Scientists develop new tool to measure radio waves in fusion plasmas


Newswise – Scientists seeking to bring the fusion energy that powers the sun and stars to Earth are using radio frequency (RF) waves – the same waves that bring radios and televisions into homes – to heat and conduct the current in the plasma that powers the fusion reactions. Scientists have now developed a way to establish the pathway for measuring the waves that could be used to validate predictions of their impact, paving the way for future improved experiments that could involve the delivery of 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 the National Spherical Tokamak Experiment-Upgrade (NSTX-U), the flagship fusion experiment at PPPL under repair, as well as other fusion facilities around the world. “If our method proves successful, 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 a paper in the Examination of scientific instruments which he wrote as a Brown University DOE Science Undergraduate Laboratory (SULI) intern 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 those fluctuations, we can go back and see what those RF fields were that created the fluctuations,” Rutherford said.

However, the high frequency of the RF waves causes the oscillations to occur too quickly to be measured. So the researchers created a “beat wave” by launching two waves at different frequencies, a technique that produced measurable oscillations. “If we were able to both create a beat wave fluctuation and measure it, we would have a new tool to validate predictions for RF heating and current control,” 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 paper, and could allow validation of RF computational tools developed throughout the research community. fusion. Additionally, said David Smith, University of Wisconsin physicist and co-author of the paper, “Our calculations provide an initial assessment of the technique and motivate follow-up experiments on NSTX-U.”

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

Test the technique

Rutherford and his co-authors tested their technique by creating a synthetic version of a 2D beam emission spectroscopy (BES) diagnostic to evaluate 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 heating and current conducting processes, but we leave that for future work,” Rutherford said. Such work could also show whether the BES diagnostic on which the scientists based their model could measure density variations in actual fusion plasmas, or if another diagnostic would do the critical job better.

The DOE Office of Science (FES) supported this work.

PPPL, at Princeton University’s Forrestal Campus in Plainsboro, NJ, is dedicated to creating new knowledge about the physics of plasmas – ultra-hot, charged gases – and developing practical solutions for creating energy of merger. The lab is operated by the University for the U.S. Department of Energy Office of Science, which is the largest supporter of basic physical science research in the United States and works to address some of the most pressing challenges From our era. For more information, visit


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