Electron density calculation based on Stark broadening of D Balmer line from detached plasma in EAST tungsten divertor

The electron density within the volume of the tungsten divertor of the Experimental Advanced Superconducting Tokamak （EAST） is calculated based on Dε line （396.9 nm） Stark broadening （SB） measurements. The quasistatic approximation is employed in the SB calculation of the Dε line. The influences of other broadening mechanisms on the calculation error of electron density have been evaluated. The SB method is applied to the study of spatial distribution and time evolution of the electron density in the W divertor. Two electron density bands are observed in the detached divertor plasma during an L-mode discharge sustained by low hybrid wave （LHW） heating, which could be related to the striated particle flux distribution induced by LHW. After the onset of detachment, the upper electron density band corresponding to outer strike point firstly increases then decreases, while the lower density band corresponding to striated particle flux increases continually although the electron densities from Langmuir Probes at the divertor plate keep a descending trend. This could indicate a downward movement of the radiation region that approximately moves along the magnetic field lines after the onset of detachment.

Magnetic field topology modeling under resonant magnetic perturbations on EAST

In order to understand the mechanism by which the resonant magnetic perturbation (RMP)mitigates or suppresses the edge-localized mode (ELM),the topological study of the edge magnetic field in ELM mitigation or suppression phase is a critical issue.To model the three-dimensional magnetic field topology superposed RMP on Experimental Advanced Superconducting Tokamak,a numerical model using the field line tracing method for both vacuum and ideal plasma response approximations is proposed.Using the numerical model,the topological change and the penetration depth of the stochastic field lines in the edge magnetic field are studied in an RMP experiment.Comparing profiles of minimum9 on edge stochastic field lines and the particle flux pattem,the ideal plasma response changes the field line penetration depth while remaining similar profile relative to vacuum approximation.To mitigate and suppress ELM strongly,the deep penetration of RMP fields and topological changes of the edge magnetic field is a key from our modeling.

Observation of deuterium molecule emission spectra under an active feedback control of H-mod plasma divertor detachment experiment on the EAST tokamak

Based on neon gas puffing, an active feedback control of H-mod plasma divertor detachment experiment was successfully operated on the EAST tokamak. During the feedback control discharge, the plasma was detached by puffing neon gas and the strike point splitting phenomenon on divertor target was also clearly observed by divertor probes diagnostic.In boundary region, many neutral particle processes(atom and molecule) were happened and accompanied by their emission spectra under the detachment discharge. By studying these emission spectra, it is helpful for us to understand the role of atoms and molecules in boundary recycling, which is important for studying the physical mechanism of divertor detachment. For the Fulcher-α system(d(3 p)3Πu±→ a(2 s)3Σg+), D2 emission spectra in the range from 601 nm to 606 nm were observed, identified and fitted in the detachment experiment for the first time on the EAST, and the spectra in the Q(0–0) band(d3Πu-→ a(2 s)3Σg+) in the Q branch of the Fulcher-α system were used for detailed analysis to acquire the boundary region temperature Te(below 5eV), which could not be provided very well by other diagnostics on the EAST. An electronic version deuterium molecular spectral line database was established to identify the spectral lines and a multi-peak fitting program was developed to fit and analyze the observed spectra.

Divertor detachment operation in helium plasmas with ITER-like tungsten divertor in EAST

Detachment in helium(He)discharges has been achieved in the EAST superconducting tokamak equipped with an ITER-like tungsten divertor.This paper presents the experimental observations of divertor detachment achieved by increasing the plasma density in He discharges.During density ramp-up,the particle flux shows a clear rollover,while the electron temperature around the outer strike point is decreasing simultaneously.The divertor detachment also exhibits a significant difference from that observed in comparable deuterium(D)discharges.The density threshold of detachment in the He plasma is higher than that in the D plasma for the same heating power,and increases with the heating power.Moreover,detachment assisted with neon(Ne)seeding was also performed in L-and H-mode plasmas,pointing to the direction for reducing the density threshold of detachment in He operation.However,excessive Ne seeding causes confinement degradation during the divertor detachment phase.The precise feedback control of impurity seeding will be performed in EAST to improve the compatibility of core plasma performance with divertor detachment for future high heating power operations.

Achieving temporary divertor plasma detachment with MARFE events by pellet injection in the EAST superconducting tokamak

A new pellet injection system has been equipped on the experimental advanced superconducting tokamak（EAST） in the 2012 campaign,with a pellet size of Ф 2 mm×2 mm,a frequency of1 Hz–10 Hz and velocity of 150 m s^-1–300 m s^-1.The deuterium pellet is well-known for plasma fuelling as well as for triggering the edge localized mode（ELM）.In the 2012 campaign,pellet injection experiments were successfully carried out on EAST.Temporary plasma detachment achieved by deuterium pellets has been observed in a double null（DN） divertor configuration,with multi-pellet injections at a repetition frequency of 2 Hz.The partial detachment of the outer divertors and complete detachment of the inner divertors was achieved after 35 ms of each pellet injection,which have a duration of 30–60 ms with the maximum degree of detachment（DOD） reaching 3.5 and 37,respectively.Meanwhile,the multifaceted asymmetric radiation from the edge（MARFE） phenomena was also observed at the high field side（HFS） near both the lower and upper X-points with radiation loss suddenly increased to about 15%–70%,which may be the main cause of divertor plasma detachment.The temporary detachment induced by pellet injection may act as a new way to study divertor detachment behaviors.