Stark broadening of hydrogen lines is investigated in low-density magnetized plasmas, at typical conditions of magnetic fusion experiments. The role of time ordering is assessed numerically, by using a simulation code accounting for the evolution of the microscopic electric field generated by the charged particles moving at the vicinity of the atom. The Zeeman effect due to the magnetic field is also retained. Lyman lines with a low principal quantum number are first investigated, for an application to opacity calculations; next Balmer lines with successively low and high principal quantum numbers are considered for diagnostic purposes. It is shown that neglecting time ordering results in a dramatic underestimation of the Stark effect on the low- lines. Another conclusion is that time ordering becomes negligible only when ion dynamics effects vanish, as shown in the case of high- lines. 1. Introduction In magnetic fusion, detailed line shapes are of interest for accurate diagnostics or radiative transfer simulations. For plasma conditions and magnetic fields encountered in the divertor of present and future tokamaks, an accurate model for the line shape of the hydrogen isotopes should include Zeeman and Stark effects, and retain the dynamics of the ion-emitter interaction. Since we then have to solve a quantum time-dependent problem, understanding the role of time ordering becomes an important issue both from the fundamental and computational points of view (note, this problem is also investigated in other contexts, e.g., [1–3]). Time ordering has already been studied in the Stark broadening literature, but generally for the electron broadening [4–7]. Our aim here is to investigate the role of time ordering for the ion perturbation on hydrogen lines for plasmas with temperature in the eV range, and densities of about , conditions which are expected in the divertor of the future ITER tokamak. We recall in Section 2 the basic formalism used for line shape calculations in the presence of Stark and Zeeman effects, and briefly introduce the issue of time ordering. Line shapes in the atom’s frame of reference are considered, that is, in the Doppler free case. We present in Section 3 an ab initio simulation technique able to provide accurate line shapes including all the effects of time ordering. Calculations of hydrogen line shapes of Lyman and Balmer series are presented in Section 4, with and without the effect of time ordering, and compared to calculations performed in the static ion limit. The role of time ordering and the issue of retaining it in a line
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