A new experiment using a tokamak-type reactor—that is, a toroidal chamber with a magnetic coil—has been successful. The plasma was successfully sustained for more than one minute.
Tokamak. Source: Wikipedia
Need for regulation of extreme thermal loads in a tokamak
For the first time, a research team has demonstrated, within a metal-walled environment, a plasma regime that simultaneously achieves partial divertor separation, a high-confinement regime (H-mode) without edge localized modes (ELMs), and high “pedestal” values. This complex regime was maintained for several minutes, and the results of the study were published in the journal Physical Review Letters.
The team was led by Professor Xu Guosheng of the Institute of Plasma Physics at the Hefei Institute of Physical Science of the Chinese Academy of Sciences.
For controlled nuclear fusion, it is necessary to regulate the extreme thermal loads on the divertor plates while maintaining plasma stability. Although impurity gases can reduce the divertor heat flux through dissipation, excessive cooling can damage the plasma edge, and H-mode plasmas are prone to sudden, destructive ELMs. Reaching a steady state that would resolve both issues was the primary international goal.
In this study, the team controlled the injection of light impurity gases to create a new plasma mode on the EAST tokamak, known as the detached divertor and turbulence-dominated pedestal (DTP) regime.
Thanks to precise real-time adjustment of the gas flow, the team achieved partial divertor separation while maintaining plasma stability. In this mode, the heat flux of the divertor plates was significantly reduced, ELMs were completely suppressed, and the electron temperature at the pedestal increased significantly, which improved the overall energy content.
Maintaining the plasma for one minute
Partial separation, combined with the closed geometry of the diverter and the trapping and pumping of neutral particles, reduced the cooling of the pedestal and enhanced the temperature gradient.
The enhanced gradient led to the emergence of microturbulence, defined as modes of confined electrons driven by the temperature gradient, which naturally transported particles and heat outward.
This transport channel limited the pressure buildup in the pedestal, prevented the onset of extreme localized regimes, and ensured a stable, high-performance plasma for one minute—an important step toward the stable operation of long-pulse fusion.
According to the team, this study offers a potential solution to the long-standing problem of balancing divertor thermal load control with effective plasma containment.
According to phys.org