Ray-tracing analysis for combined Doppler backscattering and cross-polarization scattering diagnostic on the HL-2M tokamak.

To measure plasma density and magnetic fluctuations on the HL-2M tokamak simultaneously, a new diagnostic system combining Doppler backscattering (DBS) and cross-polarization scattering (CPS) is under development. It is essential to understand the propagation of injected and scattered rays to support the electronic/quasi-optical design and subsequent interpretation of the detected signals of the multi-channel DBS/CPS measurements. Thus, ray-tracing analysis with the axisymmetric ray-tracing code BORAY has been performed to estimate the scattering location and wavenumbers of the density and magnetic fluctuations. In addition, the influence of accordance between toroidal and poloidal launch angles is investigated. The received DBS/CPS signal quality can be improved by matching the parallel wavenumber in the direction of magnetic field lines.