Alessandro Simonetto

The EC Upper Launcher (UL) and Ex-vessel waveguide (EW) are integral components of the ITER Electron Cyclotron (EC) system [1], which plays a key role in achieving and maintaining the high temperatures required for nuclear fusion within the tokamak, providing plasma heating and current drive, and magnetohydrodynamics (MHD) stabilization, which are crucial for ITER’s operational success. The EC system is increasingly becoming the reference mechanism for plasma heating in both present and future devices. Notably, ITER is placing significant reliance on the EC system, with the recent re-baseline proposal initially doubling the EC installed power from 24 MW to 48 MW, ultimately reaching a final configuration of up to 80 MW. The F4E contribution to the current ITER baseline configuration comprises four Upper Launchers and five sets of ex-vessel waveguides. The UL and EW systems, currently in its Final Design phase under the frame of a Procurement Agreement between Europe and ITER Organization, have released the Final Design Documentation Package, which is here described, as input to the Final Design Gate Review that took place in July 2025. The full set of documents released is composed by: 1) a Design Description Dossier composed by a UL & EW Design Description (DD) document and supported by a set of 3D models, drawings and diagrams; 2) a Design Justification Dossier encompassing a set of end-to-end engineering analyses verifying the functionality and structural integrity of the components according to the applicable requirements, and the RAMI analysis of both systems; and 3) a Product lifecycle Dossier covering documentation for subsequent phases including manufacturing, assembly, installation, commissioning, operations, maintenance and decommissioning. Furthermore, the validation of the design is supported by currently on-going activities of prototyping and testing of the most critical components.

The electron cyclotron heating (ECH) launchers for the Divertor Tokamak Test (DTT) facility are currently being designed. The aim is to inject power in different plasma locations with high flexibility to allow plasma current ramp-up and ramp-down, central heating with tailored deposition profiles, and neoclassical tearing modes (NTMs) stabilization. Two antennas are developed, one for the equatorial port with six beam lines and one for the upper port with two beam lines, with similar front-steerable mirror modules. Each beam-line module is composed of a cooled corrugated waveguide launching a beam toward a fixed shaping mirror (M1) and then to the plasma-facing plane mirror (M2), movable around two axes, both cooled to sustain the high heat load due to the ohmic losses of the incident 1 MW beam and the plasma radiation. Thermal loads also include plasma and microwave stray radiation. Main structural loads on the mirrors and their supports, including the launcher supporting baseplate, are forces and torques due to the induced electro-magnetic (EM) currents, during normal operation and disruptions, interacting with the high magnetic field in which the mirrors and supports are immersed. Thermal and structural challenges, in particular on the M1 and M2 mirrors, have opposite solutions that require a delicate trade-off: optimal cooling requires high-thermal-conductivity materials such as copper alloys, while low-electrically-conductive materials are needed to have lower induced currents during disruptions. Solutions under study for the mirror cooling for minimal deformations and stresses, and for drive mechanisms, are presented. The possible reduction of induced currents during disruptions using different materials, supporting structures, and layouts is discussed.

Four Electron Cyclotron Upper Launchers will be used in ITER to inject power at 170 GHz, mainly for suppression of MHD instabilities, especially Neoclassical Tearing Modes. For each UL, the quasi-optical section injecting millimetre waves into the plasma consists of eight beams divided in two rows (upper and lower) reflecting on three fixed and one steering mirrors. In this work a simplified model of the launcher was simulated with GRASP, a commercial antenna package, in order to follow the evolution of the nominal HE11 beams through the launcher, map them on all the mirrors and calculate the spillover loss. The impact of the addition of spurious LP11 mode up to 15% of total power has also been assessed.The first-pass distribution of the stray radiation has been mapped on about 1/3 of the simplified model of the UL, evaluating also the peak and average incident and absorbed power.

Many current and next generation fusion experiments use Electron Cyclotron Resonance Heating for current profile tailoring and mode stabilization. Millimetre-wave power is delivered to the plasma in the form of Gaussian beams, either radiated by corrugated waveguides or via quasi-optical transmission lines. The size of the beams dictates that of the ducts in the neutron shielding, with the conflicting requirements of minimizing volume -to prevent loss of shielding- and reducing power loss in the wall -to lower the cooling requirements.This paper is stating scalable criteria for estimating millimetre-wave loss, to aid in assessing a minimum duct size for given power loss requirements.

Plasma-sprayed coatings on metal substrates are often used to absorb radiation for high-power applications in the millimeter-wave range [1]. ISTP-CNR (formerly IFP-CNR) has used plasma-sprayed coatings for many years in high power bolometric loads for millimeter waves [2]. Literature on electromagnetic properties of the coatings is sparse in this frequency range. This paper reports measurements on the same samples of Al2O3(40%)+TiO2(60%), Cr2O3 used in [3] over an extended frequency range, including frequencies of interest for diagnostics on the JT60SA tokamak [4]. TiO2 samples were measured too, but they are too thick for extracting useful information from the measurements with the method used in this paper.

The divertor tokamak test (DTT) facility is designed to study the power exhaust methods in scenarios similar to those expected in future fusion plants like DEMO. The project foresees 45 MW of external additional heating power to the plasma, provided by electron cyclotron heating (ECH), ion cyclotron heating, and neutral beam injector. This article focuses on the present status of the design of the transmission lines (TLs) and antennas for the ECH system. In the first operational phase, the system shall include 16 gyrotrons (1 MW/170 GHz/100 s), grouped into two clusters of eight sources each. In a later stage, the total installed power shall be doubled for a total of four clusters. Quasi-optical TLs connect the EC sources, located in a dedicated building, to the tokamak, via mirrors transmitting the microwave beams inside vacuum pipes to reduce losses and risks of arcing in air. Each TL consists of three main sections: two single-beam (SB) sections with small mirrors dedicated to a single beam at the beginning and the end of the line and a midsection of multibeam (MB) mirrors for the transmission of all the eight beams of the cluster. The beams at the output of the TL match the antennas installed in the equatorial and upper ports of the same vacuum vessel sector, through corrugated circular waveguides (WGs). The WGs are needed to reduce the vacuum conductance between the DTT vessel and TLs environments, being the connection with the vacuum vessel managed by all-metal gate valves without diamond windows. The two antennas consist of independent launching modules for each beam composed by two mirrors, one fixed and one steerable. All the components of the system are actively water-cooled to limit deformations of the mirrors surface to ensure the required quality of the beams and to reduce the transmission losses.

We study the interaction between a positron beam in the single-particle regime in an interferometric configuration and a microwave electromagnetic field. We discuss the conditions under which quantum interference can be affected by the field and we outline its possible experimental study in the framework of QUantum interferometry and gravitation with Positrons and LASers (QUPLAS) experiment.