Electromagnetic VDE and Disruption Analysis in the SMART Tokamak

Abstract

The SMall aspect ratio tokamak (SMART) is a new spherical device, that is, currently being constructed at the University of Seville. The operation of SMART will cover three phases reaching a maximum plasma current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{P}$ </tex-math></inline-formula> ) of 400 kA, a toroidal magnetic field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{T}$ </tex-math></inline-formula> ) of 1 T, and a pulse length of 500 ms. Such operating conditions present notable challenges to the design and verification of SMARTs structural integrity during normal and off-normal operations. In particular, vertical displacement events (VDEs) and disruptions (Boozer, 2012) are most important as they can cause severe damage to the components directly exposed to the plasma due to the significant electromagnetic (EM) and thermal loads delivered over ms timescales. As a consequence, a detailed evaluation of the EM loads during plasma disruptions is mandatory for the correct dimensioning of the machine, in particular the vacuum vessel. The EM loads are mainly produced by: the poloidal flux variation during the thermal and current quench, halo currents (Boozer, 2013) that flow into the vacuum vessel and interacts with the toroidal magnetic field; and toroidal flux variation during the thermal and current quench. We present, here, the EM and structural analysis performed for the design of SMART. The modeling has been carried out by combining equilibrium scenarios obtained through the FIESTA code (Cunningham, 2013), estimating VDE and disruption time-scales by comparing other machines (Chen et al. 2015), (Hender et al. 2007), and (Bachmann et al. 2011) and computing EM forces through a finite element model (FEM) taking into account the effects of both eddy and halo currents (Roccella et al. 2008), (Titus et al. 2011), and (Ortwein et al. 2020). Finally, the structural assessment of the vacuum vessel is performed in order to verify its integrity during normal and off-normal events in phase 3.