Finalization of the conceptual design of the remote steering ECH launcher for ITER

Abstract

The design of a remote steering (RS) variant of the electron cyclotron heating (ECH) upper port launcher (UPL) for neo-classical tearing mode (NTM) stabilization in ITER is being finalised. The RS variant is the fall-back option for the reference design, which is a front steering (FS) UPL. This paper presents the changes made in the design of the RS UPL with respect to the previous baseline (the October 2005 baseline) design. The changes are motivated by a demand to improve the reliability of the launching system by solving a number of pressing issues. To accomplish this, a reduction in the steering range of the launcher was proposed. This reduction yields more tolerable head loads on the focusing elements for a given performance. Modifications of the launcher layout allow for an increase of the toroidal injection angle, which improves the NTM stabilization efficiency. A mode converter can reduce the stray radiation in the vicinity of the steering mechanism down to tolerable levels. Abandoning the concept of the mini-duct leads to a reduction of stray radiation concerns and allows for the implementation of improved alignment facilities of the individual steerable mirror units. The work shows that a launcher based on the RS principle is feasible. This launcher can be made reliable, flexible and easily accessible for maintenance purposes accepting the consequent limitations in the achievable steering range inside the ITER plasma.