The Wendelstein 7-X experiment is a concept test for properties of reactor relevant plasmas in advanced stellarators. Prominent features include a modular superconducting coil assembly, a fivefold toroidal symmetry, and a helical magnetic axis. Due to the optimization process, W7-X is characterized by a vacuum magnetic field configuration with smooth magnetic surfaces, improved equilibrium properties with a weak dependence of rotational transform and shear on the plasma pressure β, good magneto-hydrodynamic stability properties due to magnetic well stabilization, reduced neoclassical transport losses and negligible bootstrap current in the long mean-free-path regime, good collisionless α-particle confinement in an equivalent reactor, and, as a technical aspect, good feasibility of the superconducting modular coils. W7-X will be heated by continuous electron cyclotron resonance heating and pulsed neutral beam injection and ion cyclotron resonance heating. The envisaged parameters are Te⩽10 keV, Ti⩽6 keV central densities ⩽3×1020 m−3 with an averaged 〈β〉⩽5%. Despite the complicated geometrical structure, all basic diagnostics are compatible with W7-X. Generally, diagnostic methods and applications in a stellarator are not different from those in tokamaks. However, special efforts are being made to equip the experiment with those diagnostics necessary to measure the quantities directly related with the optimization of the machine: the verification of the predicted magnetic topology and characterization of the configuration throughout the entire parameter range, the identification of equilibrium and stability, and the determination of the confinement properties. The article describes the strategy developed which assures that the detailed measurement needs of the W7-X experimental program can be met.
A version of the FAMER neutral beam injection code that takes a radial electric field into account is applied to the VU-AS stellarator. The influence of the strength and radial profile of an assumed eleceic field is studied with respect to heating profiles and global effieienw. The resulting profiles decisively depend on the electric field profile io contrast to the global effidency. Wlth increasing electric potential (from -5 kV to +5 kv) the heating efficiency decreases for m-injection and increases for munterinjection. This is different to the mrresponding ODIN results obtained for the W7-A stellarator, where the mnfinement of fast ions was strongly enhanced by negative as well as positive electric potentials. These differences are mainly mused by the different beam injection geometries in these devices perpendicular in W7-A and tangential in W7-AS.
On the basis of a n extended attractive Hubbard model with nearest-neighbour interaction of opposite spins two functional methods are adopted for deriving a self-consistent equation for the superconducting order parameter. The functional-integral formalism is exploited in saddle-point approximation. The functional-derivative technique using Schwinger source fields leads via the self-energy in Hartree-Fock-Bogolubov approximation t o a nonlinear gap equation. The superconducting transition temperature is investigated for the case of s-wave pairing.Auf der Grundlage eines erweiterten anziehenden Hubbard-Modells mit einer Wechselwirkung benachbarter Elektronen entgegengesetzten Spins werden zwei funktionale Methoden getestet, um Selbstkonsistenzgleichungen fur den supraleitenden Ordnungsparameter abzuleiten. Der Funktional-Integral-Formalismus wird in Sattelpunktsnaherung behandelt. Die BunktionalAbleitungs-Technik, die Schwingersche Quellfelder verwendet, fuhrt uber die Selbstenergie in Hartree-Fock-Bogolubov-Approximation zu einer nichtlinearen Gap-Gleichung. Die supraleitende ubergangstemperatur wird fur den Fall der s-Wellenpaarung untersucht.
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