First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

D. A. Spong; W. W. Heidbrink; C. Paz-Soldan; X. D. Du; K. E. Thome; M. A. Van Zeeland; C. Collins; A. Lvovskiy; R. A. Moyer; M. E. Austin; D. P. Brennan; C. Liu; E. F. Jaeger; C. Lau

doi:10.1103/PhysRevLett.120.155002

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

D. A. Spong, W. W. Heidbrink, C. Paz-Soldan, X. D. Du, K. E. Thome, M. A. Van Zeeland, C. Collins, A. Lvovskiy, R. A. Moyer, M. E. Austin, D. P. Brennan, C. Liu, E. F. Jaeger, C. Lau

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Abstract

DIII-D experiments at low density (ne∼1019 m-3) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.

Original language	English
Article number	155002
Journal	Physical Review Letters
Volume	120
Issue number	15
DOIs	https://doi.org/10.1103/PhysRevLett.120.155002
State	Published - Apr 11 2018

Funding

This work has been supported by the U.S. DOE Frontier Science Program and under the Contracts No. DE-FC02-04ER54698, No. DE-FG02-07ER54917, No. DE-SC0016268, No. DE-AC05-060R23100, No. DE-FG03-94ER54271, No. DE-AC02-09CH11466, and No. DE-AC05-00OR22725. Useful and encouraging discussions with D. C. Pace, N. A. Crocker, Z. Guo, J. H. Harris, and R. J. Buttery have contributed to this effort. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan.

Funders	Funder number
U.S. Department of Energy	DE-AC05-00OR22725, DE-FG03-94ER54271, DE-AC02-09CH11466, DE-FC02-04ER54698, DE-SC0016268, DE-FG02-07ER54917, DE-AC05-060R23100

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10.1103/PhysRevLett.120.155002

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Spong, D. A., Heidbrink, W. W., Paz-Soldan, C., Du, X. D., Thome, K. E., Van Zeeland, M. A., Collins, C., Lvovskiy, A., Moyer, R. A., Austin, M. E., Brennan, D. P., Liu, C., Jaeger, E. F., & Lau, C. (2018). First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks. Physical Review Letters, 120(15), Article 155002. https://doi.org/10.1103/PhysRevLett.120.155002

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title = "First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks",

abstract = "DIII-D experiments at low density (ne∼1019 m-3) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.",

author = "Spong, {D. A.} and Heidbrink, {W. W.} and C. Paz-Soldan and Du, {X. D.} and Thome, {K. E.} and {Van Zeeland}, {M. A.} and C. Collins and A. Lvovskiy and Moyer, {R. A.} and Austin, {M. E.} and Brennan, {D. P.} and C. Liu and Jaeger, {E. F.} and C. Lau",

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year = "2018",

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doi = "10.1103/PhysRevLett.120.155002",

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AU - Spong, D. A.

AU - Heidbrink, W. W.

AU - Paz-Soldan, C.

AU - Du, X. D.

AU - Thome, K. E.

AU - Van Zeeland, M. A.

AU - Collins, C.

AU - Lvovskiy, A.

AU - Moyer, R. A.

AU - Austin, M. E.

AU - Brennan, D. P.

AU - Liu, C.

AU - Jaeger, E. F.

AU - Lau, C.

PY - 2018/4/11

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N2 - DIII-D experiments at low density (ne∼1019 m-3) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.

AB - DIII-D experiments at low density (ne∼1019 m-3) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.

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First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

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