Thermo-oxidation of tokamak carbon dust

Abstract

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.

Dust in magnetic fusion devices

“…Different techniques for the removal of dust, flakes and co-deposits are now under discussion. At present the cleaning techniques using lasers [56][57][58][59], flash lamps [60,61], oxygen baking for carbon dust removal [62][63][64][65], liquid or air flows [60,66] and electrostatic devices [67,68] are considered as possible candidates for usage in ITER. A recent review of some of these techniques can be found in [69].…”

Multifaceted physics of edge plasma in magnetic fusion devices

“…In order to prevent accumulation of dust in fusion reactors a few dust removal techniques are now envisioned, including lasers and flash lamps [81], oxygen backing [82,83], liquid or air flow [84] and some others.…”

Experimental and modeling study of chemical-based strategies for mitigating dust formation in fusion reactors

“…Although different methods have been investigated to remove carbon deposits from plasma-facing components of fusion reactors (e.g. chemical oxidation, laser ablation [12][13][14][15][16]), simultaneous operation and cleaning by means of chemical oxidation was not tested before. A proposed method to prevent hydrocarbon accumulation during reactor operation is to add oxygen to the input stream of gases to generate carbon monoxide/dioxide instead of carbon dust.…”