Stark broadening of hydrogen lines in low-density magnetized plasmas

Abstract

Stark broadening of hydrogen lines in the presence of a magnetic field is revisited, with emphasis on the role of the ion component under typical conditions of magnetized fusion devices. An impact theory for ions valid at low density ͑N e Շ 10 14 cm −3 ͒ and taking into account the Zeeman degeneracy removal of the atomic states is developed. It is shown that the Stark widths of the Lorentz triplet components strongly depend on the magnetic field. The model is validated by a computer simulation method. For the lateral components of Ly␣, we show that the impact approximation still holds for densities as high as N e ϳ 10 15 cm −3 . In contrast, for the central component as well as for the other lines from low principal quantum number, significant discrepancies between the proposed theory and the simulation results appear at high density. Application to D␣ in tokamak divertor plasma conditions shows that, in this case, the quasistatic approximation becomes more relevant.

Stark-Zeeman Line Shape Modeling for Magnetic White Dwarf and Tokamak Edge Plasmas: Common Challenges

“…An extension of the GKS impact collision operator that accounts for this degeneracy removal can be devised through the use of an alternative S operator in Equation (4) involving the Zeeman Hamiltonian. The method employs an adaptation of the GBKO model (Griem, Baranger, Kolb, Oertel [18]), initially developed for helium lines, for hydrogen lines with Zeeman effect; details can be found in [6,19]. The result is a collision operator with a dependence on the m quantum number.…”

“…The so-called "strong collision radius"-here, b α st -coincides with the Weisskopf radius at the limit B → 0, and is different at finite magnetic field. It can be determined by the solving of an integral equation; see [6,19] for details. The mitigation of Stark broadening due to the Zeeman effect is all the more important so that the Zeeman energy Atoms 2017, 5, 36 5 of 10 sublevels are separated.…”

“…Balmer lines with a low principal quantum number like Dα are also affected by the microfield and Stark broadening enters into competition with both Doppler broadening and Zeeman splitting [5]. The need for accuracy in spectroscopic diagnostics of tokamak edge plasmas has prompted an interest in the development of line broadening models accounting for the simultaneous action of electric and magnetic fields on atomic energy levels, e.g., [6]. Recently, a line shape database for the first Balmer lines accounting for the Stark and Zeeman effects has been devised for tokamak spectroscopy applications using computer simulations [7].…”

Stochastic Processes Applied to Line Shapes

“…This ab initio technique uses variable time steps following as closely as possible the variations of the simulated microfield. After three decades of development, such computer simulations have now been used many times to benchmark studies on the effect of the emitter-perturbers dynamic on a line shape (Calisti et al 1987;Gigosos & Cardenoso 1987;Rosato et al 2009;Stambulchik & Maron 2010). The drawback of such simulations is that they require large computer resources for complex atomic systems.…”

Division Xii / Commission 14 / Working Group Collision Processes

“…For hot dense stars such as white dwarfs this is often the most important broadening mechanism. Rosato et al (2009) have reexamined the Stark broadening of hydrogen lines in the presence of a magnetic field and developed an impact theory for ions, valid for low electron densities (N e 10 14 cm −3 ), which takes into account the Zeeman splitting of the atomic energy levels. Rosato et al (2010) have also studied numerically the role of time ordering in such plasmas, by using a simulation code that accounts for the evolution of the microscopic electric field generated by the charged particles moving close to the atom.…”