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A key issue for next-generation fusion reactors is the possible impact of many unstable Alfvén eigenmodes, wave-like disturbances produced by the fusion reactions that ripple through the plasma in doughnut-shaped fusion facilities called "tokamaks." Deuterium and tritium fuel react when heated to temperatures near 100 million degrees Celsius, producing high-energy helium ions called alpha particles that heat the plasma and sustain the fusion reactions.
These alpha particles are even hotter than the fuel and have so much energy that they can drive Alfvén eigenmodes that allow the particles to escape from the reaction chamber before they can heat the plasma. Understanding these waves and how they help alpha particles escape is a key research topic in fusion science.
Waves - Reaction - Chamber - Effect - Alpha
If only one or two of these waves are excited in the reaction chamber, the effect on the alpha particles and their ability to heat the fuel is limited. However, theorists have predicted for some time that if many of these waves are excited, they can collectively throw out a lot of alpha particles, endangering the reactor chamber walls and the efficient heating of the fuel.
Recent experiments conducted on the DIII-D National Fusion Facility, which General Atomics operates for the U.S. Department of Energy (DOE) in San Diego, have revealed evidence that confirms these theoretical predictions. Losses of up to 40 percent of high-energy particles are observed in experiments when many Alfvén waves are excited by deuterium beam ions used to simulate alpha particles and higher-energy beam ions in a fusion reactor such as ITER, which is now under construction in the south of France.
Wake - Research - DOE - Princeton - Plasma
In the wake of this research, physicists at the DOE's Princeton Plasma Physics Laboratory (PPPL) produced a quantitatively accurate model of the impact of these Alfvén waves on high-energy deuterium beams in the DIII-D tokamak. They used simulation codes called...
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