Abstract
Ion cyclotron range of frequencies (ICRF) wave propagation is calculated theoretically for tokamak conditions and for linear magnetized plasma device IShTAR which is dedicated to the RF sheath studies. Only the slow wave (SW) mode of ICRF waves can propagate and be studied in IShTAR. Therefore it is possible to decouple the role of the different ICRF modes in the RF sheath effects. Numerical simulations of the ICRF SW are done in COMSOL in the framework of the existing cold plasma modelling package RAPLICASOL and the SW is for the first time modelled in 3D. To date, RAPLICASOL existed as a 3D wave coupling modelling approach which targets the fast wave (FW). Plasma is implemented as a material with manually assigned physical properties and a perfectly matched layer (PML) is used to absorb the wave energy. Here it is demonstarted how to adjust the RAPLICASOL PML for models with propagating SW. Field structures in the resonance cone shape obtained for the SW differ significantly from the FW and exhibit strong dependence on the density profile in the close proximity of the antenna. The lower-hybrid (LH) resonance is a constant issue in the attempts to model the SW. In this work an approach to obtain correct numerical solutions in the LH resonance presence is demonstrated. Results of this work can be used to improve the complex tokamak ICRF simulations, where so far the SW propagation on the edge has been avoided.
Highlights
Coupling power to the plasma with ion cyclotron range of frequencies (ICRF) waves is a promising method for heating tokamak plasmas to fusion relevant temperatures
Dielectric tensor elements and shapes of the wavefront are qualitatively the same in IShTAR as the results given in the section 2 for the ASDEX Upgrade tokamak example case: the parallel electric field has significant values only for the slow wave and only at very low densities; the propagating SW has the shape of a resonance cone
A complex ICRF waves study for IShTAR is performed
Summary
Coupling power to the plasma with ion cyclotron range of frequencies (ICRF) waves is a promising method for heating tokamak plasmas to fusion relevant temperatures. IShTAR (Ion cyclotron Sheath Test Arrangement) [2] is a linear plasma experiment that is close to tokamak conditions for interactions of the ICRF waves and the edge plasma. A stable operational phase (little changes in the plasma parameters such as density and temperature) is significantly longer compared to tokamaks where dramatic changes to the density profile on the edge are introduced on very short time scales. These factors provide favourable conditions for studies of the RF sheath physics on IShTAR. The present study is committed to understanding of the SW behaviour and to a global characterization of its field structures and does not include the nonlinear sheath physics
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