Application of cross-tokamak and multi-layered criteria in DECAF for triggering of disruption mitigation action based on determination of disruption severity

Plasma disruptions can damage tokamak components on numerous fronts, however, not all plasma collapses have the potential to compromise the device integrity. Discriminating between disruptions that require mitigation and ‘benign’ collapses whose consequences can be routinely handled by the device, is of the utmost interest for devices in which the mitigation action is significantly perturbative to the subsequent device operation (such as ITER). There, the mitigation is to be deployed under the elevated risk of device damage from disruptions, while avoiding ramifications such as delayed plasma recovery due to unnecessary disruption mitigation. This work presents the DECAF* [1] code’s capability to estimate the disruption severity and thus inform on the necessity of deployment of the disruption mitigation system. As disruptions can harm the machine via various physical phenomena, DECAF evaluates the collapse severity via multiple criteria that are capturing the numerous damaging channels. A major issue can arise from the flow of the halo current [2] that is generated through the contact of vertically displaced disrupting plasma with the vacuum vessel. This results in electromagnetic forces applied on the device as the current crosses the confining toroidal magnetic field. The potential damage 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 significantly reduce the machine structural lifetime due to increased metal fatigue. Owing to their potential negative consequences, halo currents were studied across many devices [3-5] and a cross-machine halo current model was developed and implemented into DECAF as one of the indicators of the severity of the disruptions consequences. This model, together with the other criteria that evaluate the disruption severity, will be presented.

*U.S. and international patents pending

[1] Sabbagh, S.A. et al., 2023 Phys. Plasm. 30 032506

[2] Boozer, A.H. 2015 Phys. Plasmas 22 102511

[3] Gerhardt, S.P. et al., 2011 Rev. Sci. Instr. 82 103502

[4] Pautasso, G. et al., 2011 Nucl. Fusion 51 043010

[5] N. Schwarz et al., 2023 Nucl. Fusion 63 126016