Density dependence of the forbidden lines in Ni-like tungsten

The magnetic-octupole ( M3) and electric-quadrupole ( E2) transitions between the ground state 3d(10) S-1(0) and the lowest excited 3d(9)4s ( 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 angstrom line observed in tokamak experiments ( Neu R et al 1997 J. Phys. B: At. Mol. Opt. Phys. 30 5057). Utilization of the M3 and E2 line ratios for density diagnostics in high-spectral-resolution experiments is discussed as well.