Nuclear fusion devices feature electron cyclotron resonance heating systems for plasma heating and stabilization, with diamond windows acting as vacuum and safety confinement barriers. Diamond is the only option for long-pulse operation in the MW-range applications, given its exceptional combination of optical, thermal and mechanical properties. Dielectric measurements have qualified almost one hundred disks of artificial diamond for their integration into metallic structures to form the complete windows. Optical and mechanical investigations of the disks, together with dedicated numerical analyses of the windows, complete the characterization of these essential components in nuclear fusion.

One of the fundamental challenges in the development of a fusion power plant is to integrate all the systems required for the operation of the power plant into a machine that fulfills all the design requirements. This includes designing sufficient shielding against neutrons and gamma rays to ensure that the machine can operate reliably throughout its planned lifetime. The electron cyclotron (EC) heating is one of the systems critical to heating and controlling the fusion plasma. In the EU-DEMO reactor, the EC system is integrated into an equatorial port. However, the challenge with this system is that the waveguides required for it to function act as neutron and gamma ray streaming paths, which makes controlling the nuclear loads inside and behind the EC port a challenge. This concerns both the components of the EC system itself and components and systems outside the equatorial port where the EC system is located, e.g. the superconducting toroidal field coils. The latest iteration of the EU-DEMO EC heating system from 2023 was analyzed. The main nuclear loads have been calculated and the shielding performance optimized to ensure that the design limits are met. These analyses include calculations of nuclear heating in EC port, determination of peak nuclear heating in the toroidal field coils and peak neutron-induced damage (DPA) in the components exposed to the plasma neutrons.

The EUropean DEMOnstration power plant (EU-DEMO) project, a EUROfusion initiative, seeks to advance fusion power technology by developing a reliable Electron Cyclotron (EC) heating and current drive system capable of delivering up to 130 MW of auxiliary heating power presently through six equatorial ports. This paper introduces an innovative alternative to the baseline ex-vessel waveguide (EW) system design, which could be major for effective EC operations. The proposed design reduces vacuum-sealed interfaces significantly - from 173 to seven - minimizing failure points and reducing the need for extensive monitoring in confined port spaces. Enhanced for remote maintainability, the design simplifies maintenance tasks and mitigates vacuum breach risks. The vacuum dimple-plated casing, acting as the primary confinement boundary, ensures nuclear safety and enables integration with current infrastructure, while addressing challenges like dynamic loads and vessel movements to maintain structural integrity. These advancements indicate that the modular and sealless waveguide approach offers a more reliable, maintainable solution.

The European DEMO (EU-DEMO) reactor studies within EUROfusion aim to develop a fusion power plant concept. The large tokamak device needs an auxiliary heating power which, at the present stage, is provided by the Electron Cyclotron (EC) heating system with up to 130 MW foreseen to reach different regions of plasma for heating, suppression of instabilities and the possibility to support ramp-up and ramp-down phases. The present conceptual design of the system is based on 2 MW coaxial-cavity gyrotron sources, a transmission line (TL) using both circular corrugated waveguides and quasi-optical evacuated multi-beam TLs, and mirror antennas located in the Equatorial Port. In order to create a modular system, the sources are grouped in ‘clusters’, whose powers are combined in the quasi-optical TL, up to the tokamak building, where they are split and routed as single waveguides. In the launcher, they are combined together again on the launching mirrors, to save space for the apertures in the Breeding Blanket. The present EC heating system has a certain flexibility to adapt to changing design guidelines. The development status of the system is presented.

The EU DEMO Tokamak is foreseen to be equipped with an electron cyclotron (EC) system for plasma heating, magnetohydrodynamic (MHD) control, and thermal instability suppression. Up to six launchers will be installed into equatorial ports with the aim to inject a maximum of 130 MW millimeter wave power at frequencies of 136/170/204 GHz toward dedicated positions into the plasma. This article presents the current layout of the typical EC system launcher components within the available space reservation areas in the equatorial level of the DEMO baseline model. Beside the general arrangement of the EC launcher components, preliminary design features of the launcher port plug modules, an active cooling system approach, integration concepts for mirrors and waveguides (WGs) of the optical system, the shielding component formation, and safety important elements of the first containment barrier of the launcher are presented. Furthermore, relevant aspects of assembly and potential remote maintenance (RM) procedures are discussed.

The EU DEMO Tokamak is foreseen to be equipped with Electron Cyclotron (EC) launching systems for plasma heating, MHD control and thermal instability suppression. Up to six launchers will be installed into equatorial ports with the aim to inject a maximum of 130 MW millimeter wave power at dedicated positions into the plasma. The integrated design of the EC launcher is made of two equatorial port plug modules mounted into the equatorial port extensions of the vacuum vessel that mainly serve as housing for the eight optical system´s mirrors.To guarantee reliable operation of the launcher, in the latest year, a structural system has been designed which provides secure fastening and alignment of the optical components, sufficient heat dissipation and protection of sensitive areas against nuclear loads from neutrons by adequate shielding capability.To prove the fastening concept of the port plug modules and mirrors, a set of mechanical loads acting on these components is essential. EM loads caused by plasma instabilities are major contributions of mechanical load set for components close to the plasma.The present paper describes the EM analysis carried out to support the assessment of the pre-conceptual design solution. A dedicated Finite Element (FE) model was developed using ANSYS® solid236 element type (edge-based formation). Transient electromagnetic analysis was performed under centered plasma disruption event. Total force and moment due to Lorentz and ferromagnetic loads on the EC launcher port plugs and mirrors were computed. The resulting EM loads can be used for the preliminary design assessment.

The European DEMO is a pulsed device with pulse length of 2 hours. The functions devoted to the heating and current drive system are: plasma breakdown, plasma ramp-up to the flat-top where fusion reactions occur, the control of the plasma during the flat-top phase, and finally the plasma ramp-down. The EU-DEMO project was in a Pre-Concept Design Phase during 2014-2020, meaning that in some cases, the design values of the device and the precise requirements from the physics point of view were not yet frozen. A total of 130 MW was considered for the all phases of the plasma: in the flat top, 30 MW is required for neoclassical tearing modes (NTM) control, 30 MW for burn control, and 70 MW for the control of thermal instability (TI), without any specific functions requested from each system, Electron Cyclotron (EC), Ion Cyclotron (IC), or Neutral Beam (NB) Injection. At the beginning of 2020, a strategic decision was taken, to consider EC as the baseline for the next phase (in 2021 and beyond). R&D on IC and NB will be risk mitigation measures. In parallel with progresses in Physics modelling, a decision point on the heating strategy will be taken by 2024. This paper describes the status of the R&D development during the period 2014-2020. It assumes that the 3 systems EC, IC and NB will be needed. For integration studies, they are assumed to be implemented at a power level of at least 50 MW. This paper describes in detail the status reached by the EC, IC and NB at the end of 2020. It will be used in the future for further development of the baseline heating method EC, and serves as starting point to further develop IC and NB in areas needed for these systems to be considered for DEMO.

The EU demonstration power plant (DEMO) Tokamak will be equipped with an electron cyclotron (EC) system for plasma heating and magnetohydrodynamic (MHD) control. Up to six launchers will be installed into equatorial ports with the aim to inject maximum 130-MW millimeter-wave (mm-wave) power at dedicated positions into the plasma. The mm-waves will be generated in gyrotrons placed in a distinct building at distant location. From this gyrotron hall, a combined transmission line (TL) system of quasi-optical multibeam mirrors and individual waveguides (WGs) will propagate the mm-waves into the tokamak building. That followed, an optical system, composed of miter bends, diamond windows, valves, and microwave bellows, connects the TL through the gallery and the port cell with the EC launchers. This article presents the preconceptual computer-aided design (CAD) of this latter section of the EC system. Based on its general scheme and the given WG trajectories, the model takes into account the available space in the port cell with respect to required clearance for supply systems, assembly, and maintenance. At the preconceptual state, the design includes CAD models of all relevant mm-wave components in realistic dimensions at a level of details, appropriate to demonstrate the feasibility of the concept.

This article describes the DEMO cryostat, the vacuum vessel, and the tokamak building as well as the system configurations to integrate the main in-vessel components and auxiliary systems developed during the Pre-Conceptual Design Phase. The vacuum vessel is the primary component for radiation shielding and containment of tritium and other radioactive material. Various systems required to operate the plasma are integrated in its ports. The vessel together with the external magnetic coils is located inside the even larger cryostat that has the primary function to provide a vacuum to enable the operation of the superconducting coils in cryogenic condition. The cryostat is surrounded by a thick concrete structure: the bioshield. It protects the external areas from neutron and gamma radiation emitted from the tokamak. The tokamak building layout is aligned with the VV ports implementing floors and separate rooms, so-called port cells, that can be sealed to provide a secondary confinement when a port is opened during in-vessel maintenance. The ports of the torus-shaped VV have to allow for the replacement of in-vessel components but also incorporate plasma limiters and auxiliary heating and diagnostic systems. The divertor is replaced through horizontal ports at the lower level, the breeding blanket (BB) through upper vertical ports. The pipe work of these in-vessel components is also routed through these ports. To facilitate the vertical replacement of the BB, it is divided into large vertical segments. Their mechanical support during operation relies on vertically clamping them inside the vacuum vessel by a combination of obstructed thermal expansion and radial pre-compression due to the ferromagnetic force acting on the breeding blanket structural material in the toroidal magnetic field.

The pre-conceptual layout for an electron cyclotron system (ECS) in DEMO is described. The present DEMO ECS considers only equatorial ports for both plasma heating and neoclassical tearing mode (NTM) control. This differs from ITER, where four launchers in upper oblique ports are dedicated to NTM control and one equatorial EC port for heating and current drive (H&CD) purposes as basic configuration. Rather than upper oblique ports, DEMO has upper vertical ports to allow the vertical removal of the large breeding blanket segments. While ITER is using front steering antennas for NTM control, in DEMO the antennas are recessed behind the breeding blanket and called mid-steering antennas, referred to the radially recessed position to the breeding blanket. In the DEMO pre-conceptual design phase two variants are studied to integrate the ECS in equatorial ports. The first option integrates waveguide bundles at four vertical levels inside EC port plugs with antennas with fixed and movable mid-steering mirrors that are powered by gyrotrons, operating at minimum two different multiples of the fundamental resonance frequency of the microwave output window. Alternatively, the second option integrates fixed antenna launchers connected to frequency step-tunable gyrotrons. The first variant is described in this paper, introducing the design and functional requirements, presenting the equatorial port allocation, the port plug design including its maintenance concept, the basic port cell layout, the transmission line system with diamond windows from the tokamak up to the RF building and the gyrotron sources. The ECS design studies are supported by neutronic and tokamak integration studies, quasi-optical and plasma physics studies, which will be summarized. Physics and technological gaps will be discussed and an outlook to future work will be given.

The DEMOnstration fusion power plant (DEMO) is being developed within EUROfusion and one of the challenges is the integration of all the systems into a fusion reactor by designs that meet strict design criteria required for safe and reliable long-term reactor operation. Neutronics analyses are required as an important contribution to this effort. The work described here has analysed the equatorial port plugs of the electron cyclotron (EC) system in terms of neutronic aspects. The EC port plugs are needed for heating the fusion plasma and for plasma control. Necessary openings in the breeding blanket and port plug structures foreseen for the mm-wave heating beams of microwaves coming from launchers of the EC system in equatorial port plugs are a challenge in terms of neutron shielding. Both the neutron streaming through the EC port and nuclear loads in its critical components like mirrors have to be considered in the system design and integration.

•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 final design process of the ITER EC upper launcher (UL) was carried out between 2011 and 2018 under a Grant agreement between the European Domestic Agency F4E and a consortium of European associations, namely KIT (D), SPC (CH), DIFFER (NL), IPP (D), CNR (I), and IPF (D). The final design is scheduled for 2019. The final design review (FDR) will be split into several review processes for dedicated sub-components. One of these sub-components is the structural system of the EC launcher. This article presents a brief overview on the final design status of the ITER EC UL structure of spring 2018, including the history of development since 2004. It highlights the most challenging design issues and debates demanding project management steps. The lesson learned in the technical development of the design will be discussed, in view of the design work for future fusion devices.

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.

The ITER torus diamond window unit is part of the electron cyclotron (EC) upper launcher (UL) used to direct high power microwave beams generated by the gyrotrons into the plasma for heating and current drive (H&CD) applications. The UL consists of an assembly of ex-vessel waveguides (WGs) and an in-vessel port plug (PP). The diamond window units form vacuum and confinement boundaries between the torus volume and the transmission lines (TLs) which guide beams between 1 and 1.5 MW at 170 GHz from the gyrotrons to the launcher. There are eight window units attached to the assembly of the WGs, one unit for each WG. The design strategy of the unit is to have a very rigid outer frame able to withstand the potential external loads acting on the unit while thin copper cuffs brazed to the diamond disk allow indirect cooling of the disk to remove the EC power absorption during the beam transmission. The load combination given by the stringent ITER seismic level 2 (SL-2) event occurring during baking of the torus vessel is the design driver for the outer frame of the unit. In fact, the assembly of the WGs is connected from one side to the ceiling of the ITER port cell area by a support frame and to the UL PP from the other side. Movements of the torus vessel due to baking, seismic and plasma disruption events, result in forces and moments acting on the units. Furthermore, during a seismic event, the unit is subject to additional loads induced by the oscillation of the support frame attached to the ceiling. An outer frame surrounding the window unit is thus required to ensure the structural integrity and the confinement function of the unit. This paper shows how the design of the window unit was assessed and optimized by finite element method (FEM) analyses. A specific methodology was developed to carry out the analyses with respect to the seismic and baking loads. At Karlsruhe Institute of Technology (KIT), FABRY-PEROT resonators measure the loss tangent of the diamond disk and it is then used as input to the computational fluid dynamics and FEM analyses aiming to assess the design. The impact of the FEM analyses on the design of the window unit is discussed also together with the manufacturing aspects of the unit.

The ITER ECRH system consists of 24 gyrotrons with up to 24 MW installed millimeter wave heating power at 170 GHz, power supplies, control system, transmission lines, one Equatorial and the four Upper Launchers. With its high frequency and small beam focus the ECRH has the unique capability of driving locally current. While the Equatorial Launcher mainly acts for central heating and current profile shaping, the Upper Launchers aim on suppressing MHD instabilities, especially neoclassical tearing modes (NTM) triggering plasma disruptions. The Upper Launchers inject millimeter waves through a quasi-optical section consisting of three fixed and the front steering mirror set. The eight overlapping beams have focal points optimized for suppression of the q = 3/2 and q = 2/1 NTMs. Several project change requests required the redesign of the Upper Launchers and the connected ex-vessel system. This redesign includes a new boundary geometry of the launchers as well as a newly designed cooling system for the Blanket Shield Module (BSM), a modified flange of the BSM to the structural main frame and a refined optical design. Additionally shield blocks with integrated in-vessel waveguides were added and the closure plate with waveguide and supply line feedthroughs was adapted. Further changes, not all caused by PCRs, include newly designed ex-vessel waveguide components with a reduced aperture and redesigned ultra low-loss CVD diamond windows. Finally several components originally foreseen as off-the-shelf components have become part of the design scope. The new launcher design status is presented with selected results on numerical design validation.

ITER will be equipped with four EC (Electron Cyclotron) Upper Launchers (UL) of 8 MW microwave power each with the aim to counteract plasma instabilities during operation. These launcher antennas will be installed into four upper ports of the ITER vacuum vessel. Beside their functional purpose the port plugs which are the structural system of the launchers, have to provide as much shielding as possible in order to protect adjacent components from neutrons and photons and to minimize the shutdown dose rate in the port interspace and the port cell, being located further back in the ITER Tokamak building. Thus appropriate shielding blocks shall be installed at proper positions inside the plug. In addition several structural components will be dressed up geometrically in order to provide maximum shielding capability. This paper presents the general design of the shielding elements and their technical integration into the EC Upper Launcher.