Application of the Scrape-Off-Layer Fast Ion (SOLFI) code to assess particle motion in mirrors and tokamaks

TL;DR

This paper presents SOLFI, a new Monte Carlo code for tracking fast ion orbits in tokamaks, demonstrating its accuracy and applying it to study particle confinement effects in various tokamak geometries.

Contribution

The paper introduces SOLFI, a versatile full-orbit Monte Carlo code, and applies it to analyze particle motion and confinement in different tokamak configurations.

Findings

SOLFI conserves particle energy and magnetic moment.

It correctly predicts ambipolar potential and ion-electron current balance.

Negative triangularity enhances particle confinement in tokamaks.

Abstract

This paper introduces the Scrape-Off-Layer Fast Ion (SOLFI) code, which is a new and versatile full-orbit Monte Carlo particle tracer developed to follow fast ion orbits inside and outside the separatrix in tokamaks. SOLFI is benchmarked in a simple straight mirror geometry, showing that the code conserves particle energy and magnetic moment, obtains the correct passing boundary for particles moving in the magnetic mirror field with an imposed electrostatic field, and correctly observes equal ion and electron current at the ambipolar potential predicted from analytical theory. This result has consequences for collisionless scrape-off-layers in spherical tokamaks. We then utilize SOLFI for fundamental physics studies in novel tokamak geometries, exploring the effect of shaping on the trapped particle fraction and bounce locations in tokamaks and demonstrating that negative triangularity can be used to maximize the fraction of particles bouncing in the good-curvature region, potentially leading to enhanced confinement.