For the development of a DEMOnstration Fusion Power Plant the design of auxiliary heating systems is a key activity in order to achieve controlled burning plasma. The present heating mix considers Electron Cyclotron Resonance Heating (ECRH), Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating (ICRH) with a target power to the plasma of about 50MW for each system. The main tasks assigned to the EC system are plasma breakdown and assisted start-up, heating to L-H transition and plasma current ramp up to burn, MHD stability control and assistance in plasma current ramp down. The consequent requirements are used for the conceptual design of the EC system, from the RF source to the launcher, with an extensive R&D program focused on relevant technologies to be developed. Gyrotron: the R&D and Advanced Developments on EC RF sources are targeting for gyrotrons operating at 240GHz, considered as optimum EC Current Drive frequency in case of higher magnetic field than for the 2015 EU DEMO1 baseline. Multipurpose (multi-frequency) and frequency step-tunable gyrotrons are under investigation to increase the flexibility of the system. As main targets an output power of significantly above 1MW (target: 2MW) and a total efficiency higher than 60% are set. The principle feasibility at limits of a 236GHz, conventional-cavity and, alternatively, of a 238GHz coaxial-cavity gyrotron are under investigation together with the development of a synthetic diamond Brewster-angle window technology. Advanced developments are ongoing in the field of multi-stage depressed collector technologies. Transmission Line (TL): Different TL options are under investigation and a preliminary study of an evacuated quasi-optical multiple-beam TL, considered for a hybrid solution, is presented and discussed in terms of layout, dimensions and theoretical losses. Launcher: Remote Steering Antennas have been considered as a possible launcher solution especially under the constraints to avoid movable mirrors close to the plasma. With dedicated beam tracing calculations, the deposition locations coverage and the wave absorption efficiency have been investigated, considering a selection of frequencies, injection angles and launching points. An option for the EC system structure is proposed in clusters, in order to allow the necessary redundancy and flexibility to guarantee the required EC power in the different phases of the plasma pulse. Number and composition of the clusters are analysed to have high availability and therefore maximum reliability with a minimum number of components.
Gyrotron R&D within EUROfusion Work Package Heating and Current Drive is addressing the challenging requirements posed on gyrotrons by the European concept for a demonstration fusion power plant (EU DEMO). The paper reports on the progress of these activities, on the recent results, and on near-term planning.
An in‐house full‐wave numerical code COCHLEA based on the Finite Difference in Time Domain (FDTD) method has been developed and used to study the dispersion properties of corrugated waveguide structures. The mathematical formulation of the corresponding electromagnetic problem is presented in detail. Numerical results are derived for axially corrugated waveguides similar to those appeared in gyrotron stacked beam tunnels and are compared with those obtained by the in‐house semi‐analytical numerical code FISHBONE.
Coordinated by the EUROfusion Consortium, several European research institutes are working on fusion technologies towards options for a European DEMOnstration Fusion Power Plant (FPP), as a single step between ITER and a commercial FPP, to deliver net electricity by mid of this century. One of the focus areas is the research on a proper Electron Cyclotron Resonance Heating (ECRH) and Current Drive (ECCD) system for which the fusion gyrotron is one of its major key components [1].A future FPP will probably require an ECCD operating frequency ranging from 170 GHz up to 240 GHz depending on the DEMO baseline. An RF output power of significantly higher than 1 MW (target: 2 MW) and a total gyrotron efficiency better than 60% are required. Multi-purpose operation at multiples of the λ/2-resonance frequency of the vacuum window of the gyrotron, hence in leaps of about 30 GHz (e. g. 170 / 204 / 238 GHz) needs to be considered for plasma start-up, heating and current drive. Optionally for possible steering of the absorption layer the gyrotron shall allow a fast frequency tuning in steps of around 2-3 GHz. The R&D work within the EUROfusion work package "WP HCD EC Gyrotron R&D and Advanced Developments (AD)" is focusing on all of the named targets.
Verification of the coaxial-cavity technologyThe coaxial-cavity gyrotron is a promising technology for future multi-MW fusion gyrotrons [2]. In [3] a world record RF output power of 2.2 MW at short pulses (ms-range) was demonstrated. Nevertheless, the 2 MW coaxial-cavity technology, already considered for the first installation in ITER earlier [4], is still lacking its proofof-concept regarding long-pulse operation. Major concerns are the proper alignment and thermal loading of the cavity wall and its inner conductor as well as the thermal loading of the collector. Its feasibility shall be finally demonstrated by upgrading the existing KIT 2 MW 170 GHz short-pulse pre-prototype to pulse lengths up to 1 s [5]. In parallel, work is ongoing in the field of advanced cooling concepts [6,7]. Additionally, two new coaxial-cavity Magnetron Injection Guns (MIGs) are under manufacturing. The first is employing an advanced emitter technology whose major element is a new nonemissive coating. That will significantly reduce the velocity spread of the electrons at the emitter [8]. Secondly, a newly designed Inverse Magnetron Injection Gun (IMIG) will allow for a significant larger emitter radius and therefore increased output power at operating frequencies significantly above 200 GHz by keeping the same or even smaller size of the bore hole of the gyrotron SC magnet [9].
Studies towards a 240 GHz gyrotronA frequency up to 240 GHz was selected for the theoretical research work towards a future FPP, considering the requirements for "multi-purpose" and "fast frequency step-tunable" operation at high-field tokamaks and for a wide range of RF beam steering. The coaxialcavity gyrotron technology, and, as a possible fallback solution, the conventional hollow-cavity gyrotron are under investigation. ...
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