The effect of impurity seeding on edge toroidal rotation in the ADITYA-U tokamak

Intrinsic toroidal rotation velocity (Vφ) has been measured from the Doppler shift of C5+ carbon spectral lines (at 529.05 nm) in the edge region of the ADITYA-U tokamak without any auxiliary torque input in an ohmically heated pure hydrogen (H2) plasma as well as in H2 plasmas seeded with medium-Z (neon and argon) impurities . The toroidal rotation in the edge region is observed to reverse its direction from the counter-current to the co-current direction with an increase in plasma current beyond Ip ∼ 145–150 kA. Furthermore, a systematic decrease in the co-current Vφ has been observed with the edge density, which tends to decrease to almost zero velocity with an increase in the edge density. The injection of medium-Z (neon and argon) impurities is observed to influence the edge toroidal rotation significantly. In low Ip discharges, argon injection leads to a reversal of edge intrinsic rotation from the counter-current to the co-current direction. In high Ip discharges, both neon and argon seeding enhance the co-current rotation by about ∼5–10 km s−1, at a constant Ip compared to pure H2 discharges. Simultaneous measurements of the edge radial electric field, Er, shows that the Er × Bθ flow seems to be driving the edge toroidal rotation in ADITYA-U. With impurity injection, the Er also gets modified, leading to an observed increase in the edge toroidal rotation.