Design of MW-Class Coaxial Gyrotron Cavities With Mode-Converting Corrugation Operating at the Second Cyclotron Harmonic

This article presents investigations on the design of coaxial gyrotron cavities with mode-converting corrugations, operating at the second harmonic of the electron cyclotron frequency with output power of the order of megawatts. The suppression of the competing modes interacting at the fundamental cyclotron frequency is achieved by the combination of a corrugated coaxial insert and mode-converting corrugation on the outer wall. The outer corrugation couples the key competing modes to lower order modes with reduced quality factor. The design steps, which form a generally applicable design procedure, are described in detail. As an illustrative example, the proposed procedure is used for the design of a cavity for a fusion-relevant, second-harmonic MW-class gyrotron, operating at 170 GHz with the TE 37,1837,18 mode. From the simulations, it is found that for the proposed design, this mode is excited with an output power of around/ ∼ 1.5 MW. Two additional paths for cavity optimization toward even higher output power are also presented

Investigation of Cylindrical Waveguides with Periodic Wedge-Shaped Azimuthal Corrugations Excited by TE Modes Using the FDTD Method

Modern gyrotron beam tunnels are rather complicated structures designed to enhance the suppression of the parasitic oscillations, which may be excited there. In some beam tunnel designs, azimuthal corrugations are engraved on their walls to further improve the suppression of these oscillations. In this work, we investigate the effect of the geometrical properties of the corrugations on the propagation characteristics of TE modes for the simplified model of a smooth waveguide with an azimuthally corrugated region. For this structure, the scattering parameters are calculated and the mode conversion is investigated with the in-house FDTD code COCHLEA

EU DEMO EC system preliminary conceptual design

The engineering design and R&D of auxiliary heating systems and their sub-systems are a key activities in the frame of the present conceptual design phase for a first of a kind DEMOnstration Fusion Power Plant in order to develop a system capable of achieving and controlling burning plasmas. In the frame of the EU DEMO reference design, the R&D activities consider the injection of about 50 MW of Electron Cyclotron (EC) power to support and assist different plasma phases. As the project is still in the conceptual phase, a range of options for gyrotrons, transmission lines and antennas is under assessment taking into account the guidelines for the integration of the EC system in a nuclear reactor and a maximal achievable reliability and availability of the EC power during operation

Overview of recent gyrotron R&D towards DEMO within EUROfusion Work Package Heating and Current Drive

Gyrotron R&D within the EUROfusion Work Package Heating and Current Drive (WPHCD) is addressing the challenging requirements posed on gyrotrons by the European concept for a demonstration fusion power plant (EU DEMO). These requirements, as specified within WPHCD, ask for highly reliable and robust long-pulse operation of the gyrotron, delivering 2 MW of microwave power at frequencies above 200 GHz with a high overall efficiency above 60% and the option for fast frequency step-tunability. To meet these targets, which are clearly beyond today's state-of-the-art, the R&D activities within WPHCD are organized in five main branches: these are the experimental verification of the advanced coaxial gyrotron technology at long pulses, the development of a coaxial gyrotron meeting the EU DEMO requirements, the development of multi-stage depressed collectors for enhanced energy recovery, the development of large broadband diamond windows to allow fast frequency tunability of the gyrotron, and the studies on further innovations and improvement of critical gyrotron components, in view of optimization of performance, reliability, and industrialization. The paper presents the progress made on these activities, the recent results, and the near-term planning. The major recent achievements include (i) the experimental validation of the fabrication of the new, water-cooled components for the longer-pulse coaxial gyrotron at Karlsruhe Institute of Technology, by demonstrating 2.2 MW at 170 GHz with 33% efficiency without depressed collector, (ii) the design of key components for a 2 MW, 170/204 GHz dual-frequency coaxial gyrotron, (iii) the design of a two-stage depressed collector with 77% efficiency, (iv) the first-ever production, in an industrial plasma reactor, of large chemical vapor deposition diamond wafers of 180mm diameter, (v) the procurement of an advanced electron gun with coated emitter edges, and (vi) advances in the theoretical and numerical modelling for investigating improved concepts for the gyrotron beam tunnel and cavity

From W7-X Towards ITER and Beyond: 2019 Status on EU Fusion Gyrotron Developments

In Europe, the research and development with main focus on achieving robust industrial designs of series gyrotrons for electron cyclotron heating and current drive of today's nuclear fusion experiments and towards a future DEMOnstration fusion power plant is constantly progressing. The R&D is following two different paths. Both are complementing each other: Firstly, it is the adaption of the physical design and basic mechanical construction of the reliably operating 140 GHz, 1 MW CW (spec.: 920 kW, 1800 s) gyrotron of the stellarator Wendelstein 7-X (W7-X), Greifswald, Germany. With regards to time and costs it is the target to perform reliable developments of fusion gyrotrons with advanced specifications for today's plasma fusion experiments. Main focus is on the development of the first EU 170 GHz, 1 MW CW (3600 s) gyrotron for the installation in ITER, Cadarache, France. Another adaption is the dual-frequency 126/84 GHz 1 MW (2 s) gyrotron upgrade for the medium size TCV tokamak, Lausanne, Switzerland. Finally, it is the upgrade of the W7-X gyrotron design towards an RF output power per unit of up to 1.5 MW and possible dual-frequency operation by keeping the basic mechanical construction. Additional to the proven design it allows to fit the new 1.5 MW gyrotron into the already existing infrastructure and to reuse existing W7-X gyrotron auxiliaries, e. g. the high-power voltage supply (HV PS) and the superconducting (SC) magnet. The second R&D path is defined by the complementary approach with regards to development risks towards a future gyrotron which shall fulfil the significant more advanced specifications of a future EU DEMO. The starting point is the 2 MW EU/KIT coaxial-cavity gyrotron design. Main requirements are an RF output power of 2 MW CW at above 200 GHz, multiple operating frequencies, frequency step-tunability and a total efficiency above 60 %