Calculation of the magnetic surface function gradient in stellarators with broken stellarator symmetry

Abstract

The computation of the gradient of the magnetic surface function, ٌ, plays an essential role in plasma physics, e.g., for investigations of plasma equilibrium currents or transport fluxes in stellarators. The evaluation of ٌ becomes more complicated if the magnetic field B does not exhibit stellarator symmetry. Here, a scheme for computation of ٌ for magnetic configurations which do not show stellarator symmetry is presented. The proposed method is based on computations of gradients of integrals of magnetic field line equations. This new technique for ٌ calculations is applied to Uragan-2M ͓O. S. Pavlichenko for the U-2M group, Plasma Phys. Controlled Fusion 35, B223 ͑1993͔͒. Taking into account the influence of current feeds and detachable joints of the helical winding the magnetic configuration does not exhibit stellarator symmetry. Computations of ٌ, the effective ripple ⑀ eff , and the geometrical factor b for the bootstrap current in the 1 / transport regime are performed.