Density compensation and stored energy recovery in resonant magnetic perturbation suppressed edge-localized mode H-mode plasmas using pellet fueling on EAST

Abstract

The fueling of plasmas using frozen pellets in steady-state quiescent H-mode plasmas with edge-localized modes (ELMs) suppressed by external magnetic perturbations (RMPs) was successfully demonstrated on the EAST tokamak in plasmas with similar shapes to those in ITER with q 95 ~ 3.8, and triangularity δ ~ 0.45. During the fully suppressed-ELM phase using RMPs, the plasmas were refueled by deuterium pellets with a frequency of 5 Hz from ~40 cm above the mid-plane on the low field side. The results show that the pellet fueling would partially compensate density, which decreased due to the effect of pump-out induced by RMPs. It was interesting to discover that the stored energy of the plasma could be raised to the value from before RMP application using pellet injection, which is rarely reported in other tokamaks. As for ELMs, they reappeared with a size smaller than the ELMs before RMP application accompanied with a magnetic coherent mode termination, however, the ELMs were still mitigated to a certain extent. Meanwhile, a similar experiment using supersonic molecular beam injection fueling was also carried out, which confirmed that pellet fueling is better for raising plasma stored energy. This investigation on the synergistic effect of pellet fueling and RMPs would be useful for simultaneous control of plasma density and ELMs in high performance H-mode plasmas in future devices, such as ITER.

Integrated ELM and divertor power flux control using RMPs with low input torque in EAST in support of the ITER research plan

“…One typical shot #93536 is shown in figure 4. In this discharge, each frozen deuterium pellet containing about (1.03 ± 0.01) × 10 20 particles is injected from the low field side at about 0.4 m above the mid-plane with a velocity of about 100 m s −1 and a frequency of 10 Hz [15,38]. With these parameters, a simple modelling method described in [39] is applied to this EAST discharge and result predicts that the highest density increase caused by the pellet is around located ρ t = 0.88 as shown in figure 5(a).…”

“…Experiments in DIII-D showed that injecting pellets trigger frequent ELMs for full ELM suppressed H-modes while reduce the number of ELM events for partially ELM suppressed H-modes [14]. Similarly, previous experiments in EAST showed that injecting pellets into an ELM-suppressed H-mode with n = 2 RMPs returns the plasma to an ELMmitigated state [15].…”

Compatibility of pellet fuelling with ELM suppression by RMPs in the ASDEX Upgrade tokamak

“…One of the ELM control techniques is the application of external resonant magnetic perturbations (RMPs) [3][4][5][6] and such a system is planned on ITER [7]. Both pellet fuelling and RMPs act on the plasma periphery and therefore it is not surprising that these actuators are coupled as seen on DIII-D [3,[8][9][10], ASDEX Upgrade [11][12][13][14], MAST [15,16] and EAST [17]. This coupling takes the form of two effects.…”

Pellet source density in toroidal plasma configurations based on a 2D Gaussian deposition model

“…Figures 1(c) and (d) show the fitted electron temperature and density profiles before pellet injection. In this discharge, deuterium pellets are injected horizontally from the low field side (LFS), at about 0.4 m above the mid-plane, with a velocity of about 100 m s −1 [55]. In addition to the LFS-horizontal (LFS0.4) injection case, we also consider in our simulations the LFS-vertical (LFSv) injection case and the LFS-midplane (LFSm) horizontal injection case as shown in figure 1(a).…”