Effect of elastic scattering between ions and neutral particles on ion transport perpendicular to magnetic fields in divertor plasmas

In divertor plasmas, atomic processes play a significant role in reducing the divertor heat load. In particular, the elastic scattering between ions and neutral particles can be characterized as a large-angle scattering; this is in contrast with Coulomb scattering, which is dominated by small-angle scattering. In a large-angle scattering, a large fraction of the ion energy is transferred to the neutral particle, and the particle flight direction can be changed significantly. This process can generate additional particle transport perpendicular to magnetic field lines and affect plasma density profile in neutral-rich divertor regions. However, in most edge plasma simulation codes, the elastic scattering with neutral particles is not taken into account in the direction perpendicular to the magnetic field lines. In this study, we performed a 2D orbital calculation without other drifts such as diamagnetic and E x B drifts to assess the effect of the elastic scattering on the density profile. The peak density is found to be decreased by 11.1 (6.3)% compared with the model that ignores the transport due to the elastic scattering, even at 3.0 (5.0) T magnetic field similar to that of the JT-60SA (JA DEMO reactor) class. In addition, the ion transport can be expressed as a diffusion model by integrating the differential cross section over the large-angle scattering range & pi;/2-& pi;$$ \pi /2-\pi $$. The proposed method may be easily introduced into any integrated codes to consider the elastic scattering.

Automated summary

In divertor plasmas, atomic processes have a significant impact on reducing the heat load. Large-angle scattering in particular plays a role in transferring ion energy to neutral particles and changing their flight direction, leading to additional particle transport perpendicular to magnetic field lines and affecting plasma density profile in neutral-rich regions. However, current simulation codes often neglect the elastic scattering in the direction perpendicular to magnetic field lines.