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Following two initial campaigns [1], Stellarator Wendelstein 7-X (W7-X) has now completed the construction phase by installation of active cooling of all plasma facing components. The machine is presently commissioned for the next campaign (OP2) aiming at 1 GJ per pulse, e.g. 100 s at 10 MW, eventually aiming at 18 GJ, e.g. 1800 s at 10 MW. The key heating system is the Electron Cyclotron Resonance Heating (ECRH) system, consisting of 10 gyrotrons with power per gyrotron ranging from 0.6 MW up to 1.0 MW at 140 GHz. A phased upgrade of the installation is in progress with the addition of 2 gyrotrons and the development of 1.5 MW and 2.0 MW gyrotrons, such that at the end of the upgrade 4 gyrotrons will be available in each power class of 1.0, 1.5 and 2.0 MW [2]. The increased ECRH power, combined with O2 and X3 heating schemes at high densities, will lead to increased microwave stray radiation. This is non-absorbed microwave power that diffuses inside the vessel and is incident on all in-vessel components including vacuum windows and attached diagnostic systems. A fraction of the stray radiation is absorbed by resistive or dielectric losses of these components, leading to thermal loads that scale with stray radiation levels and pulse length. At W7-X a high power microwave stray radiation launch facility 'MISTRAL' is available that is used to qualify invessel components for use at specified microwave surface power densities [Wm−2]. This paper reports on MISTRAL campaigns in 2020 2021 for testing of stray radiation loads during OP2 in W7-X, as well as on an EUROfusion program assessing stray radiation loads on ITER components. A dedicated, absolutely calibrated, caloric load was developed for the campaign to obtain measurement of stray radiation power levels as well as to conveniently expose samples. Amongst other we report on shielding concepts using metal enclosures combined with microwave absorbing coatings and dielectric heating of vacuum windows. [ABSTRACT FROM AUTHOR]

A new series of MW-class, RF loads were developed that can dissipate power levels exceeding 1.5 MW at frequencies from 28 GHz to 180 GHz. The new loads are designed to reflect less than 0.25% of the input power and operate continuously (CW). Stainless-steel and anodized aluminum versions were developed. The stainless steel version is designed to meet requirements for nuclear facilities, such as ITER, while the aluminum version is capable of power levels exceeding 2 MW CW. The aluminum version is also lighter and less expensive. This paper describes the design and capabilities of the loads. [ABSTRACT FROM AUTHOR]

The ITER ECH&CD system is designed to inject 20 MW of millimetre-wave at 170 GHz into the vacuum vessel. The system is composed of many sub-systems, namely High-Voltage Power Supplies (HVPS), Gyrotrons, Transmission Lines (TL), Ex-vessel Waveguides (EW), Launchers. It is the role of the EC Plant Controller (ECPC) to integrate all the Sub-system Control Units (SCU), to prepare the system for operation and to execute the real-time requests coming from the plasma control system. The ECPC also implements plant level protection functions involving more than one sub-system and it interfaces with the ITER Central I&C. This paper gives an overview of the EC system and a description of the control system development focusing on the architecture and the interfaces. Control and protection functions are presented together with a functional allocation to better define interfaces and responsibilities. The preliminary design of the interface with the Plasma Control System to implement advanced control functions is also presented. [ABSTRACT FROM AUTHOR]

The integration of the voltage-source converter based high voltage direct current (VSC-HVDC) system makes the set-point of its active power adaptive to the changes in the power flow, and contributes to the curative congestion management. To further exploit the dynamic behavior of a hybrid AC/DC power system in curative congestion management scenarios, this paper investigates a novel control scheme for voltage angle droop controlled HVDC (VAD-HVDC) systems. The proposed scheme to alleviate the circuit overload is estimated firstly by calculating the severity index when the power flow changes under N-1 situations. Then the voltage angle controlled HVDC system is applied on the modified IEEE 39-bus 10-machine test power system for the time-domain simulation. The dynamic behavior in the HVDC station validates that the VAD control can stabilize the DC voltage and possess a good ability against interference. In addition, the dynamic characteristics analysis on the AC transmission lines proves that the hybrid AC/DC system integrated with the VAD controlled HVDC system are in possession of good stability after the N-1 contingency event. The VAD controller employed in the HVDC system is capable of effective congestion management to mitigate the critical loadings on the transmission lines. [ABSTRACT FROM AUTHOR]

The Electron Cyclotron Resonance Heating (ECRH) system of China Fusion Engineering Test Reactor (CFETR) is designed to inject 20 MW RF power into the plasma for heating and current drive (H&CD) applications. The ECRH system consists of 20 gyrotrons, the associated power supplies, the transmission lines and one launcher. In order to compare the launcher performance from equatorial and upper ports, two types of launcher are designed in this paper. In equatorial launcher (EL), twenty in-vessel transmission lines are divided into four groups. Every five gaussian beams from in-vessel transmission lines face one fixed focusing mirror and one steering mirror. All gaussian beams are injected into the plasma with optimal toroidal and poloidal angles calculated by C3PO/LUKE code. In upper launcher (UL), twenty-one transmission lines are supposed and divides into three groups. Every seven gaussian beams are injected into one fixed focusing mirrors and all twenty-one beams reflected to one common steering mirror finally. The optical transmission characteristics and the convergence information of gaussian beams are checked and optimized. The EL or UL is installed on the equatorial or upper port with a port-plug modular structure. [ABSTRACT FROM AUTHOR]

This paper presents a review of the state of the art for fault location methods in transmission lines based on travelling waves. The motivations that led to these methods are explained historically. Also, a critical analysis, showing the advantages and disadvantages of each of them and their most common applications, is performed. Finally, a comparative analysis between two of the most widely used methods is carried out using real faults, in order to show the results' sensitivity to changes in the line parameters. [ABSTRACT FROM AUTHOR]

The 2 MW cw requirement for ITER EC transmission lines has led GA to design a number of new and modified components, namely power monitors and polarizers to meet this requirement. In addition, the ITER transmission lines may require sliding joints or bellows to accommodate the thermal expansion of the lines and/or vessel motion. The ex-vessel sections of the EC launchers require double seal waveguides, miter bends and possibly double seal sliding joints to assure tritium retention in this region. GA has developed designs for many of these components and some of them have already been tested at high power at the JAEA RF Test Stand. Thermal analyses of the standard GA power monitor miter bend show that our standard design is suitable for 1 MW cw operation when the H-field is in the plane of the miter bend. For 2 MW cw operation a modified design, which also requires H-plane orientation, has been developed and a prototype has been fabricated and is ready for testing. For long pulse/cw operation, a 2 MW calorimetric miter bend with thermally isolated mirror has been designed and a prototype has been fabricated. Since the mirror is thermally isolated, calorimetry on the mirror cooling water can provide a measure of absorbed power. Such a miter bend, when made in a double seal version, could be useful for monitoring total power at the end of an EC transmission line just before the in-vessel section of an EC launcher. A mode analyzer using an all metal water-cooled beam splitter is being developed for use in measuring in real time the HE11 and higher order mode content or total power in EC transmission lines. Such a high power diagnostic can be very useful in optimizing the alignment of the MOU output into a transmission line and in monitoring the HE11 mode purity at various locations in a transmission line. Prior to making a 63.5 mm 170 GHz version suitable for use on ITER, several prototype 31.75 mm 110 GHz versions have been fabricated and tested at DIII-D. A 170 GHz version is now being fabricated. This paper addresses the performance characteristics, design features and test results for the new and modified components being developed to assure low loss transmission and acceptable component stresses for 2 MW cw opération. [ABSTRACT FROM AUTHOR]