Abstract
The off-axis current drive using electron cyclotron (EC) wave is typically very low due to the low density and temperature and electron trapping effect when it is launched from outside midplane. However, the heating and current drive by EC wave is being regarded as a essential element as an off-axis current drive source together with lower hybrid current drive (LHCD) for advanced tokamak operation research in KSTAR in future. Therefore, the reliable and high efficient ECCD using top launch has been studied for two different launch schemes of down-shift and up-shift resonance with various EC frequencies which will be available in the future KSTAR ECRH system. The ray tracing (GENRAY) simulation studies show that a broad ECCD profile peaked off axis is obtained with a high current drive efficiency for both schemes. It is almost twice as high as that of the outside midplane launch for the fundamental O-mode EC wave.
Highlights
KSTAR aims to develop advanced tokamak operation mode with enhanced broad off axis current drive using off-axis NBI and RF heating devices [1]
This paper presents the further ray tracing simulation study on the vertical top launch in KSTAR following the previous ray tracing simulations focused on the second harmonic X-wave
This study is focused on the reliable and high efficient EC current drive (ECCD) using two different launch schemes of up-shift and down-shift electron cyclotron resonance with various EC frequencies which will be available in the future KSTAR ECRH system
Summary
KSTAR aims to develop advanced tokamak operation mode with enhanced broad off axis current drive using off-axis NBI and RF heating devices [1]. It is seen that there is advantage and disadvantage between the down-shift and up-shift vertical launch in terms of launch angle tolerance and current drive efficiency. Upgrade plan of various EC frequencies (105/140/170 GHz) in KSTAR enables the vertical top launch of second harmonic 170 GHz EC wave using up-shift resonance with low toroidal magnetic field and using down-shift resonance with high toroidal magnetic field. We discuss the ray tracing results for the case of the fundamental harmonic up-shift, and for the fundamental and second harmonic down-shift vertical top launches
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