Preparing the ICRH System for the Wendelstein 7-X Stellarator

Le résumé fourni par la source

An important aim of W7-X is to demonstrate fast ion confinement at volume averaged beta values up to 5%, corresponding to plasma densities above 10 20 m -3 .To this end, an ICRH system is prepared for W7-X, with RF power up to ~1.5 MW (depending on the coupling) at frequencies between 25-38 MHz in pulses up to 10 s.Energetic ions in W7-X with energies 50 < E < 100 keV mimic alphas in a reactor.To generate such a population is challenging in high-density plasmas with traditional ICRH heating scenarios and different auxiliary heating methods.However, fast particles can be very efficiently using the H-( 3 He)-D three-ion heating ICRH scenario, foreseen for f ~ 25 MHz in W7-X.ICRH is an ideal heating method to deposit power in the plasma center at such high density as it is not hampered by a high-density cut-off, a fundamental property of the propagation of Fast Alfvén Waves in plasmas.A two-strap ICRH antenna is under construction for W7-X.Each strap is on one side connected to a tuning capacitor (15-200 pF) and grounded to the antenna box at the other end.A prematching has been implemented by connecting the RF transmission lines at an intermediate position on each strap.The main dimensions of straps and antenna box have been optimized to maximise the power delivered to the plasma, using the reference plasma density profile in front of the antenna, provided by the W7-X team.A dedicated test stand is under construction in IEK-4 / FZJ to perform main functional tests on the antenna.

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