[en] The paper discusses inertial confinement fusion research carried out at several different laser facilities including the VULCAN laser at the Rutherford Appleton Laboratory, the TRIDENT laser at the Los Alamos National Laboratory and the PHEBUS laser at Limeil. Low density foam targets were irradiated either with nanosecond laser or soft x-ray pulses. Laser imprinting was studied and in particular saturation of areal density perturbations induced by near-single mode laser imprinting has been observed. Several issues important for the foam buffered direct drive scheme were investigated. These studies included measurements of the absolute levels of Stimulated Brillouin and Raman Scattering observed from laser irradiated low density foam targets either bare or overcoated with a thin layer of gold. A novel scheme is proposed to increase the pressure in indirectly driven targets. Low density foams that are mounted onto a foil target are heated with an intense pulse of soft x-ray radiation. If the foam is heated supersonically the pressure generated is not only the ablation pressure but the combined pressure due to ablation at the foam/foil interface and the heated foam material. The scheme was confirmed on planar targets. Brominated foil targets overcoated with a low density foam were irradiated by a soft x-ray pulse emitted from a hohlraum. The pressure was obtained by comparing the rear side trajectory of the driven target observed by soft x-ray radiography to one dimensional radiation hydrodynamic simulations. Further, measurements were carried out to observe the transition from super- to subsonic propagation of an ionisation front in low density chlorinated foam targets irradiated by an intense soft x-ray pulse both in open and confined geometry. The diagnostic for these measurements was K-shell point projection absorption spectroscopy. In the fast ignitor area the channeling and guiding of picosecond laser pulses through underdense plasmas, preformed density channels and microtubes were investigated. It was observed that a large fraction of the incident laser energy can be propagated through preformed channels and microtubes. Magnetic fields in the megagauss range have been measured, with a polarimetric technique, during and after propagation of relativistically intense picosecond pulses on solid targets and preionised plasmas. Two types of toroidal fields, of opposite orientation, generated through different mechanisms, were detected. In addition, the production and propagation of an electron beam through solid glass targets irradiated at intensities above 10¹⁹ Wcm^-2 was observed using optical probing techniques. (author)

No abstract available

[en] The way of understanding laser matter experiments is to use specific instrumentation which needs new techniques, in terms of triggering, fast high voltage ramps generation and fiducial, using fast optoelectronic switches. Some experiments realized around large lasers as Phebus and P102 installed on the CEA-Limeil-Valenton center and described in this paper illustrate the possible applications of these cells for the always more exacting requirements of the physics of the condensed plasmas. (author)

No abstract available

[en] Laser imprinting has been studied and, in particular, saturation of areal density perturbations induced by near single mode laser imprinting was observed. Several issues important for the foam buffered direct drive scheme have been investigated. These studies included measurements of the absolute levels of stimulated Brillouin and Raman scattering observed from laser irradiated low density foam targets, either bare or overcoated with a thin layer of gold. A novel scheme is proposed to increase the pressure in indirectly driven targets. By heating a foam supersonically that is attached to a solid target the pressure generated is not only the ablation pressure but also the combined pressure due to ablation at the foam-foil interface and the heated foam material. Planar brominated plastic foil targets overcoated with a low density foam were irradiated by a soft X ray pulse. The pressure was obtained by comparing the rear side trajectory of the driven target observed by soft X ray radiography with one dimensional radiation hydrodynamic simulations. Observations were also carried out of the transition from supersonic to subsonic propagation of an ionization front in low density chlorinated foam targets irradiated by an intense soft X ray pulse. The diagnostic for these measurements was K shell point projection absorption spectroscopy. In the fast ignitor area the channelling and guiding of picosecond laser pulses through underdense plasmas, preformed density channels and microtubes were investigated. It was observed that a large fraction of the incident laser energy can be propagated. Megagauss magnetic fields were measured, with a polarimetric technique, during and after propagation of intense picosecond pulses in preionized plasmas. Two types of toroidal fields, of opposite orientation, were detected. In addition, the production and propagation of an electron beam through solid glass targets irradiated at intensities above 10¹⁹ W/cm² were observed using optical probing techniques. (author)

No abstract available

[en] This paper discusses the experimental results obtained at the Phebus laser (neutron yield and radiation temperature). Next it covers numerical simulations to design targets adapted to a MJ laser. This includes three stages: (1) 1-D calculation of the capsule alone to optimize the radiation temperature; (2) 2-D calculation of the cavity to optimize symmetry; and (3) 2-D calculation of the capsule with geometric perturbations and/or non-uniformity. Lastly, it summarizes the main features of the MJ laser

[en] The paper develops the non-destructive examinations, with a special emphasis on transmission tomography, performed in the Phebus facility, using a linear accelerator associated with a line scan camera based on PCD components. This particular technique enabled the high level of penetration to be obtained, necessary for this high density application. Spatial resolution is not far from the theoretical limit and the density resolution is often adequate. This technique permitted: 1) to define beforehand the cuts on a precise basis, avoiding a long step-by-step choice as in previous in-pile tests; 2) to determine, at an early stage, mass balance, material relocations (in association with axial gamma spectrometry), and FP distribution, as an input into re-calculations of the bundle events. However, classical cuttings, periscopic visual examinations, macrographies, micrographies and EPMA analyses remain essential to give oxidation levels (in the less degraded zones), phase aspect and composition, to distinguish between materials of identical density, and, if possible, to estimate temperatures. Oxidation resistance of sensors (thermocouples or ultrasonic thermometers) is also traced. The EPMA gives access to the molten material chemical analyses, especially in the molten fuel blockage area. The first results show that an important part of the fuel bundle melted (which was one of the objectives of this test) and that the degradation level is close to TIMI-2 with a molten plug under a cavity surrounded by an uranium-rich crust. In lower and upper areas fuel rods are less damaged. Complementaries between these examination techniques and between international teams involved will be major advantages in the Phebus FPT0 test comprehension. 3 refs, 9 figs

[en] In Europe an initiative for the reduction of uncertainties in severe accident safety issues was initiated. Generally, the error made in predicting plant behaviour is called uncertainty, while the discrepancies between measured and calculated trends related to experimental facilities are called the accuracy of the prediction. The purpose of the work is to assess the accuracy of the calculations of the severe accident International Standard Problem ISP-46 (Phebus FPT1), performed with two versions of MELCOR 1.8.5 for validation purposes. For the quantitative assessment of calculations the improved fast Fourier transform based method (FFTBM) was used with the capability to calculate time dependent code accuracy. In addition, a new measure for the indication of the time shift between the experimental and the calculated signal was proposed. The quantitative results obtained with FFTBM confirm the qualitative conclusions made during the Jozef Stefan Institute participation in ISP-46. In general good agreement of thermal-hydraulic variables and satisfactory agreement of total releases for most radionuclide classes was obtained. The quantitative FFTBM results showed that for the Phebus FPT1 severe accident experiment the accuracy of thermal-hydraulic variables calculated with the MELCOR severe accident code is close to the accuracy of thermal-hydraulic variables for design basis accident experiments calculated with best-estimate system codes. (author)

[en] The international Phebus FP programme, initiated in 1988 is one of the major research programmes on light water reactors severe accidents. After a short description of the facility and of the test matrix, the main outcomes and results of the first four integral tests are provided and analysed. Several results were unexpected and some are of importance for safety analyses, particularly concerning fuel degradation, cladding oxidation, chemical form of some fission products, especially iodine, effect of control rod materials on degradation and chemistry, iodine behaviour in the containment. Prediction capabilities of calculation tools have largely been improved as a result of this research effort. However, significant uncertainties remain for a number of phenomena, requiring detailed physical analysis and implementation of improved models in codes, sustained by a number of separate-effect experiments. This is the subject of the new Source Term programme for a better understanding of the phenomenology on important safety issues, in accordance with priorities defined in the EURSAFE project of the 5^th European framework programme aiming at reducing the uncertainties on Source Term analyses. It covers iodine chemistry, impact of boron carbide control rods degradation and oxidation, air ingress situations and fission product release from fuel. Regarding the interpretation of Phebus, an international co-operation has been established since over ten years, particularly helpful for the improvement and common understanding of severe accident phenomena. Few months ago, the Phebus community was happy to welcome representatives of a large number of organisations from the following new European countries: the Czech republic, Hungary, Lithuania, Slovakia, Slovenia and also from Bulgaria and Romania. (author)