The two-dimensional equilibrium with flexible boundaries is solved via using a MAT-LAB Equilibrium Code (MEC), which has applied the finite element method to handle the changeable plasma shape and employed the trust-region dogleg method to solve the nonlinear partial differential equation. The corresponding driven current profile is also calculated by coupling with the lower-hybrid simulation code (LSC). The results are applied to optimize the lower hybrid current drive (LHCD) efficiency for the Experimental Advanced Superconductor Tokamak (EAST) and suggested that both elongation and triangularity have a notable effect on the efficiency because of the competition between the increase in the resonant area and in the Shafranov shift. Moreover, large aspect-ratio has a negative effect on the efficiency. These effects are studied numerically, which might be considered carefully for both good plasma confinement and high LHCD efficiency.
Radio-frequency (rf) waves can penetrate fusion plasmas and deposit energy and momentum through collisionless mechanisms, resulting in plasma heating and, in some cases, current drive and flow drive. The advantage of this noninductive current drive is that a tokamak-type fusion reactor can be operated at a steady state. Meanwhile, an appropriate profile of plasma current and a significant plasma flow are important in stabilizing magnetohydrodynamics instabilities and realizing and sustaining high-performance confinement regimes. Therefore, rf current drive and flow drive are important in research on the physics of magnetic confinement fusion plasma. This paper presents the elementary physics of wave-particle interactions in plasmas, reviews the present status and challenges of research on rf current drive and flow drive, and suggests possible research strategies. Several problems are highlighted. These include the intrinsic relation of resonant absorption to the reduction of rf current drive efficiency in high-density plasmas; the existence/feasibility of a nonresonant drive scheme; the possibility of increasing the drive efficiency within the resonant mechanism; the direct and indirect effects of rf waves in flow drive, especially the generalized ponderomotive force generated by rf waves; and nonlinear processes during the coupling and propagation of waves, such as parametric decay instabilities, and their possible effects on current drive and flow drive.
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