M. Victoria

PIREX II — A new irradiation facility for testing fusion first wall materials

Abstract A new irradiation facility, PIREX II (Proton Irradiation Experiment), became operational in March 1987. It is located on a dedicated beam line split from the main beam of the 590 MeV proton accelerator at the Paul Scherrer Institute (PSI). Irradiation with protons of this energy introduces simultaneously displacement damage, helium and other impurities. Because of the penetration range of 590 MeV protons, both damage and impurities are homogeneously distributed in the target material. The installation has its own beam line optics that can support a proton current of up to 50 μA. At a typical beam density of 4 μA mm 2 , the damage rate in steel is 0.7 × 10−5 dpa s (dpa: displacements per atom), and the helium production rat He/dpa. Both flat tensile specimens of up to 0.4 mm thickness and tubular fatigue samples of 3 mm diameter can be irradiated. Cooling of the sample is performed by flowing pressurized helium gas over the sample. Irradiation temperatures can be controlled between 100 ° C and 800 ° C. Installation of an in situ low cycle fatigue device is foreseen. Beams of up to 20 μA have been obtained, the beam having an approximately Gaussian distribution of elliptical cross section with 4σxbetween 0.8 and 8 nun by 4σy of up to 10 mm. Irradiations for a dosimetry program have been completed on samples of Al, Cu, Fe, Ni, Au, W, and 1.4914 ferritic steel. The evaluation of results allows the correct choice of reactions to be used for determining total dose, from the standpoint of half life and gamma energy. A program of irradiations on candidate materials for the Next European Torus (NET) design (Cu and Cu alloys, 1.4914 ferritic martensitic steel, W and W-Re alloys and Mo and Mo alloys), where the above mentioned characteristics of this type of irradiation can be used advantageously, is now under way.

Production of helium by medium energy (600 and 800 MeV) proton

Abstract There are no neutron sources that can produce simultaneously displacement cascade damage, gases and other transmutation product impurities, at levels significant to a fusion reactor such as the Next European Torus (NET). However, this same combination of damage is produced in materials bombarded by medium energy protons. Therefore, proton irradiation facilities have been added to the worlds most intense medium energy proton accelerators, SIN in Switzerland and LAMPF in the USA, to study the effects of these damage forms in combination. To confirm the accuracy of the computer codes used to model the nuclear reactions, especially regarding helium production, Fe, Cu, Mo, W, Ni, Al and Au were bombarded in the LAMPF proton beam. The buildup of 4 He and 3 He per proton was determined by vaporization of the samples and analysis of the gases released by isotope dilution mass spectrometry.

Simulation by medium energy proton irradiation

Abstract Experiments have been performed in two proton accelerators, at the Swiss Nuclear Research Institute (SIN) and at the LAMPF (Los Alamos, NM, USA) to establish the use of medium energy proton beams for simulation of first wall damage conditions. Due to the high penetrating power and low energy deposition of the beam, high helium and displacement damage can be introduced uniformly in large sample thicknesses. Values for helium retained have been established by analyses of irradiated samples and are in reasonable agreement with the calculated ones. Microstructural and mechanical properties of many materials irradiated by medium energy protons have been investigated. The results have encouraged both the Swiss and LAMPF-USA groups to design and construct new radiation facilities which will allow in-situ testing of larger specimens of most alloys of interest.

The microstructure of the 1.4914 MANET martensitic steel before and after irradiation with 590 MeV protons

Abstract Optical and transmission electron microscope observations, together with SEM (scanning electron microscope) and ASTEM (analytical scanning transmission electron microscope) microanalysis have been performed in samples of the DIN 1.4914 martensitic steel (MANET cast), both before and after irradiation with 590 MeV protons to doses up to 1 dpa at temperatures between 363 and 703 K. The chemical composition of the different carbide geometries have been obtained. No substantial modification of the carbide and precipitate structure is observed after either deformation under fatigue or after irradiation to 1 dpa at 703 K. No bubbles have been observed in a specimen irradiated to 0.7 dpa, containing 87 appm He.

The strength of the spallation neutron flux of SINQ for radiation damage fusion technology

The SINQ spallation neutron source being installed in Switzerland was simulated and its source strength measured in terms of the radiation damage parameters: total flux of spallation neutrons with E > 1.0 MeV, and helium and displacement damage rates. This simulation used the proton beam of the TRIUMF accelerator in Canada and its lead beam stop as the source of spallation neutrons. The production of helium, per proton of beam in materials irradiated with the spallation neutrons, was measured by vacuum extraction inside a calibrated mass spectrometer. The neutron spectrum and neutron flux intensity were determined by multiple foil activation measurements. The helium production in iron per year at full beam power (2 mA) at a radial distance of 15 cm is 12 appm compared to 310 at the end of life in the first wall of NET.

Liquid drop model and effects of electronic energy loss on radiation damage cascades

Abstract We present two aspects of the thermal behaviour of cascades, related to the mechanisms of heat transport. The first aspect concerns the PKA energy range where subcascades are produced and discusses the thermal interaction between them. For this description we couple the results of the Binary Collision Approximation (BCA) to a simplified solution of the heat equation. Comparison with Molecular Dynamics (MD) results when available supports this approach. However this analysis only considers lattice conductivity, neglecting the possible effects of electronic transport. In the second part of this presentation we consider the effects of the electronic energy loss on the dynamics of thermal spikes in Cu. This study is based on a simple model of the stopping power and the electron phonon interaction in the framework of the Embedded Atom Model (EAM) for MD. This approach is only valid for weak-coupling systems, like Cu, where we obtain quantitative information on the effect.

A channeling goniometer with a wide temperature range sample holder

Abstract A three-axes goniometer with an x−y sample stage for application in ion beam channeling has been constructed. The fully computer controlled goniometer is driven by optically encoded dc-motors that are located within the vacuum system. The angular precision of the rotational axes is better than 0.01°. The sample holder can be heated to 800 K and cooled down to 20 K by a liquid helium cryostat. The system has been designed to allow the combination of channeling RBS (Rutherford backscattering spectrometry) with PIXE (particle induced X-ray emission), NRRA (nuclear resonant reaction analysis) and ERDA (elastic recoil detection analysis). Test measurements on silicon crystals have been performed successfully. First results of measurements on KNbO3 crystals are presented.