Sawtooth Activities During Impurity Injection by Laser Blow-off in HL-2A

In order to study impurity transport and their progression in the plasma, small amount of high-Z impurities were injected into HL-2A ohmic heated plasmas by laser blow-off and traced with good spatial temporal resolution by a soft X-ray camera. An analysis of the evolution of the impurities' radiation distribution in the plasma revealed that impurity transport in the central region was profoundly different from that outside of it. It was found that the sawteeth tended to be inverted on the central soft X-ray chord signals after the impurity injection and the soft X- ray profiles exhibited discontinuities during the movement of the impurities in the plasma central region. Detailed 2D visualization of the evolution of impurities' radiation using computer tomography has provided further understanding of the properties of impurity transport in the HL-2A plasma