[en] In tokamak plasma, a weak or reversed magnetic shear configuration is an important candidate for the future fusion reactor, it is helpful to build a hollow current profile, establish an internal transport barrier (ITB), improve the plasma confinement, and realize the long-pulse discharge. In experiments, auxiliary heating systems, including NBI (Neutral Beam Injection), ECRH (Electron cyclotron resonance heating), ICRH (Icon cyclotron resonance heating), and LHCD (Lower hybrid current drive), are used to control the plasma current as the Ohmic current driving efficiency is limited, consequently, achieving the weak or reversed magnetic shear configuration. An improved confinement plasma operation can be obtained with these heating systems. On EAST (Experimental Advanced Superconducting Tokamak), both of the four heating systems are applied to heat plasma. In recent experiments, optimized confinement plasma is obtained with the interaction between LHCD and ECRH, the simulation and experiments results are in good agreement. (author)

[en] Highlights: • In 2012, the water-cooling Mo wall was installed in EAST. • A schottky barrier diode detector is designed and used on EAST for the first time. • The three-channel far-infrared laser interferometer can measure the electron density. • The improved measurement and latest experiment results are reported. • The signal we get in this experiment campaign is much better than we got in 2010. -- Abstract: A three-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer is in operation since 2010 to measure the line averaged electron density on experimental advanced superconducting tokamak (EAST). The HCN laser signal is improved by means of a new schottky barrier diode (SBD) detector. The improved measurement and latest experiment results of the three-channel FIR laser interferometer on EAST tokamak are reported

[en] The radioactive aerosol and loose contamination generated in disassembling the contaminated equipment by plasma cutting was harmful to the operator's health. The method of atomizing capture liquid was used to capture and encapsulate the radioactive aerosol. The result of the engineering test indicated that reducing the capture liquid's surface tension can decrease the atomized droplet's particle diameter. That benefits the aerosol particle capturing. The higher viscosity contributes to encapsulate the loose contamination. On the decommissioning site, the selected capturing liquid in engineering test was effective in capturing the high concentration α radioactive aerosol and encapsulating the loose contamination. The encapsulating effort could prevent the loose contamination from resuspension for several days. (authors)

[en] The far infrared laser interferometer on EAST, DCN laser, is introduced. Helium, CD₄, D₂ and N-2 are used in the laser. The output power is optimized by changing the supply current, gas pressure and gas ratio. Experimental results show that the best parameter can be achieved with the gas ratio He: CD₄ : D₂ : N₂ = 2 : 3 : 5 : 3 and gas pressure 32Pa. The output power increases with current increase. (authors)

[en] Measurements of boundary parameters and their fluctuations have been performed in ohmic (OH) plasma and Ion Bernstein Wave (IBW) and Lower Hybrid Current Drive (LHCD) enhanced confinement plasma using a pneumatically driven Langmuir probe array on HT-7 tokamak. In the enhanced confinement plasma, the gradients of electron density and temperature become higher and a transport barrier comes into being in the vicinity of the limiter. The boundary potential shows a clear modification in the same region. The fluctuation levels are significantly depressed and the coherences between fluctuations are reduced evidently in the enhanced plasma. Meanwhile, we obtained the spectral features and the poloidal phase velocity of fluctuations using a two-point correlation technique and found obvious modifications of the turbulence and the poloidal flow. The results suggest that the improved confinement in the IBM and LHCD enhanced plasma is at least partially due to the modification of the boundary parameters and the suppression of the boundary fluctuations and fluctuation induced fluxes

[en] By applying ion Bernstein wave (IBW) heating into the lower hybrid current drive (LHCD) plasma, improved confinements have been obtained in the HT-7 tokamak. The central electron temperature was doubled and the storage energy was increased significantly. The core electron density and temperature were broadened and their profiles near the edge were steepened. A transport barrier has been formed in the vicinity of the limiter radial location. An enhanced shear in poloidal phase velocity was found in the same region with reduction of the fluctuation levels and the coherencies between fluctuations. The results suggest that the improved confinement in the IBW and LHCD plasma is at least partially due to the modification of shear in poloidal velocity and then the suppression of fluctuations and fluctuation induced fluxes via de-correlation effect

[en] Ion cyclotron range of frequencies (ICRF) heating has been considered as an effective means for upraise ion temperature in magnetic confinement fusion plasma. We were employment the time resolved neutron fluence and energy spectrum diagnostics to study the ICRF heating on EAST tokamak. The phenomenon of neutron yield rapid rise has been observed during the power of wave effect launch into deuterium plasma. However, that obvious increase was difficult occur in Lower Hybrid Wave (LHW) heating alone. The ICRF dominant heat minority hydrogen ions were supported by below 5% of n_H/n_D and depression high-energy tail in neutron spectrum that measurement by liquid scintillator. In this case, adopt neutron fluence and plasma density signals to inverse calculation the central ion temperature by classical fusion equation. Calculation results indicate that central ion temperature growth approximate 30% in L-mode plasma, and excess 50% in H-mode plasma during ICRF heating. Compare with other diagnostics, such as x-ray crystal spectrometer (XCS), those results were accordant. Furthermore, the relationship of neutron yield associate with plasma current and ICRF inject power has been statistic in this article. (author)

[en] The radioactive aerosol generated in decommissioning the reprocessing facilities should be treated for its high concentration. CaCO₃ powder was selected as the source to produce simulative aerosol in this study. The ultrasonic atomizing technology was applied to capture and encapsulate the aerosol. The experiment result shows that the concentration of simulative aerosol decreases with capture time; large particlesin aerosol can beeasily captured; when the capture liquid dose reduced to the certain value, the result of aerosol particle capturing and encapsulating became better evidently with the increase of dose. The experiment that carried out in a ²⁴¹Am contaminated glove-box proved the radioactive aerosol concentration could reduce from 183 Bq/m³ to 1.51 Bq/m³ after the capturing process. The radioactive concentration in the glove-box had no obvious change on the seventh day. Resuspension rate of the aerosol was 6.5% when opened the ventilation at the fourteenth day. The capture liquid had good encapsulating result for radioactive aerosol and loose contamination. (authors)

[en] Upper and lower graphite divertor in EAST tokamak have been updated to tungsten divertors in 2014 and 2021 respectively to investigate the tungsten divertor operation and to realize high-performance long pulse discharge. Therefore, studies on the tungsten behavior are crucially important for improving the plasma performance. For the purpose four fast-time-response and four space-resolved extreme ultraviolet (EUV) spectrometers have been installed on EAST to observe line emissions from tungsten ions and their intensity radial profiles in wavelength ranges of 5 − 520 Å.

[en] A single-channel far-infrared (FIR) laser interferometer was developed to measure the line averaged electron density on the EAST tokamak. The structure of the single-channel FIR laser interferometer is described in detail. The evolution of density sawtooth oscillation was measured by means the FIR laser interferometer, and was identified by electron cyclotron emission (ECE) signals and soft X-ray intensity. The discharges with and without sawtooth were compared with each other in the Hugill diagram.