Preliminary results of in situ laser-induced breakdown spectroscopy for the first wall diagnostics on EAST

Post-mortem methods cannot fulfill the requirement of monitoring the lifetime of the plasma facing components （PFC） and measuring the tritium inventory for the safety evaluation. Laserinduced breakdown spectroscopy （LIBS） is proposed as a promising method for the in situ study of fuel retention and impurity deposition in a tokamak. In this study, an in situ LIBS system was successfully established on EAST to investigate fuel retention and impurity deposition on the first wall without the need of removal tiles between plasma discharges. Spectral lines of D, H and impurities （Mo, Li, Si ） in laser-induced plasma were observed and identified within the wavelength range of 500-700 nm. Qualitative measurements such as thickness of the deposition layers, element depth profile and fuel retention on the wall are obtained by means of in situ LIBS. The results demonstrated the potential applications of LIBS for in situ characterization of fuel retention and co-deposition on the first wall of EAST.

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.

Improvement of Raman spectrum uniformity of SERS substrate based on flat electrode

The distribution of metal nanoparticles on the surface of a surface enhancement Raman scattering(SERS)-active substrate plays a prominent part in not only the enhancement of Raman vibration signal,but also the spectrum uniformity.Here,a facile method to fabricate SERS substrates with excellent homogeneity and low cost was proposed,in which a lyotropic liquid crystal soft template was introduced for the coordinated growth of the silver nanoflowers in the process of electrochemistry deposition.Simulation was carried out to illustrate the dominated influence of the distance of electrodes on the deposited nanoparticle number.Two kinds of conductive materials,silver plate and indium tin oxide(ITO)glass,were chosen as the anode,while the cathode was fixed as ITO glass.The simulated conjecture on the effect of electrode flatness on the uniformity of deposited nanoparticles in silver is experimentally proved.More importantly,it was demonstrated that with a relatively smooth and flat ITO glass anode,a SERS substrate featuring higher spectrum uniformity could be achieved.This work is of great significance to the actual applications of the SERS substrate for quantitative detection with high sensitivity.

GaN∶Eu^(3+)材料发光特性的调控研究进展

GaN∶Eu^(3+)作为红光发射材料,在GaN基单片集成全色显示器件应用方面具有很大的潜力。目前的研究重点是如何进一步调控和优化GaN∶Eu^(3+)材料的发光特性,促使其迈向实用阶段。本文主要从生长调控,Mg^(2+)、Zn^(2+)、Si^(4+)元素共掺调控,其他稀土元素共掺调控等方面综述了GaN∶Eu^(3+)材料发光特性的研究进展,比较各调控方法的应用潜力,指出GaN∶Eu^(3+)材料今后的研究重点,并对该领域的发展趋势进行了展望。

Plasma-tungsten interactions in experimental advanced superconducting tokamak(EAST)

Tungsten(W)is used as the armor material of the International Thermonuclear Experimental Reactor(ITER)divertor and is regarded as the potential first wall material of future fusion reactors.One of the key challenges for the successful application of W in fusion devices is effective control of W at an extremely low concentration in plasma.Understanding and control of W erosion are not only a prerequisite for W impurity control,but also vital concerns to plasma-facing component(PFC)lifetime.Since the application of ITER-like water-cooled full W divertor in EAST in 2014,great efforts were made to inves-tigate W erosion by experiment and simulation.A spectroscopic system was developed to provide a real-time measurement of W sputtering source.Both experiment and simulation results indicate that carbon(C)is the dominant impurity causing W sputtering in L-mode plasmas,which comes from the erosion of C plasma-facing material(PFM)in the lower divertor and the main chamber limiters.The mixture layer on the surface of W PFCs formed through redeposition or the wall coating can effectively suppress W erosion.Increasing the plasma density and radiation can reduce incident ion energy,thus alleviating W sputtering.In H-mode plasmas,control of edge localized mode(ELM)via resonant magnetic perturbation(RMP)proves to be capable of suppressing intra-ELM W erosion.The experiences and lessons from the EAST W divertor are beneficial to the design,manufacturing and operation of ITER and beyond.