A forward modeling technique is developed for determining the characteristic features of observed MHD modes from the line-of-sight data of the soft x-ray (SXR) tomography diagnostics in the Wendelstein 7-X (W7-X) stellarator. In particular, forward modeling is used to evaluate the poloidal mode numbers m, radial location, poloidal rotation direction and ballooning character of the MHD modes. The poloidal mode structures have been modeled by the radially localized Gaussian-shaped emission regions rotating along the magnetic surfaces. In the present study the cases of rigid-shape emission regions and flexible emission regions are modeled. Various mode phase velocity dependences on the magnetic surface position are simulated. The modeled phase dynamics of line-integrated oscillations and the distribution of oscillation amplitudes are compared with the experimental signals of the SXR cameras which observe the plasma at various viewing angles in the poloidal cross-section. Application of this technique enables describing of the 1–50 kHz modes. In particular, in the discharge W7X-PID 20180918.045 three identified branches with the poloidal mode numbers m= 8, m= 10 and m= 11 localized at ρ ≈ 0.3 are rotating in the clockwise poloidal direction. The present paper reports the first application of the forward modeling technique to the data from the SXR diagnostics in W7-X. The high m-modes are identified by forward modeling in W7-X.
Wendelstein 7-X（W7-X）仿星器中，开发了一种正向建模技术，用于从软X射线（SXR）层析诊断的视线数据中确定观测到的MHD模的特征。特别是，利用正向建模来评估MHD模的极向模数m、径向位置、极向旋转方向和气球模特性。极向模结构已通过沿磁面旋转的径向局域高斯形发射区域进行建模。在本研究中，对刚性形状发射区域和柔性形状发射区域的情况进行了建模。模拟了各种模相位速度对磁面位置的依赖性。将建模的线积分振荡相位动力学和振荡振幅分布与SXR相机的实验信号进行了比较，这些相机在极向截面中以不同视角观测等离子体。应用该技术能够描述1–50 kHz的模。特别是，在放电W7X-PID 20180918.045中，三个已识别的分支，其极向模数m=8、m=10和m=11，局域于ρ≈0.3，沿顺时针极向方向旋转。本文报告了该正向建模技术首次应用于W7-X中SXR诊断数据的情况。通过W7-X中的正向建模识别了高m模。