Design and first experimental results of the laser blow-off system on EAST tokamak

To advance impurity transport researches in Experimental Advanced Superconducting Tokamak (EAST), this study develops a novel Laser Blow-Off (LBO) impurity injection system and presents the first experimental test results on EAST. The system employs a Nd:YAG laser to ablate a thin metal film coated on the quartz glass and inject tracer amount of impurity atoms into the plasma. The optical system comprises of four single-wavelength mirrors and a three-dimensional adjustable focusing lens, which enable control of the spot diameter and precise positioning of the laser spot. Experimental results demonstrate that the system is capable of controlling impurity injection time and quantity without perturbing plasma parameters. The measured temporal evolution of plasma radiation intensity clearly reveals the radial transport process after impurity injection, and the relaxation times at different radial positions are computed to estimate the impurity transport characteristics. The successful deployment of the LBO system provides an effective tool for investigating impurity transport behaviors in the EAST.