G. Granucci

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.

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.

On the present status of the EU demo H&CD systems, technology, functions and mix

Under the umbrella of the EUROfusion Consortium and within the Power Plant Physics and Technology (PPPT) Conceptual Design Activities, the project Heating and Current Drive (H&CD) conducts a number of design activities and developments for a next generation clean and environmental friendly, long pulsed (~2 hours) Demonstration fusion power plant (DEMO). This paper covers the results of the most important state-of-the-art and cutting edge technologies for the H&CD systems, as defined in the European Fusion Roadmap and in more detail specified in the Annual Work Plans (AWPs) in the Work-Package H&CD (WPHCD): (i) Gyrotron developments up to 240 GHz with multi-stage-depressed collector (MSDC) energy recovery for the Electron Cyclotron (EC) system; (ii) Neutral beam (NB) injector investigations with gas or alternatively photo-neutralization in the range of 25 - 35 MW as a modular 1 MeV injector type with reduced Cs consumption sources or alternatively volume-production based non-Cs sources; (iii) Ion Cyclotron (IC) antenna conceptual design for a distributed antenna, representing a new type of design and a transition from the commonly used port plugged antennas.

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.