Tungsten impurity behaviors from x-ray imaging crystal spectrometer on Korea superconducting tokamak advanced research (KSTAR).

Highly charged tungsten impurity behaviors measured from the x-ray imaging crystal spectrometer (XICS) utilizing a double crystal assembly (DCA) for the Korea Superconducting Tokamak Advanced Research (KSTAR) are studied. The XICS equipped with the DCA can provide multiple impurity lines depending on the electron temperature and discharge conditions since the measurable wavelength range is wide, from 3.9480-4.0250 Å from the first quartz (110) crystal to 3.6650-3.7350 Å from the second quartz (102) crystal. Therefore, XICS is used to investigate impurity identification within the measurable wavelength range, including tungsten lines, since the full W tiles in the lower diverter are installed in KSTAR. A reduction of highly charged W radiation following electron cyclotron heating (ECH) termination is observed in KSTAR plasmas where the strike points face the W divertor with a lower power on-axis ECH injection.