Description
Microwaves play a significant role in magnetically confined plasmas, from heating and current drive to a variety of diagnostic techniques. As such, it is important to calculate the electric field of such microwave beams, for example, as the basis of synthetic diagnostics. The beam-tracing approach balances computational cost and fidelity, accounting for Gaussian beam propagation, refraction, and diffraction, with each simulation typically taking under ten seconds.
We present the version 4 release of Scotty [1], an open-source beam-tracing code written in Python. Compared with the first public release of Scotty [2], the current version features various improvements in both physics capabilities and software engineering, including finite-temperature corrections to the electron mass, code modularity, automated unit testing, and a GUI. Most importantly, this latest version can take as input 3D equilibria, in addition to axisymmetric equilibria, enabling beam tracing for stellarator plasmas. Scotty also has diagnostic-specific analysis routines, such as Doppler backscattering, which can accept both Scotty and third-party beam-tracing results as input.
Scotty was then benchmarked with the analytical beam-tracing solution in slab geometry and the TORBEAM beam-tracing code [3] in tokamak geometry. Scotty’s solvers for axisymmetric and 3D equilibria are then benchmarked with each other. Finally, Scotty was benchmarked with ray tracing in stellarator geometry. In all of these cases, excellent agreement was found. These results establish Scotty v4 as a robust, efficient, and flexible platform for microwave beam tracing in both axisymmetric and fully 3D magnetic equilibria, supporting synthetic microwave diagnostics in tokamak, magnetic mirror, and stellarator plasmas. As microwave diagnostics are expected to be central to future burning-plasma devices such as STEP, Scotty is well positioned for expanded use.
Acknowledgements: This work was partially funded by the FEAT SRTT, A*STAR, and a Young Individual Research Grant, M23M7c0127. This work was also in part supported by grants from the Engineering and Physical Sciences Research Council (EPSRC) [EP/R034737/1], [EP/W026341/1], and PlasmaFAIR [EP/V051822/1].
[1] https://github.com/beam-tracing/Scotty
[2] V.H. Hall-Chen, F.I. Parra, & J.C. Hillesheim (2022). PPCF, 64(9), 095002.
[3] E. Poli, A. Bock, ... & G.V. Pereverzev (2018). CPC, 225, 36-46.