TOPICA: an accurate and efficient numerical tool for analysis and design of ICRF antennas

Abstract

The demand for a predictive tool to help in designing ion-cyclotron radio frequency (ICRF) antenna systems for today's fusion experiments has driven the development of codes such as ICANT, RANT3D, and the early development of TOPICA (TOrino Polytechnic Ion Cyclotron Antenna) code. This paper describes the substantive evolution of TOPICA formulation and implementation that presently allow it to handle the actual geometry of ICRF antennas (with curved, solid straps, a general-shape housing, Faraday screen, etc) as well as an accurate plasma description, accounting for density and temperature profiles and finite Larmor radius effects. The antenna is assumed to be housed in a recess-like enclosure. Both goals have been attained by formally separating the problem into two parts: the vacuum region around the antenna and the plasma region inside the toroidal chamber. Field continuity and boundary conditions allow formulating of a set of two coupled integral equations for the unknown equivalent (current) sources; then the equations are reduced to a linear system by a method of moments solution scheme employing 2D finite elements defined over a 3D non-planar surface triangular-cell mesh. In the vacuum region calculations are done in the spatial (configuration) domain, whereas in the plasma region a spectral (wavenumber) representation of fields and currents is adopted, thus permitting a description of the plasma by a surface impedance matrix. Owing to this approach, any plasma model can be used in principle, and at present the FELICE code has been employed. The natural outcomes of TOPICA are the induced currents on the conductors (antenna, housing, etc) and the electric field in front of the plasma, whence the antenna circuit parameters (impedance/scattering matrices), the radiated power and the fields (at locations other than the chamber aperture) are then obtained. An accurate model of the feeding coaxial lines is also included. The theoretical model and its TOPICA implementation have been fully validated against measured data both in vacuo and in plasma-facing conditions for real-life structures.

ICRF specific plasma wall interactions in JET with the ITER-like wall

“…Fig. 7 shows first E || calculations for the A2 antenna using TOPICA [23] (same code as used to model the ICRF antennas in ITER) with a 3D antenna model adapted to flat geometry and JET L-mode plasma density and temperature profiles. Scaled to ITER relevant ICRF power, E || absolute values for the A2 antenna are a factor of > 2 higher than the E || values in front of the ITER antenna for the high density reference profiles [22].…”

SIDON: A simulator of radio-frequency networks. Application to WEST ICRF launchers

“…The front-face of the WEST ICRF launchers has been modeled on TOPICA [7] for 8 L-mode and 9 H-mode density profiles at 55 MHz [1,2]. By associating discrete plasma indices for the 17 calculated Z-matrices (properly de-embedded to the capacitors positions), one can easily interpolate a Z-matrix for any plasma index.…”

“…Moreover, previous ICRF experiments illustrated that a refined understanding and a comprehensive modelling of the ICRF launchers RF circuit is of high importance for the preparation of their operation [6]. For these reasons, and thanks to the availability of full-wave electromagnetic solvers such as ANSYS HFSS® and TOPICA [7], the WEST ICRF launchers design has been rigorously validated during their conception phase using RF network calculations with all launchers elements described by full matrices got from full-wave modeling. These RF network computations include calculations using commercial software as ANSYS Designer® [2].…”

3-Dimensional density profiles in edge plasma simulations for ICRF heating

“…Several codes are commonly used to numerically simulate these electromagnetic waves [4,5]. The vast majority, or perhaps all, of these codes until now use a 1D density profile, which depends only on the radial coordinate.…”