Fusion energy is being explored as a new source of electricity that could help achieve a carbon-neutral society. At the National Institute for Fusion Science, research is being conducted on magnetically confined plasma using the Large Helical Device (LHD). One key characteristic of plasma, compared to other gases, is its extremely low density—about one millionth that of the atmosphere. Due to this low density, particle collisions are rare, causing the plasma's velocity distribution function (a histogram of particle motion) to become distorted. These distortions can lead to unexpected plasma behaviours, such as sudden temperature changes and current generation. As a result, a deeper understanding of the underlying physics is crucial.

Figure 1. Plasma Phase Space

Spectroscopy, which measures the light emitted from plasma, is often used to determine the plasma’s velocity distribution function. However, because the total light emitted is limited, spatial resolution must be sacrificed to measure the time variations in the velocity distribution. To predict and control plasma behaviour for fusion energy applications, it is essential to understand how the plasma’s phase-space distribution, which resolves both velocity and spatial coordinates, changes over time. Figure 1 shows Plasma Phase Space.

A research team led by Associate Professor Tatsuya Kobayashi, Assistant Professor Mikio Yoshinuma, and Professor Katsumi Ida at the National Institute for Fusion Science has made significant progress by achieving high-speed, high-precision measurements of the plasma phase distribution. They applied tomography techniques, commonly used in the medical field, to the plasma diagnostics. They installed a "high-speed luminescence intensity monitor" alongside existing "high-resolution" and "high-speed spectrometers," enabling coordinated operation of all three instruments. By integrating the data from these systems, they used tomographic analysis to reconstruct the plasma phase-space distribution. This allowed them to measure the plasma phase-space distribution at an unprecedented speed of 10,000 Hz (10,000 times per second)—a 50-fold improvement over the previous 200 Hz.

Phase-space tomography was applied in LHD experiments to study the energy exchange between plasma and beam particles via waves. It was found that particles moving at velocities close to the waves are accelerated by them, gaining energy in a process similar to how surfers gain speed by moving with waves. This wave-particle interaction is crucial for efficient plasma heating, which is key to successful fusion energy production. The study revealed that, in addition to waves moving primarily in the toroidal direction, rightward and leftward waves can occur simultaneously, leading to more efficient particle acceleration and improved plasma heating.

This research demonstrates that by simultaneously operating different diagnostic tools and integrating their data, researchers can achieve measurement capabilities that exceed the performance of any single instrument. This technique is expected to play a vital role in future fusion energy experiments, helping scientists better control plasmas by analysing their phase-space distribution. Since collision less plasmas are also present in natural phenomena such as the sun and auroras, phase-space tomography could have broader applications in various fields.

Reference:

1. https://www.eurekalert.org/news-releases/1066554
2. https://www.eurekalert.org/news-releases/1065641
3. https://www.labmedica.com/molecular-diagnostics/articles/294803273new-approach-to-help-predict-drug-resistance-in-malaria-and-infectious-diseases.html

Cite this article:

Priyadharshini S (2024), Advancing the Plasma Phase-Space: Harnessing Data Science for Predictive Insights and Unexplored Phenomena , Anatechmaz, pp.94