Researchers visualize energetic ion flow in fusion devices

In a burning plasma, maintaining confinement of energetic ions produced by fusion is essential for energy production. These fusion plasmas host a wide range of electromagnetic waves that can drive energetic ions out of the plasma.

This reduces the heating of the plasma due to fusion reaction products and ends the burning state of the plasma. Recent measurements at the DIII-D National Fusion Facility provide the first direct observations of energetic ions moving through space and energy in a tokamak.

The researchers combined these measurements with advanced computer models of electromagnetic waves and their interaction with energetic ions. The results provide a better understanding of the interaction between plasma waves and energetic ions in fusion plasmas.

Plasma and fusion physics research is moving from experimental setups to demonstration power plant designs. To do this successfully, researchers need accurate simulations and other tools to predict the performance of power plant designs. Most current installations do not produce burning plasmas.

However, researchers understand much of the relevant physics and develop simulations to reproduce the observed experimental behavior. Ongoing research has made it possible to carry out new measurements of the flow of energetic ions in the DIII-D tokamak. This will accelerate the development of models that take into account all relevant wave-ion interaction dynamics. This improved understanding also enables the application of phase space engineering.

Researchers can use this process to design new fusion plasma scenarios based on predicted ideal interactions between waves and ions. Notably, these interactions can also damage satellites, so this research could help improve their reliability.

Researchers at the DIII-D National Fusion Facility, a Department of Energy user facility, used the first measurements from a new diagnostic system, the Imaging Neutral Particle Analyzer (INPA), to observe the flow of energetic ions in a tokamak.

A multi-year effort to conceptualize, design, and construct the INPA has now provided the first-ever ability to observe this behavior. After being injected into the tokamak by neutral beams, the energetic ions interact with electromagnetic waves from the plasma and flow in energy and position through the tokamak. Simulations reproduce observed behavior, demonstrating the accuracy of first-principles models in describing the underlying physics.

A better understanding of these wave-particle interactions is relevant for the design of fusion power plants and for understanding the behavior of plasmas observed in space.

INPA measures the energy of energetic ions injected by a neutral beam, which have energies higher than that of the background plasma, in time and spatial position, from the core of the hot plasma to the edge of the cold plasma , where ions can be lost.

Coupled with advanced high-performance computing simulations that model both the spectrum of electromagnetic waves and interactions with energetic ions, these experiments provide the most detailed understanding of the interaction between plasma waves and energetic ions in fusion plasmas.

This improved understanding also allows researchers to apply phase space engineering, a process in which they design new fusion plasma scenarios based on the predicted ideal interactions between waves and ions. These types of interactions occur in space.

For example, electromagnetic ion cyclotron (EMIC) waves flow electrons through space and energy. In some cases, the electrons were accelerated to the point of causing malfunctions in the satellites. A better understanding of resonant wave-particle interaction processes through fusion plasma research contributes to space plasma simulations, which could improve the reliability of future satellite missions.

The results are published in the journal Nuclear fusion.