Achievement of radiative feedback control for long-pulse operation on EAST

Abstract

The active feedback control of radiated power to prevent divertor target plates overheating during long-pulse operation has been developed and implemented on EAST. The radiation control algorithm, with impurity seeding via a supersonic molecular beam injection (SMBI) system, has shown great success in both reliability and stability. By seeding a sequence of short neon (Ne) impurity pulses with the SMBI from the outer mid-plane, the radiated power of the bulk plasma can be well controlled, and the duration of radiative control (feedforward and feedback) is 4.5 s during a discharge of 10 s. Reliable control of the total radiated power of bulk plasma has been successfully achieved in long-pulse upper single null (USN) discharges with a tungsten divertor. The achieved control range of is 20%–30% in L-mode regimes and 18%–36% in H-mode regimes. The temperature of the divertor target plates was maintained at a low level during the radiative control phase. The peak particle flux on the divertor target was decreased by feedforward Ne injection in the L-mode discharges, while the Ne pulses from the SMBI had no influence on the peak particle flux because of the very small injecting volume. It is shown that although the radiated power increased, no serious reduction of plasma-stored energy or confinement was observed during the control phase. The success of the radiation control algorithm and current experiments in radiated power control represents a significant advance for steady-state divertor radiation and heat flux control on EAST for near-future long-pulse operation.

Recent advances in EAST physics experiments in support of steady-state operation for ITER and CFETR

“…Seeded impurities can convert a large fraction of the thermal energy into radiated power, and thus reduce the peak heat flux and total power incident on the divertor target plates. The active feedback control of radiation power and thus heat load towards long pulse operation has been developed and successfully achieved in EAST using neon (Ne) impurity seeding [16]. By seeding a sequence of short neon impurity pulses with the super molecular beam injection (SMBI) from the outer mid-plane, the radiated power of the bulk plasma can be well controlled.…”

Recent progress in Chinese fusion research based on superconducting tokamak configuration

“…Since the beginning of its operation, the EAST has made significant contributions to the basic physical understanding of fusion and developed new control techniques for divertor/PWI long-pulse operation, including (1) steady-state heat flux control, (2) fueling particle exhaust, and (3) impurity screening, which have been successfully applied to achieve high-confinement (H-mode) plasma for over 100 s 21 , 51 by making full use of the active water-cooling ITER-like tungsten divertor. Many heat and particle flux control approaches have been developed and tested on the EAST, such as power footprint broadening and 3D deposition; 18 , 29 , 47 active heat load control, 52 advanced plasma equilibrium development, such as the quasi-snowflake divertor configuration; divertor particle exhaust optimization; recycling; and tungsten souring control. The upper divertor of the EAST was upgraded from graphite to active water-cooling ITER-like tungsten in 2014, leading to an enhanced heat removal capability.…”

Correcting for non-periodic behaviour in perturbative experiments: application to heat pulse propagation and modulated gas-puff experiments

“…Detachment requires active feedback control to prevent reattachment and/or core confinement degradation [39]. Various experiments have been carried out on a wide range of machines, relying on the real-time interpretation of different plasma diagnostics such as Langmuir probes, bolometry, and thermocouples [40,41,42,43].…”