Envelope-PIC Hybrid Method for the Simulation of Microwave Reflectometry

Abstract

We developed a new hybrid method for the simulation of microwave reflectometry, which are commonly used to measure the plasma density and the density fluctuation in magnetically confined plasmas. For the simulation study of reflectometry, they usually solve a full wave equation assuming linear and steady-state response of the plasma. However, the dynamic properties of the plasma can be important near cutoff as the characteristic frequency of the plasma becomes comparable to that of the probe wave. In addition, highly nonlinear behavior is expected to emerge as the density fluctuation develops by numerous types of instability, which can be simulated self-consistently by the particle-in-cell (PIC) method. In our numerical scheme, the full PIC is employed to simulate the cutoff region, while the conventional steady-state dielectric model of the plasma is used for the low-density region. The advantage of the new method is the improved computational speed by at least threefold, while maintaining the overall accuracy of the PIC. The critical point of the new method is minimizing the numerical reflection in the heterogeneous domain.