Magnetic Turbulence and Current Drive During Local Helicity Injection

Magnetic measurements during dc helicity injection tokamak startup indicate Alfvenic 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-Alfvenic electrons excite instabilities that drive the observed turbulence. Measured fluctuation helicity is consistent with an alpha-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.