G. Grossetti

A Real-Time Tracking for Optimal Wave Injection in Overdense Plasma Heating Experiments at 140 GHz in FTU

Experiments on overdense plasma heating through the mode-coupling scheme known as “O-X-B Double Mode Conversion” obtained launching a narrow beam of millimeter waves at 140-GHz frequency and 400-kW power are scheduled for the next experimental campaigns of the FTU tokamak. Such a scheme, not yet demonstrated at electron density higher than the critical one (2.4 ·1020m-3) for the 140-GHz ordinary mode, and consequently at such a high frequency, exploits the conversion of an ordinary polarized wave (O) into the extraordinary (X) one, followed by a subsequent conversion to Bernstein (B) waves, which are then absorbed by the plasma. In the specific case of FTU, the overall efficiency of this scheme is mainly determined by the coupling efficiency between the O- and the X-wave, which can occur only for ordinary polarized radiation propagating in a very narrow angular range at the cutoff region. The simulations performed with a single ray tracing show that the required precision in the injection of the wave into the plasma is very high and an angular deviations of ±1° with respect to the optimal injection, in either vertical or horizontal direction, implies a 50% drop in the power transmitted to X-mode. Moreover, the application of models able to take into account the real shape of the incident beam shows that the maximum reachable efficiency, under optimal wave injection, is expected not to exceed 45% of the EC power injected, while the diameter of the angular window corresponding to 50% of power conversion keeps ≤ 3° in both polidal and toroidal directions. The new E CH&CD launcher, now being installed in FTU, will be able to provide the angular precision required for the steering. The basic idea of a control algorithm, aimed to track in real time the optimal angular window for the wave injection in experiments on O-X-B mode conversion, is presented in the paper. The control will use the stray gyrotron radiation as observable, which is detected by a set of sniffer probes located at different toroidal positions in the FTU vessel.

The ITER ECH & CD Upper Launcher: Steps towards final design of the first confinement system

The ITER Electron Cyclotron Heating and Current Drive (ECH&CD) Upper Launcher, whose preliminary design was approved in 2009, is on its way towards the final design. The design work is being done by a consortium of several European research institutes in tight collaboration with F4E. The main focus is the finalization of the design of all components for the First Confinement System (FCS), which forms the vacuum and Tritium barrier. The FCS comprises structural components as well as the external waveguide components in the port cell. Structural components of the FCS include the flange seal, backend frame and closure plate. The external waveguide components include the isolation valve, CVD diamond windows, miter bends and straight waveguides. Because finalizing of the design of these components is directly influenced by the layout of many in-vessel components, the design work includes also further development of the entire launcher. This paper summarizes the most recent status of the design work on the structural components of the launcher FCS, which are the support flange, the socket, the closure plate and feed-throughs for waveguides and cooling pipes. The design work includes the engineering layout of these components in accordance with system requirements, load specifications and Quality and Safety classification. An outline of the overall design of the launcher will be presented. The design progress was based on a set of related analyses, of which particular results are given. Also the integration of the associated mm-wave components, assembly strategies, neutronic aspects and the design of the shielding components will be described.

Review of the Innovative H&CD Designs and the Impact of Their Configurations on the Performance of the EU DEMO Fusion Power Plant Reactor

Heating and current drive (H&CD) systems are being investigated for a demonstration fusion power plant DEMO to deliver net electricity for the grid around 2050. Compared to ITER, which has to show the generation of 500-MW thermal power, the target of DEMO is the successful production of 300 to 500 MW electrical power to the grid and to aim for a self-sufficient tritium fuel cycle. Three H&CD systems are under development for DEMO in Europe, the electron cyclotron (EC) system, the neutral beam injection (NBI) system, and the ion cyclotron system. Based on present studies for plasma ramp-up, ramp-down, and flat top phases, to be further validated in more detailed simulations, the assumed total launched power needed from the H&CD system in DEMO is in the range of 50–100 MW, to be provided for plasma heating and control. This paper describes the design and Research and Development status of selected H&CD systems, considered for their deployment in the EU DEMO. It was always considered that different H&CD configurations and design variants will have an impact on the performances for the whole fusion plant. It shall be noted that the basis for the H&CD integrated design and system development is the actual version of the European fusion electricity roadmap. The project also elaborates on H&CD efficiency improvements which will reduce the recirculating power fraction in the future fusion power plants. Different studies under investigation will be discussed such as for NBI the photoneutralization and for EC novel concepts for gyrotron multistage-depressed collector.

From W7-X towards ITER and beyond: Status and progress in EU fusion gyrotron developments

In Europe, significant progress in gyrotron research, development and manufacturing has been made in 2014, starting from the successful continuation of the 1 MW, 140 GHz gyrotron production for the stellarator Wendelstein 7-X (W7-X) at Greifswald, Germany and the accelerated development of the EU 1 MW, 170 GHz conventional cavity gyrotron for the ITER tokamak at Cadarache, France. Based on that, a physical design activity was started which shall lead to a dual frequency gyrotron for TCV, Lausanne, Switzerland. Within the European fusion development consortium (EUROfusion), advanced gyrotron research and development has started towards a future gyrotron design which shall fulfil the needs of DEMO, the nuclear fusion demonstration power plant that will follow ITER. Within that research and development, the development of advanced design tools, components, and proper test environment is progressing as well. A comprehensive view over the status and prospects of the different development lines shall be presented.

DEMO: Heating and current drive system integration with blanket system

A preliminary design integration study of the Electron Cyclotron Heating and Current Drive, and Neutral Beam heating systems with the outboard Multi-Module blanket Segments in DEMO, is being presented. Scope of the work is to provide a first assessment on requirement analysis, concept generation and evaluation of the remote maintenance for a DEMO fusion power plant, in order to maximize its availability. The work has been divided into three phases: firstly, assessments to define the required openings for Electron Cyclotron and Neutral Beam launchers have been made. For the former, a Remote Steering concept has been considered, while for the latter a properly rescaled-ITER-like system has been taken into account. Secondly, CAD model of a DEMO sector has been modified to contain the port openings and a coarse port plug. Thirdly, a preliminary structural and electro-magnetic analysis has been carried out, considering two blanket concepts: Helium Cooled Lithium Lead and Helium Cooled Pebble Bed.

DEMO — Initiation of remote maintenance requirements

A preliminary assessment on remote maintenance for DEMO (DEMOnstration Power Plant) has been launched in 2011, mainly to revisit the rationale and technology development assumptions that have led to the selection of some design choices in the past. A more detailed assessment of the proposed schemes was required. The development of remote maintenance concepts for DEMO and future fusion power plants is driven by a couple of key requirements to maximize the overall plant availability. That includes heading for feasibility and high reliability of the plant maintenance system. This work is particularly important within the PPPT work programme as novel maintenance concepts must be developed and validated for use in DEMO. Thus one of the objectives for the European Fusion Development Agreement in Power Plant Physics and Technology (EFDA PPPT) 2012 work programme was to establish an initial set of system requirements that the DEMO fusion power plant will place on its Remote Maintenance System (RMS). Based on a preliminary DEMO model, developers of Remote Handling Equipment (RHE) should be provided with a set of comprehensive available information about the working area of RHE for in-vessel and ex-vessel maintenance. The task was not dedicated to repeat a row of top level requirements but to give technical information about different items. Work progress and results are shown in this paper. Being in a pre-conceptual phase, one of the results was that at present there are only few “real” requirements but lots of assumptions. All information was collected, further investigated and brought out as a valuable set of primary boundary conditions for the RHE developers.

A real-time tracking for optimal wave injection in overdense plasma heating experiments at 140 GHz in FTU

Experiments on overdense plasma heating through the mode-coupling scheme known as “O-X-B Double Mode Conversion”, obtained launching a narrow beam of millimeter-waves at 140 GHz frequency and 400 kW power, are scheduled for the next experimental campaigns of the FTU tokamak. Such a scheme, not yet demonstrated at electron density higher than the critical one (2.4·1020m−3) for the 140 GHz ordinary mode, and consequently at such a high frequency, exploits the conversion of an ordinary polarized wave (O) into the extraordinary (X) one, followed by a subsequent conversion to Bernstein (B) waves, which are then absorbed by the plasma. In the specific case of FTU the overall efficiency of this scheme is mainly determined by the coupling efficiency between the O- and the X-wave, which can occur only for ordinary polarized radiation propagating in a very narrow angular range at the cutoff region.