Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Lasers for nuclear technologies

International audienceA wide spectrum of laser applications for nuclear technologies and industry on the basis of the latest RandD in CEA (France) will be presented. In particular, the problems of paint and metal decontamination, tokamak plasma facing walls detritiation, remote characterisation and testing (radiometry and thermography, laser induced breakdown spectroscopy, plasma diagnostics) will be discussed. The experiments were made along with the fundamental studies on laser beam/matter interaction (laser ablation with ns, ps, fs and double-pulses) and the modelling of these processes. Other laser applications (art and cultural heritage, Mars curiosity mission, optical elements, micro-fabrication, additive manufacturing) will be under discussion as well

Laser methods development for nuclear technologies

International audienceLaser methods and their applications for nuclear industry are regarded as very attractive and promising as they may provide remote measurements and surface processing without undesirable production of additional nuclear wastes. Laser methods for chemical analysis, non-destructive testing and control, surface decontamination and processing are under intensive development and study. Different laser methods, Laser Induced Breakdown Spectroscopy (LIBS- method) for elemental and isotopic analysis, laser active radiometry and pyrometry for surface non-destructive characterization, laser decontamination of metal surfaces and paint removal from concrete, laser detritiation and cleaning of tokamak walls and optics will be presented and discussed. The presentation is based on both the experimental and theoretical results obtained in our Department [1-6] in a wide collaboration with French national laboratories and other international teams (Russia, UK, Germany, and Japan). Special attention will be given to physical interpretation of laser methods performances in correlation with the development of adequate theoretical models and simulations. Future possible applications of laser methods for characterization and detritiation of ITER plasma facing walls and components, for surface micro-processing for micro-fluidic applications, and also for nano-analysis by a tip enhanced near-field ablation will be presented

Laser cleaning of paints and metals problems and possible solutions

International audienceLaser cleaning of complex surfaces (paints and metals with a micrometric oxide layer) should beregarded as a complicated multi parametric physical-chemical process and a tough technicalprocedure. To ensure surface laser cleaning with a required quality, high efficiency and minimumof undesirable effects and to avoid possible thermo-chemical changes in the surface undercleaning, one should take into consideration numerous laser parameters, optical and physicalchemicalfeatures of a surface under cleaning, laser beam/surface interaction regime,environmental conditions, etc.A summarized review of the experimental results on the laser cleaning of paints on concrete,metal mirrors and stainless steel surfaces with a micrometric oxide layer performed with highrepetition rate (1-20 kHz) nanosecond lasers (5-100 ns) will be presented along with the results ofmulti parametric studies. Theoretical modeling (3D+t) for an adequate explanation of theobtained results and physical-chemical processes associated with laser cleaning will be underdiscussion. The problems of cleaning regime optimization, the appropriate choice of the laserwavelength (infrared, visible or ultraviolet) and the pulse duration (nanosecond, picosecond orfemtosecond) for complex surfaces and art objects, in particular, will be under special discussion

Nano-sampling of metals with ultra-short laser pulses

International audienceIn sample microanalysis by laser ablation (LA), spatial resolution is determined by laser beam diffraction limits (of the order of a laser wavelength) and thermal diffusion of a deposited heating energy during laser pulse (proportional to the square root of pulse duration and matter diffusivity). Being limited by these laser beam features and those of heating energy, spatial resolution (a crater diameter) of $\sim$1 $\mu$m was obtained with 4 ns laser pulses on 266 nm wavelength. To improve spatial resolution of microanalysis, the application of lasers with the pulses of shorter durations (ps and fs) may be advised. As another way to improve spatial resolution of microanalysis up to $\sim$100 nm, one may advise LA with a highly localized laser field created by a tip near-field enhancement. The experiments with ns laser pulses were made along with multi-parametric theoretical studies based on one-temperature heating model. In this work, the theoretical studies were extended on ultra-short laser pulses (ps or fs) to analyze the effect of pulse duration and matter properties (absorption coefficient, thermal conductivity and capacity) on the resulting temperature field spatial distribution T (t, x, y, z). A two-temperature model was applied for T (t, x, y, z) calculations. The results of these simulations are compared to temperature distributions for ns laser pulses. Discussion on advantages of ultra-short pulses application for LA with a tip near-field enhancement for consecutive chemical analysis with nanometric resolution will be presented

L'academicien Evguenii Konstantinovitch ZAVOiSKII (1907-1976) et la decouverte de la RPE

International audienc

Analytical performances of laser-induced micro-plasma of Al samples with single and double ultrashort pulses in air and with Ar-jet : A comparative study

International audienceUltrashort pulse laser microablation coupled with optical emission spectroscopy was under study to obtain several micro-LIBS analytical features (shot-to-shot reproducibility, spectral line intensity and lifetime, calibration curves, detection limits). Laser microablation of Al matrix samples with known Cu- and Mg-concentrations was performed by single and double pulses of 50 fs and 1 ps pulse duration in air and with Ar-jet. The micro-LIBS analytical features obtained under different experimental conditions were characterized and compared. The highest shot-to-shot reproducibility and gain in plasma spectral line intensity were obtained with double pulses with Ar-jet for both 50 fs and 1 ps pulse durations. The best calibration curves were obtained with 1 ps pulse duration with Ar-jet. Micro-LIES with ultrashort double pulses may find its effective application for surface elemental microcartography

Mathematical modeling of Laser Active Radiometry in application to Non-Destructive Testing

International audienceNew technological methods for non-destructive testing (NDT) for in situ and real time control of complex physico-chemical processes are under constant development in the French Alternative Energies and Atomic Energy Commission (CEA) [1-12]. These methods should be developed along with mathematical model and computer code to provide both the adequate analytical physical model and the rapid computation of a process under research. In our NDT-studies with Laser Active Radiometry method, samples representative for nuclear and thermonuclear (ITER) installations were under repetitive heating by a pulsed laser radiation. The development of the analytical models and simplified solutions was aimed to simulate laser heating and related temperature distribution T(x, y, z, t) in relation with numerous physical and chemical features of this complex multi-parametric process. The results of our mathematical modeling were validated by the experiments. The simulation and experimental results were in good correlation. The principal results of our theoretical studies, their applicability for rapid NDT and the prospects for future models development for heating temperature calculation in application to complex surfaces with micrometric layers or undersurface defects will be presented and discussed.References[1]Semerok A, Fomichev S V, Brygo F, Weulersse J-M, Thro P-Y and Grisolia C 2006, Proceedings of “LTL Plovdiv 2005” (IV International Symposium Laser Technologies and Lasers “LTL Plovdiv 2005” (Bulgaria, Plovdiv, 8–10 October 2005) pp 76–83[2]Grisolia C, Semerok A, Weulersse J-M, Le Guern F, Fomichev S V, Brygo F, Fichet P, Thro P-Y, Coad P, Bekris N et al. 2007 J. Nucl. Mater. 363–365 1138[3]Semerok A, Fomichev S V, Weulersse J-M, Brygo F, Thro P-T and Grisolia C 2007 J. Appl. Phys. 101 084916 [4]Melyukov D, Sortais C, Semerok A, Thro P-Y, Courtois X and Farcage D 2010 10th International Conference on Quantitative Infra-Red Thermography (July 27-30, 2010, Québec, Canada) http://dx.doi.org/10.21611/qirt.2010.089 [5]Courtois X, Sortais S, Melyukov D, Gardarein J-L, Semerok A and Grisolia C 2011 Fusion Eng. Des. 86 1714[6]Semerok A, Fomichev S V, Brygo F, Thro P-Y and Grisolia C 2012 J. Nucl. Mater. 420 198[7]Semerok A, Jaubert F, Fomichev S V, Thro P-Y, Courtois X and Grisolia C 2012 ‎Nucl. Instr. Meth. Phys. Res. A 693 98[8]Semerok A, Jaubert F, Fomichev S V, Thro P-Y and Grisolia C 2012 Fusion Eng. Des. 87 267[9]Semerok A, Grisolia C, Fomichev S V and Thro P-Y 2013 Proc. of SPIE vol 9065 (Bellingham, WA) 90650A.[10]Semerok A, Fomichev S V, Jaubert F and Grisolia C 2014 ‎Nucl. Instr. Meth. Phys. Res. A 738 25[11]Pham Tu Quoc S, Cheymol G and Semerok A 2014 ‎Rev. Sci. Instrum.85 054903[12]Semerok A, Pham Tu Quoc S, Cheymol G, Gallou C, Maskrot H and Moutiers G 2016 EPJ Nuclear Sci. Technol. 2 2

Mathematical modeling of Laser Active Radiometry in application to Non-Destructive Testing

International audienceNew technological methods for non-destructive testing (NDT) for in situ and real time control of complex physico-chemical processes are under constant development in the French Alternative Energies and Atomic Energy Commission (CEA) [1-12]. These methods should be developed along with mathematical model and computer code to provide both the adequate analytical physical model and the rapid computation of a process under research. In our NDT-studies with Laser Active Radiometry method, samples representative for nuclear and thermonuclear (ITER) installations were under repetitive heating by a pulsed laser radiation. The development of the analytical models and simplified solutions was aimed to simulate laser heating and related temperature distribution T(x, y, z, t) in relation with numerous physical and chemical features of this complex multi-parametric process. The results of our mathematical modeling were validated by the experiments. The simulation and experimental results were in good correlation. The principal results of our theoretical studies, their applicability for rapid NDT and the prospects for future models development for heating temperature calculation in application to complex surfaces with micrometric layers or undersurface defects will be presented and discussed