Local three-dimensional magnetostatic equilibria

An analytic representation of a three-dimensional (3-D) magnetostatic equilibrium that is localized to a magnetic flux surface is introduced. This model, which generalizes prior work for axisymmetric systems, allows one to completely specify the structure of the equilibria through a finite number of 3-D shaping and profile variations. This model can be implemented to study the effects of the equilibrium variations on localized instabilities, such as ballooning modes or microinstabilities.