The effect of lower hybrid current drive (LHCD) on edge velocity shear and turbulence in the HL-2A tokamak has been investigated. Experimental results demonstrate that the LHCD leads to an increase in edge velocity shear at both the inner and outer shear layers, with the magnitude of increment found to be proportional to the applied LHCD power. This enhancement of edge velocity shear is primarily attributed to the changes in the plasma pressure gradient induced by the heating effect of lower hybrid wave. In addition, LHCD also modifies the turbulence at the plasma edge, and it is observed that turbulence at higher wavenumbers exhibits a clear increase with LHCD, whereas turbulence at lower wavenumbers shows no significant change. These observations emphasize the requirement for employing multiple diagnostic tools to capture the full complexity of edge turbulence in tokamak plasmas. Further investigation during the L-H transition reveals that turbulence intensity in the inner shear layer significantly decreases, promoting the formation of the edge transport barrier. However, the turbulence in the outer shear layer remains nearly unchanged during this process. The results indicate that LHCD can affect the edge plasma in tokamaks, particularly in enhancing edge shear flows and influencing turbulence, which is critical for achieving the edge transport barrier in fusion devices.
This paper investigates how lower hybrid current drive (LHCD) affects the edge velocity shear and turbulence in the HL-2A tokamak. LHCD was found to increase the edge velocity shear, which is important for forming the edge transport barrier in fusion devices. LHCD also influenced turbulence, with higher wavenumber turbulence increasing while lower wavenumber turbulence remained unchanged.