Key Technology Study Of High Performance RF Sliding Contact For ITER ICRH Antenna

ICRH is one of the most important heating methods for tokamaks, and on ITER,there are two ICRH antennas designed that will supply about 40MW heating power to ITER plasma. In order to improve the maintainability of the antennas as well as to absorb the thermal expansion of the RF conductor during operation, RF sliding contacts are designed on the RF transition lines. Before the operation of the ITER ICRH antennas, all the in-vessel structures will be baked at 250? during a long time for outgassing. And one of the RF contacts is designed to be operated at 2kA with a current density of 4.6 kA/m, which induces large heat deposition on the RF contact area and causes melting failure of the RF contact louver at last. In CEA, the R&D work towards RF contact development has been carried out for 10 years, and 600s operation at 2kA was achieved. There is still large gap between the current experimental results and the ITER design requirements (1200s @ 2kA). In order to support the next R&D stage of the RF sliding contacts, in this research, the failure mechanism of the RF contact during RF operation was deeply analyzed and the possible materials that can be used for RF sliding contacts manufacturing were well studied.Firstly, the TITAN test bed was updated for the new R&D campaign and the upgraded LA-CUT contact was tested on it. Based on the material characterizations,the diffusion between Ag coating to the CuCrZr substrate was verified. The thermal analysis model of the RF sliding contact was developed and based on the FEM analysis, the effects of material selection, cooling parameter and contact resistance to the operation temperature on the RF sliding contact louvers were researched.Secondly, based on the general electrical contact functional coatings like Ag,Au and Rh, alloy coatings were achieved by electroplating on 316L and CuCrZr,which are commonly used as base materials on tokamak. By mimicking the ITER ICRH RF contacts operation conditions, the coated samples were thermal aged under vacuum at 250? for 500h, after which the materials properties changes such as hardness,grain size and attachment force were characterized. In addition,the coatings, life time was evaluated through the diffusion characterizations.Thirdly, in order to carry out the electrical and tribological study towards the coating material pairs, a dedicated and innovative test bed was designed and developed successfully. On this test bed the samples can be heated up to 350 ? and the vacuum can reach to 10-5Pa. Static contact resistance as well as transient contact resistance/coefficient of friction of sliding pairs can be obtained on this test bed.Lastly, on the dedicated multi-functional test bed, the sliding tests and electrical tests of Ag/Rh, Au-Ni/Rh and 316L/CuCrZr were carried out. The relationships between vacuum condition, temperature and contact force to the static contact resistance were studied and the optimal contact force was selected. Under the optimal contact force, the sliding tests were launched and the evolutions of coefficient of friction as well as contact resistance were obtained. Through wear characterizations, the life times of the coatings were evaluated.