Speakers
Description
The main objective of the stellarator Wendelstein 7-X (W7-X) is to show the potential of optimized stellarators. The main heating system is ECRH up to 10 MW steady-state at 140 GHz. NBI is also foreseen in pulses up to 10 s. 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 1020 m-3. Mimicking the behaviour of alpha particles in a future stellarator requires the presence of energetic ions in the core of W7-X plasmas with energies in the range 50-100 keV. Given the expected high plasma densities, this is a challenging task. It can however be done using Ion Cyclotron Resonance Heating (ICRH) and currently an ICRH system is being constructed for W7-X, aiming at delivering RF power levels up to ~1.5 MW in the frequency range 25-38 MHz with pulse lengths up to 10 s using a two strap antenna. To ensure optimal coupling in the various magnetic configurations of W7-X the antenna surface is carefully matched to the standard magnetic configuration of W7-X, resulting in a complex 3D shape of the antenna requiring state of the art CNC machining equipment for its fabrication. In addition the antenna can be radially moved (over 35cm) and a gas puffing system is implemented to improve local coupling whenever needed. The system is intended to be ready in the operational phase 1.2b of W7-X.
