In the heart of China, scientists are unraveling the mysteries of plasma behavior, edging us closer to a future powered by fusion energy. At the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, researchers have observed a phenomenon that could significantly impact the development of sustainable, clean energy sources. The findings, led by Dr. C.X. Luo of the Institute of Plasma Physics at the Chinese Academy of Sciences and the University of Science and Technology of China, were recently published in Nuclear Fusion, a journal that translates to “Nuclear Fusion” in English.
Imagine a tokamak, a doughnut-shaped device designed to confine hot plasma using magnetic fields. Inside this magnetic cage, a complex dance of particles unfolds. Among these particles are runaway electrons, which, under certain conditions, can excite waves known as Beta-induced Alfvén eigenmodes (BAEs). These waves, observed in low-density Ohmic discharges, rotate in the electron diamagnetic drift direction and have a toroidal mode number mainly of n = −1.
Dr. Luo and his team found that these BAEs become unstable when the electron density drops below a critical threshold. “As the electron density decreases, the resistive current is gradually replaced by the current carried by runaway electrons,” Dr. Luo explained. This shift leads to the simultaneous observation of multiple branches of unstable BAEs, each located at different rational surfaces within the plasma.
The sensitivity of these BAEs to the plasma beta contributed from runaway electrons is a crucial finding. Plasma beta is a measure of the plasma pressure relative to the magnetic pressure. Understanding how BAEs respond to changes in plasma beta is vital for controlling plasma stability in future fusion reactors.
The implications of this research are profound for the energy sector. Fusion power, if harnessed effectively, could provide a nearly limitless source of clean energy. However, controlling the plasma within a tokamak is a formidable challenge. The observations made at EAST bring us one step closer to understanding and mitigating the instabilities that can disrupt the fusion process.
Simulation results using the global eigenvalue code magnetohydrodynamic Alfvén spectra suggest that trapped energetic particles are responsible for the destabilization of these BAEs. These particles match the resonance condition, and the mode locations are close to the plasma boundary. This insight could inform the design of future tokamaks, helping engineers to create more stable and efficient fusion reactors.
The energy sector is keenly watching developments in fusion research. Companies and governments worldwide are investing heavily in fusion technology, hoping to tap into its potential. The observations at EAST, published in Nuclear Fusion, add a new layer of understanding to the complex interplay of forces within a tokamak. As Dr. Luo and his team continue their work, the world watches, hopeful that their efforts will bring us closer to a future powered by the same process that fuels the sun.