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

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

doi:10.1103/jz8f-ck22

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

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

Fusion Theory and Modeling

Research output: Contribution to journal › Article › peer-review

1 Scopus citations

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 (∼4MeV) 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.

Original language	English
Article number	025101
Journal	Physical Review Letters
Volume	136
Issue number	2
DOIs	https://doi.org/10.1103/jz8f-ck22
State	Published - Jan 16 2026

Funding

The authors wish to thank J. Hanson for help on the plasma error-field correction, M. P. Ross for help programming the helicon waveforms, D. Liu for help setting up the hard x-ray scintillators, and R. Pinsker for helpful discussions about helicon wave propagation. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards No. DE-FC02-04ER54698, No. DE-SC0022270, No. DE-SC0021622, No. DE-SC0020337, No. DE-AC05-00OR22725, and No. DE-FG02-07ER54917. We thank the U.S. Department of Energy Office of Fusion Energy Sciences through the Basic Plasma Science Program at Los Alamos National Laboratory (LANL) under Contract No. 89233218CNA000001. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 using NERSC Award No. FES-ERCAP0032298, and the LANL Institutional Computing Program, which is supported by the U.S. Department of Energy National Nuclear Security Administration under Contract No. 89233218CNA000001.

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10.1103/jz8f-ck22

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Choudhury, H., Battey, A., Paz-Soldan, C., Lestz, J., Leuthold, N., Lvovskiy, A., Marini, C., Barr, J., Heidbrink, W., Spong, D., Tang, S., Van Compernolle, B., Zhang, Q., Zhang, Y., & Tang, X. (2026). First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves. Physical Review Letters, 136(2), Article 025101. https://doi.org/10.1103/jz8f-ck22

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title = "First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves",

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 (∼4MeV) 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.",

author = "H. Choudhury and A. Battey and C. Paz-Soldan and J. Lestz and N. Leuthold and A. Lvovskiy and C. Marini and J. Barr and W. Heidbrink and D. Spong and S. Tang and \{Van Compernolle\}, B. and Q. Zhang and Y. Zhang and X. Tang",

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Choudhury, H, Battey, A, Paz-Soldan, C, Lestz, J, Leuthold, N, Lvovskiy, A, Marini, C, Barr, J, Heidbrink, W, Spong, D, Tang, S, Van Compernolle, B, Zhang, Q, Zhang, Y & Tang, X 2026, 'First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves', Physical Review Letters, vol. 136, no. 2, 025101. https://doi.org/10.1103/jz8f-ck22

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T1 - First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves

AU - Choudhury, H.

AU - Battey, A.

AU - Paz-Soldan, C.

AU - Lestz, J.

AU - Leuthold, N.

AU - Lvovskiy, A.

AU - Marini, C.

AU - Barr, J.

AU - Heidbrink, W.

AU - Spong, D.

AU - Tang, S.

AU - Van Compernolle, B.

AU - Zhang, Q.

AU - Zhang, Y.

AU - Tang, X.

PY - 2026/1/16

Y1 - 2026/1/16

N2 - 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 (∼4MeV) 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.

AB - 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 (∼4MeV) 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.

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JF - Physical Review Letters

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

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