Full wave propagation modelling in view to integrated ICRH wave coupling/RF sheaths modelling

Abstract

RF sheaths rectification can be the reason for operational limits for Ion Cyclotron Range of Frequencies (ICRF) heating systems via impurity production or excessive heat loads. To simulate this process in realistic geometry, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code is a minimal set of coupled equations that computes self-consistently wave propagation and DC plasma biasing. The present version of its wave propagation module only deals with the Slow Wave assumed to be the source of RF sheath oscillations. However the ICRF power coupling to the plasma is due to the fast wave (FW). This paper proposes to replace this one wave equation module by a full wave module in either 2D or 3D as a first step towards integrated modelling of RF sheaths and wave coupling. Since the FW is propagative in the main plasma, Perfectly Matched Layers (PMLs) adapted for plasmas were implemented at the inner side of the simulation domain to absorb outgoing waves and tested numerically with tilted BD in Cartesian geometry, by either rotating the cold magnetized plasma dielectric tensors in 2D or rotating the coordinate vector basis in 3D. The PML was further formulated in cylindrical coordinates to account for for the toroidal curvature of the plasma. Toroidal curvature itself does not seem to change much the coupling. A detailed 3D geometrical description of Tore Supra and ASDEX Upgrade (AUG) antennas was included in the coupling code. The full antenna structure was introduced, since its toroidal symmetry with respect to the septum plane is broken (FS bars, toroidal phasing, non-symmetrical structure). Reliable convergence has been obtained with the density profile up to the leading edge of antenna limiters. Parallel electric field maps have been obtained as an input for the present version of SSWICH

Modelling of radio frequency sheath and fast wave coupling on the realistic ion cyclotron resonant antenna surroundings and the outer wall

“…In order to compare with the 3D experimental results, one has to use a multiple-2D approach, i.e. exciting several independent 2D simulations with full-wave field maps from the 3D RAPLICASOL code [40] at different z (poloidal) altitudes. This section tries to recover the double-hump structure in figure 6(a) in [6] and the left-right asymmetry of the differential temperature map in figure 5 in [7], by joint simulations using 2D SSWICH-full wave and 3D RAPLICASOL.…”

Making ICRF power compatible with a high-Z wall in ASDEX Upgrade

“…This estimate is made by using the asymptotic version of the SSWICH-SW code [12]. It calculates V DC sheath on the basis of the RF field maps in front of the antennas from the RAPLICASOL code [24], which allows the use of the latest version of SSWICH-SW. A homogenous density distribution in front of the antennas is used for the cases described in this paper. Figure 11 presents the calculations of the radial-poloidal (xy plane) distribution of V DC sheath on the leading edge of the antenna side limiter using the radial distance from the leading edge Δx, both for the original 2-strap (left) and for the 3-strap (right) antenna with P cen /P out = 2.0.…”

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

“…RAPLICASOL [7] is a program based on the commercial software COMSOL [5]. COMSOL provides the capability of solving Maxwell's equations in frequency domain using…”

“…Several codes to model the wave behaviour have been developed, notably TOPICA (TOrino Polytechnic Ion Cyclotron Antenna [1][2][3][4]), RAPLICASOL (based on COMSOL [5]) and more recently ERMES [6] (open-source). RAPLICASOL (radiofrequency wave coupling for ion cyclotron antenna in scrape-off-layer [7]) is a finite element approach to this problem. Although it has been used successfully to predict the influence of gas puffing on the coupling resistance [8], it has not thus far been validated as thoroughly as TOPICA, which is the goal of this paper.…”