An experiment is described for studying effects of penetrating light ions on microstructure and mechanical properties of metals. Damage rates and gradients, specimen cooling and contamination and beam monitoring are discussed in detail, and an experiment which addresses these problems is described. Microstructure and tensile test results are given of nickel and niobium test specimens irradiated[with 16 MeV protons in the described apparatus. Comparisons are made with 14 MeV neutron irradiation results from other experiments.
Introducti onThis paper describes an experiment to investigate effects of penetrating 16 MeV protons on metals. The experiment was developed to induce a nearly uniform distribution of damage under controlled environmental conditions and to measure and compare the effects of this damage on microstructure and tensile properties.Anticipation of a fusion energy break-even experiment that will lead to development of fusion reactor energy sources provides the incentive to better understand the effects of 14 MeV neutrons on the microstructure and mechanical properties of metals. A direct approach to the analysis of these effects is not possible since high energy neutron sources which provide fluxes and fluences anticipated at the plasma vacuum confinement wall of a fusion power reactor do not exist. Damage effects can not be predicted with certainty either; experimental verification of the theoretical models is lacking.Microstructure evolution and mechanical properties in fusion-like environments can be studied using high flux, penetrating particle beams generated in existing accelerators. Protons are potentially good candidates for such irradiations; they can be produced and focused to high fluxes, they have relatively long ranges and the calculated primary knock-on spectrum for 16 MeV protons is similar to the knock-on spectrum calculated for 14 MeV neutrons.(1,2) Consequently, understanding the bulk damage induced by 16 MeV protons may lead to a better understanding of the high flux, high energy neutron induced bulk damage effects which will occur in first wall materials of a fusion reactor. Several irradiation effects, that are very difficult to study when using present day fusion neutrons to induce the damage, can be investigated with relative ease by using 16 MeV protons for the damage production. These include both static and cyclic temperature and stress effects on mechanical properties and microstructure.Comparison of neutron and proton induced damage requires that experiments be designed to minimize damage gradients due to stopping power variations as the proton penetrates the sample; high energy neutrons exhibit a small stopping power and produce a damage which is uniformly distributed along the penetration depth of test samples. The maximum thickness of specimens which can be used for proton induced damage studies is dependent on stopping power characteristics of the materials.However, specimen thickness can also influence tensile properties and could conceivably dominate the effects due...