Magnetic equilibrium design for the SMART tokamak

Abstract

The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius R-geo >= 0.40 m, minor radius a >= 0.20 m, aspect ratio A >= 1.7) spherical tokamak, currently in development at the University of Seville. The SMART device has been designed to achieve a magnetic field at the plasma center of up to B-phi = 1.0 with plasma currents up to I-p = 500 kA and a pulse length up to tau(ft) = 500 ms. A wide range of plasma shaping configurations are envisaged, including triangularities between -0.50 <= delta <= 0.50 and elongations of kappa <= 2.25. Control of plasma shaping is achieved through four axially variable poloidal field coils (PF), and four fixed divertor (Div) coils, nominally allowing operation in lower-single null, upper-single null and double-null configurations. This work examines phase 2 of the SMART device, presenting a baseline reference equilibrium and two highly-shaped triangular equilibria. The relevant PF and Div coil current waveforms are also presented. Equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.