Advanced ICRF Antennas for Fusion Energy Devices

Abstract Ion cyclotron range of frequency (ICRF) power is anticipated to be a primary auxiliary heating source in next step tokamak experiments like ITER. From a technological perspective, electrical breakdown is a significant challenge for ICRF utilization in present experiments and will become more challenging for future devices like ITER and other reactors. An ICRF system utilizes an antenna to couple power to the plasmas. Current antennas use materials with high conductivity, like copper, where the copper has been deposited onto a structural material like Inconel 625 or stainless steel. However, coppers low melting temperature and deteriorating mechanical properties at elevated temperatures result in electrical breakdown of the antenna and strong material displacement. ICRF antenna performance could be significantly improved by replacing the copper coating with a refractory metal such as tungsten. During this investigation, innovative coating techniques are being developed to enable the deposition of dense, high purity, well-adhered tungsten coatings on ICRF antennas. Testing of tungsten coatings produced during the Phase I effort has shown considerable promise. For example, electrical breakdown testing of tungsten coated samples at MIT has shown up to a 35% improvement in power handling capability as compared to copper reference samples with a similar surface finish. During Phase II, the tungsten coatings will be optimized and a tungsten coated ICRF antenna will be produced and tested in Alcator C-Mod to determine antenna performance in a tokamak environment. The antenna & apos;s voltage and power limits under various conditions will be characterized and compared to a traditionally copper coated antenna. Commercial Applications and Other Benefits: The development of dense, well-bonded refractory metal coatings on Inconel and stainless steel substrates will enable the fabrication of advanced ICRF antennas. Other applications that will benefit from the technology to be developed include aerospace, defense, propulsion, power generation, semiconductor, crucibles, heat shields, x-ray and sputtering targets, wear and corrosion protection coatings.