Observation of Forbidden Magnetic Dipole Transitions Emitted from Highly Charged Argon in LHD Discharges

Vacuum ultraviolet (VUV) and visible spectra have been measured using a 3 m normal incidence and two 50 cm Czerny-Turner spectrometers with CCD detectors, respectively, in order to observe forbidden magnetic dipole (M1) transitions in 2s22px (x = 1 to 5) ground and 2s2p excited configurations of highly charged argon produced in argon discharges of Large Helical Device (LHD). One of observed VUV lines was precisely identified as an M1 transition of Ar XII (2s22p3 S3/2 − P3/2 : 649.03 ± 0.02 Å) by analyzing Doppler broadening. Four M1 transitions of Ar X (2s22p5 2P3/2−2P1/2 : 5533 Å), Ar XI (2s22p4 3P2−3P1 : 6917 Å), Ar XIV (2s22p P1/2 − P3/2 : 4413 Å) and Ar XV (2s2p P1 − P2 : 5944 Å) have been observed in the visible spectral region. Temporal behaviors of the VUV and visible lines were examined for reliable identification, and a clear difference was confirmed in comparison with those of Ar lines in lower-ionized stages. Wavelengths of the obtained M1 transitions were determined with high accuracy and compared with previous experimental and calculated values.