ORB5 is a global, gyrokinetic, electromagnetic, multi-species code based on a Lagrangian variational description, discretized with a particle representation of the distribution functions and a finite element representation of the fields. It can be considered as a variation of the Particle-In-Cell (PIC) method.

Among other features, the code can be coupled to an ideal MHD Grad-Shafranov solver (CHEASE). It includes a nonlinear multi-species collsion operator. It can be run in temperature-gradient-driven mode or in flux-driven mode. It is equivalent to a full-f code, with the exception of the linearized polarization density. It makes use of verious numerical noise reduction and control schemes: control variates, quadtree smoothing, etc.

The code is massively parallelized, with both distributed memory (MPI) and shared memory (OpenMP) models. It is GPU-enabled (OpenACC) and has been ported to several HPC platforms such as Piz Daint at CSCS, Marconi at CINECA, and Summit at ORNL. It scales well up to hundreds of thousands of CPU cores and tens of thousands of GPUs.

The main reference for the ORB5 code is:

E. Lanti, N. Ohana, N. Tronko, T. Hayward-Schneider, A. Bottino, B. F. McMillan, A. Mishchenko, A. Scheinberg, A. Biancalani, P. Angelino, S. Brunner, J. Dominski, P. Donnel, C. Gheller, R. Hatzky, A. Jocksch, S. Jolliet, Z.X. Lu, J.P. Martin Collar, I. Novikau, E. Sonnendrücker, T. Vernay, L. Villard, ORB5: A global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry, Comput. Phys, Commun., 251, 107072 (2020)

The ORB5 code was first written in the 1990s at the CRPP (the former name of SPC) and then its developer and user base was enlarged to include mainly the Max-Planck IPP in Garching and Greifswald and the University of Warwick.

The source code is available upon request by sending a message to laure.nosp@m.nt.v.nosp@m.illar.nosp@m.d@ep.nosp@m.fl.ch. You then become part of the Users & Developers team. Users & Developers of the ORB5 code have to commit to simple rules such as:

• All publications that make use of results produced with the ORB5 code must cite the above reference.
• The code name should not be modified.
• All changes made to the code are systematically made available to the whole ORB5 community of developers and users.