Magnetic equilibrium design for the SMART tokamak

Abstract The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius R g e o ≥ 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 ϕ = 1.0  T with plasma currents up to I p = 500  kA and a pulse length up to τ f t = 500  ms. A wide range of plasma shaping configurations are envisaged, including triangularities between − 0.50 ≤ δ ≤ 0.50 and elongations of κ ≤ 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.