Spherical tokamak physics research in preparation for the operation of NSTX-U
Year: 2026
Type: article
Abstract: The National Spherical Torus Experiment Upgrade (NSTX-U) is preparing to resume operation, representing a crucial step toward realizing compact, cost-effective fusion pilot plants. In advance of this, extensive modeling and data analysis have been conducted to advance the physics basis for low-aspect-ratio, high-performance plasma regimes, focusing on three core objectives: confinement and stability, power and particle handling, and steady-state operation. Significant progress has been made in understanding the electron temperature flattening in high- β plasmas, which is shown to be driven by a complex interplay of magnetohydrodynamic instabilities (e.g. non-resonant infernal modes), fast-ion-driven Alfvén eigenmodes, and electron and ion-scale micro-instabilities, particularly Kinetic Ballooning Modes (KBMs), whose destabilization is strongly dependent on parallel magnetic field fluctuations ( δ B ∥ ). Furthermore, a new gyrokinetic critical pedestal model was developed, accurately predicting pedestal structure by identifying KBMs as the primary stability limit, offering a critical constraint for future high-confinement scenarios. To address the challenge of high heat flux, novel liquid lithium plasma-facing components were modeled. The analysis confirmed that lithium vapor shielding is a self-regulating mechanism for heat mitigation, while also emphasizing that strong main ion parallel flow is essential to minimize core lithium contamination. Finally, progress toward steady-state operation was anchored by developing the required physics basis and control tools. This includes predictive modeling for reversed magnetic shear sustainment, demonstrating that magnetic island-induced bootstrap current reduction is negligible in STs, and advancing real-time control and disruption avoidance capabilities. The development of high-speed surrogate models (e.g. MMMNet) provides computationally efficient tools vital for non-inductive scenario optimization and integrated, low-disruptivity operations planned for NSTX-U.
Source: Nuclear Fusion
Authors: S. Munaretto, P.O. Adebayo-Ige, H. Anand, G. Avdeeva, S.G. Baek, K. Barada, E. Belli, E.V. Belova, J.W. Berkery, T.N. Bernard, N. Bertelli, P. Bonofiglo, P.T. Bonoli, M.D. Boyer, J. Candy, C.S. Chang, H. Chung, C. Clauser, M. Comanescu, D. Corona, N.A. Crocker, R. De Levante Rodriguez, E.W. DeShazer, A. Diallo, J. Dominski, V.N. Duarte, F. Ebrahimi, E.D. Emdee, S. Ethier, N.M. Ferraro, E.L. Foley, E.D. Fredrickson, M.E. Galante, K.F. Gan, S. Gerhardt, R.J. Goldston, M. Gorelenkova, W. Guttenfelder, R. Hager, F.D. Halpern, J. Halpern, D. Hatch, F. Hoffmann, M.S. Islam, S.C. Jardin, S.M. Kaye, A. Khodak, J.E. Kinsey, A. Kleiner, E. Kolemen, S. Ku, M. Lampert, B. Leard, B.P. LeBlanc, J.B. Lestz, F.M. Levinton, P.-Y. Li, N.C. Logan, N.A. Lopez, R. Lunsford, T. Macwan, R. Maingi, J. McClenaghan, A.G. McLean, J.E. Menard, Y.-S. Na, A.O. Nelson, M. Ono, A. Pajares, A. Pankin, J. Parisi, F.I. Parra, M.S. Parsons, B.S. Patel, M. Podestá, F.M. Poli, M. Porcelli, T. Rafiq, R. Raman, J.D. Riquezes, S.A. Sabbagh, A. Sanchez-Villar, E. Schuster, S. Shiraiwa, T. Singh, S.P. Smith, D. Smith, V.A. Soukhanovskii, G.M. Staebler, B. Stratton, K.E. Thome, M. Tobin, I.U. Uzun-Kaymak, B. Van Compernolle, W.X. Wang, W. Wehner, A.S. Welander, B.D. Wirth, J. Yang, V. Zamkovska, X. Zhang
Institutions: Princeton Plasma Physics Laboratory, University of Tennessee at Knoxville, General Atomics (United States), Massachusetts Institute of Technology, University of California, Los Angeles, Commonwealth Fusion Systems (United States), Seoul National University, Nova Photonics (United States), Type One Energy, Columbia University, The University of Texas at Austin, Lawrence Livermore National Laboratory, CompX (United States), Princeton University, Lehigh University, Tokamak Energy (United Kingdom), United Kingdom Atomic Energy Authority, École Polytechnique Fédérale de Lausanne, ITER, University of Washington, University of Wisconsin–Madison, Oak Ridge National Laboratory
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,595
Funder: Fusion Energy Sciences
Award: G180959178
OpenAlex ID: W7124457586