An evaluation of high-field-side (HFS) X-mode injection for the electron-Bernstein-wave (EBW) scenario is performed using the GENRAY ray-tracing code. In the early stage of low-density plasma start-up, when the electron cyclotron resonance and upper hybrid resonance layers are close to each other, efficient and localized heating by the EBW is attainable. We show that, when the electron density rises, the HFS scenario spontaneously shifts to current drive with successful electron heating. This shift can be explained as a change in heating mechanism from collisional to electron cyclotron damping. Also, we discuss a possible O-X-B scenario to continue the plasma current drive beyond the formation of an over-dense plasma.
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