A high-density and high-confinement tokamak plasma regime for fusion energy

The tokamak approach, utilizing a toroidal magnetic field configuration to confine a hot plasma, is one of the most promising designs for developing reactors that can exploit nuclear fusion to generate electrical energy1,2. To reach the goal of an economical reactor, most tokamak reactor designs3-10 simultaneously require reaching a plasma line-averaged density above an empirical limit-the so-called Greenwald density11-and attaining an energy confinement quality better than the standard high-confinement mode12,13. However, such an operating regime has never been verified in experiments. In addition, a long-standing challenge in the high-confinement mode has been the compatibility between a high-performance core and avoiding large, transient edge perturbations that can cause very high heat loads on the plasma-facing-components in tokamaks. Here we report the demonstration of stable tokamak plasmas with a line-averaged density approximately 20% above the Greenwald density and an energy confinement quality of approximately 50% better than the standard high-confinement mode, which was realized by taking advantage of the enhanced suppression of turbulent transport granted by high density-gradients in the high-poloidal-beta scenario14,15. Furthermore, our experimental results show an integration of very low edge transient perturbations with the high normalized density and confinement core. The operating regime we report supports some critical requirements in many fusion reactor designs all over the world and opens a potential avenue to an operating point for producing economically attractive fusion energy.

[A case of sclerocornea combined with open-angle glaucoma]

A patient complained of progressive visual acuity decline in the left eye for 3 years was admitted. The appearance of the patient was bilateral microcornea. After ocular ultrasonography, ultrasound biomicroscopy, etc, the patient was diagnosed as sclerocornea of the left eye with open-angle glaucoma. Trabeculectomy of the left eye was performed after drug treatment failed, and there were no surgical complications. The intraocular pressure of the left eye was normal and the anterior chamber was well formed 6 months after surgery.

Experimental Evidence of Intrinsic Current Generation by Turbulence in Stationary Tokamak Plasmas

High-β_{θe} (a ratio of the electron thermal pressure to the poloidal magnetic pressure) steady-state long-pulse plasmas with steep central electron temperature gradient are achieved in the Experimental Advanced Superconducting Tokamak. An intrinsic current is observed to be modulated by turbulence driven by the electron temperature gradient. This turbulent current is generated in the countercurrent direction and can reach a maximum ratio of 25% of the bootstrap current. Gyrokinetic simulations and experimental observations indicate that the turbulence is the electron temperature gradient mode (ETG). The dominant mechanism for the turbulent current generation is due to the divergence of ETG-driven residual flux of current. Good agreement has been found between experiments and theory for the critical value of the electron temperature gradient triggering ETG and for the level of the turbulent current. The maximum values of turbulent current and electron temperature gradient lead to the destabilization of an m/n=1/1 kink mode, which by counteraction reduces the turbulence level (m and n are the poloidal and toroidal mode number, respectively). These observations suggest that the self-regulation system including turbulence, turbulent current, and kink mode is a contributing mechanism for sustaining the steady-state long-pulse high-β_{θe} regime.

Integration of full divertor detachment with improved core confinement for tokamak fusion plasmas

Divertor detachment offers a promising solution to the challenge of plasma-wall interactions for steady-state operation of fusion reactors. Here, we demonstrate the excellent compatibility of actively controlled full divertor detachment with a high-performance (βN ~ 3, H98 ~ 1.5) core plasma, using high-βp (poloidal beta, βp > 2) scenario characterized by a sustained core internal transport barrier (ITB) and a modest edge transport barrier (ETB) in DIII-D tokamak. The high-βp high-confinement scenario facilitates divertor detachment which, in turn, promotes the development of an even stronger ITB at large radius with a weaker ETB. This self-organized synergy between ITB and ETB, leads to a net gain in energy confinement, in contrast to the net confinement loss caused by divertor detachment in standard H-modes. These results show the potential of integrating excellent core plasma performance with an efficient divertor solution, an essential step towards steady-state operation of reactor-grade plasmas.

[Stable Nitrite Accumulation and Phosphorus Removal from High-nitrate and Municipal Wastewaters in a Combined Process of Partial Denitrification and Denitrifying Phosphorus Removal (PD-DPR)]

In this study, a novel process combining partial denitrification (PD, NO₃^--N→NO₂^--N) and denitrifying phosphorus removal (DPR) in an anaerobic-anoxic-aerobic sequencing batch reactor (SBR) was developed. By comprehensively controlling the influent C/N ratio, anaerobic drainage ratio, and anoxic duration, the nitrite accumulation and phosphorus removal performance of a system treating high-strength nitrate and municipal wastewaters was investigated. The results showed that, after 140 days, the nitrate-to-nitrite transformation ratio (NTR) was 80.1%, and PO₄^3--P removal efficiency was 97.64%. In the anaerobic stage (180 min), glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) efficiently utilized the carbon source in municipal wastewater to enhance intracellular carbon storage. In the anoxic stage (150 min), denitrifying GAOs (DGAOs) and heterotrophic denitrifying bacteria (DOHOs) carried out endogenous and exogenous short-range denitrification, respectively, to achieve stable nitrite accumulation; simultaneously, denitrifying PAOs (DPAOs) carried out denitrifying phosphorus uptake to achieve efficient phosphorus removal. In the aerobic stage (10 min), without initiating ammonia/nitrite oxidation, PAOs absorbed excessive phosphorus, which improved the phosphorus removal performance of the system. The effluent NO₂^--N/NH₄⁺-N of a ratio of 1.31:1 (close to the theoretical value of ANAMMOX process, 1.32:1), with little PO₄^3--P and COD (0.30 and 12.94 mg·L^-1), meets the requirements for deep-level nitrogen removal by coupling with ANAMMOX process.

Promising High-Confinement Regime for Steady-State Fusion

A reproducible stationary high-confinement regime with small "edge-localized modes" (ELMs) has been achieved recently in the Experimental Advanced Superconducting Tokamak, which has a metal wall and low plasma rotation as projected for a fusion reactor. We have uncovered that this small ELM regime is enabled by a wide edge transport barrier (pedestal) with a low density gradient and a high density ratio between the pedestal foot and top. Nonlinear simulations reveal, for the first time, that the underlying mechanism for the observed small ELM crashes is the upper movement of the peeling boundary induced by an initial radially localized collapse in the pedestal, which stops the growth of instabilities and further collapse of the pedestal, thus providing a physics basis for mitigating ELMs in future steady-state fusion reactors.

[Nitrogen and Phosphorus Removal from Low C/N Municipal Wastewater Treated by a SPNDPR System with Different Aeration and Aerobic Times]

An anaerobic (180 min)/aerobic operated sequencing batch reactor (SBR) fed with urban sewage was optimized by regulating the aeration quantity to investigate the deep-level nitrogen (N) and phosphorus (P) removal. The amount of aeration was regulated by adjusting the volume of gas per unit volume of reactor passed in unit time, when the unit is L·(min·L)^-1, from 0.125 L·(min·L)^-1 gradually to 0.025 L·(min·L)^-1, and aerobic times from 3 h to 6 h. The experimental results show that the effluent NH₄⁺-N, NO₂^--N, NO₃^--N, and PO₄^3--P concentrations of the optimized SPNDPR system were 0, 8.62, 0.06, and 0.03 mg·L^-1. The effluent TN concentration was about 9.22 mg·L^-1, and the TN removal efficiency was up to 87.08%. When the aeration quantity was decreased from 0.125 L·(min·L)^-1 to 0.100 L·(min·L)^-1; then decreased to 0.075 L·(min·L)^-1, the nitrification rate of the system recovered and stabilized at 0.16 mg·(L·min)^-1. However, when the aeration quantity continuously decreased to 0.050 L·(min·L)^-1 and then to 0.025 L·(min·L)^-1, the nitrification rate decreased to 0.09 mg·(L·min)^-1 and 0.06 mg·(L·min)^-1. With reduction of the aeration quantity[from 0.125 L·(min·L)^-1 to 0.100, 0.075, 0.050 and 0.025 L·(min·L)^-1] and extension of aerobic time (from 3 h to 6 h), the TN removal efficiency increased gradually from 62.82% to 87.08%, and the SND efficiency increased from 19.57% to 72.11%. It was proven that reducing the aeration quantity can enhance the SPND function and deep denitrification by the system was realized. By enhancing the anaerobic intracellular carbon storage and aerobic phosphorus uptake, denitrifying phosphorus removal, partial nitrification, and endogenous nitrification were achieved. The SPNDPR system, after reducing aeration and prolonging aerobic time, was able to realize deep-level denitrification and dephosphorization using low C/N urban sewage.

[Effect of Influent C/N Ratio on the Nutrient Removal Characteristics of SNEDPR Systems]

To determine the performance of nitrogen and phosphorus removal within a simultaneous nitrification endogenous denitrification system (SNEDPR), an extended anaerobic/low aerobic (dissolved oxygen:0.5-2.0 mg·L^-1)-operated sequencing batch reactor (SBR) was fed with simulation wastewater. The SBR was initiated under a constant influent C/N ratio of 10, with the simultaneous enrichment of polyphosphate-accumulating organisms (PAOs). It was then investigated at different influent C/N ratios of 10, 7.5, 5, and 2.5. The experimental results indicated that, when the influent C/N ratio was 10, SNEDPR could be successfully started up. The effluent PO₄^3--P and total nitrogen (TN) concentrations were 0.1 mg·L^-1 and 8.1 mg·L^-1. PO₄^3--P efficiency, TN efficiency, and SNED efficiency were 99.79%, 89.38%, and 58.0%, respectively. When the influent C/N ratio increased from 5 to 10, the nitrogen and phosphorus removal performance of the system improved with PRA, and SNED efficiency increased from 16.0 m·L^-1 and 48.0% to 24.4 mg·L^-1 and 69.2%, respectively. When the C/N ratio was 10, the TN and PO₄^3--P removal efficiencies increased to 94.5% and 100%, respectfully. When the C/N ratio was decreased to 2.5, the nitrogen and phosphorus removal performance of the system decreased. The PRA and SNED efficiencies were only 1.36 mg·L^-1 and 10%, respectively. During the stable phase of the system (C/N ratio were 10, 7.5 and 5), SNED efficiency reached to 85.9%, with the average effluent concentration of NH₄⁺-N, _x^--N, and PO₄^3--P being 0.0, 8.1, and 0.1 mg·L^-1, respectively.

[Nitrite Accumulation Characteristics of Partial Denitrification in Different Sludge Sources Using Sodium Acetate as Carbon Source]

In order to explore the characteristics of nitrite accumulation during the operational period of partial denitrification in different sludge sources using sodium acetate as a carbon source, No.1 SBR and No.2 SBR were used to inoculate with surplus sludge taken separately from a secondary sedimentation tank of a sewage treatment plant and simultaneous nitrification and denitrifying phosphorus removal system. By reasonably controlling the initial nitrate concentration and anoxic time, partial denitrification was realized. The carbon and nitrogen removal characteristics under different initial COD and NO₃^--N concentrations were investigated. The results showed that, using sodium acetate as the carbon source, the partial denitrification process in No.1 SBR and No.2 SBR sludge successfully began in 21 d and 20 d, respectively. The accumulation of NO₂^--N and nitrite accumulation rate (NAR) in reactors were maintained at high levels (12.61 mg·L^-1, 79.76% and 13.85 mg·L^-1, 87.60%, respectively). When the initial NO₃^--N concentration of No.2 SBR was 20 mg·L^-1 and the initial COD concentration increased from 60 mg·L^-1 to 140 mg·L^-1, the operation time for achieving the highest NO₂^--N accumulation in the system was shortened from 160 min to 6 min. The NO₃^--N ratio of the denitrification rate (in VSS) increased from 3.84 mg·(g·h)^-1 to 7.35 mg·(g·h)^-1. Increased initial COD concentration was beneficial to the accumulation of NO₂^--N during partial denitrification. When the initial COD concentration of No.2 SBR was 100 mg·L^-1 and the initial NO₃^--N concentration increased from 20 mg·L^-1 to 30 mg·L^-1, NAR was maintained above 90% and up to 100% (the initial NO₃^--N concentration was 25 mg·L^-1). When the initial NO₃^--N concentration was ≥ 35 mg·L^-1, insufficient COD caused NO₃^--N to be completely reduced to NO₂^--N. Under different initial COD concentrations (80, 100, or 120 mg·L^-1) and different initial NO₃^--N concentrations (20, 25, 30, or 40 mg·L^-1), the nitrogen and carbon removal and partial denitrification performance of the No.2 SBR was better than that of No.1 SBR.

[Denitrification and Phosphorus Removal from Low C/N Urban Sewage Based on a Post-Partial Denitrification AOA-SBR Process]

This study focuses on the investigation of the nitrogen (N) and phosphorus (P) removal characteristics of a combination of enhanced phosphorus removal (EBPR) with simultaneous partial nitrification endogenous denitrification (SPND) and post-partial denitrification process. An anaerobic/aerobic/anoxic (A/O/A) operated sequencing batch reactor (SBR) fed with urban sewage was optimized by regulating the aeration rate and anoxic time. Based on this optimization, deep-level nitrogen and phosphorus removals from low C/N urban sewage could be realized. The experimental results show that the effluent PO₄^3--P concentration decreased from 0.06 mg·L^-1 to 0 mg·L^-1, the effluent NH₄⁺-N, NO₂^--N, and NO₃^--N concentrations gradually decreased from 0.18, 18.79, and 0.08 mg·L^-1 to 0, 16.46, and 0.05 mg·L^-1, respectively, and the TN removal efficiency increased from 72.69% to 77.97% when the aeration rate decreased from 1.0 L·min^-1 to 0.6 L·min^-1 and the anoxic duration was 180 min. With the reduction of the aeration rate, the SPND phenomenon became notable and the SND rate increased from 19.18% to 31.20%. When the anoxic duration was extended from 180 min to 420 min, the effluent PO₄^3--P, NH₄⁺-N, and NO₃^--N concentrations stabilized at~0, 0, and 0.03 mg·L^-1, respectively. The effluent NO₂^--N concentration was as low as 3.06 mg·L^-1, the SND rate was~32.21%, the TN removal performance gradually improved, and the TN removal efficiency was as high as 99.42%. Thus, deep-level nitrogen and phosphorus removals could be realized with the SPNDPR-PD system.

Non-inductive vertical position measurements by Faraday-effect polarimetry on EAST tokamak

Vertical instability control in an elongated plasma is highly desirable for a tokamak reactor. A multi-channel 694 GHz far-infrared laser-based polarimeter-interferometer system has been used to provide a non-inductive vertical position measurement in the long-pulse EAST tokamak. A detailed comparison of vertical position measurements by polarimetry and external inductive flux loops has been used to validate Faraday-effect polarimetry as an accurate high-time response vertical position sensor.

Electromagnetic interference reduction design of alternating integrator for EAST

An alternating integrator has been designed for the Experimental Advanced Superconducting Tokamak that is intended for long pulse operation of up to 1000 s. The electromagnetic operating environment for the device is so complex that it could affect the performance of the integrator. The new integrator system is carefully designed and actualized based on specific reduced electromagnetic interference requirements, which were formulated based on consideration of processing of the input signals, the isolation properties, and the circuit board layout and grounding. The developed integrator shows excellent electromagnetic compatibility and low-drift properties.

New edge coherent mode providing continuous transport in long-pulse H-mode plasmas

An electrostatic coherent mode near the electron diamagnetic frequency (20-90 kHz) is observed in the steep-gradient pedestal region of long pulse H-mode plasmas in the Experimental Advanced Superconducting Tokamak, using a newly developed dual gas-puff-imaging system and diamond-coated reciprocating probes. The mode propagates in the electron diamagnetic direction in the plasma frame with poloidal wavelength of ∼8  cm. The mode drives a significant outflow of particles and heat as measured directly with the probes, thus greatly facilitating long pulse H-mode sustainment. This mode shows the nature of dissipative trapped electron mode, as evidenced by gyrokinetic turbulence simulations.

Magnetic topology changes induced by lower hybrid waves and their profound effect on edge-localized modes in the EAST tokamak

Strong mitigation of edge-localized modes has been observed on Experimental Advanced Superconducting Tokamak, when lower hybrid waves (LHWs) are applied to H-mode plasmas with ion cyclotron resonant heating. This has been demonstrated to be due to the formation of helical current filaments flowing along field lines in the scrape-off layer induced by LHW. This leads to the splitting of the outer divertor strike points during LHWs similar to previous observations with resonant magnetic perturbations. The change in the magnetic topology has been qualitatively modeled by considering helical current filaments in a field-line-tracing code.

New dual gas puff imaging system with up-down symmetry on experimental advanced superconducting tokamak

Gas puff imaging (GPI) offers a direct and effective diagnostic to measure the edge turbulence structure and velocity in the edge plasma, which closely relates to edge transport and instability in tokamaks. A dual GPI diagnostic system has been installed on the low field side on experimental advanced superconducting tokamak (EAST). The two views are up-down symmetric about the midplane and separated by a toroidal angle of 66.6°. A linear manifold with 16 holes apart by 10 mm is used to form helium gas cloud at the 130×130 mm (radial versus poloidal) objective plane. A fast camera is used to capture the light emission from the image plane with a speed up to 390,804 frames/s with 64×64 pixels and an exposure time of 2.156 μs. The spatial resolution of the system is 2 mm at the objective plane. A total amount of 200 Pa.L helium gas is puffed into the plasma edge for each GPI viewing region for about 250 ms. The new GPI diagnostic has been applied on EAST for the first time during the recent experimental campaign under various plasma conditions, including ohmic, L-mode, and type-I, and type-III ELMy H-modes. Some of these initial experimental results are also presented.

[Determination of protocatechuic acid in Blumea riparia (Bl.) DC. by RP-HPLC]

OBJECTIVE

To determine the content of protocatechuic acid in Blumea riparia by RP-HPLC.

METHOD

mu-Bondapak C18 column was used, mobile phase consisted of methanol-water-glacial acetic acid(19:80:1) and detection was performed at UV 260 nm.

RESULT

The standard curve was linear in the range of 3.31-41.8 micrograms.ml-1. The correlation coefficient was 0.9999. The average recovery rate and RSD were 98.05% and 1.94% (n = 6) respectively.

CONCLUSION

The method provides scientific indexes for quality control of riparia.