7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

First MHD stability analysis of the SMall Aspect Ratio Tokamak (SMART)

J. Dominguez-Palacios1, M. Garcia-Munoz1, Y. Liu2, A. Mancini1, D.J. Cruz-Zabala1, Y. Todo3,
A. Reyner-Viñolas1, M. Toscano-Jimenez1, J. Berkery4, P. Oyola1, E. Viezzer1, S. Futatani5 and thePSFT Team*1
University of Seville, Seville, Spain
2
General Atomics, PO Box 85608, San Diego, California 92186-5608, USA3
National Institute for Fusion Sciences, Toki, Japan
4Princeton Plasma Physics Laboratory, Princeton, USA5Universitat Politècnica de Catalunya, Barcelona, Spaine-mail (speaker): jdominguezpalacios@us.es
The SMall Aspect Ratio Tokamak (SMART), a newspherical tokamak (ST) under construction in theUniversity of Seville, will explore the viability ofnegative triangularity (NT) plasmas in STs for a future
fusion power plant [1-4]. SMART has been designed tooperate at Bt ≤ 1 T, Ip ≤ 1 MA, major radius Rmag = 0.45m, triangularities -0.6 ≤ δ ≤ 0.6, aspect ratios 1.4 ≤ A ≤3.0 and elongation κ < 3.
To estimate the operational windows of SMART, andwith the aim of guiding the diagnostic and power supply
designs, linear and nonlinear MHD stability analysis has
been conducted for SMART tokamak with MARS-F [5]and MEGA [6] codes, respectively, to identify all thepossible MHD instabilities that could degrade SMART
performance. The target case is an ohmic baseline
scenario with Bt = 0.4 T and Ip = 0.2 MA. At the plasmacore, n = 1 internal kink and n = 2, …, 10 infernal modes
are found to be stable in advanced scenarios withmoderate triangularity (δ = 0.3) up to βN ≈ 2 in MARS-F
simulations. These modes are more unstable in NT
plasmas compared to positive triangularity (PT) plasmas.
MARS-F simulations including toroidal flows have been
performed and reveal a significant stabilizing effect on
infernal modes, which is stronger in NT plasmas.
Nonlinear MHD MEGA simulations predict that thesecore MHD instabilities may lead to Internal
Reconnection Events (IRE) and, thus, to a significant
reduction of the core plasma pressure.

ThelinearMHD
stabilityboundaryofpeeling-ballooning (PB) modes at the plasma edge ofSMART has been obtained for PT and NT plasmas andfor two different aspect ratios, A = 1.98 (the expectedaspect ratio of SMART) and A = 3.00 (the typical aspectratio of conventional tokamaks), as seen in Fig. 1. The
stability boundary of PB modes is reduced when we
increase the aspect ratio from 1.98 to 3 in both PT andNT plasmas; as expected, ST plasmas have betterstability properties compared to conventional tokamak
plasmas. In NT plasmas, the stability boundary of thesemodes is reduced, which indicates that NT plasmas could
be a path to avoid the steep pressure gradients of H-mode
while keeping a substantial plasma β in SMART.
References[1] A. Mancini et al., Fusion Eng. Des. 192, 113833(2023).
[2] M. Agredano-Torres et al., Fusion Eng. Des. 168,112683 (2021).
[3] S.J. Doyle et al., Fusion Eng. Des. 171, 112706(2021).
[4] S.J. Doyle et al., PREX 3, 044001 (2021).
[5] Y.Q. Liu et al., Phys. Plasmas 7, 3681 (2000).
[6] Y. Todo et al., Phys. Plasmas 5, 1321 (1998).
[7] R. Akers et al., Nucl. Fusion 40, 1223 (2000).
*See http://www.psft.eu/people/Figure 1: MHD stability diagram for PB modes for aspect ratio A = 1.98 (top row) and A = 3.00 (bottom row), with δ = 0.3 (a), (c)and δ = -0.3 (b), (d). Colour indicates linear growth rate of the most unstable mode at each grid point of the (αmax, jped/<j>) mesh.