A multi-machine analysis of non-axisymmetric and rotating halo currents*

Halo currents measured during tokamak disruptions exhibit non-axisymmetric and rotating features in several machines including Alcator C-Mod,\footnote{Granetz et al., \textit{Nucl. Fusion} \textbf{36}, 545 (1996)} ASDEX Upgrade,\footnote{Pautasso, et al., \textit{Nucl. Fusion} \textbf{51}, 043010 (2011)} and NSTX.\footnote{Gerhardt, \textit{Nucl. Fusion} \textbf{53}, 023005 (2013)} Such non-axisymmetries are of great interest to ITER because they can increase mechanical stresses during a disruption, especially if the rotation resonates with the natural frequencies of the vessel.\footnote{Hender et al., \textit{Nucl. Fusion} \textbf{47}, S128 (2007)} This paper presents an ITPA-initiated multi-machine analysis of these phenomena. The ITPA non-axisymmetric halo current database presently includes data from NSTX, DIII-D, AUG, and C-Mod. These data are analyzed here within a common numerical framework. Emphasis is placed on the evolution of the $n=1$ component of the halo current over the course of the disruption, as well as on how the non-axisymmetries and rotation depend on the equilibrium plasma parameters at the start of the disruption.