W. Kerner et al., ELECTROMAGNETIC INTERCHANGE INSTABILITY INDUCED BY SHEATH RESISTIVITYIN THE SOL, Plasma physics and controlled fusion, 39(7), 1997, pp. 1101-1114
A linear analysis of MHD instabilities driven by the combined effects
of unfavourable curvature and the pressure gradient is performed in th
e scrape-off layer of a limiter configuration. The dispersion relation
of fast growing (electromagnetic) modes is derived by means of both a
nalytical and numerical techniques. The growth rate dependence on the
sheath resistivity and the magnetic shear is investigated. Perturbatio
ns are not completely stabilized by conducting end walls due to finite
sheath conductivity. Modes develop into ideal ballooning modes as the
plasma beta increases. The comparison of their behaviour to resistive
ballooning modes shows that in most cases of interest the plasma stab
ility is determined by the electromagnetic modes. As a consequence, a
new dependence of the instability growth rate on the plasma parameters
is found, where the key parameter is the density close to the end pla
tes. Results given here can be applied to a single-null divertor confi
guration.