioning

confidence: 99%

Effect of sputtering on self-damaged ITER-grade tungsten

Voitsenya

Balden

Bardamid

et al. 2014

Abstract. Simulation of neutron irradiation and sputtering on ITER-grade tungsten was studied. The effects of neutron-induced displacement damage have been simulated by irradiation of tungsten target with W 6+ ions of 20 MeV energy. Bombardment by Ar + ions with energy 600 eV was used as imitation of impact of charge exchange atoms in ITER. The sputtering process was interrupted to perform in between measurements of the optical properties of the eroded surface and the mass loss. After sputtering was finished, the surface was thoroughly investigated by different methods for characterising the surface relief developed due to sputtering. The damaging to, at least, the level that would be achieved in ITER does not lead to a decisive additional contribution to the processes under impact of charge exchange atoms only.

“…However, it is understood that the nature of the dust created in ITER may be significantly different from that in current tokamaks, as the much greater duty cycle is likely to increase the fraction of codeposit flakes [5]. Procedures proposed for the removal of dust from ITER include mechanical intervention, such as liquid washing [6], or vibratory conveyors [6,7].…”

Section: Introductionmentioning

confidence: 99%

“…Previous measurements on the oxidation of codeposit flakes from TFTR were reported in [5] for a sample of flakes which was heated in air to 773 K and the release of tritium atoms was detected. Oxidation is also being used in the JET active gas handling facility to recover tritium from dust and flakes removed from the tokamak [8].…”

Section: Introductionmentioning

confidence: 99%

Thermo-oxidation of tokamak carbon dust

Davis

Fitzpatrick

Sharpe³

et al. 2009

The oxidation of dust and flakes collected from the DIII-D tokamak, and various commercial dust specimens, has been measured at 350 ºC and 2.0 kPa O 2 pressure. Following an initial small mass loss, most of the commercial dust specimens showed very little effect due to O 2 exposure. Similarly, dust collected from underneath DIII-D tiles, which is thought to comprise largely Grafoil™ particulates, also showed little susceptibility to oxidation at this temperature. However, oxidation of the dust collected from tile surfaces has led to ~ 18% mass loss after 8 hours; thereafter, little change in mass was observed. This suggests that the surface dust includes some components of different composition and/or structure -possibly fragments of codeposited layers. The oxidation of codeposit flakes scraped form DIII-D upper divertor tiles showed an initial 25% loss in mass due to heating in vacuum, and the gradual loss of 30-38% mass during the subsequent 24 hours exposure to O 2 . This behavior is significantly different from that observed for the oxidation of thinner DIII-D codeposit specimens which were still adhered to tile surfaces, and this is thought to be related to the low deuterium content (D/C ~ 0.03 -0.04) of the flakes.