Quasi-single helicity states in the reversed field pinch: Beyond the standard paradigm

This paper reports experimental results showing that coherent helical struc tures are formed in the reversed field pinch (RFP) self-organizing plasma c ore as a result of transitions to states where the n-spectrum of the m=1 mo des is dominated by a single (1,n(max)) geometrical helicity. These states are dubbed quasi-single helicity (QSH) states. Their magnetic and thermal p roperties measured in the reverse field experiment (RFX) [G. Rostagni, Fusi on Eng. Des. 25, 301 (1995)] device are described. The present theoretical understanding of QSH states is discussed and some recent theoretical result s are presented. The role of aspect ratio is discussed. These results repre sent a significant step to open a path beyond the standard paradigm that a bath of magnetohydrodynamic (MHD) modes is intrinsic to the RFP. (C) 2000 A merican Institute of Physics. [S1070-664X(00)97505-0].