In-vessel piezoelectric actuation system for DTT ECRH launchers: Conceptual design

The Electron Cyclotron Resonance Heating (ECRH) system of Divertor Tokamak Test (DTT) facility will feature up to 35.2 MW installed power. At the time of its completion, it will be the most powerful ECRH system ever realized. In full power configuration, 4 sectors of the tokamak will be equipped with equatorial and upper antennas with respectively 6 and 2 launchers each, for a total of 32 launchers, fed by 16 1-MW, 170-GHz gyrotrons and 16 1.2-MW, 170-GHz gyrotrons. The last mirror of each ECRH launcher should be independently steerable about two axes to provide the required operational flexibility. Due to the high number of independent launchers in a relatively small space, a compact driving mechanism is required. In state-of-the-art ECRH systems, out-of-vessel drives are connected to the steering mirror through long shafts or bellows. In this paper, we present the conceptual design of an innovative driving mechanism, which relies on in-vessel piezoelectric actuators and compliant hinges to meet compactness requirements, minimize system's inertia, friction and backlash, while maximizing positioning accuracy. The work includes a general overview of the system, the model of the semi-compliant transmission, the identification of candidate materials and the sizing of the driving mechanism.