Development Of Pellet Injection System And Experimental Investigation Of Fueling In High Confinement Plasmas On EAST Tokamak

In tokamak magnetic confinement fusion device,cryogenic deuterium pellet injection is an important technique for core fueling to achieve high density plasma operation in international thermonuclear fusion reactor(ITER)or other reactors in the future.In addition to maintaining high density plasma operation,pellet injection with an appropriate pellet speed and size can be also used to control the extremely high heat load exhausted by edge localized mode(ELM)for protecting the first wall.EAST is the first all superconducting tokamak developed by our country in the world.It has ITER-like operation modes and magnetic field configurations.It is very meaningful for EAST,ITER,and future fusion reactors to carry out the pellet fueling experiments in high confinement mode(H-mode)plasmas on EAST.In this paper,a high frequency deuterium pellet injection system developed for EAST will be described,as well as the related experiments.Using the original built pellet fueling system,the characteristics of pellet fueling in H-mode plasmas with different types of ELM have been investigated on EAST.And the first experiment on EAST with simultaneous pellet fueling and ELM suppression by external magnetic perturbation(RMP)has been also carried out in ITER shaped plasmas.Compared with the supersonic molecular beam fueling(SMBI),pellet fueling is better for compensating plasma density and restoring plasma energy due to a deeper particle deposition.Firstly,a 50 Hz high frequency pellet injection system with pellet size and velocity adjustable,which is based on screw extrusion forming ice and pneumatic acceleration,has been built and developed for EAST.And a continuous pellet injection of 1-50Hz for more than 1000 seconds has been realized.The reliability of launching pellets is more than?85%when the frequency is 50 Hz,which reaches advanced level in the world.Recently,we have tested the system systematically and small ELMs have been triggered by multiple pellets injected into Type-? ELMy H-mode plasmas with negligible impact on density and stored energy on EAST for the first time.This lays a foundation for further research on ELM control with pellet pacing in the future for EAST.Secondly,pellet fueling experiments were performed in Type-? and Type-?ELMy H-mode plasmas on EAST.In Type-? ELMy H-mode plasmas,the pellet fueling efficiency is only?30%,and each pellet triggers a small ELM,which is similar with the results of other devices.Multiple pellets have been injected into Type-? ELMy H-mode plasmas continuously,thus obtaining a maximum density 0.73×nGW.At the same time,it is found that the pellet fueling can modify the behaviors of the Type-? ELM,and a series of high frequency small ELMs have been induced after each pellet injection.The boundary cooling caused by pellet injection is proposed as the main reason for the ELM modification.This is useful for understanding the impact of pellet fueling on plasma confinement.More importantly,the fueling of plasmas using frozen pellets in steady-state quiescent H-mode plasmas with ELM suppressed by RMP was successfully demonstrated on EAST tokamak for the first time.During the fully suppressed-ELM phase using RMP,the plasmas with safety factor q95?3.8,and triangularity ??0.45 were refueled by deuterium pellets at a frequency of 5 Hz with the velocity of?100 m/s from low field side(LFS).The results show that the pellet fueling would compensate plasma density effectively,which was decreased due to the pump-out effect induced by RMP.It was also interesting to discover that the stored energy of the plasma could be raised to the value before RMP application using pellet injection,which was rarely reported in other tokamaks.This investigation is of great significance for the integrated operation of pellet fueling and ELM control by RMP on ITER and future fusion reactors.The development of pellet injection system on EAST and related physical experimental research can provide advanced techniques for plasma fueling and ELM control for EAST to improve the plasma operation parameters.And they can provide data accumulations and references for ITER,as well as the synergistic operation of pellet fueling and ELM control by RMP in the future.