# Efficient and robust evaluation of fast particle losses in non-axisymmetric tokamak plasmas

## TL;DR

This paper introduces advanced techniques for faster, more reliable orbit-following Monte Carlo simulations to evaluate collisionless fast particle losses in non-axisymmetric tokamak plasmas, linking magnetic structures to loss mechanisms.

## Contribution

It develops methods to identify loss channels, improve signal estimation, and treat particle transport as an advection-diffusion process, enhancing simulation accuracy and efficiency.

## Key findings

- Loss channels identified in constants of motion space.
- Transport coefficients evaluated as advection-diffusion.
- Alpha particle loss estimates for ITER under various conditions.

## Abstract

We present various techniques that make orbit-following Monte Carlo simulations faster and more reliable when assessing collisionless fast particle losses due to magnetic field perturbations. These techniques are based on identifying various loss channels in constants of motion space using the so-called loss maps. We demonstrate that this allows one to attribute losses quantitatively to different transport mechanisms, increase signal-to-noise ratio when estimating FILD signal and peak power loads, and connect magnetic field structure directly to fast particle losses. Furthermore, we show that collisionless fast particle transport can be treated as an advection-diffusion process where the transport coefficients can be evaluated with the orbit-following method. Applying these techniques has the potential to make orbit-following simulations faster to perform, or to avoid them completely, while making the results more reliable as they become more clearly connected to underlying physics. We demonstrate these techniques for ITER by showing how alpha particle losses are affected by various magnetic field perturbations, estimating ICRH losses in reduced field scenarios, and performing a scan on alpha particle losses as a function of ELM control coil current phases.