Fusion Science and Technology / Volume 60 / Number 4 / November 2011 / Pages 1463-1466
Interaction with Materials / Proceedings of the Ninth International Conference on Tritium Science and Technology (Part 2)
Applying a tritium tracer technique, we have investigated hydrogen plasma driven permeation (PDP) through tungsten (W) near room temperature. The technique was confirmed to give reliable data on diffusion and permeation coefficients of pure W for gas driven permeation (GDP), and then it was applied to observe PDP in W near room temperature. It was found that PDP in earlier phase was controlled by diffusion giving reliable diffusion coefficients. Taking literature data at higher temperatures and present ones near room temperature determined from PDP into account, we have proposed new diffusion coefficients
DUpper limit = (3.8±0.4)x10-7 exp ((-39.8±1.5) (kJ/mol)/RT), m2s-1. (1)
The activation energy for permeation determined by PDP was similar to that by GDP. The extrapolation of the present data to higher temperature agreed well with Frauenfelder's data, suggesting the activation energy of around 65 kJ/mol for permeation is quite reasonable. However prolonged measurements resulted in significant reduction of PDP. The cause of the reduction was attributed to the increase of reemission owing to surface cleaning and/or roughening by incidence of energetic hydrogen.