Comparison of saturation rules used for gyrokinetic quasilinear transport modeling

TL;DR

This paper compares three heuristic saturation rules in gyrokinetic quasilinear transport modeling using local linear gyrokinetic simulations with experimental plasma parameters, finding qualitative agreement among rules and insights into their predictive capabilities.

Contribution

It provides a systematic comparison of common saturation rules in gyrokinetic quasilinear models using realistic plasma parameters and simulation data.

Findings

Saturation rules yield qualitatively similar flux predictions.

Comparison helps explain the success of different transport models.

Insights into the validity of heuristic saturation rules.

Abstract

Theory-based transport modeling has been widely successful and is built on the foundations of quasilinear theory. Specifically, the quasilinear expression of the flux can be used in combination with a saturation rule for the toroidal mode amplitude. Most transport models follow this approach. Saturation rules are heuristic and difficult to rigorously derive. We compare three common saturation rules using a fairly accurate quasilinear expression for the fluxes computed using local linear gyrokinetic simulation. We take plasma parameters from experimental H-mode profiles and magnetic equilibrium and include electrons, Deuterium, and Carbon species. We find that the various saturation rules give qualitatively similar behavior. This may help explain why the different theory-based transport models can all predict core tokamak profiles reasonably well. Comparisons with nonlinear local and global gyrokinetic simulations are also discussed.