Contribution of LPP/ERM-KMS to the modern developments of ICRH antenna systems

• Overview of ICRF antenna coupling physics, showing from first principles how to develop a state of the art ICRF system for ITER and DEMO.
• Physics of conceptual solutions for the compact ITER antenna array, intended to radiate ∼10 MW/m2.
• Implementing novel ideas into the matching-decoupling network of the ITER antenna array to avoid cross-coupling and to control the RF current distribution in the array.
• Experimental tests of the theoretical predictions using scaled mock-ups of the ICRF antenna, including a dielectric dummy load to mimick the plasma.
• Demonstrating an operational feedback control of the matching-decoupling network for the ITER antenna array, with 23 simultaneously active actuators.

The paper gives an overview of the coupling physics of an ICRF antenna array to the plasma and of the original conceptual solutions proposed by the LPP/ERM-KMS group for the compact ITER antenna array and its matching to the RF power sources. The main contributions are (i) the use of an array of short straps grouped in triplets, (ii) the triplet feed by a four port junction and the use of a service stub to enlarge its frequency response, (iii) the multistep prematching to decrease the VSWR and minimise the voltage in the feeding transmission lines, (iv) the use of a decoupler network to neutralize the mutual coupling effects between different RF power sources and to simultaneously control the current distribution of the antenna array, (v) the various options to connect the decouplers and 3 dB hybrids for different array phasing cases in order to maintain the correct functioning of the decouplers together with load resiliency to fast variations of the plasma density in the edge (caused by e.g. pellet injection or Edge Localized Modes), (vi) the solution of the grounding problem of the ITER antenna plug-in, (vii) the test on mock-ups in front of a dielectric dummy load of the performance of the different solutions and particularly of the automatic matching and decoupling control of the complete ITER antenna array.