Deuterium Retention and Trapping in Polycrystalline Tungsten under Simultaneous Implantation of Deuterium with Helium and with Neon

The ITER tokamak is the next step by the international fusion community towards nuclear fusion power plants. Still, some issues remain: tungsten used in the divertor may become recrystallized and melt during the deuterium-tritium phase of operations. Helium production from DT fusion reactions will influence W surface roughness, and D and T retention in the W. Neon is a candidate for radiative cooling, to prevent melting, however little research exists on its effects on D retention in W. Using specimens of polycrystalline tungsten (PCW) and recrystallized tungsten (RCW) irradiated with deuterium ions (D-only) or deuterium and helium ions simultaneously (SIM D-He) at 300-700 K, the effects of W grain size on D retention in the presence of He was studied. The effects of Ne on D retention were studied by irradiating RCW with SIM D-Ne ion beams at 300-700 K. Deuterium, helium, and neon retention and concentration depth profiles were measured using thermal desorption spectroscopy (TDS), nuclear reaction analysis (NRA), and elastic recoil detection analysis (ERDA). No significant difference was found in D retention between PCW and RCW under D-only or SIM D-He irradiation at all temperatures. Modelling using the Tritium Migration Analysis Program, version 7 (TMAP7) showed that in RCW, D appears trapped in higher proportions in high energy traps (vacancy clusters or dislocation loops) than in PCW. Post-implantation damage caused by NRA and ERDA probe ion beams resulted in an additional high temperature TDS peak, associated with retrapping of D at ~1.8-2.1 eV vacancy clusters and dislocation loops. Modelling also suggested that the mechanism for He reducing D retention may consist of D trapping around near surface He bubbles, faster D diffusion to the surface through interconnected He bubbles, and another process such as dislocations or trace amounts of He extending beyond the He bubble layer, up to ~1 µm depth. Ne decreased D retention by greater amounts than He at temperatures above ~500 K, likely due to increased near surface D trapping at vacancies, dislocation loops and Ne-vacancy traps, as well as surface sputtering.

Department dc:contributor.department

Aerospace Science and Engineering

Year dc:date.issued

2018

Author dc:creator

• Finlay, Tamara Jean

Advisors dc:contributor.advisor

• Davis, James W
• Haasz, Anthony A

• Deuterium
• Fusion Energy
• Helium
• Neon
• Retention
• Tungsten

Handle dc:identifier.uri

http://hdl.handle.net/1807/89752

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/89752