Stable current profile in a stellarator with shear

Abstract

The authors have studied the stability of helical modes in a current carrying stellarator, ignoring the curvature of the axis and plasma pressure. They show that it is possible to fully stabilize a current column with a given arbitrary current value against both ideal and tearing modes by superimposing an external stellarator rotational transform with a sufficiently large value of its difference along the radius, |Δth| = |th(a) − th(0)|, in configurations of two types, namely with the total rotational transform increasing or decreasing with the radius. The value of the difference |Δth| needed for stabilization increases with the value of the total current.

Spherical tokamaks with outboard stellarator windings

“…(c) It might be advantageous (there are a few theoretical and experimental publications, for example, Refs [24,[29][30][31], stating that stellarator effects might be profitable) to use OSWs even at the later hot plasma stage for stabilization of the disruptive instability, which otherwise might be a total disaster for a reactor. At least, an OSW might be necessary for controlling this instability.…”

LHD Bootstrap Current Coefficient Calculations with the VENUS+δ f code

“…According to theoretical predictions (see, for example, [19]), a positive bootstrap current density suppresses the island width when the shear is positive (ι' > 0), a negative bootstrap current density will increase the island size provided the same positive sign of the shear.…”

Effects of Ohmic current in the TJ-II stellarator

“…The stability of a given MHD equilibrium in the presence of a net plasma current can be studied estimating the energy functional. Disregarding curvature and pressure terms, the change of plasma energy due to a perturbation in the presence of toroidal net current in cylindrical geometry is given by [24]…”