H. Roche

Infrared surface temperature measurement for long pulse real time feed-back control in an actively cooled machine

Tore-Supra is an actively cooled machine aiming at long pulse operation. Surface temperature measurements are necessary in this context to achieve a real time feed-back control on plasma parameters, as well as auxiliary heating systems. Safety interlock is also mandatory when using such actively cooled elements to prevent any damage due to overheating by the plasma, or a loss of active cooling. As an example, it will be shown how the actively cooled pump limiters test campaign has been conducted. The CIEL project for Tore-Supra is aimed at replacing the old generation of plasma facing components designed in 1984, by new ones with a full coverage of the inside vessel. A set of dedicated infrared systems will be used to measure the surface temperatures. They will be included in the real time feed-back loop control and the safety system.

Surface temperature measurements on Tokamak target plates with two types of infra red fibres

Abstract Tore Supra has chosen to protect the most heavily solicited and actively cooled target plates by thermography using optical fibres. In consequence to previous experience [J. Nucl. Mater. 290–293 (2001) 701], the prototype periscope for the 2001 experimental campaign was equipped not only with silica fibres but also with a ZrF 4 fibre, transparent up to 4 μm. As then, the measurements in the mid infrared range give lower temperatures than the ones in the near infrared range. The silica fibres are more robust and easier to calibrate, which may justify to use both types side by side using a cross calibration formula. Measurements with an silica fibre embedded in the interior of the target plate exhibited only during discharges with LHCD heating sufficient signal levels to be spectrally analysed. Under these conditions the same kind of additional near infrared radiation as on the silica fibres looking at the exterior of the target plates was observed.

Deposited layer removal by laser ablation: from laboratory to Tore Supra integration

In-vessel carbon layer removal by using laser ablation is for the first time presented here. However, prior to these tests, careful virgin carbon fiber composite (CFC) tile studies were carried out in order to determine the bulk ablation threshold fluence. Then, laser ablation was applied to Tore Supra at a laser fluence below that value in order to protect the bulk material. It is shown that layers of up to 50 μm are easily removed. Use of several metrology techniques such as confocal microscopy and IR measurements enabled the local determination of the deposited material, confirmation of the layer removal and determination of the depth of the layers removed. Within the accuracy of these measurements, the bulk has not been eroded.

2D surface temperature measurement of plasma facing components with modulated active pyrometry

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 (ɛ ∼ 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 (ɛ ∼ 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.

Surface temperature measurement of plasma facing components with active pyrometry

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 unknown emissivity (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.

Measurement methods associated to laser ablation technique in layer removal process on Plasma Facing Components

During tokamak operation, Plasma Facing Components (PFC) are exposed to high heat load from plasma radiation and particle overflow. Thus, materials forming the PFC armor are eroded in high flux areas and deposited in low flux areas, in form of layers, more or less thick and sticky. These layers can pollute the plasma discharge, and above all trap a part of the plasma hydrogen isotopes (deuterium or tritium). For safety reasons, the in vessel tritium inventory is limited and it is essential to control and/or to develop methods for removing the tritium trapped in the vessel walls. Laser ablation techniques are well suited to achieve this goal.

Surface temperature measurement of plasma facing components with pulsed active pyrometry

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 (ε~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 (ε~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.

Concept And Development Of Instruments For ITER Thermography

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.