Otto Vihtori Asunta, Shereen Abouelazayem, Tara Ahmadi, А. И. Алиева, Michail Anastopoulos-Tzanis, Yasmin Andrew, Thomas Ashton-Key, Nicola Bertelli, H. Bohlin, Trenton R. Brewer, Joe Bryant, J.W. Buck, Peter Francis Buxton, Choong Seock Chang, Cary Colgan, Ephrem Delabie, Aleksei Dnestrovskii, V. N. Duarte, Alexandra Dudkovskaia, Joanne Flanagan, M. Fontana, Michael Gemmell, Travis Gray, Mikhail Gryaznevich, Jussi Hakosalo, M. Iliasova, Filip Janky, Jisung Kang, Stanley M Kaye, D Kos, Seung-Hoe Ku, J D Lee, B. Lomanowski, Nicolas Lopez, Hazel Lowe, E. Maartensson, R Maingi, C. Marsden, L. Martinelli, Steven A.M. McNamara, Sergei Y Medvedev, Reza Mirfayzi, L. Morgan, Yong-Su Na, Graham Naylor, Vadim Nemytov, T. O’Gorman, Masayuki Ono, Yasushi Ono, A. P. K. Prokopyszyn, Yang Ren, A. Rengle, Matthew Robinson, M. Romanelli, Andrea Scarabosio, M. Scarpari, M. Sertoli, Vladimir F Shevchenko, Taaj Sian, J. Sinha, Alsu Sladkomedova, Sundaresan Sridhar, James Hutchison Stirling, Y. Takase, Hiroshi Tanabe, Paul Thomas, Erin Tinacba, Jari Varje, Elena Vekshina, Benjamin Vincent, H. Weisen, Hannah Victoria Willett, C. G. Windsor, Jonathan Wood, Emma Wooldridge, Xin Zhang
Abstract The goal of the ST40 programme is to explore the physics of high-field spherical tokamaks (STs), to validate empirical and theoretical models and, hence, to build confidence in predictions required to support the design of future generations of STs. ST40 is a compact high-field ST that has achieved the following parameters: R 0 = 0.4–0.55 m, I p = 0.20–0.85 MA, B t ( R = 0.4 m) = 0.7–2.1 T, κ ⩽ 1.9, and A = 1.6–1.9. Highlights of recent experimental results include (i) H-mode and confinement studies at B t ⩽ 2.1 T, (ii) observation of bifurcation of the scrape-off-layer power fall-off width, λ q , into a ‘wide’ branch that follows existing H-mode scalings and a ‘narrow’ branch that exhibits λ q values that are up to 10 times lower than the predictions of established scalings, (iii) development of high-performance scenarios with plasma current, I p , up to 0.85 MA, (iv) development of highly non-inductive scenarios with high β p , and (v) the first ST40 experiments utilising the newly commissioned impurity powder dropper. The work on all these topics has been supported by a number of advancements in ST40 hardware and software, from plasma control to data analysis and interpretation. At the end of 2025, ST40 embarked on a major upgrade to further expand its capabilities by introducing, among other improvements, all-metal plasma-facing components, 1 MW of electron cyclotron heating, a pellet injector, and a pair of lithium evaporators for wall conditioning.