Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments

Abstract

In this paper we validate the Finite Element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap antenna, and for a 4-strap WESTlike antenna. Although RAPLICASOL requires considerably fewer computational resources than TOPICA, we find that the predicted quantities of experimental interest (including reflection coefficients, coupling resistances, Sand Z-matrix entries, optimal matching settings, and even radiofrequency electric fields) are in good agreement provided we are careful to use the same geometry in both codes.

Numerical solutions of Maxwell's equations in 3D in frequency domain with linear sheath boundary conditions

“…To complement the boundary conditions, one needs another scalar equation defined on the boundary and describing the sheath properties at the RF level (typically the RF impedance of the sheath). This is the role of equation (11). Eqs.…”

“…Eqs. (10) and (11) are the "asymptotic linear sheath boundary conditions" (SBC) 3 (∇ × E) n = 0 or equivalently ∇ t × E = 0 (10) D n = 0 (11) If the sheath thickness δ sh is known, we want to impose the "non-asymptotic sheath boundary condition" instead 3,8 :…”

“…Maxwell's equations asymptotic SBC eqs. (10,11) Maxwell's equations non-asymptotic SBC eq. 12DC plasma biasing eqs.…”

“…Although eqs. (10) and (11) suffice to uniquely (and nontrivially) define Ψ RF , implementing these boundary conditions within commercial Finite Element solvers has proven challenging 3 . So far, SSWICH has gotten around this problem by resorting to 2D approaches [1][2][3] : in a 2D domain, eq.…”

“…In the multi-2D approach, Ψ RF is calculated on many 2D radial-parallel slices (radial: red arrow, parallel (to the confining magnetic field): cyan arrow). One such slice is shown here with the flat RAPLICASOL model 2,11,12 of the ASDEX Upgrade 3-strap antenna. On every slice, eq.…”