J. Sapper

NEUTRAL BEAM HEATING IN W VII-A STELLARATOR

Abstract A high density current-free deuterium plasma withs(o) > 0,5 %, n e (o) > 10 14 cm -3 , T e , Ti > 350 eV can be maintained in W VII A stellarator by injection of 600 kW of H° at 27 kV. The plasma energy content rises linearly with power, and in first experiments with 1.1 MW of neutral power 3.5 kJ have been achieved. The plasma shows no major instabilities but the energy balance is dominated by radiation losses, which are attributed to an increase of impurity ions in the plasma center, predominantly oxygen. The observed heating efficiency in particular for the plasma ions, seems to be higher than predicted by the beam deposition code. Possible mechanisms for this are discussed. It appears that radial electric fields as low as kT e /a improve the computed efficiency as well as the ion heating considerably. Despite the uncertainty about actual input power, it can be shown that the plasma confinement improves during injection.

THE WENDELSTEIN 7-X STELLARATOR: Technical Design and Engineering

At the Max-Planck-Institut fur Plasmaphysik, Garching (IPP) the WENDELSTEIN 7-X Stellarator experiment is in the final stage of preparatory design. It will be a large machine in the range of next step devices, aiming at plasma parameters which can be extrapolated to reactor size. The confinement system is of modular design and uses one set of nonplanar coils for generation of the standard field configuration. n nThe main parameters are: n n nmajor radius R0 = 5, 5 m, n n nstored magnetic energy Wm = 600 MJ. n n n n nmagnetic induction B0 = 3 T, n n naverage plasma radius ro = 0.53 m. n n n n nThe expected plasma parameters are: n n ncentral temperatures Ti(0), Te(0) = 2 - 5 keV, n n nenergy confinement time τE = 0.1 - 0.5 s, n n n n ncentral electron density ne(0) = 0.1 - 2 . 1020 m−3, n n naverage beta value ≤ 0.05. n n n n nThis paper presents an overview on the design features of the machine and describes a schedule for the development and construction of the experiment.

The WENDELSTEIN VII-AS Experiment

The aims of the Advanced Stellarator WENDELSTEIN VII-AS are: - the investigation of plasma behavior In an optimized Stellarator configuration; the investigation of a plasma without ohmic heating currents;

Plasma Confinement in Stellarator Systems

The stellarator is a plasma confinement system in which the magnetic field configuration is produced by currents in conductors outside the plasma. Plasma current is not necessarily required for confinement or for heating the plasma. Results from the CLEO and W VIIA experiments are presented to illustrate the progress in the understanding of containment and heating in the stellarator configuration.