Description
Inward particle transport plays a critical role in the formation of transport barriers and the improvement of plasma confinement. It is closely associated with the development of peaked density profiles, which significantly improve the fusion rate and contribute to achieving steady-state discharge. Although previous studies have indicated that shear flows can influence inward particle flux, the underlying formation mechanism has not yet been fully clarified experimentally. A deeper understanding of this process is essential for achieving effective control of particle fueling in magnetized plasmas.
To further investigate this phenomenon, studies of inward particle transport have been conducted on the PKU Plasma Test (PPT) device, a linear plasma confinement device in China. Streamer structures observed in the device are found to simultaneously induce inward and outward particle flux, suggesting a possible mechanism for inward transport generation. To conduct experimental research on the inward particle transport mechanism, biases voltages are applied at different radial and axial positions to modify the radial electric field. The inward particle flux increases with increasing biased voltage, demonstrating the capability for active control of inward transport. During the bias experiment, the generation of inward particle flux is observed to coincide with the emergence of vorticity flux.
Motivated by the recently proposed topological pinch theory, particle transport is further examined in hydrogen, helium and argon plasmas under various experimental conditions. The results show that the inward particle flux is quantitatively correlated with the vorticity flux and agrees with theoretical predictions. These findings provide experimental evidence that inward particle transport can be driven by vorticity flux and offer new insight into the fundamental physics of particle transport in magnetized plasmas.