Abstract
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.
Highlights
The tokamak configuration is a leading concept for the use of magnetic plasma confinement to develop controlled nuclear fusion power [1]
Developing an understanding of the underlying physical mechanisms that lead to local current drive is required to confidently extrapolate any such technique to fusion-scale experiments
This Letter reports the first measurements of local magnetic turbulence excited during a dc helicity injection technique and quantifies its contribution to global current drive in a spherical tokamak configuration
Summary
The tokamak configuration is a leading concept for the use of magnetic plasma confinement to develop controlled nuclear fusion power [1]. This Letter reports the first measurements of local magnetic turbulence excited during a dc helicity injection technique and quantifies its contribution to global current drive in a spherical tokamak configuration.
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