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The physical design of cavity and magnetron injection gun (MIG) for a realistic, DEMO-compatible, coaxial-cavity 238 GHz 2 MW CW fusion gyrotron is developed in this work, having auxiliary frequencies at 170 GHz and 204 GHz. Novel systematic approaches towards multi-frequency mode selection, magnet requirements, and MIG design are presented. Mode deterioration and voltage depression variation due to insert misalignment versus cavity wall and/or versus electron beam are studied.

koaxialer Innenleiter --- misalignment --- coaxial insert --- nuclear fusion --- Kernfusiongyrotron --- Versatz --- Mehrfrequenz-Gyrotron --- Gyrotron --- multifrequency gyrotron

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Gyrotrons are high-power mm-wave tubes. Here, the design, construction and experimental investigation of a 20 kW, 28 GHz gyrotron (2nd harmonic) are reported. This tube was designed to evaluate new emitters for future highly efficient and reliable fusion gyrotrons and for material processing applications. Following experimental results have been achieved in CW operation: 22.5 kW output power at 23.4 kV electron beam voltage and 2.23 A beam current with the world record efficiency of 43 %.

Microwave-Materials-Processing --- Wirkungsgrad --- Efficiency --- Kernfusion --- Emitter-Technologien --- Nuclear-Fusion --- Emitter-Technologies --- Gyrotron --- MikrowellenmaterialprozesstechnikGyrotron

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In this work, a novel measurement system for the analysis of the gyrotron RF output spectrum was developed. It enables unprecedented time dependent measurements within a large bandwidth, dynamic range and unambiguous RF indication in the entire D-Band (110-170 GHz). Special attention was given to the investigation of parasitic RF oscillations, and the analysis of the interplay of thermal cavity expansion and ionization-based space charge neutralization at the start of long RF pulses.

spectrum analysis --- Mikrowellenmesstechnik --- millimeter waves --- Gyrotron --- Spektralanalyse --- Millimeterwellen --- microwave measurement techniques

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Dynamic after-cavity interaction (ACI) in megawatt-class gyrotrons is investigated that could lead to lower output mode purity and increased level of internal stray radiation. The self-consistent KIT-IHM multi-mode-code SELFT has been modified to extend the simulation domain into the radius up-taper section of the gyrotron cavity where the probability of ACI exists. Studies on four different gyrotron configurations confirm that undesired interactions in the up-taper region can result in additional parasitic oscillations with relative power in the 1%-range.

After-Cavity Interaction --- Fusion Plasmas --- Electron-Cyclotron-Heating --- High-Power Gyrotron

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In nuclear fusion technology, thermal-hydraulics is a key discipline employed in the design phase of the systems and components to demonstrate performance, and to ensure the reliability and their efficient and economical operation. ITER is in charge of investigating the transients of the engineering systems; this included safety analysis. The thermal-hydraulics is required for the design and analysis of the cooling and ancillary systems such as the blanket, the divertor, the cryogenic, and the balance of plant systems, as well as the tritium carrier, extraction and recovery systems. This Special Issue collects and documents the recent scientific advancements which include, but are not limited to: thermal-hydraulic analyses of systems and components, including magneto-hydrodynamics; safety investigations of systems and components; numerical models and code development and application; codes coupling methodology; code assessment and validation, including benchmarks; experimental infrastructures design and operation; experimental campaigns and investigations; scaling issue in experiments.

packing structure --- contact force --- porosity distribution --- tritium breeder pebble bed --- breeding blanket --- discrete element method --- DEMO --- primary heat transfer system --- balance of plant --- RELAP5 --- loss of flow accident --- once through steam generators --- DEMO-EU fusion reactor --- IFMIF-DONES facility --- lithium technology --- CFD --- thermo-fluid dynamics --- lead-lithium eutectic --- In-box LOCA --- HCLL TBS --- liquid metal blanket --- MHD benchmarking --- COMSOL multiphysics --- magneto-convection --- turbulent MHD --- large eddy simulations --- magnetohydrodynamics (MHD) --- MHD pressure drop --- system codes --- liquid metal technology --- WCLL BB --- small ESS --- transient --- Apros --- Magnetohydrodynamics --- heat transfer --- WCLL --- thermal hydraulic --- WLLC blanket --- CFETR --- wakes --- open channel flow --- experimental methods --- DONES --- fusion --- liquid lithium --- LOCA --- Melcor --- numeric coupling --- liquid metal blankets --- tritium --- corrosion --- convection --- turbulence --- WCLL blanket --- DCLL blanket --- WCLL-BB --- MELCOR --- PHTS --- safety analysis --- HCPB BB --- CRAFT --- blanket and divertor --- experiment plan --- water loop design --- DEMO blanket --- first wall --- ODS steel layer --- tungsten functionally graded coating --- experimental investigation --- EU-DEMO --- helium-cooled pebble bed --- thermal storage --- indirect coupled design --- energy balance --- power conversion system --- simulation --- gyrotron resonator --- multi-physic simulation --- thermal-hydraulics --- cooling --- mini-channels --- Raschig rings --- validation --- divertor --- plasma facing components --- thermal hydraulics --- SIMMER code --- RELAP5 code --- in-box LOCA --- WCLL breeding blanket --- LIFUS5/Mod3