Quasi-optical beam tracing module development for millimeter-wave high-wavenumber collective scattering on the NSTX-U and EAST tokamaks

• A python3-based quasi-optical beam tracing module is developed and applied to high-wavenumber collective scattering systems on NSTX-U and EAST tokamaks . • The module is applied to the L-mode and H-mode plasma cases for both NSTX-U and EAST tokamaks . The comparison of the beam trajectory and the beam profile shows the effect of refraction and diffraction. The higher density gradient in H-mode distorts the beam more severely. • When the Rayleigh length is comparable with the length of the trajectory, and the beam waist is comparable with the density scale length, beam distortion should be taken into consideration. • The symplectic Euler method is used as the integration scheme in the module. • Various of integration schemes are evaluated. Including conventional Euler's method, Heun's method, Runge-Kutta method, and symplectic methods. The efficiency and accuracy are compared and the symplectic Euler method has a good balance between them. A Python3-based beam tracing code utilizing Quasi-Optics has been developed to track both incident and receiving beams in high-k collective millimeter wave scattering systems within magnetic fusion plasmas. In contrast to existing ray tracing codes that solely consider refraction, this beam tracing code incorporates diffraction phenomena, providing a more comprehensive calculation. This enhanced capability allows for a more accurate calculation of the scattering volume and spatial resolution in high-k collective scattering systems, crucial for evaluating system performance and facilitating data analysis. Unlike Geometrical Optics, Quasi-Optics employs the complex eikonal method, representing a Gaussian beam as a collection of coupled rays to accurately preserve diffraction characteristics. The developed code is intended for application in NSTX-Upgrade and EAST high-k beam tracing analyses, targeting frequencies of 693 GHz and 270 GHz, respectively. The high-k system's primary objective is the observation of electron-scale instabilities. Employing a symplectic integrator, the code ensures numerical accuracy, assessed through the conservation of the Hamiltonian. With its precision and efficiency, the code facilitates rapid inter-shot analyses.