Modeling of the Leaky Coax Antenna Concept for Reducing Impurity Generation in High Field Tokamak ICRH Heating*

We present the design and performance analysis of a novel ICRH antenna configuration utilizing a slotted aperture in a vertically-oriented coaxial waveguide geometry. The modeling is aimed at high-field tokamak plasma environments, such as the SPARC/ARC designs, whose high-density pedestal and SOL make impedance-matched coupling from this unusual geometry possible.

Our objective was to replicate beam-like radiation patterns observed in simulations of SPARC ICRH antenna operation coupling comparable power to the core plasma while reducing the number of PFCs. The absence of Faraday shields and exposed strap reduces RF sheath formation that can cause sputtering and thus plasma impurities. We performed simulations of the electromagnetic fields using the VSim software. These simulations incorporated nonlinear RF sheath boundary conditions and considered a 50/50 D/T plasma composition with field and plasma profiles consistent with SPARC operational scenarios.

We also applied methodologies from the RF-SciDAC, running the hPIC2 particle code and the RustBCA ion surface interaction code to investigate the wall impurity fluxes produced during antenna operation. VSim outputs were utilized by hPIC2 to determine IEADs, while RustBCA was used to analyze W sputtering behavior and impurity fluxes.