Evaluation of deuterium recycling properties by fueling termination in the EAST superconducting tokamak

Abstract

• Hydrogen recycling properties have been investigated by evaluating the density decay time after the fueling termination. • A repeat of discharges diminishes the wall conditioning effect and enhances hydrogen recycling. • Approach of the strike point position to the pumping slot enhances the particle exhaust capability. • The hydrogen recycling coefficient of the LHCD discharge is increased during stop of fueling, although such increase appears not to be seen in the ohmic discharges. Deuterium recycling properties have been investigated in the EAST superconducting tokamak by evaluating the density decay time after the fueling termination. The density decay time of the latter discharge of the experiment of a day is ∼2.9 s, which is more than three times longer than that of the beginning discharge (∼0.88s), indicating that a repeat of discharges diminishes the wall conditioning effect by lithium coating. However, the difference in deuterium recycling among three magnetic configurations (lower single null, double null, and upper single null) is unclear. The density decay times are 3.3 s and 4.1 s when the strike point (SP) positions are located on the horizontal and vertical plates of the lower outer divertor, showing that the particle exhaust capability becomes stronger as the SP position approaches the pumping slot. Furthermore, the lower hybrid current drive (LHCD) power enhances deuterium recycling since the density decay times of high (∼2.7 MW) and low (∼0.8 MW) power LHCD discharges are 4.3 s and 1.2 s, respectively. The density decay time in the LHCD discharge linearly increases with an increase in a period of exponential fitting, implying that the recycling coefficient increases during the stop of fueling. However, the density decay time in the ohmic discharge is independent of the fitting time.