Optimization of Bootstrap Current in a Large Helical System with L = 2

摘要

Neoclassical bootstrap currents in the banana and plateau regions are evaluated for an L = 2 large helical system with the major radius of 5 m. Various vacuum magnetic field configurations are invoked to optimize the bootstrap current. In the banana region shifting the magnetic axis and shaping magnetic surfaces have remarkable effects on the bootstrap current and it is clarified that a small outward shift of the magnetic axis and vertically elongated magnetic surfaces are favorable to reduce the bootstrap current. On the contrary, the bootstrap current in the plateau region depends strongly on the toroidal pitch number of helical winding coils but shifting the axis and shaping magnetic surfaces are not effective. The magnitude of bootstrap current is estimated for plasmas in the large helical system predicted by a one dimensional transport code.