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.