Line identification of extreme ultraviolet (EUV) spectra from iron, copper and molybdenum ions in EAST tokamak

Extreme ultraviolet (EUV) spectra emitted from iron and copper ions in a range of 8-500 angstrom and molybdenum ions in a range of 8-400 angstrom were measured in Experimental Advanced Superconducting Tokamak (EAST) discharges accompanied with spontaneous sputtering events, by which metallic impurity influxes are suddenly increased in the discharge. Several spectral lines from L-, M-, and N-shell partially ionized ions have been successfully observed with two EUV spectrometers named EUV_Short and EUV_Long working in wavelength ranges of 8-130 angstrom and 20-500 angstrom, respectively. The wavelength position is accurately calibrated in-situ based on several well-known spectra of low-Z impurity ions. The line identification is carefully performed based on the National Institute of Standards Technology (NIST) database and previously published experimental data. As a result, it is found that B-, Be-, and Li-like iron and copper spectra Al-, Mg-, and Na-like molybdenum spectra appear in discharges with high central electron temperature (>1.8 keV). The highest ionization stages identified here are Li-like iron and copper and Na-like molybdenum, e.g. Fe XXIV at 192.028 angstrom (1s(2)2p P-2(3/2) -> 1s(2)2s S-2(1/2)), Cu XXVII at 153.513 angstrom (1s(2)2p P-2(3/2) -> 1s(2)2s S-2(1/2)) and Mo XXXII at 127.868 angstrom (2p(6)3p P-2(3/2) -> 2p(6)3s S-2(1/2)). Two unresolved transition arrays of molybdenum ions (Mo-UTAs) appear at wavelength ranges of 15-30 angstrom and 65-95 angstrom, and are preliminarily identified as Mo XX-Mo XXXII and Mo XVII-Mo XXXII, respectively. In addition, six spectral lines are newly found by comparing a time evolution of the line intensity from impurity ions in different ionization stages, i.e. Fe XVIII at 17.60 +/- 0.02 angstrom, Cu XXI at 13.15 +/- 0.02 angstrom, Cu XVIII at 260.32 +/- 0.07 angstrom, Cu XVIII at 261.00 +/- 0.06 angstrom, Mo XXVIII at 85.30 +/- 0.03 angstrom and Mo XXIX at 89.59 +/- 0.03 angstrom. The wavelengths of EUV spectra identified in this work are summarized in tables with transitions for each impurity species.

Automated summary

In this study, the EUV spectra emitted from iron, copper, and molybdenum ions during EAST discharges were measured. It was found that the spectra of highly ionized states of iron, copper, and molybdenum appeared in discharges with high electron temperature. Two unresolved transition arrays and six new spectral lines were also identified.