Modification of far-SOL flow by substantial gas injection in the inboard poloidal field null configuration on QUEST*

Spontaneous plasma flow is generated in the inboard poloidal field null (IPN) configuration on QUEST spherical tokamak. Previous research has found that there is a significant relationship between plasma current and far-SOL flow. Consequently, the SOL flow is influenced by global modification of IPN plasma. For further understanding of the far-SOL flow, a hybrid probe measuring plasma flow, electron density $n_{\mathrm{e}}$, and temperature $T_{\mathrm{e}}$, was installed in the far-SOL. Using the hybrid probe and divertor probe array, two-point observation on an open flux surface was performed to study the SOL-divertor relationship and the particle transport. Substantial gas injection (GI) from private region of the IPN configuration leads to high core density but $I_{\mathrm{p}}$-drop by 50 $\%$. $n_{\mathrm{e}}$ and $T_{\mathrm{e}}$ in the far-SOL and divertor region are modified appreciably due to the GI. Poloidal flow reversal occurs and toroidal velocity drops by about 50 $\%$ in the far-SOL. We investigate modifications of pressure gradient, electric field and particle transport, and study complex structure of the far-SOL flow.