Session CI2B - Plasma Technology for Magnetic Confinement.
INVITED session, Monday afternoon, November 15
Room Chatham C, SCC
An important goal of Ion Cyclotron Range of Frequencies (ICRF) technology development is to improve launcher performance in target plasmas with dynamic edge conditions, such as during ELMy H-mode operation. For these plasmas, the antenna resistive loading can increase by an order of magnitude during the short ELM time, resulting in sudden mismatches and RF power trips. Current efforts are being directed toward providing load-tolerant ICRF launchers to accommodate the sudden mismatches produced by the ELMs. Antenna feed circuits are modified to feed paired elements or groups of elements whose outputs are combined so that impedance changes caused by plasma transients cancel each other. This was first accomplished by the use of hybrid power splitters on DIII-D and ASDEX-U. A newer approach is the conjugate-tee concept, in which tuning elements in the feedlines to an antenna pair fed by a tee are adjusted to give imaginary admittance cancellation at the tee. Initial tests on several devices are quite promising, and recent results on JET show excellent high power coupling in the presence of large ELMs. The 2001 reference design for the ITER antenna employs this concept. In addition to the impedance change, ELMs can produce changes in the plasma edge near the antenna that can enhance electrical breakdown. In this paper, the advances that have been made in the development of robust, load tolerant ICRF launchers are reviewed and their relevance to ITER discussed.