Hydrogen retention in fusion reactor materials

点击翻译按钮获取中文摘要

Materials issues related to the interaction of solid surfaces with high temperature plasmas – erosion, melting, redeposition, and tritium retention – represent some of the greatest challenges in the design of current and future fusion reactors.*******For the past 35 years, our fusion materials group at U of T has been part of world-wide research activities in key areas related to the concerns above; namely, the erosion of, and hydrogen retention in, plasma-facing components in fusion reactors. In particular, our expertise in the trapping and transport of hydrogen in tungsten and in the removal of hydrogen-containing deposited layers closely match some of the greatest concerns. Within the area of plasma-materials interactions, my planned research for the next five years will focus on two key areas: 1) hydrogen trapping and transport in tungsten and 2) characterization and removal of carbon-based tokamak deposits.*******1) Hydrogen in Tungsten: A key area of interest, and one in which we are uniquely equipped to investigate, is the co-bombardment of tungsten with hydrogen and other species; e.g., He, N, Ne, Ar., etc. Previous studies have shown that co-bombardment of tungsten with helium and hydrogen dramatically reduces the transport of hydrogen in tungsten materials. Ultimately, this could lead to orders of magnitude smaller tritium inventories in tungsten components in an operating reactor. Less is known about the effect of other species on hydrogen transport. With our dual-beam high-flux low-energy particle accelerator we are able to simultaneously expose specimens to two ion species (e.g., D+ and He+) with independently controlled energies and fluxes, allowing us to systematically investigate the fundamental aspects of such interactions.*******2) Carbon-based Deposits: Material erosion is an inevitable consequence of the interaction between a fusion plasma and the solid surfaces which face the plasma. Eroded atoms enter the plasma and are, eventually, deposited on surfaces which may be far from their point of origin. In current tokamaks it is observed that much of the deposition occurs in specific areas, and these surfaces may accumulate thick (mm's) deposits which can seriously disrupt plasma operation. While we have studied many aspects of such deposits, we have been limited to deposits from current tokamaks (DIII-D, ASDEX-U and JET), all of which operate with base wall temperatures < 300 C. Future fusion reactors, however, are likely to operate at base temperatures above 700 C, leading to deposits with very different characteristics. While such high-temperature deposits are not currently available for us to test, we can simulate some aspects of the deposits through heating current deposits. The DIII-D tokamak plans to introduce heated internal surfaces which will provide appropriate specimens within the next few years.*********