Control of elongation for field-reversed configuration plasmas using axial field index of a mirror confinement field

摘要

The separatrix shape of a field-reversed configuration (FRC) plasma formed by a negative-biased theta-pinch is quite elongated due to a uniform confinement field, except at the end coils (simple mirror field). The elongation of the shape, which is the ratio of half the separatrix length to the separatrix radius, is about 5-10. The control of elongation is attempted by introducing a field gradient along the confinement field (axial field index) over the whole plasma region (smooth mirror field). Since mirror effects act on all portions of the plasma, the FRC plasma is compressed axially and expanded radially. As a result, the elongation becomes almost half that in the simple mirror field. It is found that a poloidal flux in the smooth mirror field is 2.6-fold the value in the simple mirror field. (C) 2004 American Institute of Physics.