Abstract
The modulation of the ion cyclotron fast wave coupling to the plasma due to non-axisymmetric changes of the distance antenna-R-cutoff is studied. These changes can arise when magnetic perturbation (MP) fields are used, or when MHD activity is present. The application of MP fields can excite a low field side midplane plasma kink response that amplifies the vacuum perturbation field, leading to appreciable 3D plasma displacements. This effect is studied via NEMEC simulations. Rigid rotation of the MP field is found to produce a coherent antenna loading resistance modulation, suggesting an interplay between the non-axisymmetric magnetic field structure and the wave coupling properties. MHD modes are shown to introduce similar loading resistance oscillations, coherent with the mode rotation frequency. The case of a (2,1) mode is presented.
Highlights
The excitation of the fast magnetosonic wave in the ion cyclotron range of frequencies is an effective technique to transport several megawatt of power up to the core plasma of a fusion device
We address non-axisymmetric changes of the distance «d» arising from the application of magnetic perturbation (MP) fields from in-vessel saddle coils and naturally occurring MHD modes
The applied MP field is affected by the passive stabilization loop (PSL), a copper bulk holding the saddle coils that serves to increase the resistive time constant of the vertical instability
Summary
The excitation of the fast magnetosonic wave in the ion cyclotron range of frequencies (few tens of MHz) is an effective technique to transport several megawatt of power up to the core plasma of a fusion device. Its excitation is produced by launchers, usually, antennas that are flushed with the first wall of the plasma device, such as a tokamak [1], and the wave energy is deposited via damping mainly into the ion species. For a monotonically increasing perpendicular refractive index n2⊥,FW ∈ n20⊥,FW , 0 , the transported power can be approximated as Ptrans ≈ P0e−1.1k d [2] with d being the distance from the antenna up to the R-cutoff where the wave becomes propagative, i.e. n2⊥,FW > 0. Measurements of the antenna performance via loading resistance are used in order to assess their effect on the accessibility of the fast wave to the propagating region. Simulations are performed with the ideal non-linear MHD code
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