DECAF multi-device investigation of halo currents generated during tokamak disruption interval*

Tokamak plasma disruption is a multi-step process in which the loss of the plasma vertical position control is typically among the last events that precede the plasma deconfinement. A flow of current between the plasma and the vessel components -the halo current- is generated through the contact of vertically displaced plasma with the vacuum vessel, resulting in an electromagnetic force applied on the device as the current crosses the confining toroidal magnetic field. The damaging potential of the resulting force scales with the pre-disruptive plasma current level, to an extreme of next-step devices carrying high plasma current in which the peak force amplitude could reduce structural lifetime due to an increased metal fatigue. Owing to their potential negative consequences, halo currents were studied across many devices and strategies for their mitigation were developed. Here, we report on a multi-device implementation of the halo current calculation into the DECAF code [1]. Dependencies of the halo current magnitude on plasma parameters are presented, yielding a multi-device model for the critical current characteristics during the disruption interval. A new DECAF’s capability that evaluates criteria that discriminate between disruptions that require mitigation of the halo current and those for which the halo currents are expected to be benign is presented.

[1] S.A. Sabbagh, et al., PoP 30 (2023) 032506