KNOSOS: a fast orbit-averaging neoclassical code for stellarator geometry

TL;DR

KNOSOS is an open-source, fast orbit-averaging code for calculating neoclassical transport in three-dimensional magnetic confinement devices like stellarators and tokamaks with broken axisymmetry.

Contribution

It introduces a rapid, orbit-averaged method for neoclassical transport calculations that rigorously accounts for magnetic drift components and flux surface potential variations.

Findings

Successfully benchmarked against standard local codes.

Demonstrated efficiency in stellarator and tokamak calculations.

Applicable to low-collisionality plasmas in complex magnetic geometries.

Abstract

KNOSOS (KiNetic Orbit-averaging SOlver for Stellarators) is a freely available, open-source code (\href{https://github.com/joseluisvelasco/KNOSOS}{https://github.com/joseluisvelasco/KNOSOS}) that calculates neoclassical transport in low-collisionality plasmas of three-dimensional magnetic confinement devices by solving the radially local drift-kinetic and quasineutrality equations. The main feature of KNOSOS is that it relies on orbit-averaging to solve the drift-kinetic equation very fast. KNOSOS treats rigorously the effect of the component of the magnetic drift that is tangent to magnetic surfaces, and of the component of the electrostatic potential that varies on the flux surface, {\varphi}_1. Furthermore, the equation solved is linear in {\varphi}_1, which permits an efficient solution of the quasineutrality equation. As long as the radially local approach is valid, KNOSOS can be applied to the calculation of neoclassical transport in stellarators (helias, heliotrons, heliacs, etc.) and tokamaks with broken axisymmetry. In this paper, we show several calculations for the stellarators W7-X, LHD, NCSX and TJ-II that provide benchmark with standard local codes and demonstrate the advantages of this approach.