Impact of resonant magnetic perturbation on blob motion and structure using a gas puff imaging diagnostic on the HL-2A tokamak

The impact of resonant magnetic perturbation (RMP) on blob motion and structure in the SOL of the HL-2A tokamak is studied using a gas puff imaging diagnostic. Ellipse fitting is applied to study the structure and motion of blobs quantitatively. The radial locations, amplitudes and scale sizes of blobs are obtained based on the fitted ellipse. Furthermore, based on the measurement of blob location, the radial and poloidal velocities of blobs are calculated. With the application of RMP, the edge poloidal shear flow is significantly weakened and the wave number spectrum changes from quasisymmetric to significantly up-down asymmetric. The application of RMP also causes the detected blob location to be much further into the far scrape-off layer (SOL) and increases the blob amplitude. Blob poloidal velocity in the SOL is slowed. Larger-size and longer-lifetime blobs are observed with RMP. With the application of RMP, stronger-amplitude and larger-size blobs are detected in the far SOL and they may cause a more serious erosion problem to the first wall.