Breakthrough in China's fusion energy: HL-3 tokamak achieves high ion temperature and fusion triple product

Controlled nuclear fusion represents the holy grail of clean energy, offering a nearly limitless power source with minimal environmental impact: China’s HL-3 tokamak, a key experimental device in the country’s fusion program.1,2 The deuterium-trillium (DT) fusion reaction depends on the plasma ion temperature. The reaction rate increases exponentially with increasing Ti. The fusion triple product (niTiτE) is a key metric for the fusion performance, where ni and τE are the plasma ion density and energy confinement time, respectively. China’s HL-3 tokamak has achieved groundbreaking plasma performance based on the hot ion mode, which is a kind of plasma operational regime where Ti significantly exceeds Te in the core plasma,3 namely, Ti(0)/Te(0) > 1, reaching ion temperatures Ti = 10 keV, exceeding 100,000,000°C (equal to 8.6 keV), and crossing the threshold for efficient DT fusion, and a fusion triple product surpassing 0.65 × 1020 keV s/m3, setting new national records approaching reactor-relevant conditions. These breakthroughs position HL-3 as a cornerstone of China’s fusion strategy and contribute valuable data to international efforts such as ITER. These milestones demonstrate significant progress in China’s quest for controlled thermonuclear fusion and provide critical data for next-generation fusion reactors. This news details the technological innovations behind these achievements and discusses their implications for China’s fusion energy roadmap.

Technological innovations

HL-3’s success stems from cutting-edge engineering solutions. These include (1) upgrading power supplies to enable an enhanced toroidal magnetic field (Bt = 2.0 T) and producing highly shaped plasma with large elongation (k ≥ 1.6) and strong triangularity (δ ≥ 0.5) to enhance plasma current and stored energy. (2) Deploying high-power neutral beam injection (NBI) systems. Heating power injected into plasma higher than 5 MW is available. A maximum beam current and accelerating voltage of 34 A/78 kV and 40 A/46 kV, respectively, have been successfully achieved. (3) Implementing comprehensive diagnostics and data integration. Charge exchange recombination spectroscopy (CXRS), based on a triple-grating spectrometer with a radial resolution of 1.5 cm, is used to measure the ion temperature and toroidal rotation, and the Thomson scattering (TS) diagnostic, featuring 60 spatial channels, is capable of precisely measuring the electron density and temperature profiles. The hot ion mode scenario involves a mega Ampere current ramp-up to create weak magnetic shear, accompanied by high-power NBI for heating and strong flow shear production.