Net radially inward turbulent particle flux was observed in a linear plasma device, the linear experimental advanced device (LEAD). The amplitude of the inward particle flux is comparable with outward particle flux. The inward particle flux peak value locates in the outer Er shear layer. Cross-phase evolution dominates the radial evolution of particle flux from outward to inward. In the frequency domain, a 1 kHz mode contributes most of the inward particle flux. Frequency-resolved energy transfer analysis infers that this mode obtains energy nonlinearly from very low frequency fluctuations below 0.5 kHz. Moreover, turbulence spreading could also transfer energy to the position where the inward flux peak locates from nearby positions, and thus acts as a nonlocal, nonlinear drive for the 1 kHz mode.
Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport