Conceptual study of an ICRH traveling-wave antenna system for low-coupling conditions as expected in DEMO

For the central heating of a fusion reactor ion cyclotron radio frequency heating (ICRH) is the first choice method as it is able to couple RF power to the ions without density limit. The drawback of this heating method is the problem of excitation of the magneto-sonic wave through the plasma boundary layer from the antenna located along the wall, without exceeding its voltage standoff. The amount of coupling depends on the antenna excitation and the surface admittance at the antenna output due to the plasma profile. The paper deals with the optimization of the antenna excitation by the use of sections of traveling-wave antennas (TWAs) distributed all along the reactor wall between the blanket modules. They are mounted and fed in resonant ring system(s). First, the physics of the coupling of a strap array is studied by simple models and the coupling code ANTITER II. Then, after the study of the basic properties of a TWA section, its feeding problem is solved by hybrids driving them in resonant ring circuit(s). The complete modeling is obtained from the matrices of the TWA sections connected to one of the feeding hybrid(s). The solution is iterated with the coupling code to determine the loading for a reference low-coupling ITER plasma profile. The resulting wave pattern up to the plasma bulk is derived. The proposed system is totally load resilient and allows us to obtain a very selective exciting wave spectrum. A discussion of some practical implementation problems is added

Juvenile Hippocampus guttulatus from a neuston tow at the French-Belgian border

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The initial tolerance to sub-lethal Cd exposure is the same among ten naïve pond populations of Daphnia magna, but their micro-evolutionary potential to develop resistance is very different

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Tests on a mock-up of the feedback controlled matching options for the ITER ICRH system

For the ICRH of ITER 20MW must be coupled to the plasma in the 40-55MHz frequency band via an array of 24 radiating shorted straps fed by four generators. The matching system must provide automatic matching control on the mean load provided by the plasma and be resilient (|Γ| < 0.2) to a wide range of fast antenna load excursions occurring in ELMy plasmas. Furthermore, good control of the current distribution in the strap array must be possible for the various heating and current drive scenarios. Two load resilient matching options have been considered for ITER: the 4 “Conjugate-T” (CT) and the 4 hybrids ones, the first being presently considered as a back-up option. Automatic control of these 2 options is presently developed, and tested for optimization on a low-powered scaled mock-up. Successful implementation of the simultaneous feedback control of 11 actuators for the matching of the 4CT and for the control of the toroidal phasing has already been achieved. The matching and the array current control of the 3dB hybrid option is provided by simultaneous feedback control of the decouplers and double stub tuners (in total 23 actuators) and is being progressively implemented. The simultaneous control of matching and antenna current has already been successfully tested on part of the array