Dispersion properties of rectangularly‐corrugated waveguide structures by the in‐house 3D FDTD code COCHLEA in cylindrical coordinates

Abstract

An in‐house full‐wave numerical code COCHLEA based on the Finite Difference in Time Domain (FDTD) method has been developed and used to study the dispersion properties of corrugated waveguide structures. The mathematical formulation of the corresponding electromagnetic problem is presented in detail. Numerical results are derived for axially corrugated waveguides similar to those appeared in gyrotron stacked beam tunnels and are compared with those obtained by the in‐house semi‐analytical numerical code FISHBONE.

Overview of recent gyrotron R&D towards DEMO within EUROfusion Work Package Heating and Current Drive

“…In order to first validate the construction and assembly of the new components, the upgraded gyrotron was tested in short pulses (< 10 ms) using the diode electron gun of the short-pulse gyrotron with the goal to reproduce the previous behavior of the short-pulse tube [14]. The validation was fully successful, since, at nominal parameters, the operating TE 34,19 mode was stably excited at 169.9 GHz with an output RF power close to 2.1 MW and an efficiency slightly above 30 % in non-depressed collector operation. After further parameter optimization, the RF power was increased to 2.2 MW with ~33 % efficiency.…”

“…The challenge lies primarily in the accurate modelling of the complicated and highly overmoded structure of the beam tunnel. To address this, semi-analytical as well as purely numerical modelling tools have been under development [32][33][34]. In parallel, studies on an alternative, fully ceramic beam tunnel concept have also been ongoing [35].…”

“…For this reason, the development of COCHLEA, which is a new 3D full-wave code based on finite-difference time-domain and particle-incell (PIC) methods and focusing on cylindrical geometries, has been initiated in 2016 at the National and Kapodistrian University of Athens. The electromagnetic module of the code is currently being benchmarked by calcul ation of dispersion characteristics of finite-length periodically corrugated waveguides [55]. The PIC module is still under development.…”