Abstract
Detailed designs of ICRF antennas were made possible by the development of sophisticated commercial 3D codes like CST Microwave Studio® (MWS). This program allows for very detailed geometries of the radiating structures, but was only considering simple materials like equivalent isotropic dielectrics to simulate the reflection and the refraction of RF waves at the vacuum/plasma interface. The code was nevertheless used intensively, notably for computing the coupling properties of the ITER ICRF antenna. Until recently it was not possible to simulate gyrotropic medias like magnetized plasmas, but recent improvements have allowed programming any material described by a general dielectric or/and diamagnetic tensor. A Visual Basic macro was developed to exploit this feature and was tested for the specific case of a monochromatic plane wave propagating longitudinally with respect to the magnetic field direction. For specific cases the exact solution can be expressed in 1D as the sum of two circularly polarized waves connected by a reflection coefficient that can be analytically computed. Solutions for stratified media can also be derived. This allows for a direct comparison with MWS results. The agreement is excellent but accurate simulations for realistic geometries require large memory resources that could significantly restrict the possibility of simulating cold plasmas to small-scale machines.
Highlights
General tensor materials can be incorporated into Microwave Studio R (MWS) and we have written a Visual Basic macrocommand that allows to create a cold magnetized plasma
If we look at the value of the reflection coefficient for 10 layers we obtain a reflection of 3 10-6, which is sufficient to guarantee an effective perfectly matched layer (PML)
The work presented here is a first step in the direction of more realism in the predictions obtained from MWS
Summary
General tensor materials can be incorporated into MWS and we have written a Visual Basic macrocommand that allows to create a cold magnetized plasma. As long as thermal effects can be neglected, i.e. far from resonances and confluence regions, the propagation of waves in plasmas can be described by the cold plasma model. In this model we consider a plasma immersed in a static magnetic induction field B0, aligned with the z-axis of the Cartesian coordinate system. The components of the cold-plasma dielectric tensor ε were given by Stix [10]. In the ICRF, when ω ∼ ωci and ωce ωci, the perpendicular term can be approximated by ε⊥ ≈ − i ω2pi/ ω2 − ω2ci where the sum is limited to the ion contributions, the offdiagonal term becomes εxy ≈ s ω2psΩcs/ (Ω2cs − ω2)ω , while the parallel term includes only the electron contribution
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