The effects of negative bias on the turbulence and particle transport in edge plasma of J-TEXT tokamak are addressed in this work. An obvious decline in the turbulent particle transport is observed when the bias voltage reaches −200 V. The suppression time of turbulence intensity after the bias turned on is very short (<200 μs), much less than the reconstruction time of equilibrium electric field Er (several milliseconds), which signifies that the turbulence suppression cannot be attributed to the decorrelation effect of mean Er × B shear flow. Analysis of the radial wavenumber (kr) spectrum of the floating potentials at the edge plasma shows that when increasing the bias voltage, the amplitude of wavenumber spectrum decreases monotonously. Whereas, only when the bias voltage reaches a threshold (−200 V), the kr corresponding to the peak of the spectrum (i.e. kr,peak) shifts toward more negative values, followed by the suppressions of turbulence intensity and particle transport. Meanwhile, the Reynolds stress is found to be reduced and the tilt of turbulent eddy structures is verified in this experiments. The results are in agreement with the spectral shift model (Staebler et al 2013 Phys. Rev. Lett.110 055003), which indicates the turbulence suppression in short time is due to scattering turbulence energy to the high kr region where the energy is easy to dissipate.
This paper investigates the effects of negative bias on turbulence and particle transport in the edge plasma of the J-TEXT tokamak. It shows that increasing the bias voltage reduces the amplitude of the radial wavenumber spectrum, and when the bias reaches a threshold, the peak wavenumber shifts to more negative values, leading to turbulence suppression and reduced particle transport.