In the quest to harness fusion energy, scientists are continually refining techniques to protect the tokamak devices that house these reactions. A recent study published in the journal *Nuclear Fusion*, titled “Effects on characteristics of plasma disruption mitigation using shattered pellet injection with different shatter tubes on EAST,” sheds light on a critical aspect of this process. Led by L. Li from the Institute of Plasma Physics at the Chinese Academy of Sciences and the University of Science and Technology of China, the research explores how different designs of shattered pellet injection (SPI) systems can influence the mitigation of plasma disruptions.
Plasma disruptions pose significant risks to tokamak devices, potentially causing severe damage. SPI is a technique used to mitigate these disruptions by injecting small, shattered pellets of impurities into the plasma. The study compares the standard 20°-bend shatter tube with a newly developed horizontal straight tube, referred to as the insufficiently shattered pellet injection (ISPI) system. This comparison aims to understand how different tube designs affect the characteristics of disruption mitigation.
The findings reveal that ISPI produces larger and off-axis injected fragments without reducing their velocity. This results in a pre-thermal quench (pre-TQ) duration about 1.5 times longer than that achieved with conventional SPI. According to the study, this is attributed to reduced impurity assimilation. However, the current quench duration is 0.83 times shorter with ISPI, likely due to the fast dissipation of plasma current via halo current caused by a cold vertical displacement event (VDE).
“ISPI facilitates a slightly more uniform poloidal radiation distribution during the TQ phase,” explains Li. “However, it is associated with weaker mitigation of halo currents, with a mitigation rate of 27.3% compared to SPI’s 64.7%.”
These insights are crucial for optimizing the SPI strategy for ITER, the world’s largest tokamak under construction in France. Balancing radiation homogeneity, electromagnetic load management, and magnetohydrodynamic (MHD) stability is essential for the safe and efficient operation of such advanced fusion devices.
The research highlights the importance of tailoring SPI systems to achieve the best possible mitigation of plasma disruptions. As Li notes, “Understanding the nuances of different shatter tube designs can significantly impact the effectiveness of disruption mitigation strategies.”
For the energy sector, these findings could pave the way for more robust and efficient fusion reactors. By refining SPI techniques, scientists can enhance the safety and reliability of tokamak devices, bringing us closer to the realization of practical fusion energy. The study, published in *Nuclear Fusion*, underscores the ongoing efforts to optimize these technologies, offering a glimpse into the future of fusion energy research.