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The fusion machines under development or construction (ITER, W7X) use several hundreds of actively cooled plasma facing components (ACPFC). They are submitted to leak tightness requirements in order to get an appropriate vacuum level in the vessel to create the plasma. During the ACPFC manufacturing and before their installation in the machine, their leak tightness performance must be measured to check that they fulfill the vacuum requirements. A relevant procedure is needed which allows to segregate potential defects. It must also be optimized in terms of test duration and costs. Tore Supra, as an actively cooled Tokamak, experienced several leaks on ACPFCs during the commissioning and during the operation of the machine. A test procedure was then defined and several test facilities were set-up. Since 1990 the tightness of all the new ACPFCs is systematically tested before their installation in Tore Supra. During the qualification test, the component is set up in a vacuum test tank, and its cooling circuits are pressurized with helium. It is submitted to 3 temperature cycles from room temperature up to the baking temperature level in Tore Supra (200 °C) and two pressurization tests are performed (6 MPa at room temperature and 4 MPa at 200 °C) at each stage. At the end of the last cycle when the ACPFC is at room temperature and pressurized with helium at 6 MPa, the measured leak rate must be lower than 5 × 10 −11 Pa m 3 s −1 , the pressure in the test tank being −5 Pa. A large experience has been gained on ACPFCs with carbon parts on stainless steel and CuCrZr structures (toroidal pumped limiter (TPL) composed of 12 sectors of 48 fingers) but also on all metallic ones (ICRH antennas and LHH launchers, vacuum vessel protection walls ∼60 m 2 ). During the tests, some leaks were found and the components had to be repaired. The analysis of the results database allows defining guidelines to optimize the presently used procedure for the new ACPFCs generation which will be set-up in WEST or ITER (tungsten (W) elements, high mass components). This paper presents the experience of the Tore Supra teams in the implementation of ACPFC with regard to the tightness issues including the tests procedures which were developed and used since 1990. The prospects for the new generation actively cooled machines are also discussed. |
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