Speaker
Description
Future fusion power plants will operate in the burning plasma regime, where a substantial fraction of the plasma heating is provided by fusion-born alpha particles produced in DT reactions. Understanding the generation, slowing down and confinement of these energetic particles is therefore essential and remains a major objective of present experimental, theoretical and modelling efforts in preparation for ITER operation.
Following the end of the JET programme, no currently operating large tokamak is able to use DT fuel because of the stringent safety and regulatory constraints associated with the high neutron yield of DT reactions. This is the case for the JT-60SA tokamak in Naka, Japan, presently the largest operating tokamak in the world. Nevertheless, alternative routes for alpha-particle production can be explored in JT-60SA-relevant plasmas ahead of future experimental campaigns.
In this work, first-of-a-kind numerical studies are presented for JT-60SA based on two fusion schemes: D+3He ®4He+p [1] and p+11B®34He [2]. The alpha-particle birth energies associated with these reactions are comparable to 3.5MeV alphas produced in DT fusion: the D+3He channel generates 3.6 MeV alpha particles, while the two most energetic alpha particles produced in the p+11B reaction carry energies of approximately 4 MeV. Since beam–target reaction rates in JT-60SA are enhanced by the high-power (up to 10MW) negative-ion neutral beam injection system [3], capable of beam energies up to 500 keV on both deuterons and protons, the device is a particularly favourable platform for establishing a solid alpha physics programme (see also Fig. 1 from cross section dependency on beam energy in lab frame), along similar lines but at higher alpha birth rates as previously done at JET i.e. investigating alpha generation and confinement, the role of alphas on MHD and turbulence, and the development and validation of dedicated alpha-particle diagnostics in reactor-relevant conditions [4-6,7].
Using the state-of-the-art ASCOT5 suite to model neutral beam injection, fast-ion slowing down and fusion reactions with beam–thermal distributions, we investigate the production and confinement during the typical 0.5- 0.7s of slowing down time of alpha particles arising from both D-3He and p-B scenarios relevant for future JT- 60SA operations. The sensitivity of alpha-particle generation to plasma density, temperature, vertical plasma position is assessed in order to identify trends relevant for scenario optimisation and future experiments. Alpha loss channels from MHD are also investigated. This exploratory work opens the way for a sustained alpha-particle physics programme in JT-60SA. Although the expected fusion yields remain below those achievable in DT plasmas, they are nevertheless expected to be sufficiently high to access key energetic-particle physics processes under reactor-relevant conditions. In particular, recent estimates [8] indicate that, at half the 3He concentration used at JET during the highest alpha birth rates achieved in D+3He experiments (up to 25% 3He concentration), alpha birth rates at least twice as large may be obtained, thereby extending the accessible parameter space for the study of alpha-driven transport, interactions with MHD activity and turbulence, and the possible emergence of collective energetic-particle phenomena not previously observed experimentally.
Figure 1 online
Figure 1: JT-60SA enables studies of alpha-particle physics without introducing tritium into the plasma by utilizing the high-power N-NBI system. (a) Fusion cross-section for D+3He reactions between N-NBI deuterons and 3He ions (in red) and DT reactions between N-NBI deuterons and T ions (dashed black); (b) Fusion cross-section for p-B reactions between N-NBI protons and B impurities (link: https://www.dropbox.com/scl/fi/q0i80ot6u5hs8srjhxk8k/Figure1.png?rlkey=jfe32h06qtftf8bce98j7lrs9&dl=0)
References
[1] Jacquinot, J., Sadler, G. J., Fusion Technology, 21(4), 2254–2264 (1992)
[2] Magee, R.M., Ogawa, K., Tajima, T. et al., Nat Commun 14, 955 (2023)
[3] Garcia J. et al, Nucl. Fusion https://doi.org/10.1088/1741-4326/ae74e1 (2026)
[4] Kazakov Ye. O., et al., Nucl. Fusion 60, 112013 (2020)
[5] Kiptily V., et al., Plasma Phys. Control. Fusion 64, 064001 (2022)
[6] Nocente M., et al., Rev. Sci. Instrum. 93, 093520 (2022)
[7] Kiptily V., see presentation at this conference.
[8] Coelho R., et al., submitted to Nucl. Fusion (2026)