ORNL’s pellet injector enables world record performance in W7-X
Advances in continuous pellet injection fueling lead to performance record on Wendelstein 7-X stellarator experiment
image: A plastic replica of the pellets formed by the system on W7-X, next to a dime, for size reference, and the cutter that extracts the pellet from the extrusion, as seen in the video below.
Credit: Larry Baylor/ORNL, U.S. Dept. of Energy
A key milestone in the pursuit of fusion energy is achieving a high “triple product,” an important metric of the temperature and density of a burning plasma and how well it is confined. The Wendelstein 7-X stellarator in Greifswald, Germany recently sustained a plasma with a record high triple product for 43 seconds – far surpassing previous performance – in part due to a novel fuel pellet injection system developed by researchers at Oak Ridge National Laboratory.
“The W7-X device had previously achieved high performance for short durations, but they couldn’t sustain it at high plasma density,” said ORNL engineer Steve Meitner. “That’s where we came in.”
The ORNL pellet fueling system designed for the W7-X device injects a continuous, high-speed stream of solid hydrogen pellets – formed at 12 degrees above absolute zero – directly into the 30-million-degree plasma. This supplies more fuel to the core of the plasma than other fueling approaches and maintains a higher plasma density, which in stellarators also plays a uniquely important role in improving the confinement of plasma energy.
The record-breaking W7-X campaign was led by the Max Planck Institute for Plasma Physics, in partnership with ORNL, Princeton Plasma Physics Laboratory, and the National Institute of Fusion Science in Japan.