Complete suppression of PfirschSchlüter current in a toroidal l = 3 stellarator

Pfirsch-Schlüter current (PSC) is an inherent property of a finite pressure toroidal plasma equilibrium in tokamaks and stellarators. However, it has been pointed out (V.D. Pustovitov, Nucl. Fusion 36 (1996) 583) that the PSC in a conventional stellarator could be suppressed completely by adjusting the external vertical magnetic field so that it satisfies the condition that the quantity characterizing the inhomogeneity of the magnetic field strength on a flux surface is a flux function. In this article an example is presented of such an l = 3 stellarator equilibrium. Complete suppression of PSC in a finite beta plasma is shown numerically by using the fixed boundary version of the VMEC code. The calculated equilibrium is also analysed from the viewpoint of the Boozer magnetic spectrum. It is shown that a reduction of the poloidal inhomogeneity of the magnetic field strength is essential for reducing the PSC.