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International audience; The present paper deals with the thermal characterization of the Surface Carbon Layer (SCL) usually poorly attached to the Plasma Facing Component (PFC) inside the nuclear fusion machines (Tokamak). A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to characterize in situ the time variation of the thermal resistance Rh of a surface layer. A numerical feasibility is presented with a realistic virtual experiment design. The accuracy of the method is examined by using simulated exact and inexact infrared measurements obtained on the SCL surface. The advantages of applying the CGM with the adjoint state in the present study, are that no prior information is needed on the time variation and the initial guess of the unknown thermal resistance. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; The present paper deals with the surface heat flux estimation with embedded thermocouples (TC) in a Plasma Facing Component (PFC) of the WEST Tokamak. A 2D nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time evolution of the heat flux amplitude and decay length lambda_q. The method is applied on different synthetic measurements in order to evaluate the accuracy of the method. The synthetic measurements are generated with realistic values of lambda_q and magnitudes as those expected for ITER.

International audience; The present paper deals with the heat flux estimation and the thermal characterization of the poorly attached Surface Carbon Layer (SCL) to the Plasma Facing Component (PFC) observed on the inner vertical tiles of the JET Tokamak. A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time variation of the heat flux necessary to characterize in situ the space and time variations of the thermal resistance Rth of the SCL. The method is applied on L mode power step plasma discharge (#58850). One embedded thermocouple (TC) is used to the heat flux estimation (another embedded TC is used for validate the estimation) and infrared (IR) measurements coming from the IR camera KL3 are used to estimate the SCL thermal resistance. The estimated SCL thermal resistance is compared to the history of the strike point location to highlight the correlation between the spatial distribution of the SCL thermal resistance and the location of the maximum heat flux.

The components used in fusion devices, especially high heat flux Plasma Facing Components (PFC), have to withstand heat fluxes in the range of 10–20 MW/m2. So, they require high reliability which can be only guaranteed by accurate Non Destructive Examinations (NDE). The SATIR test bed operating at Commissariat a l’Energie Atomique (CEA) Cadarache performs NDE using transient infrared thermography sequence which compares the thermal response of a tested element to a Reference element assumed to be defect free. The control parameter is called DTref max. In this paper, we present two innovative image processing techniques of the SATIR signal allowing the qualification of a component without any Reference element. The first method is based on a spatial image autocorrelation and the second on the resolution of an Inverse Heat Conduction Problem (IHCP) using a BEM (Boundary Element Method) technique. After a validation step performed on numerical data, these two methods have been applied to SATIR experimental data. The results show that these two techniques allow accurate defect detection, without using a Reference tile. They can be used in addition to the DTref max, for the qualification of plasma facing components.

This paper summarizes the results of experimental and numerical studies concerning boiling heat transfer inside vertical minichannels. The objective here is to provide basic knowledge on the systems of biphasic cooling in minichannels for several gravity levels (μg, 1g, 2g). To fully understand the high heat transfer potential of boiling flows in microscale’s geometry, it is vital to quantify these transfers. To achieve this goal, an experimental device has been set up and in order to study the influence of gravity, the device has been embarked on board A300 Zero-G to make Parabolic Flights experiments. Analysis is made up by using an inverse method in order to estimate the local heat coefficient while boiling occurs inside a minichannel. The results concern two-phase flow during convective boiling and this investigation leads to solve an inverse heat conduction problem (IHCP). The estimation consists in inversing experimental data measurements located in the heating rod of our experiment to obtain the wall temperature and the heat flux on the minichannel surface. Images and video sequences have been performed with a high speed camera. The experiments are conducted with HFE-7100 as this fluid has a low boiling temperature at the cabin pressure of the A300. This choice was governed by the capillary length which is 4.3 mm in microgravity (0.05 m.s). The experimental loop allows the control of the heat flux and the liquid flow rate for three hydraulic diameters (DH): 0.49 mm; 0.84 mm and 1.18 mm. The influence of three different parameters on the heat transfer coefficient are carried out: the gravity level, the Reynolds number and the vapor quality. First results show that whatever the gravity level, the local heat transfer decreases sharply from the inlet to the outlet channel. In the annular slug regime, the average heat transfer is found around 6000 W.m.K and we observe that the heat transfer coefficient is higher in microgravity (30 %) compared to normal and hypergravity conditions.

This study is concerned with supercritical Benard–Marangoni flows of a high Prandtl number (Pr≈4000) fluid in cylinders of small to medium aspect ratio, 5⩽A⩽10. Laboratory experiments and numerical simulations, handled with an accurate spectral solver of the unsteady three-dimensional Boussinesq equations, are used to get a good understanding of the flow behavior. Experimental and numerical results are successively presented and then discussed. The confinement effects are especially pointed out and carefully analyzed.

This paper deals with an inverse problem which consists in the location identification of multiple-line heat sources placed in an homogeneous solid in the stationary case. The location and strength of the line heat sources are unknown. The identification procedure is based on the boundary integral formulation using Green functions. The discretized problem is non-linear if the location of the line heat sources is unknown. In order to solve the problem we use an iterative procedure to minimize a quadratic norm. The proposed numerical approach is applied to an experimental 2D example using measurements provided by an infrared scanner. The number of line heat sources is supposed to be known but we give some examples involving a number of sources superior or inferior to the real number.

International audience; The present paper deals with a nonlinear unsteady heat flux calculation in the case when measurements are provided by only one thermocouple (TC) embedded in the material and the spatial shape of the unknown surface heat flux is given. This inverse problem is solved with the Conjugate Gradient Method (CGM) combined with the adjoint state, the direct problem being solved with the finite element method. This heat flux estimation technique is illustrated in the case of the plasma facing components located in the JET tokamak divertor that can be exposed to several MW m(-2) during more than 10 s. In those tiles, few embedded thermocouples (TC) located 1 cm below the tile surface are used to measure the bulk temperatures of the Carbon Fiber Composite (CFC) composite tiles (which are coated with 14 mu m of tungsten for the International Thermonuclear Experimental Reactor (ITER) like wall). A numerical study is first presented in order to validate the heat flux calculation and to study the accuracy of the method. Then experimental data from a recent shot with the ITER-like wall configuration are used in the heat flux calculation presented here. Results are compared with those obtained with the deconvolution technique in the linear case, on a simplified geometry of the tiles. (c) 2013 EURATOM. Published by Elsevier B.V. All rights reserved.

International audience; Internal components of magnetic confinement fusion machines are subjected to significant heat fluxes. A large part of this power is directed towards plasma facing components. Even if these components are designed to receive about, surface temperature and heat flux measurements are important issues to guarantee safe plasma operations. In JET tokamak, few embedded thermocouples (TC) located 1 cm below the tile surface are used to measure the bulk temperatures of the Carbon Fiber tiles (coated with about 20m of tungsten with the ITER-like wall). We propose here to use an inverse thermal calculation based on Thermal Quadrupole method to locally deduce the deposited heat flux. The calculation requires the location of the peak and the normalized 1D-shape of the heat flux deposited on the target.

In fusion devices, like Tore Supra, the surface temperature of the carbon plasma facing components (PFC) is measured by standard infrared (IR) system in real time for control of integrity of PFCs. The emissivity of carbon is known and high (e~0.8-0.9) and therefore the contribution of the reflected flux in the total flux collected can be neglected. For future tokamaks like WEST and ITER, PFCs will be in metal (Be/W) with low and variable emissivities (e~0.1-0.4). Consequently, the surface temperature measurement will become challenging due to low emissivity and non-negligible reflected fluxes. The pulsed active pyrometry proposed in this paper allows a punctual surface temperature measurement independently of the emissivity and the reflected fluxes. Experimental results for aluminium and tungsten samples are reported. In addition it is shown that using the local measurement by active pyrometry, an overall 2D standard IR perturbed by a reflected flux can be corrected to recover the full 2D real surface temperature.

International audience; In fusion devices like ITER, plasma facing components will be in metal, (Tungsten and Beryllium), with emissivity in the range of 0.1-0.4. Therefore, surface temperature monitoring by infrared system will become more challenging due to low emissivity and consequently non negligible reflected flux. The active pyrometry method proposed in this paper allows surface temperature measurements independently of reflected and parasitic fluxes. A local increase of the surface temperature (ΔT(t)~10 °C) introduced by a transient heating source (pulsed or modulated) results in an additional component of the flux collected by the detector. A filtering of the signal allows extracting a temporal flux proportional only to the variation of the emitted flux. The ratio of simultaneous measurements at two wavelengths allows solving the unknownemissivity (same as for classical bicolour pyrometry). In this paper, it is described how the active pyrometry method is adapted to the surface temperature measurements of metallic PFCs independently of the reflected fluxes. Experimental results for carbon and tungsten samples are reported. Finally, it is shown how, by using the active pyrometry, the overall 2D standard IR perturbed by a reflected flux is corrected to recover the full 2D surface temperature close to the real surface temperature.

6th European Thermal Sciences Conference (Eurotherm), Poitiers, FRANCE, SEP 04-07, 2012; International audience; We present here the numerical feasibility of using two thermal diagnostics (IR, surface and embedded thermocouple temperature measurements), that outfit the same carbon tile inside the JET Fusion reactor and whose combination enables to identify, on one hand, a surface heat flux history and, on the other hand, the spatial and time variation of the thermal resistance of an unknown deposited surface carbon layer (SCL). The Conjugate Gradient Method (CGM) and the adjoint state were applied to perform these two identifications.

International audience; Drop evaporation is a basic phenomenon but the mechanisms of evaporation are still not entirely clear. A common agreement of the scientific community based on experimental and numerical work is that most of the evaporation occurs at the triple line. However, the rate of evaporation is still predicted empirically due to the lack of knowledge of the governing parameters on the heat transfer mechanisms which develop inside the drop under evaporation. The evaporation of a sessile drop on a heated substrate is a complicated problem due to the coupling by conduction with the heating substrate, the convection/conduction inside the drop and the convection/diffusion in the vapor phase. The coupling of heat transfer in the three phases induces complicated cases to solve even for numerical simulations. We present recent experimental results obtained using an infrared camera coupled with a microscopic lens giving a spatial resolution of 10 mu m to observe the evaporation of sessile drops in infrared wavelengths. Three different fluids fully characterized, in the infrared wavelengths of the camera, were investigated: ethanol, methanol and FC-72. These liquids were chosen for their property of semi-transparency in infrared, notably in the range of the camera from 3 to 5 mu m. Thus, it is possible to observe the thermal motion inside the drop. This visualization method allows us to underline the general existence of three steps during the evaporating process: first a warm-up phase, second (principal period) evaporation with thermal-convective instabilities, and finally evaporation without thermal patterns. The kind of instabilities observed can be different depending on the fluid. Finally, we focus on the evolution of these instabilities and the link with the temperature difference between the heating substrate and the room temperature. (C) 2010 Elsevier Inc. All rights reserved.

The main results of the Tore Supra experimental programme in the years 2007–2008 are reported. They document significant progress achieved in the domain of steady-state tokamak research, as well as in more general issues relevant for ITER and for fusion physics research. Three areas are covered: ITER relevant technology developments and tests in a real machine environment, tokamak operational issues for high power and long pulses, and fusion plasma physics. Results presented in this paper include test and validation of a new, load-resilient concept of ion cycotron resonance heating antenna and of an inspection robot operated under ultra-high vacuum and high temperature conditions; an extensive experimental campaign (5 h of plasma) aiming at deuterium inventory and carbon migration studies; real-time control of sawteeth by electron cyclotron current drive in the presence of fast ion tails; ECRH-assisted plasma start-up studies; dimensionless scalings of transport and turbulence; transport experiments using active perturbation methods; resistive and fast-particle driven MHD studies. The potential role of Tore Supra in the worldwide fusion programme before the start of ITER operation is also discussed.

On the limiter of Tore Supra, the heat loads map computed from deconvolution of IR surface temperatures shows good agreement with calorimetry measurements. This experimental heat pattern allows deducing the heat fluxes in the scrape-off layer using a 3D magnetic calculation and assuming only parallel heat transport along field lines. This calculation leads to an underestimation of the power circulating in the edge plasma according to the power balance, similarly to RFA measurements. The comparison between experimental heat loads on the limiter and modelling also shows a spreading of heat fluxes near the LCFS that cannot be explained only by parallel transport in the SOL.

This paper presents several 2D heat flux calculation methods applied to temperature data of one of the most exposed plasma facing components of the JET tokamak. We have two temperature diagnostics: a high time resolution infrared system is used to measure the surface temperature and two embedded thermocouples to measure the temperature in the bulk at 1 cm depth from the surface. A direct calculation is possible using the surface temperature but the presence of thin carbon layers disturb the measurements and leads us to make an inverse computation of the heat flux using the thermocouple data.

A boundary element approach is used to solve inverse heat conduction problems in multidimensional and nonlinear situations. In stationary and transient cases, discretized boundary integral equations are expressed and, to obtain satisfying results, are associated with regularization procedures over space and time (transient case). The efficiency of the method, which depends on the accuracy of the measurements, is explored through an example of transient bidimensional application. A comparison with the superposition method (linear problems) is presented.

We give here a short overview of the status of the development for ITER thermography as performed by the CEA‐Cadarache and some of its collaboration partners. The topics that have been included in this synthesis are the status of the optical design, the role of multi‐wavelength mesurements, multicolour pyroreflectometry, photothermal methods, and reflection simulations and measurements.

International audience; In the course of the development of a concept for a spectrally resolving thermography diagnostic for the ITER divertor using optical fibres experimental development work has been carried out in three different areas. Firstly ZrF4 fibres and hollow fibres (silica capillaries with internal AG/AgJ coating) were tested in a Co60 irradiation facility under c irradiation up to doses of 5 kGy and 27 kGy, respectively. The ZrF4 fibres suffered more radiation induced degradation (>1 db/m) then the hollow fibres (0–0.4 db/m). Secondly multi-colour pyroreflectometry is being developed towards tokamak applicability. The emissivity and temperature of tungsten samples were measured in the range of 700–1500 degC. The angular working range for off normal observation of the method was 20–30deg. The working distance of the method has been be increased from cm to the m range. Finally, encouraging preliminary results have been obtained concerning the application of pulsed and modulated active thermography.

International audience; This paper deals with an inverse problem which consists of the experimental identification of line heat source strength in an homogeneous solid using temperature measurements. An inverse formulation using the boundary element method, is used to identify the strength of line heat sources. In the case of multiple sources identification the location is assumed to be known but, in the case of a single source, an iterative algorithm for the location identification is proposed. The experiment consists of the identi®cation of the power dissipated by Joule effect in one or two thin wires placed in a long square section cement bar. The measurements necessary to solve the inverse problem are provided by thermocouples for the internal temperatures and by infrared thermography for the superficial temperatures. A time regularization procedure associated to future time steps is used to correctly solve the ill-posed problem.

Two-phase and boiling flow instabilities are complex, due to phase change and the existence of several interfaces. To fully understand the high heat transfer potential of boiling flows in microscale's geometry, it is vital to quantify these transfers. To perform this task, an experimental device has been designed to observe flow patterns. Analysis is made up by using an inverse method which allows us to estimate the local heat transfers while boiling occurs inside a microchannel. In our configuration, the direct measurement would impair the accuracy of the searched heat transfer coefficient because thermocouples implanted on the surface minichannels would disturb the established flow. In this communication, we are solving a 3D IHCP which consists in estimating using experimental data measurements the surface temperature and the surface heat flux in a minichannel during convective boiling under several gravity levels (g, 1g, 1.8g). The considered IHCP is formulated as a mathematical optimization problem and solved using the boundary element method (BEM).

Équipe 107 : Physique des plasmas chauds; International audience; In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented.

The objective is to provide a method to obtain local heat transfer coefficients in small channels when flow boiling occurs. The experimental device has been developed to perform investigations in parabolic flights campaigns on board A300-ZeroG. Simultaneously flow visualization and thermo-hydraulic measurements are carried out to investigate the two phase flow and heat transfer in minichannels. The experiments are conducted with HFE-7100 in several operating conditions for three hydraulic diameters.

The experiment detailed in this paper presents results obtained on the nucleation, growth and detachment of HFE-7100 vapor bubbles confined in a two-dimensional plane created on an artificial nucleation site. The experiments were performed by varying the shear flow and the bubble nucleation rate through the heat flux supplied under normal gravity and microgravity. The distance between the plates was kept constant at 1 mm. The first results of these experiments are mainly related to the formation of a bubble on an isolated site with or without convection and to the associated heat transfer when confinement is imposed on a bubble. To this effect, we implemented an experimental device allowing the observation of the flow by means of both a visible video camera and an infrared video camera. Here, we present the first results obtained from the campaign performed in December 2007 concerning the influence of gravity on the bubble detachment diameter and the first images of 2D bubbles obtained in microgravity by means of an infrared camera.Copyright © 2008 by ASME

International audience; In nuclear fusion devices, such as Tore Supra, the plasma facing components (PFC) are in carbon. Such components are exposed to very high heat flux and the surface temperature measurement is mandatory for the safety of the device and also for efficient plasma scenario development. Besides this measurement is essential to evaluate these heat fluxes for a better knowledge of the physics of plasma-wall interaction, it is also required to monitor the fatigue of PFCs. Infrared system (IR) is used to manage to measure surface temperature in real time. For carbon PFCs, the emissivity is high and known (epsilon similar to 0.8), therefore the contribution of the reflected flux from environment and collected by the IR cameras can be neglected. However, the future tokamaks such as WEST and ITER will be equipped with PFCs in metal (W and Be/W, respectively) with low and variable emissivities (epsilon similar to 0.1-0.4). Consequently, the reflected flux will contribute significantly in the collected flux by IR camera. The modulated active pyrometry, using a bicolor camera, proposed in this paper allows a 2D surface temperature measurement independently of the reflected fluxes and the emissivity. Experimental results with Tungsten sample are reported and compared with simultaneous measurement performed with classical pyrometry (monochromatic and bichromatic) with and without reflective flux demonstrating the efficiency of this method for surface temperature measurement independently of the reflected flux and the emissivity. (C) 2014 AIP Publishing LLC.

La réfrigération secondaire permet de réduire drastiquement la quantité de frigorigène (à fort potentiel de réchauffement global), et donc les fuites. Les coulis d’hydrate transportent de la chaleur latente délivrée à une température qui peut être adaptée à l’utilisation. Cette étude évalue l’influence de la cinétique du changement de phase sur les performances énergétiques du procédé, et analyse les couplages et les paramètres pilotant cette influence. Les calculs comparent les coulis de glace et d'hydrates de tetra-n-butylphosphonium bromide et expliquent leurs différences de comportement.