Density dependence of the forbidden lines in Ni-like tungsten

The magnetic-octupole (M3) and electric-quadrupole (E2) transitions between the ground state 3d¹⁰ ¹S₀ and the lowest excited 3d⁹4s $(5/2,1/2)$ J = 3 and J = 2 states in the Ni-like tungsten are shown to exhibit a strong dependence on electron density Nₑ in the range of values typical for tokamak plasmas. Remarkably, the total intensity of these overlapping lines remains almost constant, which may explain the strong emission in the 7.93 line observed in tokamak experiments (Neu R et al. 1997 J Phys B { 30} 5057). Utilization of the M3 and E2 line ratios for density diagnostics in high-spectral-resolution experiments is discussed as well.