Low Power Tests on the New Front Steering EC Launcher for FTU

A new electron cyclotron (EC) antenna for real time control experiments on FTU tokamak has been tested at IFP-CNR laboratory. mm-Wave characterization was performed at the operating frequency of 140 GHz with low power measurements, primarily to test the internal optics of the launcher in terms of focusing properties and beam directivity. The antenna is devoted to the injection of high power EC waves in different working configurations using a front steering setup. The beam direction is controlled with a fast mirror (steerable both toroidally and poloidally) and the available launching angles have been determined to fix the steering mirror working space. Beam dimension can also be controlled, using a sliding structure in the plug-in system, equipped with a focusing mirror that provides zooming capabilities. This paper contains results of low power tests performed on the antenna in order to characterize the launcher in its quasi-optical design. Beams are found to be slightly astigmatic (maximum ratio w(y)/w(x) = 1.1) and with an expected beam radius in the plasma ranging from 18.6 to 26.0 mm due to cited zooming effects. Additional beam patterns and linear scans of the launched mm-wave power for different injection angles have been measured, in some cases in realistic conditions (using a mock-up of the FTU port provided with metallic side-walls) to evaluate diffraction and beam truncation effects. (C) 2011 EURATOM ENEA - CNR - Association/Instituto di Fisica del Plasma. Published by Elsevier B.V. All rights reserved.