Doppler reflectometry (DR) can measure the turbulence in magnetic confinement fusion plasma by detecting backscattered signals, and has been widely used in fusion devices. On the experimental advanced superconducting tokamak (EAST), a Backscattering and Forward-scattering integrated DR system has been deployed during the 2024 experimental campaign, which can measure the turbulence across multiple scales at the same location, simultaneously. In the scattering process, the wave vector values satisfy the Bragg condition: . For Doppler backscattering (DBS), it detects the m =−1 scattered signal, whereas for the forward scattering, it detects the scattered signal with m > 0 To investigate the scattering process around the cutoff layer for DR, a two-dimensional (2D) plane-shaped O-mode full-wave simulation based on the finite-difference time-domain (FDTD) method has been done. It was found that the signal received by the DBS is mainly the m = −1 scattered signal, while the turbulence measured by the Doppler forward-scattering (DFS) corresponds mainly to low-k fluctuations (). Besides, the results indicate that for both backscattering and forward scattering, the intensity of the scattered signals increases with turbulence level, while the Doppler shift frequency remains unchanged. Therefore, based on these simulation results, the integrated Backscattering and Forward-scattering DR system can simultaneously measure the large scale (low-k) and small scale (high-k) turbulence at the same position in the plasma.
Enhanced microwave scattering with time-of-flight resolution