Tangential reconstruction of 2-D total radiation profiles during impurity seeding in KSTAR

Abstract

Impurity in fusion plasmas can degrade fusion reactivity by fuel dilution and radiative cooling. Impurity line radiation in plasma edge is also a candidate for the mitigation of divertor heat load. So, impurity transport study is a critical issue for steady operation of tokamak and plasma radiation is a key parameter for understanding impurity behavior. An infrared imaging video bolometer (IRVB) has been operational for total radiation measurement in several fusion devices. Since bolometer data is the integration of local emissivity through sight lines, tomographic reconstruction is necessary for two-dimensional radiation profiles. A tangential reconstruction code for KSTAR IRVB was develo ped using the Philli ps-Tikhonov algorithm. Phantom tests with various synthetic images were carried out for the validation of the reconstruction. Typical D-shaped phantoms and divertor radiation in the presence of ELM were reconstructed well. In 2016, the spatial resolution of IRVB is expected to be increased twice with IR camera upgrade (from 12x16 to 24x32 channels). The phantom tests with the geometry of the upgraded IRVB showed the reconstruction performance improved distinctly. The 2-dimensional radiation images during impurity seeding experiment in 2014 KSTAR campaign were reconstructed. Radiation loss in the plasma edge and divertor region was increased significantly after the argon puffing. Total radiation power in scrape-off-layer region (PSOL) was also calculated. Using the IRVB data as the input of the SANCO impurity transport code, the effect of the level of impurity seeding on plasma confinement was analyzed.