[en] An electron spectrometer is described in which k vector-dependent energy loss spectra can be measured with monochromized 30 keV electrons. The apparatus is constructed with oil-free pumps heatable in ultra-high vacuum technique to avoid contamination layers. The energy monochromization and analysis is performed each with a Wien filter in which the aperture error of 2sup(n)sup(d) order due to an inhomogeneity in the magnetic field can be corrected. The energy resolution reaches up to 0.065 eV despite the use of large diaphragms and large angles. The pulse analysis is carried out with an electrostatic deflection system with which energy loss spectra can be recorded in any k vector direction. k vector-dependent energy loss measurements were performed on TiN and Bi. Three surface and three volume plasmons could be determined in the hardware TiN. The loss spectrum showed a large number of shoulders which must be assigned to interband transitions. Due to the high energy resolution of the spectrometer, two transitions between occupied and vacant parts of the conduction bands were found at 1.35 eV and 1.8 eV. Their dispersion was measured in (110) direction. The k vector dependence of the 2.8 eV plasmon was determined in the region 0 smaller than k smaller than 0.6 Angstroem^-1. At k = 0.4 Angstroem^-1 the dispersion disappears. The plasmon decays at k = 0.6 Angstroem^-1 under the influence of the 1.8 eV transition. The 14.3 eV plasmon in Bi showed a smaller dispersion coefficient than found in the literature. (orig.)

[en] Theoretical (Zeeman energy effects) and experimental (beam polarisation problems) progress have been made in the understanding of polarized neutron reflectivity with polarisation analysis. It has been shown that modelization and numerical simulations makes it possible to avoid to have to systematically measure a full set of reflectivity curves for each field and temperature condition. It has been possible to determine a magnetic profile as a function of the field in a magnetic bilayer system by using only a few points in the reciprocal space. This technique allows to considerable reduce the experiment time. In single nickel layer systems, we have shown that it is possible to induce magnetic rotation inhomogeneities when these systems are subjects to deformation strains. The effect are related to magneto-elastic constants gradients. In trilayer systems, with a ME constant modulation, we have been able to induce large magnetic rotation gradients. A new magneto-optic technique to measure the magnetization direction without rotating the magnetic field has been developed. The field of neutron reflectivity has been extended to off-specular studies. It has been possible to account quantitatively of the off-specular diffusion on 2-D model systems (prepared by optical lithography). This new technique should make it possible in the future to determine magnetic structures with a in-depth as well as lateral resolution. (author)

[en] The thesis describes measurements of the scrape-off layer (SOL) ion temperature T_i with a retarding field analyzer (RFA) in the limiter tokamak Tore Supra. In the first chapter, some well known facts about nuclear fusion, limiter SOL, Langmuir probes, etc. are briefly recalled. Various diagnostics for SOL T_i measurements developed in the past are addressed as well. The second chapter is dedicated to the RFA. The principle of the RFA, technical details and operation of the Tore Supra RFA, and the influence of instrumental effects on RFA measurements are addressed. In the third chapter, the experimental results are presented in the form of papers published (or submitted for publication) during the thesis. Some research that was not completed at the time of writing is summarized in the last chapter. Considerable emphasis is placed on study of the instrumental effects of RFAs and their influence on T_i measurements. In general, the influence of instrumental effects on T_i measurements is found to be relatively small. Selective ion transmission through the RFA slit is found to be responsible for an overestimation of T_i by less than 14% even for relatively thick slit plates. The effect of positive space charge inside the analyzer, the influence of the electron repelling grid, the misalignment of the probe head with respect to the magnetic field, and the attenuation of the incident ion current by some of the probe components on T_i measurements is negligible. The instrumental study is followed by systematic measurements of T_i (as well as other parameters) in the Tore Supra SOL. This includes the scaling of SOL temperatures and electron density with the main plasma parameters (such as the plasma density, toroidal magnetic field, working gas, and the radiated power fraction). Except at very high densities or in detached plasmas, SOL T_i is found to be higher than T_e by up to a factor of 7. While SOL T_i is found to vary by almost two orders of magnitude, following the variation of the core temperatures, SOL T_e changes only little and seems to be decoupled from the core plasma. The first continuous T_i/T_e profile from the edge of the confined plasma into the SOL is constructed using data from different tokamaks. It is shown that T_i/T_e ≥ 1 in the SOL but also in the confined plasma, and increases with radius. Measurements of edge T_i/T_e in JET L-mode are analyzed. The first evidence of poloidal asymmetry of the radial ion and electron energy transport in the SOL is reported. Implications for ITER start-up phase are discussed. Correlation of the asymmetries of SOL T_i and T_e measured from both directions along the magnetic field lines with changes of the parallel Mach number is studied. SOL T_i was measured for the first time in Tore Supra by charge exchange recombination spectroscopy (CXRS) and compared to RFA data. A factor of 4 higher T_i measured by CXRS is a subject of further analysis. The segmented tunnel probe (STP) for fast measurements of SOL T_i and T_e has been designed, built, calibrated by particle simulations, and used for the first time in a large tokamak. Preliminary results from the STP measurements in Tore Supra are presented. The disagreement between the currents to the probe electrodes predicted by simulations and the measurements is addressed. Large floating potentials measured by the side of the probe connected to the ICRH antenna are reported. (author)

[en] Neutron reflectivity allows to characterize surfaces and interfaces of ultra-thin film layered systems down to a nanometric scale (∼2 nm). It is a powerful tool for the study of magnetic and polymer thin film structures. The neutron magnetic interaction is of the same order as the nuclear interaction and makes polarised neutron reflectivity a very sensitive tool for probing magnetic multilayers. It allows the determination of magnetic ordering and coupling in artificial magnetic multilayers (either metallic/semi-conducting or oxides). Examples of studies in the field of giant magneto resistive (GMR) sensors used in hard drive and tape read heads are given. The search for efficient spin-injection materials which could be used in spin electronics is also a growing field of activity. Several material candidates are presently evaluated. Recent studies on such materials are presented: oxide materials (Fe₂O₃-Fe₃O₄) epitaxial thin films; multilayer systems involving semiconducting materials ((Fe/Si)_n-(GaMnAs/GaAs)). Besides the high sensitivity of neutrons to magnetism, the possibility of isotopic labelling (H/D substitution) offers a way to probe polymer and protein thin film structures with great details: polymer interdiffusion or polymer grafting can be studied at the substrate-polymer or liquid-polymer interfaces. A model study of polymer grafting is presented

[en] Magnetic dipolar coupling leads to low-energy excitations in magnetic materials named as magnetostatic waves (MSW). The typical energy of these excitations is of the order of a few tens of μeV. We show that working in grazing incidence in a reflectivity geometry makes it possible to study these very low-energy excitations. We present a neutron set-up which allows to study these excitations. The studied samples were permalloy thin films. The MSW were either thermally excited or induced by a microwave (MW) field and the off-specular neutron reflectivity was measured. We have not been able to measure any inelastic scattered signal, even with a large MW excitation (1 W input)

[en] SANS offers the possibility to study nanostructures of sizes ranging from 2 to 200 nm. We have explored the possibility of using SANS in a grazing incidence geometry (GISANS) in order to study magnetic nanostructures in thin films (thickness ∼50 nm). Even though the amount of material is tiny in such films (∼50 μg), working in grazing incidence allows to look at the scattered signal from in-plane magnetic nanostructures in the films. We have performed surface diffraction on magnetic nanostructures (∼100 nm in size) on a system consisting of Fe_0.5Pd_0.5 thin films with a magnetic perpendicular anisotropy. The measurements have been performed in various magnetic field configurations. Magnetic surface diffraction can easily be observed. We present these measurements together with calculations based on a Born approximation. We discuss the information that can be extracted from such polarized neutron measurements

[en] In order to study the in-plane crystallographic structure of magnetic thin films, we have developed a neutron grazing incidence diffraction (GID) set-up that has been mounted on the EROS reflectometer at the LLB. This set-up allows us to observe the diffraction peaks in the plane of epitaxial thin films. As an example, we present polarized GID measurements on an epitaxial ferromagnetic thin film of the perovskite oxide La_0.7Sr_0.3MnO₃(0 0 1) deposited on SrTiO₃(0 0 1) (of a surface 1 cm²). This is the first report on polarized GID measurements on a very thin magnetic film (20 nm)

[en] The neutron applications using compact accelerator driven neutron sources are now becoming more and more important since it can cover various fields. To promote such activities, the Union for Compact Accelerator-driven Neutron Sources (UCANS) was established in 2010 and organizes each year an international conference. In 2019 the conference was organized in Paris. The conference covered a very wide range of topics around all aspects of compact sources, accelerators, targets, moderators, detectors, neutron scattering, radiography, isotope and nuclear data, and medical applications. The 60 presentations have been gathered around 5 themes: 1) compact sources and projects, 2) accelerators, 3) targets, 4) moderator and reflector, and 5) instrumentation

[en] We present the operation of a matrix of Fresnel zone plates consisting of 900 individual zone plates. The individual efficiency of the zone plate lenses is close to 30% for λ=13.7 A. We discuss the use of such a matrix as an optical element for performing high-resolution neutron imaging (at a sub 50 μm resolution)

No abstract available