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An electron cyclotron system (ECS) is required in the European DEMO fusion reactor for plasma heating, magnetohydrodynamic control, especially the suppression of neoclassical tearing modes (NTMs), and thermal instability control. Microwave beams of 2 MW, generated by gyrotrons, shall propagate through corrugated HE11 waveguides (WGs) of 63.5-mm inner diameter and finally reach specific locations in the plasma by a dedicated set of mirrors. The deployment of the beam may be done either by angular steering, i.e., tilting moveable mirrors, or by frequency steering, i.e., tuning the gyrotron frequency. In the last option, for long pulse operations, broadband optical grade diamond windows are required as confinement and/or vacuum barriers both at the torus and the gyrotron side. The Brewster-angle window represents a promising solution due to its intrinsic simplicity. However, the WG aperture imposes a minimum Ø180 mm for the disk at the Brewster-angle of 67.2° for diamond. This is an ambitious target, considering 140 mm as the state of the art. First, this article shows the very promising results of diamond growth experiments carried out by Diamond Materials GmbH with the first worldwide free-standing optical grade Ø180-mm disk having an average unpolished thickness of 1.3 mm. For the first time, one side of this large disk was polished and loss tangent measurements were performed at the center and over a large area. Then, the performance of the window featuring these large disks was characterized by a consistent set of thermomechanical analyses in view of the forthcoming window prototyping activity. [ABSTRACT FROM AUTHOR]

In this paper we present the methodology implemented for analyzing System Requirements and Interfaces of the Heating and Current Drive (HCD) system of the European Demonstration Fusion Power Reactor DEMO. The work consisted in updating the preliminary framework of the Model-Based Systems Engineering model of the HCD System Architecture. This is now containing an ontology, a set of 6 perspectives and a defined set of viewpoints for each Perspective, for refining the HCD System Architecture. The scope of the work is to manage the interdependencies of HCD system elements and their integration into DEMO, for a given set of system functions. On the one hand, this means to address the identification and definition of the interfaces occurring, both internally in the HCD system, and between the HCD system and neighboring systems. On the other hand, this implies studying the impact of requirements coming from the ongoing physics studies. The rationale is to provide the technical foreground for supporting the decision-making processes related to the HCD system which is planned to be carried out during the forthcoming Conceptual Design Phase. The results we show in this paper are part of the design and integration activities consisting of both systems engineering methodologies and design analysis, all aiming at ensuring consistency in the overall EU DEMO plant design. In this framework the DEMO Heating and Current Drive system has been selected as pilot project for the application of Systems Engineering methodologies. [ABSTRACT FROM AUTHOR]

Abstract In the framework of the EUROfusion Consortium, the Work Package Heating and Current Drive (WPHCD) is undertaking the development and design of the DEMO Heating and Current Drive (HCD) system, supported by the Work Package Plant Level Systems Engineering, Design Integration and Physics Integration (WPPMI). As the DEMO project is in the Pre-Conceptual phase, its development is dominated by uncertainties on system requirements, and by different DEMO designs and scenarios. In this context, a number of outstanding technology and physics issues, e.g. related to safety, neutronics, performance and reliability, need to be resolved using an integrated approach. For coping with these boundary conditions, we present an initial analysis of HCD requirements and functions through the development of a System Architecture model, i.e. through describing the HCD system in terms of its functions and their interdependencies. Scope of the work is to address uncertainties i) associated with different reference scenarios (e.g. pulsed and steady-state tokamak) and operational concepts; ii) related to system performances. The assessment is part of integration activities, consisting of both systems engineering methodologies and design analysis, all aiming to ensure consistency in the overall EU DEMO plant design. [ABSTRACT FROM AUTHOR]

• A first pre-conceptual design concept for an DEMO EC launcher is presented. • It includes all relevant components on a pre-conceptual basis. • General design requirements are taken into account. For the EU DEMO Tokamak, Electron Cyclotron (EC) launching systems for plasma heating and stabilization are under development. Various concepts for the optical system are currently studied of which the Mid Steering Antenna (MSA) with a steering mirror at a recessed position behind the breeding blanket (BB), the Open Ended Waveguide (OEWG) concept with quasi-optical beam propagation by fixed mirrors only and the Remote Steering Antenna (RSA), currently seen as back-up solution, are the basic ones. In addition, hybrid solutions, which means a port plug with different launcher concepts, are taken into consideration. In parallel, design drafts for a generic equatorial port plug are sketched with the aim to provide a versatile structural system, which allows customized installation of the potential optical systems. This paper presents a pre-conceptual hybrid design of an equatorial EU DEMO EC port plug based on MSA for plasma stabilization and OEWG for plasma heating, taking into account the exact port position with respect to the toroidal field coil, mechanical integrity, heat dissipation, neutronic shielding requirements, design integration and maintenance concepts. [ABSTRACT FROM AUTHOR]

• The preliminary conceptual design for the EC system of the future EU DEMOnstration fusion power plant is ongoing in the EUROfusion Consortium. • Different options for the antenna, RSA, OEWG and MSA are investigated, analyzing their performance for several injection angles and launch points. • Beam tracing calculations have been performed on different scenarios, providing information on plasma accessibility and deposited power. • The microwave design and initial ideas about the ex-vessel EC transmission lines routing is approached. The preliminary conceptual design for the Electron Cyclotron (EC) system of the future European DEMOnstration fusion power plant is ongoing in the EUROfusion Consortium. This represents one of the key aspects in order to assess the performances and the integration capabilities of such a system in EU DEMO as well as in the alternative reactor configuration Flexi-DEMO. Different options for the antenna, namely remote steering antenna (RSA), open ended waveguides (OEWG) and the front steering antenna (FSA) later on renamed in mid steering antenna (MSA) to notify that the MSA is protected behind the breeding blanket (BB) in DEMO, are investigated, analyzing their performance for several injection angles and launch points. This activity considers the constraints given by physics and engineering requirements, as for example the maximum power per port and the necessary local current drive to stabilize neo-classical tearing modes (NTMs) with a proper deposition width. The beam tracing calculations have been performed on different scenarios, providing information on plasma accessibility and deposited power. The microwave design and initial ideas about the ex-vessel EC transmission lines routing will be shown. [ABSTRACT FROM AUTHOR]