US laboratory's deep fueling pellet injector aids in smashing nuclear fusion milestone

In a groundbreaking achievement, scientists at the Wendelstein 7-X (W7-X) stellarator in Greifswald, Germany, have successfully sustained a high-performance plasma for an unprecedented 43 seconds, thanks to the Oak Ridge National Laboratory's (ORNL) Continuous Pellet Fueling System.

The W7-X stellarator, the world's largest stellarator-type fusion device, is a fusion device that uses twisted magnetic fields to confine plasma in a donut-shaped chamber. Without sufficient density and confinement, the plasma's energy dissipates too quickly. The high-speed injection system, developed by ORNL in the early 1990s, was the key to this record-breaking experiment.

The ORNL pellet fueling system injects a continuous, high-speed stream of solid hydrogen pellets into the stellarator's plasma core. These frozen pellets are accelerated using a high-pressure pulse of helium gas. This method of deep fueling is more effective at raising the plasma's core density compared to puffing gas from the vessel's edge.

The primary metric for this achievement is the fusion "triple product," which combines three variables: the plasma's ion temperature, its density, and its energy confinement time. Sustaining the triple product is a significant technical challenge in fusion experiments. This result represents a notable advance in fusion energy research, where a key objective is to sustain the conditions necessary for a net energy gain.

The W7-X device had previously achieved high performance for short durations, but it couldn't sustain it at high plasma density. However, with the ORNL-designed Continuous Pellet Fueling System, scientists were able to overcome this hurdle.

This landmark achievement provides valuable data for validating the stellarator concept as a potential design for a future fusion power plant. The results of this experiment are a significant step forward in the quest for sustainable, clean, and virtually limitless fusion energy.

In May this year, at the Wendelstein 7-X facility in Germany, this novel fuel pellet injector developed by ORNL enabled the world record for sustaining a fusion-grade plasma at high performance over an extended time. This result is a testament to the potential of fusion energy research and the role ORNL's technology plays in pushing the boundaries of what is possible.