Dynamics of the Disruption Halo Current Toroidal Asymmetry in NSTX
Authors: S.P. Gerhardt
Abstract:
This paper describes the dynamics of disruption halo current non-axisymmetries
in the lower divertor of the National Spherical Torus Experiment [M. Ono, et al. Nuclear
Fusion 40, 557 (2000)]. While. The halo currents typically have a strongly asymmetric
structure where they enter the divertor floor, and this asymmetry has been observed to
complete up to 7 toroidal revolutions over the duration of the halo current pulse.
However, the rotation speed and toroidal extend of the asymmetry can vary significantly
during the pulse. The rotation speed, halo current pulse duration, and total number of
revolutions tend to be smaller in cases with large halo currents. The halo current pattern
is observed to become toroidally symmetric at the end of the halo current pulse. It is
proposed that this symmeterization is due to the loss of most or all of the closed field line
geometry in the final phase of the vertical displacement event.
__________________________________________________
Submitted to: Nuclear Fusion (October 2012)
__________________________________________________
Download PPPL-4821 (pdf 13 MB 24 pp)
__________________________________________________