Transport Modeling for W7-X on the Basis of W7-AS Experimental Results

The design specications of the Wendelstein 7-X (W7-X) stellarator were chosen so as to enable this device to demonstrate the reactor potential of the advanced stellarator concept. The ultimate goal of the experimental program is thus to heat, conne and exhaust plasmas with reactor-relevant and collisionality values under steadystate conditions. This goal must be viewed in its entirety, and it is therefore mandatory to avoid the common experimental expedient of breaking it up into a number of selfexclusive portions (e.g. performing ihigh- i experiments at small values of the magnetic eld or ilow-collisionalityi experiments by reducing the density). Currently, there exists no single numerical tool capable of simulating all aspects of such a multifaceted problem but exploratory investigations have been carried out to determine the expected range of W7-X plasma parameters assuming electron cyclotron resonance heating (ECRH) and the prospects for magnetic conguration control using the accompanying current drive (ECCD). The results of these investigations are the subject of this paper. The basis for these investigations is provided by the theoretical interpretation of experimental results from the W7-AS device, which operated in Garching, Germany, from 1988 until 2002. Three observations are of principal importance for the simulations carried out here: (1) With the exception of the low-temperature edge region, high-performance W7-AS discharges (with central densities n(0) > 5 10 19 m 3 and central ion and electron temperatures T i;e (0) > 1 keV) were described well by the predictions of stellarator neoclassical theory. This was true for all quantities of interest including the radial particle ux es, energy ux es and ambipolar electric eld