Hydrogen Trapping Studies in Fusion First Wall Materials
Hydrogen trapping in the first wall of fusion reactors is one of the most serious materials problems facing the designers of magnetic confinement devices. The release of this trapped hydrogen from the near surface region of the first wall during a tokamak discharge has been shown to play a major role in the hydrogen fueling of today's plasmas, while trapped hydrogen isotopes will directly influence the on-site tritium inventory and the structural properties of future D-T reactors. This paper summarizes the laboratory ion implantation sttidies on the hydrogen trapping characteristics of first wall materials. Emphasis is placed on the near term materials problems associated with austenitic stainless steels that are currently in use in magnetic confinement devices. Hydrogen trapping experiments involving more exotic first wall structural and coating materials are briefly reviewed.
Burial of 60 keV Deuterium Ions in Stainless Steel and Titanium
IN a controlled thermonuclear plasma it is necessary to minimize the entry into the hot plasma of low energy particles produced by the impact of fast particles on the walls of the container. These particles may be either particles of wall material or reflected incident particles. They can cool the plasma by two processes. The first process is a loss of bremsstrahlung radiation as a result of the interaction of atoms of high atomic charge from wall material with the fast electrons in the plasma. The second process of charge transfer between the atoms of the wall material and the energetic hydrogen ions in the plasma produces neutral hydrogen atoms which are subsequently lost to the walls. A study has been made of the burial of deuterium ions (D+) in stainless steel and titanium since these metals are commonly used in the construction of ultra high vacuum systems. The mechanisms of hydrogen trapping in these two metals differ considerably since a hydride can be formed with titanium but not with the elements in stainless steel.
Hill country sheep production. I. The influence of age, flock, and year on some components of reproduction rate in Romney and Border Leicester × Romney ewes.
Data from 7,091 straightbred Romney and Border Leicester × Romney ewes grazed at the Whatawhata Hill Country Research Station over the period 1959 to 1967 have been used to obtain estimates of flock and age-of-ewe effects on reproduction rate and its components and of year-to-year variation. The ewes were from six groups: a Romney control (RCR) flock, a Romney flock in which ewes were mated either to Romney (RER) or to Border Leicester rams (REB), and flocks of first-cross (F1), second-cross (F2), and third-cross (F3) Border Leicester × Romney ewes mated to first-cross Border Leicester × Romney rams. The ewes' ages at lambing varied from 2 to 5 years and no selection was practised. The ratio of number of lambs weaned per ewe present at lambing increased from the RCR (0.84) to the F1 (1.07), then declined with interbreeding to the F2 (0.92) and further to the F3 (0.87) ewes. Similar changes were evident for the percentage of ewes lambing, of multiple births, and of lambs surviving to weaning. Over...