Tomographic Reconstruction of Internal Instability in a Field-Reversed Configuration

Abstract

Rotational instability with toroidal mode number n = 2 has been known as a destructive instability which limits the configuration lifetime in a field-reversed configuration plasma. In recent experiments using tomographic technique, the spatial distribution of plasma radiation (bremsstrahlung) was measured with a newly developed multi-purpose optical diagnostic system. Global deformation of the cross-sectional structure of a FRC and its time evolution were investigated by a computed tomography (CT) reconstruction technique (ART method) [T. Asai et al., Physics of Plasmas 13, 072508]. These results indicate that the FRC plasma has an internal deformation, which has different phase from the deformation of separatrix surface. These two different toroidal deformations are difficult to be observed by spatially integrated methods, for example, magnetic probes, end-on camera and so on. In this work, detailed features of this internal behavior have been investigated by a newly improved tomographic reconstruction method.