Study On Pressure And Spectral Characteristics Of Deuterium Neutral Particles In EAST Divertor

The high heat load of divertor target materials is a major challenge for future fusion devices.By forming a neutral particle layer on the surface of the divertor target.divertor plasma detachment can effectively alleviate and shield the damage of ion flow and heat flow to the target material,which means that divertor detachment is currently the most promising physical solution.The process of divertor detachment is accompanied by the enhancement of particle collision process,the rise of neutral particle pressure and strong particle energy dissipation.At the same time,the processes of ionization and recombination of atoms and molecules in the divertor change strongly.As an important engineering parameter,the neutral particle pressure of the divertor plays an important role in mastering the plasma state of the divertor and understanding the physical process of the divertor.A large number of atomic and molecular processes produce rich characteristic spectral radiation,which is an important tool to understand the physical process behind engineering parameters.In this paper,the influence of the particle flow distribution on the surface of the divertor target on the neutral pressure of the divertor on EAST is studied by using the correlation method,Then,the spectral characteristics of deuterium atoms and molecules in the process of H mode discharge density ramp-up and 5%neon impurity seeding were studied and analyzed,and the correlation between them and the neutral particle pressure(neutral pressure)in the divertor was established.,This provides a physical basis for spectral based divertor detachment control.Low hybrid wave heating and resonance magnetic perturbation(RMP)can generate magnetic disturbances at plasma boundaries in Tokamak,change the three-dimensional magnetic field structure of the boundary,and cause the change of particle flow distribution in the divertor area.In order to study the influence of the particle flow distribution on the divertor neutral pressure under these two conditions,the correlation coefficient between the particle flow at different positions on the divertor surface and the divertor neutral pressure was calculated by using the correlation method.The results show that in both cases,there is a turning region on the outer target of the divertor,and the contribution of the particle flow on both sides of the region to the neutral pressure is significantly different.Further considering the distribution of particle flow in the inner target,it is found that there are similar positions on the inner target where the contribution to the neutral pressure changes sharply.These locations can be considered as the inlet of the divertor.It is further found that the variation trend of the characteristic spectral lines of deuterium(D)atoms is correlated with the neutral pressure,indicating that the level of neutral pressure is affected by the recombination process of electron and ion.The evolution process of deuterium atomic spectrum and molecular spectrum characteristics in the process of density ramp-up and 5%neon impurity injection in H-mode discharge was studied.Based on the change of the Dδ/Dα relative ratio of the deuterium atom Balmer line,the change rule of the atom recombination process in the detachment is analyzed.The results showed that the volume recombination process was significantly enhanced at the onset of the detachment.With the increase of the main plasma density,the recombination region moves upstream.In the case of 5%neon impurity injection,the detachment process in different toroidal field directions is compared and analyzed,and the results show that in the upper single null(USN),Unfavorable magnetic field(B × ▽B↓),the volume recombination on the inner target presents a more significant enhancement process.Favorable magnetic field(B×▽B ↑),the recombination process of the outer target is significantly enhanced.Further,the evolution laws of the main characteristics of the detachment process under different conditions are statistically analyzed.The results show that the evolution of electron temperature,particle flow of the divertor target,and neutral pressure of the divertor during the density ramp-up detachment process are clearly dependent on the relative ratio of Dδ/Dα,which provides the possibility for spectral based feedback control of divertor detachment.Due to the large dispersion of data points,the dependence of the detachment under the condition of 5%neon impurity injection is not obvious.The intensity and distribution of molecular spectrum of D2 on the inner and outer targets of EAST lower divertor were observed and analyzed by using visible spectroscopic diagnostic system.It was found that the change in D2 molecular spectrum intensity was basically consistent with the change in neutral pressure before the detachment,while after the onset of the detachment,as the neutral pressure of the divertor increased,the peak position of D2 molecular spectrum showed a trend of moving towards the far SOL region,and the recombination process of D atoms near the strike point was significantly enhanced.This may reflect significant changes in atomic and molecular processes at different stages of the detachment.Understanding the important factors that affect the pressure of neutral particles,mastering the key characteristics of atomic and molecular spectra,and obtaining the correlation between the pressure of neutral particles and the characteristics of atomic and molecular spectra are of great significance for deepening the understanding of the physical process of the divertor and exploring effective detachment control schemes.