Disruption physics driving the SPARC design*

SPARC is expected to produce up to 140 MW of fusion power with a low normalized plasma beta (β_N=1.0), low Greenwald fraction (n_G=0.37), and a moderate safety factor (q₉₅=3.4), providing margin to disruption limits. The SPARC tokamak [1] is a high field compact fusion experiment to demonstrate Q>2 and is expected to reach Q=9-11 [1,2]. Disruption frequencies are derived from the C-Mod, JET, JT-60U, and DIII-D tokamaks, and realistic disruption prediction performances and learning rates are assumed to estimate mitigated disruption frequencies. Current quench duration distributions and halo current fractions are derived from the ITPA studies [3]. The maximum vertical force is bounded by the quadrupolar field and geometric considerations of the plasma and first wall. The sideways force is conservatively bounded by the highest prediction of independent theoretical models. Fluid simulations coupled with a kinetic solver show that runaway electron currents of many mega-Ampere are possible [4]. A novel passive non-axisymmetric coil to expel runaway seeds is under design and integrated simulations predict complete prevention of runaway beams [4]. Simultaneous massive gas injectors are planned for thermal and current quench mitigation.

[1] A. J. Creely et al. 2020 J. Plasma Phys. 86 865860502 

[2] P. Rodriguez-Fernandez et al. 2020 J. Plasma Phys. 86 865860503 

[3] N.W. Eidietis et al. 2015 Nucl. Fusion 55 063030

[4] R.A. Tinguely et al. 2021 Phys. Rev. Letter, Submitted