Magnetic Turbulence and Current Drive during Local Helicity Injection

Magnetic measurements during dc helicity injection tokamak startup indicate Alfvénic turbulence in the injected current streams mediates magnetic relaxation and results in macroscopic plasma current drive. Localization of such activity to the injected current streams, a bias voltage dependence to it...

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Bibliographic Details
Published in:Physical review letters 2022-03, Vol.128 (10), p.105001-105001, Article 105001
Main Authors: Richner, N J, Bodner, G M, Bongard, M W, Fonck, R J, Nornberg, M D, Reusch, J A
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
beam-plasma instability
current drive
helicity injection
magnetic confinement fusion
magnetic field generation and plasma dynamo
magnetohydrodynamic turbulence
spherical tokamaks
tokamaks
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Summary:Magnetic measurements during dc helicity injection tokamak startup indicate Alfvénic turbulence in the injected current streams mediates magnetic relaxation and results in macroscopic plasma current drive. Localization of such activity to the injected current streams, a bias voltage dependence to its onset, and higher-order spectral analysis indicate super-Alfvénic electrons excite instabilities that drive the observed turbulence. Measured fluctuation helicity is consistent with an α-dynamo electromotive force driving net current comparable to the macroscopic equilibrium current density. These results imply new constraints for scaling local helicity injection to larger devices.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.128.105001