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One of the key challenges for future fusion research is to mitigate the high steady-state heat load on the divertor target plates, and divertor detachment offers a promising solution. The Experimental Advanced Superconducting Tokamak (EAST) has developed several feedback control methods for divertor detachment. However, when an off-normal event momentarily disturbs the main plasma, impurity seeding may still be conducted by these methods for detachment, which probably drives the main plasma further away from its stable equilibrium or even causes the disruption. These off-normal events include excessive impurity seeding, loss of heating and dust droplets, which are not rare in current tokamak experiments, especially in long-pulse operation. To compensate for the drawbacks of these methods, we propose and develop a module of stored-energy monitoring to ensure stable plasmas in long-pulse operation. The stored energy usually decreases when the main plasma is away from its stable equilibrium, which is suitable for monitoring the state of the main plasma. Once the stored energy falls below a certain threshold, the module actively switches off the impurity seeding system. Without impurity seeding, the main plasma can recover with the increase in the stored energy. Only when the stored energy exceeds another threshold does the module switch on the impurity seeding to continue the detachment operation. The module function has been verified during the EAST radiative divertor experiments in the newly-upgraded lower tungsten divertor. A typical ∼20 s discharge in grassy-ELM H-mode regime with ∼5 MW source heating power is demonstrated with divertor partial detachment and good energy confinement by active impurity seeding (50% neon, 50% D2). The energy confinement factor is maintained at a high level, i.e. H 98 , y 2 ∼ 1.1. The electron temperature in the core region only has a slight change after the impurity seeding, while the electron density has a ∼10% increase. Furthermore, the ion temperature near the axis also has a remarkable increase. These achievements provide an important demonstration of the actively controlled radiative divertor mitigating the heat loads with good core confinement, which is an essential step toward steady-state operation of fusion reactors.

Thermal stratification of cryogenic propellants under the condition of external heat leakage is a dominating factor pressurizing the storage tank, which hinders long-term on-orbit storage missions for future explorations. Whether a thermodynamic venting system or cryocooler is introduced to reduce the boil-off losses or even realize zero boil-off of the cryogens, an efficient mixing and heat-exchanging device is a prerequisite for eliminating thermal stratification. Usually, a subcooled stream is introduced, which is injected into the tank through the nozzles on a spray bar. Early research provided evidence that the cooling effect is related to the arrangement of the nozzles. In contrast to adopting a heavy plate spray bar to realize the temperature profile symmetry along the tank axis, this study proposes an assembly with a rotatable nozzle head to diminish the temperature non-uniformity in the tank. In this manner, over 70% of the spray bar payload can be saved compared to the plate configuration. A three-dimensional model was established to investigate the temperature distribution of liquid hydrogen at zero gravity in a tank containing such a rotatable sprayer, which was passively driven by the counterforce of the injection flow, and therefore excluded an extra power drive demand. The injection inlet velocity, as well as the length and quantity of the nozzle arms, were analyzed parametrically to optimize the destratification performance. By employing the self-spinning sprayer, the standard deviation of the temperature in the tank could be lowered, along with the benefits of a significant payload reduction and elimination of direct power input.

The long-term storage of cryogenic propellants on orbit under thermal and pressure control is a promising enabling technology for future space exploration. Composite insulation composed of polyurethane foam (Foam), variable density multilayer insulation (VD-MLI), and a vapor-cooled shield (VCS) is considered as an effective passive thermal control method for such missions. This paper presents a theoretical model that considers three heat transfer mechanisms simultaneously within the VD-MLI and convective heat transfer inside the VCS, to predict and optimize the thermal performance of the insulation combination. The model is validated by experimental data. The influences of VCS position and warm boundary temperature (heat flux) on the thermal insulation performance are investigated for LH2, LN2, LO2, and LCH4 tanks. The temperature profiles within the insulation material with or without VCS are compared. In addition, the contributions from the VCS to reduce the heat flux into the tank are evaluated. The conclusions are valuable for the optimal design of future composite insulation with Foam/VCS/VD-MLI for cryogenic storage tanks on orbit.

Cryogenic propellant storage on orbit is a crucial part of future space exploration. Efficient and reliable thermal insulation is one of the dominant technologies for the long-duration missions. This paper presents theoretical and experimental investigation on the thermal performance of variable density multilayer insulation (VDMLI) with different configurations and spacers. A practical method for optimizing the configuration of VDMLI was proposed by iteratively predicting the internal temperature profiles and maximizing the thermal resistance based on the basic layer by layer model. A cryogen boil-off calorimeter system was designed and fabricated to measure the temperature profile and effective heat transfer coefficient of the VDMLI samples over a wide range of temperature (77–353 K). The experimental data confirm that the optimized sample as predicted does have the minimum effective heat transfer coefficient in the control group. The results indicated that the insulation performance of MLI could be improved by 45.5% after replacing the regular uniform configuration with the optimized variable density configuration. For the same optimized configuration, the performance was further improved by 54% by changing the spacing material from none-woven fiber cloth to Dacron net. It was also found that the effective heat transfer coefficient will be much less sensitive to the MLI thickness when it exceeds 30 mm for on-orbit thermal environment.

Recent Experimental Advanced Superconducting Tokamak (EAST) experiments have successfully demonstrated a long-pulse steady-state scenario with improved plasma performance through integrated operation since the last IAEA FEC in 2016. A discharge with a duration over 100 s using pure radio frequency (RF) power heating and current drive has been obtained with the required characteristics for future long-pulse tokamak reactors such as good energy confinement quality (H98y2 ~ 1.1) with electron internal transport barrier inside ρ < 0.4, small ELMs (frequency ~100–200 Hz), and good control of impurity and heat exhaust with the tungsten divertor. The optimization of X-point, plasma shape, the outer gap and local gas puffing near the low hybrid wave (LHW) antenna were integrated with global parameters of B T and line-averaged electron density for higher current drive efficiency of LHW and on-axis deposition of electron cyclotron heating in the long-pulse operation. More recently, a high β P RF-only discharge (β P ~ 1.9 and β N ~ 1.5, /n GW ~ 0.80, f bs ~ 45% at q 95 ~ 6.8) was successfully maintained over 24 s with improved hardware capabilities, demonstrating performance levels needed for the China Fusion Engineering Test Reactor steady-state operation. A higher energy confinement is observed at higher β P and with favorable toroidal field direction. Towards the next goal (≥400 s long-pulse H-mode operations with ~50% bootstrap current fraction) on EAST, an integrated control of the current density profile, pressure profile and radiated divertor will be addressed in the near future.

In this paper, the C ( t ) and C ∗ integrals, stress redistribution time t red and creep crack-tip stress distributions in the compact tension (CT) specimens with various thicknesses have been calculated by the three-dimensional (3D) finite element method, and the out-of-plane creep crack-tip constraint induced by specimen thickness is quantitatively characterized and analyzed in detail. The results show that the out-of-plane creep crack-tip constraint in the CT specimens could be characterized and analyzed by the new constraint parameter R . The 3D creep crack-tip constraint increases with increasing specimen thickness, and the 3D effect becomes more pronounced with increasing the parameter C ∗ . There is a central region with higher creep constraint along the crack front, the size of the region increases with increasing specimen thickness, and decreases with increasing creep time and parameter C ∗ . The factors of influencing the out-of-plane creep crack-tip constraint are analyzed.

In this paper, the C ( t ) and C ∗ integrals, stress redistribution time t red and creep crack-tip stress distributions in the CT specimens with various crack depths have been calculated by the finite element method (FEM), and the creep constraint induced by crack depths are quantitatively investigated in detail. The results show that the creep constraint could be characterized by the new constraint parameter R . The constraint effect induced by crack depths at non-steady-state creep is more pronounced than that at steady-state creep. The effects of the crack depths, load levels ( C ∗) and distances from the crack tips on the creep constraint parameter R are analyzed.

The paper presented experimental investigation on the heat transfer of MLI with different rarefied gases at different pressures. The investigations were carried out using an innovative static liquid nitrogen boil-off rate measurement system in the case of the small temperature perturbations of cold and warm boundaries. The heat fluxes for a number of inert and some polyatomic gases have been analyzed at different heat transfer conditions ranging from molecular to continuum regime, apparent thermal conductivities of the multilayer insulation were measured over a wide range of temperature (77 K–300 K) and pressure (10 −3 –10 5 Pa) using the apparatus. The experimental results indicated that under degraded vacuum condition, the influences of rarefied gas on the MLI thermal performance very depend on the gas rarefaction degree which impacted by the MLI vacuum degree. Under the condition of molecular regime heat transfer, the MLI thermal performance was greatly influenced by gas energy accommodation coefficients (EAC), when under the continuum regime, the performances depend on the thermal conductivity of rarefied gas itself. Compared to the results of N 2 , Ar, CO 2 , Air and He as interstitial gases in the MLI, Ar was the better selection as space gas because of its low EAC and thermal conductivity characteristics on the different vacuum condition ranging from high pressure to vacuum. So different residual gases can be utilized according to the vacuum level and gas energy accommodation coefficient, in order to improve the insulation performance of low vacuum MLI.

Numerical and experimental methods were used to explore temperature and pressure distributions inside an irregularly-shaped cavity of a novel three-dimensional space environment simulator (SES) system. In order to obtain better temperature and pressure distributions, a plenum chamber and airflow diffusion perforated plate were adopted. Three-dimensional heat and mass transfer characteristics were analyzed using the Standard k – e turbulence model. Simulation results revealed that the temperature and pressure distributions were greatly improved with improved diffusion configuration design, the temperature gradient decreased from 5 K to 1 K, and the pressure gradient decreased to 0.5% of the former value. Based on the simulation results, an improved experimental system for simulating space environment was set up. This experiment system could supply airflow with temperature ranging from 193 K to 353 K for simulating the real space environment. Experimental results showed that the temperature and pressure fields had smaller gradients across the surface and the inner cavity, which agreed considerably with the numerical results. The results of this study present useful information for the design of similar cavity structure.

In this paper, we present clear experimental evidence of core region nonlinear coupling between (intermediate, small)-scale microturbulence and an magnetohydrodynamics (MHD) mode during the current ramp-down phase in a set of L-mode plasma discharges in the experimental advanced superconducting tokamak (EAST, Wan et al (2006 Plasma Sci. Technol. 8 253)). Density fluctuations of broadband microturbulence () and the MHD mode (toroidal mode number , poloidal mode number ) are measured simultaneously, using a four-channel tangential laser collective scattering diagnostic in core plasmas. The nonlinear coupling between the broadband microturbulence and the MHD mode is directly demonstrated by showing a statistically significant bicoherence and modulation of turbulent density fluctuation amplitude by the MHD mode.

The formation of radial electric field Er in the tokamak edge region is calculated based on the collisionless ion orbit loss. The ion orbit loss generates a negative Er, which in turn affects the ion loss. As a result, Er can saturate at either a low or a high value, depending on the plasma parameters. When the ion temperature in the plasma edge is higher than a threshold, a self-sustaining growth in both ion loss and Er is found, leading to a high saturation value of Er in milliseconds. This mechanism provides a possible explanation for the formation of a strong radial electric field during the transition from the low (L) to the high (H) confinement regime observed in tokamak edge plasmas.