A frictionless steering mechanism for the Front Steering ECCD ITER Upper Port Launcher

Abstract

Abstract-A FS launcher is being designed for the ITER upper port, which offers enhanced physics performance over the RS launcher. A two mirror system is used to decouple the focusing and steering aspects of the launcher and provide a relatively small beam waist (<20mm) projected far into the plasma (>1.6m from the steering mirror). The resulting NTM stabilization efficiency (maximum CD density divided by the local bootstrap current > 1.6) is above marginal for the q=2 and 3/2 rational flux surfaces of the relevent ITER equilibria (scenarios 2, 3a and 5) and a factor of ~3 relative to an equivalent RS launcher. The performance of the FS launcher strongly depends on the reliability of the steering mechanism, which is used to rotate the plasma facing steering mirror. CRPP has designed a frictionless steering mechanism assembled in a compact cartridge capable of up to ±7˚ rotation (corresponding to a poloidal steering range of up to ±14˚ for the microwave beam around a fixed axis of rotation) that offers a high operation reliability despite the close proximity to the thermal and neutron flux coming from the ITER plasma.

Progress on the ITER H&CD EC Upper Launcher Steering-Mirror Control System

“…Two flexure pivots are used instead of traditional bearings, making the mechanism friction free, eliminating stick slip and backlash, and avoiding cold welding and other in-vessel tribological difficulties [14], [22], [23].…”

Preliminary Control-Oriented Modeling of the ITER Steering Mirror Assembly and local control system in the Electron Cyclotron Heating &amp; Current Drive actuator

“…Development of the control system can be found in [4] and [5]. Latest thermal characterization can be found in [6] and further details can be found in [7] and [8]. Final design review is expected for next year, this implying that the current design is not written in stone and could still be subject to change.…”

Progress on the ITER electron cyclotron heating and current drive upper launcher steering mirror control system

“…Two flexure pivots are used instead of traditional bearings, making the mechanism friction free, eliminating stick-slip and backlash avoiding cold welding and other in-vessel tribological difficulties [9], [10], [6].…”