New post-disruption mode rotation scalings and halo current paths on HBT-EP

A new scaling law for the rotation seen during disruptions is presented, which has the rotation frequency scale with the inverse of the toroidal field and the square of the minor radius (1/B_ta²). This scaling law agrees well with observations seen on other devices, and helps to explain the fast rotation frequencies seen during disruptions on HBT-EP. The validity of this scaling law is supported by a multi-shot analysis of the HBT-EP database with varying scale-factors. Possible physical interpretations of this scaling law are also presented, as well as a projection to ITER-like parameters that sees a rotation frequency on the order of 30 Hz. Fluctuations in Halo currents have also been observed to correlate very well with this rotation. The path of these currents and their relationship to the plasma rotation has been investigated through a series of experiments which scan the resistance between adjacent vessel sections, and seeks to characterize the current paths based on their source location (either the plasma surface or the wall). Narrowing down the current source location helps to clear up ambiguities in interpreting current driving mechanisms that have been found to be an issue in the past [1].

[1] J.P. Levesque et al 2017 Nucl. Fusion 57 086035