Pellet injection advances to next stage in the US
Researchers at the Oak Ridge National Laboratory (ORNL) have developed a continuous extruder for fusion fuel and are advancing state-of-the-art fuelling and plasma control for ITER. Reliable, high-speed continuous fuelling is essential for ITER to meet its goal of operating at 500 MW for several minutes at a time. The latest pellet injection experiments using US ITER prototype designs were performed during the week of 22 July at the DIII-D Tokamak operated by General Atomics in San Diego, California. The conceptual design review for the ITER pellet injection system was completed earlier this year, and preparations are now underway for full-scale prototype testing. The task of the pellet injection system is to provide plasma fuelling, while also lessening the impact of plasma instabilities due to large transient heat loads. The ITER pellet injectors must operate continuously, which is very different from most existing tokamak pellet injectors. The ITER machine also requires a higher rate of pellet fuelling throughput. According to Dave Rasmussen, team leader for the US ITER pellet injection and disruption mitigation systems, „The ITER pellet injectors will require an increase in the deuterium-tritium mass flow and duration by a factor of 1,000 compared to present systems.” To produce the pellets, researchers developed a twin-screw extruder which shapes a continuous ice stream of deuterium-tritium fuel into specific diameters and lengths. „There are existing extruders used on tokamaks today, but they cannot meet the requirements of ITER. On most current installations, extruders have only needed to supply a few seconds of fuel pellets at a time, but the ITER Tokamak will require almost an hour of a continuous ice stream for pellet injection. The ORNL twin-screw extruder is designed to meet t Czytaj dalej...