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The code for the analysis of the stability of three-dimensional (3-D) equilibrium (CAS3D) [C. Schwab. Phys. Fluids B 5, 3195 (1993)now treats the full ideal magnetohydrodynamic (MHD) energy principle, i.e. it includes the fluid compression term and a physical kinetic energy, so that it allows for the computation of physical growth rates in fully 3-D MHD configurations. A study of the MHD stability properties of a configuration space representing the Wendelstein 7-X (W7-X) stellarator experiment [G. Grieger et al Nucl. Fusion Suppl. (International Atomic energy Agency, Vienna 1991), vol. 3, p 525] shows that for unstable modes both the fluid compression and, as it was shown in previous work [ C. Nuhrenberg, Phys. Plasmas 3, 2401 (1996) ], the field compression vanish to a very good approximation. Points of marginal stability found for the stable MHD spectrum, eg the existence of spectral gaps and gap modes in the various continuum branches ( sound and Alfven) in the truly 30D low shear finite-B case similar results are obtained, exhibiting a strong interaction of sound and Alfven branches in the lower part of the stable spectrum. The existence of helicity induced gaps and gap modes in 3-D cases could be demonstrated. The first results indicate that in these 3-D cases global, stable perturbations exist, but that they are damped since they resonate with the continuum.

Additional information

Authors: NUHRENBURG C, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Physics of Plasmas, 6(1999)1, 137-147
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