  To provide spectroscopic data for lowly charged tungsten ions relevant to
fusion research, this work focuses on the W8+ ion. Six visible spectra lines in
the range of 420-660 nm are observed with a compact electron-beam ion trap in
Shanghai. These lines are assigned to W8+ based on their intensity variations
as increasing electron-beam energy and the M1 line from the ground
configuration in W7+. Furthermore, transition energies are calculated for the
30 lowest levels of the 4f14 5s2 5p4, 4f13 5s2 5p5 and 4f12 5s2 5p6
configurations of W8+ by using the flexible atomic code (FAC) and GRASP
package, respectively. Reasonably good agreement is found between our two
independent atomic-structure calculations. The resulting atomic parameters are
adopted to simulate the spectra based on the collisional-radiative model
implemented in the FAC code. This assists us with identification of six strong
M1 transitions in 4f13 5s2 5p5 and 4f12 5s2 5p6 configurations from our
experiments
