Abstract
Control of the current profile is a crucial issue for improved confinement and the inhibition of instability in advanced tokamak operation. Using typical discharge data for the Experimental Advanced Superconducting Tokamak, numerical simulations of driven-current profile control in mode conversion current drive (MCCD) in the ion cyclotron range of frequencies were performed employing a full-wave method and Ehst–Karney efficiency formula. Results indicate that the driven current profile in MCCD can be effectively modified by shifting the mode conversion layer. The peak of the driven current can be located at an aimed position in the normalized minor radius range (−0.60≤r/a≤0) by changing the radiofrequency and the minority-ion concentration. The efficiency of the off-axis MCCD can reach 233 kA/MW through optimization, and the mode converted ion cyclotron wave plays an important role in such scenarios. The effects of electron temperature and plasma density on the driven current profile are also investigated.
Highlights
The core energy confinement in tokamaks can be improved by modifying the plasma current profile to produce a zero or negative magnetic shear configuration, and the current profile control is needed for inhibiting instabilities.[1,2,3,4,5] A noninductive current drive method which can provides both on-axis and off-axis currents is required.[6,7,8] the driven current profile should be controlled effectively
The control of the driven current profile in mode conversion current drive (MCCD) was numerically simulated based on real discharge of Experimental Advanced Superconducting Tokamak (EAST) in the framework of full-wave code
Results showed that for different RF wave frequencies, the ion cyclotron range of frequencies (ICRF) Mode converted waves (MCW) can effectively drive a current at the aimed position by shifting the mode conversion layers
Summary
The core energy confinement in tokamaks can be improved by modifying the plasma current profile to produce a zero or negative magnetic shear configuration, and the current profile control is needed for inhibiting instabilities.[1,2,3,4,5] A noninductive current drive method which can provides both on-axis and off-axis currents is required.[6,7,8] the driven current profile should be controlled effectively. The single-pass absorption by the MCW is predicted to be much higher than direct electron absorption of the FW.[22] As a result, the driven current is localized near the MC layer, which can be positioned either on-axis or off-axis.[25] In Ref. 17, modeling work was done to optimize current drive efficiency in a minority heating regime with some initial studies of mode conversion current drive (MCCD). The ICRF MCCD has previously been investigated theoretically and experimentally.[26,27,28,29,30,31] The first experiment demonstrating that the IBW converted from the FW can efficiently drive current and heat electrons was performed on the TFTR tokamak.[26] Up to 130 kA of on- and off-axis current was noninductively driven, and a modification of the plasma current profile was detected.
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