Overview of EXL-50U experiments: addressing key physics issues for future spherical torus reactors

Le résumé fourni par la source

Abstract ENN’s Xuanlong-50U (EXL-50U) is the world’s first fully privately funded and operated MA-level magnetic confinement fusion experimental facility. EXL-50U is also the world’s first spherical torus device (ST) to achieve a magnetic field exceeding 1 Tesla and a pulse width reaching the seconds level in actual operation. The major radius of EXL-50U ranges from 0.6 m to 0.8 m, with an aspect ratio of 1.4–1.8. The key physics issues of EXL-50U’s experiments related to the future ST reactors are: non-inductive current start-up and drive, development of scenarios for stable high density hot ion mode for ST ( T i0 = 3 keV ∼ 10 keV), and investigation of energy confinement scaling through wide range scans of aspect ratio (1.4 ∼ 1.8) and B T (0.5 T ∼ 1.2 T). Another key research focus of EXL-50U is the physical properties of hydrogen–boron (p-B) plasmas and hydrogen–boron fusion, which is closely aligned with ENN’s p-B fusion roadmap. In the 2025 experiment, EXL-50U achieved a p-B plasma discharge at 1 MA (with boron ions exceeding 10% in the ion fraction), marking the world’s first MA-level discharge of high-concentration p-B plasma. A recording 270 kA fully non-inductive current by 380 kW electron cyclotron resonance heating (ECRH) is also achieved. The initial real-time boron-power injection experiments with metal wall in EXL-50U demonstrates the positive effective of boron on plasma performance. Through neutral beam injection (NBI) heating, a stable proton-boron plasma H-mode has also been achieved for the first time on EXL-50U. On the other hand, experimental results also indicate that simultaneous injection of ECRH and NBI is detrimental to ion temperature enhancement. AI technology was also applied in EXL-50U experiments, achieving stable 500 kA plasma current and displacement control for over 500 ms. Supersonic molecular beam injection was applied for density feedback control for the first time in ST device. ENN researchers plan to achieve all of EXL-50U’s milestone objectives within a three-year timeframe, contributing their efforts toward the rapid commercialization of magnetic confinement fusion.

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