European research activities on charge state breeding related to radioactive ion beam facilities

International audienceEuropean effort on charge breeders is mainly dedicated to present and future Radioactive Ion Beam facilities. The main projects are High Intensity and Energy-ISOLDE at CERN, SPIRAL2 at GANIL and EURISOL. Most of the experimental developments are funded by the European programmes EURONS (EUROpean Nuclear Structure) and EURISOL (European Isotope Separation On-Line Radioactive Ion Beam Facility). Two ion source types (EBIS and ECRIS) have been adapted to accept the injection and the capture of an ion beam, in order to increase its charge with the highest efficiency within the shortest time. Both charge breeders are advantages and disadvantages with regard to their use in a Radioactive Ion Beam facility. The most important parameters studied are acceptance (in emittance and intensity) of the charge breeder, efficiency and charge breeding time of a specific n+ charge state, emittance of the extracted n+ beam. The charge breeder parameters are studied with different 1+ ion sources dedicated to 1+ radioactive ion beam production and the tuning procedure of the charge breeder as a beam line section of a specific accelerator is established and measured too

First plasma of the A-PHOENIX electron cyclotron resonance ion source

International audienceA-PHOENIX is a new compact hybrid electron cyclotron resonance ion source (ECRIS) using a large permanent magnet hexapole (1.92 Tesla at the magnet surface) and High Temperature Superconducting Solenoids (3 Tesla) to make min-|B| structure suitable for 28 GHz CW operation. The final assembly of the source was achieved at the end of june 2007. The first plasma of A-PHOENIX at 18 GHz was done on August the 16th 2007. The technological specificities of A-PHOENIX are presented. The large hexapole builded is presented and experimental magnetic measurements show that it is nominal with respect to simulation. A fake plasma chamber prototype including thin iron inserts showed that the predicted radial magnetic confinement can be fulfilled up to 2.15 Tesla at the plasma chamber wall. Planning of experiments scheduled until end 2008 is presented

Synchrotron x-ray-diffraction study of the structure and growth of Xe films adsorbed on the Ag(111) surface

URL:http://link.aps.org/doi/10.1103/PhysRevB.59.15464 DOI:10.1103/PhysRevB.59.15464Synchrotron x-ray scattering has been used to investigate the structure and growth of perhaps the simplest of all films: xenon physisorbed on the Ag(111) surface. High-resolution x-ray scans of the in-plane structure and lower-resolution scans (specular and nonspecular) of the out-of-plane order were performed. The Xe films were prepared under both quasiequilibrium and kinetic growth conditions, and have fewer structural defects than those investigated previously by others on graphite substrates. Under quasiequilibrium conditions, the bulk Xe-Xe spacing is reached at monolayer completion, and the monolayer and bilayer lattice constants at coexistence are inferred equal to within 0.005 Å, consistent with theoretical calculations. The Xe/vacuum interface profile for a complete monolayer and bilayer grown at quasiequilibrium is found to be sharper than for kinetically grown films. At coverages above two layers, diffraction scans along the Xe(01l) rod for quasiequilibrated films are consistent with the presence of two domains having predominantly an ABC stacking sequence and rotated 60° with respect to each other about the surface normal. Annealing of these films alters neither the population of the two domains nor the fraction of ABA stacking faults. The thickest film grown under quasiequilibrium conditions exceeds 220 Å (resolution limited). Under kinetic growth conditions, x-ray intensity oscillations at the Xe anti-Bragg position of the specular rod are observed as a function of time, indicating nearly layer-by-layer growth. Up to four complete oscillations corresponding to a film of eight layers have been observed before the intensity is damped out; the number of oscillations is found to depend on the substrate temperature, the growth rate, and the quality of the Ag(111) substrate. The specular reflectivity from kinetically grown films at nominal coverages of three and four layers has been analyzed using a Gaussian model which gives a film thickness standard deviation of 0.5 and 1.0 layers, respectively. Diffraction scans along the Xe(01l) rod of these films indicate a larger fraction of ABA stacking faults than found for thicker films. These results demonstrate the difficulty of kinetically growing Xe films thicker than two layers which have an ideal slab geometry.This work was partially supported by U.S. National Science Foundation Grant Nos. DMR-8704938, DMR-9011069, and DMR-9314235 and the U.S. Department of Energy Grant No. DE-FG02-85ER45183 of the MATRIX Participating Research Team

Ultrahigh Vacuum Chamber for Synchrotron X-ray Diffraction from Films Adsorbed on Single-crystal Surfaces

An ultrahigh vacuum chamber has been developed for structural analysis of adsorbed films and single‐crystal surfaces using synchrotron x‐ray diffraction. It is particularly well suited for investigations of physisorbed and other weakly bound films. The chamber is small enough to transport and mount directly on a standard four‐axis diffractometer and can also be used independently of the x‐ray diffractometer. A low‐current, pulse‐counting, low‐energy electron diffraction/Auger spectroscopy system with a position‐sensitive detector enables in situ characterization of the film and substrate while the sample is located at the x‐ray scattering position. A closed‐cycle He refrigerator and electron bombardment heater provide controlled substrate temperatures from 30 to 1300 K. The chamber is also equipped with an ion sputter gun, a quadrupole mass spectrometer, and a gas handling system. Details of the design and operation of the instrument are described. To demonstrate the performance of the instrument, we present some preliminary results of a study of Xe physisorbed on the Ag(111) surface

Raman micro-spectroscopy as a tool to measure the absorption coefficient and the erosion rate of hydrogenated amorphous carbon films heat-treated under hydrogen bombardment

We present a fast and simple way to determine the erosion rate and absorption coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic source based on ex-situ Raman micro-spectroscopy. Results are compared to ellipsometry measurement. The method is applied to films eroded at different temperatures. A maximum of the erosion rate is found at ~ 450 {\degree}C in agreement with previous results. This technique is suitable for future quantitative studies on the erosion of thin carbonaceous films, especially of interest for plasma wall interactions occurring in thermonuclear fusion devices

The structural properties of the multi-layer graphene/4H-SiC(000-1) system as determined by Surface X-ray Diffraction

We present a structural analysis of the multi-layer graphene-4HSiC(000-1}) system using Surface X-Ray Reflectivity. We show for the first time that graphene films grown on the C-terminated (000-1}) surface have a graphene-substrate bond length that is very short (0.162nm). The measured distance rules out a weak Van der Waals interaction to the substrate and instead indicates a strong bond between the first graphene layer and the bulk as predicted by ab-initio calculations. The measurements also indicate that multi-layer graphene grows in a near turbostratic mode on this surface. This result may explain the lack of a broken graphene symmetry inferred from conduction measurements on this system [C. Berger et al., Science 312, 1191 (2006)].Comment: 9 pages with 6 figure

Raman study of CFC tiles extracted from the toroidal pump limiter of Tore Supra

International audienceThe structure of six tiles extracted from the erosion and deposition zones (thin and thick deposition) of the Tore Supra toroidal pump limiter (TPL) have been analysed in the framework of the DITS campaign using micro-Raman spectroscopy. This post-mortem analysis gives information on both carbon structure and D content. We have found that the carbon structure is most often similar to that of plasma-deposited hard amorphous carbon layers. The role of the surface temperature during the discharge in the D content is investigated: in all locations where the temperature does not reach more than 500°C the D content seems to be roughly uniform with D/D+C ≈ 20%

Dynamic fuel retention in tokamak wall materials: An in situ laboratory study of deuterium release from polycrystalline tungsten at room temperature

International audienceRetention of deuterium ion implanted in polycrystalline tungsten samples is studied in situ in an ultra-high vacuum apparatus equipped with a low-flux ion source and a high sensitivity thermo-desorption setup. Retention as a function of ion fluence was measured in the 10^17 -10^21 D+/m^2 range. By combining this new fluence range with the literature in situ experimental data, we evidence the existence of a retention = fluence^ 0.645±0.025 relationship which describes deuterium retention behavior on polycrystalline tungsten on 8 orders of magnitude of fluence. Evolution of deuterium retention as a function of the sample storage time in vacuum at room temperature was followed. A loss of 50% of the retained deuterium is observed when the storage time is increased from 2 h to 135 h. The role of the surface and of natural bulk defects on the deuterium retention/release in polycrystalline tungsten is discussed in light of the behavior of the single desorption peak obtained with Temperature Programmed Desorption