Optimization of the plasma startup scenario for the RF current drive tokamak by calculus of variations

Abstract

An analytic method is proposed to determine the startup scenario with the RF current drive. The scenario is obtained from the viewpoint of minimizing the RF injection energy by means of the calculus of variations. It is found that the scenario of RF current startup has distinct differences from that of inductive startup. For example, this analysis indicates that the poloidal beta is kept at the maximum value, the temperature is increased in an early startup phase to decrease the current drive power and the plasma current is ramped up slowly at high temperatures to suppress the return current induced. The numerical calculations reveal that the startup time and the RF injection energy are sharply decreased by the impurity contamination or the deterioration of the plasma confinement during the startup.