# ORB5: a global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry

## TL;DR

The paper updates the ORB5 electromagnetic gyrokinetic code, highlighting its capabilities to simulate plasma behavior in toroidal geometry using PIC methods, with improved noise reduction, scalability, and benchmarking.

## Contribution

It introduces new features and improvements in the ORB5 code, including collision modeling, noise reduction techniques, and GPU support, enhancing simulation accuracy and efficiency.

## Key findings

- Code accurately models electromagnetic plasma dynamics.
- Demonstrates good scalability on high-performance computing systems.
- Benchmarked successfully against other codes and analytical results.

## Abstract

This paper presents the current state of the global gyrokinetic code ORB5 as an update of the previous reference [Jolliet et al., Comp. Phys. Commun. 177 409 (2007)]. The ORB5 code solves the electromagnetic Vlasov-Maxwell system of equations using a PIC scheme and also includes collisions and strong flows. The code assumes multiple gyrokinetic ion species at all wavelengths for the polarization density and drift-kinetic electrons. Variants of the physical model can be selected for electrons such as assuming an adiabatic response or a ``hybrid'' model in which passing electrons are assumed adiabatic and trapped electrons are drift-kinetic. A Fourier filter as well as various control variates and noise reduction techniques enable simulations with good signal-to-noise ratios at a limited numerical cost. They are completed with different momentum and zonal flow-conserving heat sources allowing for temperature-gradient and flux-driven simulations. The code, which runs on both CPUs and GPUs, is well benchmarked against other similar codes and analytical predictions, and shows good scalability up to thousands of nodes.