Radio waves

Scientists develop new tool to measure radio waves in fusion plasmas

Physicist Grant Rutherford with images from his article. Credit: Natalie Rugg, collage by Elle Starkman / Office of Communications

Scientists seeking to bring the fusion energy that drives the sun and stars to Earth use radio frequency (RF) waves – the same waves that bring radio and television into homes – to heat and draw power into the plasma that feeds the fusion reactions. Scientists have now developed an innovative way to measure waves that could be used to validate predictions of their impact, paving the way for future improved experiments that could bring fusion energy to Earth.

Potential breakthrough

The potential breakthrough, led by researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), could lead to follow-up experiments on upgrading the national experiment on the tokamak spherical (NSTX-U), the flagship fusion experiment at PPPL under repair, as well as other fusion facilities around the world. “If our method works, it would be a very useful tool for many fusion reactors,” said Grant Rutherford, a first-year graduate student at the Massachusetts Institute of Technology (MIT) and lead author of an article in the Review of scientific instruments which he wrote as an intern in the Brown University DOE Undergraduate Science Lab (SULI) at PPPL.

The key to predicting the impact of RF waves is to measure the fluctuations, or oscillations, they create in the density of fusion plasmas. “Once we have these fluctuations, we would be able to work back to see what those RF fields were that created the fluctuations,” Rutherford said.

However, the high frequency of RF waves causes oscillations that are too fast to be measured. The researchers therefore created a “beat wave” by launching two waves at different frequencies, a technique that produced measurable oscillations. “If we could both create a beat wave fluctuation and measure it, we would have a new tool to validate the predictions of RF heating and current entrainment,” Rutherford explained.

Such measures would have many advantages. For example, they could facilitate the study of the performance of RF wave actuators, said PPPL physicist Nicola Bertelli, co-author of the article, and could allow validation of RF computational tools developed throughout the community of fusion. Additionally, said David Smith, a University of Wisconsin physicist and co-author of the paper, “Our calculations provide an initial assessment of the technique and motivate the follow-up experiments on NSTX-U.”

Fusion reactions combine light elements in the form of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei that make up 99% of the visible universe – to generate massive amounts of energy. Replicating and controlling this process on Earth would create a virtually inexhaustible supply of safe and clean energy to generate electricity. The merger could become a major contributor to the United States’ transition from fossil fuels to a low-carbon source of power generation.

Test the technique

Rutherford and his co-authors tested their technique by creating a synthetic version of a diagnostic 2D beam emission spectroscopy (BES) to assess simulated RF injections into plasma. Their goal was to understand and improve the ability to measure the RF field waves that create the oscillations.

Going forward, “we hope that by increasing our measurement capability we will increase our ability to understand current heating and training processes, but we leave that to future work,” said Rutherford. Such work could also show whether the BES diagnostic that the scientists based their model on could measure changes in density in actual fusion plasmas, or whether another diagnostic would do the critical work better.

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More information:
Grant Rutherford et al, Scoping Study of Detection of Fast High Harmonic Waves in NSTX-U Hot Core Plasma Directly Using Beam Emission Spectroscopy, Review of scientific instruments (2021). DOI: 10.1063 / 5.0040399

Provided by Princeton University

Quote: Scientists develop new tool to measure radio waves in fusion plasmas (2021, July 14) retrieved January 11, 2022 from -plasmas.html

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