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First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves

Year: 2025
Type: article
Abstract: Helicon waves (also known as whistler waves) satisfying the normal wave-particle cyclotron resonance are observed to limit the growth and maximum energy of relativistic electrons (REs) in low-density Ohmic DIII-D tokamak plasmas. Following the application of helicon waves, pitch-angle scattering of high-energy REs causes an increase in both synchrotron and electron-cyclotron emissions. The hard x-ray emission, a proxy for the RE population, ceases to grow. Energy-resolved hard x-ray measurements also show a striking decrease in the number of high-energy REs (above the resonance at approximately 8 MeV) to below the noise floor and an increase in low-energy (∼4 MeV) REs. This occurs despite the toroidal electric field remaining high enough to drive exponential RE growth in the absence of helicon waves. These results open new directions for limiting the maximum energy of RE populations in laboratory and fusion plasmas.
DOI: 10.1103/jz8f-ck22
Authors: H. Choudhury, A. Battey, C. Paz-Soldan, J. Lestz, N. Leuthold, A. Lvovskiy, C. Marini, J. Barr, W. Heidbrink, D. Spong, S. Tang, B. Van Compernolle, Q. Zhang, Y. Zhang, X. Tang
Institutions: Columbia University, École Polytechnique Fédérale de Lausanne, General Atomics (United States), University of California San Diego, University of California, Irvine, Oak Ridge National Laboratory, Los Alamos National Laboratory
Language: English
Open Access status: green
Funders: U.S. Department of Energy, National Energy Research Scientific Computing Center, Office of Science, National Nuclear Security Administration, Fusion Energy Sciences, Los Alamos National Laboratory
Awards: G1273338650, G1279347439, G1527966216, G333530719, G3696093938, G4137473101, G42916606, G5926961310, G7599273585
OpenAlex ID: W4417430609
FWCI: 1.894
Cites: 55
Cited by: 4
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