Electron Bernstein wave heating via the slow X-B mode conversion process with direct launching from the high field side in LHD

In the large helical device (LHD), direct oblique launching of the extraordinary (X-) mode from the high magnetic field side is available without installation of any additional mirror or installation of a launcher in the inner side of the torus. The launched X-mode first encounters the electron cyclotron resonance (ECR) layer from the high magnetic field side and then approaches the upper hybrid resonance (UHR) layer where mode conversion from the X-mode to electron Bernstein wave (EBW) occurs. Complete power absorption with a finite parallel component of the refractive index is promising whether the launched wave power is absorbed as the electromagnetic X-mode or is absorbed as electrostatic EBW even in the peripheral region. In the experiment, strong power absorption has been observed by direct oblique launching of the X-mode. Observation of the parametric decay wave suggests a fraction of the launched power reached the UHR layer that is located near the plasma boundary. The result of numerical analysis with three dimensional ray-tracing calculation using the dispersion equation in hot plasmas suggests that the launched X-mode is refracted toward the magnetic axis and strongly absorbed very close to the ECR layer that is located around ρ - 0.5. The main part of the launched power is absorbed as the X-mode in the ECR layer where the electron temperature is sufficient high, while a fraction of the power reaches the UHR that is located in almost the plasma boundary. (author)