Preliminary observation of medium-Z impurities by means of the soft x-ray pulse height analysis diagnostic on EAST

A soft x-ray pulse height analysis (PHA) system, based on a silicon drift detector (SDD), has been successfully implemented on EAST to measure spectra of soft x-ray emission. Utilizing the soft x-ray PHA diagnostic, the behavior of intrinsic and injected medium-Z impurities is first investigated on EAST and the preliminary observations are presented. There are hardly any Kα emission peaks of metallic impurities including Ti (Z = 22), Cr (Z = 24), Fe (Z = 26), Ni (Z = 28) and Cu (Z = 29) in the soft x-ray spectra for an ohmic heating plasma due to lower electron temperatures, while remarkable peaks can be seen in a lower hybrid wave (LHW) heated plasma. The profiles of Kα intensities of these metallic elements have been obtained with about 7 cm spatial resolution. It is observed that the Kα emissions come mainly from the core plasma column of ρ ≤ 0.3 and found that their intensities are roughly proportional to the power of the LHW launched into the plasma. The Ar Kα peaks can also be monitored when argon gas is puffed into the plasma. It is qualitatively confirmed that the Kα lines of argon emitted from the lower ionic states are predominantly located in the outer plasma region, whereas the Kα lines with higher energies are mainly from high ionization stages in the central region.