Spectroscopic properties of moderately charged ions of tungsten

Project leader: Lydia Tchang-Brillet and Jean-François Wyart, LERMA
Type of funding: Invited scientific visitor: Alexander N. Ryabtsev, Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow, 142190 Russia (2013). 

Tungsten spectra excited in the vacuum sparks of different setups and electric circuits were recorded on two high resolution vacuum spectrographs. For the region 190 – 500 Å, a 10 m normal incidence spectrograph with a 3600 l/mm grating was used in the Meudon Observatory. In the region below 350 Å a set of spectra was produced using a 3-m grazing incidence spectrograph with a 3600 l/mm grating in the Institute of Spectroscopy in Troitsk. A number of 187 lines in the region 160 – 271 Å were identified as transitions to the low lying odd configurations 4f135s25p6 and 4f145s25p5 from the interacting excited even 4f125s25p65d + 4f135s25p5(5d+6s) + 4f145s25p4(5d+6s) + 4f145s5p6 configurations. Based on this identification,  a number of 102 energy levels of low lying configurations were found for the fist time in the spectrum of W VIII. It was firmly established that the ground state of W VIII is 4f135s25p6 2F7/2. The fine structure splitting and relative positions of the odd terms were established.
For the first time, we have undertaken a semiempirical treatment of a spectrum with seven interacting and overlapping configurations. This case presents a good challenge for further developments of atomic calculations. The analyses of the isoelectronic spectra of neighboring elements Hf, Ta and Re are in progress in our laboratories with the aim to support, and possibly to extend, the present identification of W VIII spectrum relevant to diagnostics of tokamak divertor plasma.
The invitation of Dr Alexander Ryabtsev supported by Plas@Par has been very important for our collaborating because both groups have complementary experimental data and complementary experiences in reduction and analysis of these data.  Direct discussions are also highly desirable for preparing manuscripts of publications.