Self-consistent Neoclassical Transport Theory with Orbit Loss in a Low Collisionality Tokamak Scrape-off Layer.*

Neoclassical transport theory provides the minimum level of transport in tokamaks [1]. The theory assumes closed flux surfaces and a gradient length scale across the magnetic field line in the background plasma larger than the poloidal gyro radius, and hence it is not valid in strong gradient regions such as the pedestal in H-mode plasmas [2] or regions with open field lines like the scrape-off layer. Here, we propose a self-consistent neoclassical transport model for diverted tokamak scrape-off layers at the low collisionalities that are achievable with low recycling boundaries. The strong gradient in electric potential across magnetic flux surfaces, with a characteristic radial length of the order of the orbit width, leads to orbit loss phase space regions determined by the X-point position and the radial drifts. The neoclassical transport solutions with these orbit loss phase space regions will be discussed.

 

[1] Helander, Per, and Dieter J. Sigmar., Cambridge university press, 2005.

[2] Trinczek, Silvia, et al, Journal of Plasma Physics 89.3 (2023): 905890304.