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

Characterization of aerosols generated by nanosecond laser ablation of an acrylic paint

cited By 3This study focuses on particles produced during laser ablation of a green colored acrylic wall paint, which is frequently used in industrial buildings and in particular in nuclear installations. Ablation is carried out with a Nd: YAG laser at a wavelength of 532 nm and a pulse duration of 5 ns, in a cell at ambient pressure and temperature, which is ventilated by filtered air. The number of particles emitted was measured with a Condensation Particle Counter (CPC) and their size with an Engine Exhaust Particle Sizer (or EEPS) for the nanometric range, and an AEROSIZER (for the micrometric range). The mass and shape of particles were determined by sampling on filters as well as on the different impaction plates of a Low-Pressure Impactor (LPI). Two particle populations were detected: a population of aggregates of primary nanoparticles with an electrical mobility diameter ranging from 30 to 150 nm, and a population of spherical submicron particles with an aerodynamic diameter ranging from 400 to 1000 nm. The spherical particles are mainly composed of titanium dioxide, and the aggregates most likely of carbon. The presence of two types of particles with different size distributions, shapes, and chemical compositions, implies that particles originating from the ablation of paint are formed by two different mechanisms: agglomeration in the case of the nanometric aggregates, which is preceded by steps of nucleation, condensation, and coagulation of the primary particles, while the submicron spheres result from a direct ejection mechanism. Copyright © American Association for Aerosol Research

Influence of carrier gas flow rate, laser repetition rate, and fluence on the size distribution and number of nanoparticles generated per laser shot during paint laser ablation

This study focuses on the influence of three operating parameters (gas flow rate, laser repetition rate, and fluence) on the number and size distributions of nanoparticles generated by laser ablation of acrylic paint. These particles, produced by gas-to-particle conversion of vapors generated by polymer vaporization, can have a spherical shape with a 16 nm diameter (called primary particles) but most of them are aggregated primary particles. The most critical parameter is the gas (air) flow rate in the ablation cell. Indeed, the total number of nanoparticles produced per shot increases with the air flow rate, whereas the aggregate size decreases. Indeed, the gas flow rate controls the transit time and the related aggregation duration, which decrease with increasing flow rates. The influence of the air flow rate on the nanoparticle total number produced per shot can be attributed to the evolution of the particle residence time in the setup with the flow rate. In order to validate this point, the setup has been modeled (model based on the Smoluchowski coagulation equations). The model has shown that the primary particle aggregation mainly takes place in a sphere of a few millimetres in diameter. This sphere varies in volume with the laser fluence but does not depend on the air flow rate in the cell. Moreover, the nanoparticle final number per shot does not depend on the primary particle initial number per shot but only on the size of the interaction volume, which is related to laser fluence. Copyright © American Association for Aerosol Research

LIBS application in Joint European Torus

International audienceWe present here the results on the first successful application of LIBS for remote in situ diagnostics of PFC in Joint European Torus (JET), the biggest European tokamak (operating with D/T mixture, Be-chamber walls). LIBS in situ application in JET has required a thorough preliminary optimisation and careful adjustment of LIBS interaction parameters, and both optical and detection systems to satisfy the following conditions 10-meter remote measurements; limited apertures of optical windows and mirrors; high vacuum; tritium and Be environments; a very low repetition rate laser; non-accessible interaction zone; limited time for LIBS experiments authorised by JET. LIBS feasibility was demonstrated with JET EDGE LIDAR laser system (a Ruby laser, 3 Joules/pulse, 690 nm wavelength, 300 ps pulse duration, up to 70 GW/cm2 intensity, 1 shot per 5 minutes). A number of analytical spectral lines of D/T, C II, Cr I, W I and Be II in 400-670 nm spectral range were identified. With the increase in the number of the laser shots applied onto a divertor zone (a DL on tungsten-substrate), the spectral line intensities of D/T and from impurities (Cr I, Be II) were decreasing, while the W-spectral lines were appearing in the spectrum. The obtained results and some principal considerations on laser and spectrometer parameters for LIBS in situ application in the modern thermonuclear installations (JET, WEST, ITER), and also particular features of tritium cartography will be presented and discussed

Heating and ablation of tokamak graphite by pulsed nanosecond Nd-YAG lasers

International audienceThe results on laser heating and ablation of graphite tiles of thermonuclear tokamaks are presented. Two pulsed Nd-YAG lasers (20 Hz repetition rate, 5 ns pulse duration and 10 kHz repetition rate, 100 ns pulse duration) were applied for ablation measurements. The ablation thresholds (1.0$\pm$0.5 J/cm$^2$ for 5 ns and 2.5$\pm$0.5 J/cm$^2$ for 100 ns laser pulses) were determined for the Tore Supra tokamak graphite tiles (backside) nonexposed to plasma. The high repetition rate Nd-YAG laser (10 kHz, 100 ns pulse duration) and the developed pyrometer system were applied for graphite heating measurements. Some unexpected features of laser heating of the graphite surface were observed. They were explained by the presence of a thin surface layer with the properties different from those of the bulk graphite. The theoretical models of laser heating and near-threshold ablation of graphite with imperfectly adhered layer were developed to interpret the experimental results

Laser induced breakdown spectroscopy application in joint European torus

International audienceThe results on the first successful application of Laser Induced Breakdown Spectroscopy (LIBS) for remote in situ diagnostics of plasma facing components (a deposited layer on a divertor tile) in Joint European Torus (JET) are presented. The studies were performed with an available JET EDGE LIDAR laser system. For in-depth analysis of deposited layers on JET divertor tiles, a number of laser shots were applied onto the same divertor place without laser beam displacement. The spectral lines of D, CII and impurity elements (CrI, BeII, …) were identified in a wide spectral range (400-670 nm). With the increase in a number of laser shots applied onto the same divertor place, we observed consecutive changes in spectral line intensities of deuterium, carbon, and impurities with the appearance of spectral lines of tungsten substrate (WI). In-depth analysis of deposited layers on JET divertor tiles was made on the basis of the spectral line behaviour in reference to the applied laser shots. The possibility of surface cartography with laser beam displacement on the tile surface was demonstrated as well. Based on the results obtained, we may conclude that LIBS method is applicable for in situ remote analysis of deposited layers of JET plasma facing components

IN SITU TRITIUM MEASUREMENTS AND CONTROL BY LASER TECHNIQUES

International audienceIn this paper, in situ tritium measurements and control by laser techniques are presented. It is proposed to use Laser-Induced Breakdown Spectroscopy (LIBS) as an efficient technique to measure the tritium concentration in ablated material. However, LIBS could be limited due to material melting observed during ablation possibly leading to hydrogen losses. Laser ablation is shown to be an efficient process to recover the in vessel tritium if the dust produced during ablation is collected. This could be forbidden if ITER cannot be operated at high pressure. To overcome this difficulty and detritiate remote surfaces, laser heating could be applied since it generates gaseous compounds. However, inward diffusion could be expected leading to burry tritium in bulk material which is a counterproductive action. Finally, all these techniques must be embarked on remote handling system in order to explore and treat large surfaces. Obviously, this carrier is needed for a reliable and an efficient operation of the ITER nuclear facility

DASIE Analytical Version: A Predictive Tool for Neutrons, Protons and Heavy Ions Induced SEU Cross Section

International audienceThis paper presents the new detailed analysis of the secondary ion effect analytical version that allows fast and accurate calculation of neutron, proton and heavy ion cross sections in SRAM based memories. The advantage of this new version is a better determination of the input parameters using heavy ion data. A validation is presented by comparing simulation results with experimental data for technology from 600 to 180-n