Numerical simulation study of lower hybrid wave scattering full-wave solution in scrap-off layer

Abstract

BackgroundLower hybrid current drive (LHCD) is one of the main auxiliary heating and current driving methods for Tokamak, and studies have shown that the boundary parasitics effect of lower hybrid (LH) wave in scrap-off layer (SOL) significantly decreases current drive efficiency of LH wave. Among these, wave scattering caused by density fluctuation at the boundary results in spectral changes within the SOL, which changes the power deposition location and current drive efficiency.PurposeThis study aims to explore the lower hybrid scattering caused by density fluctuation in the scrap-off layer on the Experimental Advanced Superconducting Tokamak (EAST) device.MethodsBased on the cold plasma dispersion theory and the blob density fluctuation theory, COMSOL Multiphysics was employed to establish a full-wave solution model of lower hybrid scattering in the SOL. Based on the parameters of the EAST device, the influence of low-frequency electron density fluctuation with different characteristics on wave scattering was analyzed.ResultsThe simulation results show that the backscattering direction caused by the density wave packet "blob" is more obvious than the forward scattering, and scattering induced by blob leads to the change of spatial structure of low hybrid power flow. The density fluctuation in the blob mainly affects the amplitude of the wave field disturbance, the radius of the blob mainly affects the spatial range of the wave scattering, the full-field disturbance caused by multiple blobs increases significantly.ConclusionsThe full-wave solution model of the SOL established in this study is reliable. The simulation results using this model show that the density fluctuation will cause lower hybrid scattering, which will change the spatial structure of the power flow.

Keywords

• lower hybrid current drive
• wave scattering
• full wave solution
• scrap-off layer
• low-frequency density fluctuation