FIRM3D: An open-source suite for energetic particle confinement analysis in optimized stellarator equilibria

An important feature of optimized stellarator equilibria is the confinement of energetic particles, such as fusion-born alpha particles. We present the open-source software suite, FIRM3D (Fast Ion Reduced Models in 3D), which provides GPU- and CPU-parallelized collisionless guiding center integration routines based on the SIMSOPT [1] framework. FIRM3D is Python-based, enabling a seamless interface with the SIMSOPT or DESC [2] optimization frameworks. Performance-critical routines are implemented in C++ or CUDA to enable efficient assessment of stellarator equilibria, with Python bindings through pybind11 to improve the user interface. Tools are provided for the evaluation of transport characteristics, such as kinetic Poincaré plots, classification of orbit types, and calculation of characteristic particle frequencies. FIRM3D interfaces with the AE3D [3] and FAR3D [4] codes to evaluate transport due to Alfvén eigenmodes. Convergence properties of the adaptive Dormand Prince and symplectic integrators will be presented.

[1] M. Landreman, et al. "SIMSOPT: a flexible framework for stellarator optimization." Journal of Open Source Software 6.65 (2021).

[2] D. W. Dudt, and E. Kolemen. "DESC: a stellarator equilibrium solver." Physics of Plasmas 27.10 (2020).

[3] D. A. Spong, E. D’azevedo, and Y. Todo. "Clustered frequency analysis of shear Alfvén modes in stellarators." Physics of Plasmas 17.2 (2010).

[4] J. Varela, et al. "Stability optimization of energetic particle driven modes in nuclear fusion devices: the FAR3d gyro-fluid code." Frontiers in Physics 12 (2024).