Hot Ring Research Articles

Experimental and numerical study on integrated film cooling of turbine endwall by upstream slot leakage and blade showerhead jets

Prior emphasis on isolated turbine cooling structures resulted in low coolant utilization, but research on coolant interactions of different components remains scarce. This paper experimentally and numerically investigates the interaction effects between two inherent coolant jets from the endwall slot and blade showerhead. Their combined effect on endwall aero-thermal performance is measured by an Infrared camera, and the secondary flows under coolant mix are analyzed. The results show that blade showerhead coolant can play secondary cooling effects on endwall through reattachment, and it can also influence the endwall cooling distribution through altering the secondary flow development near leading edge. At high slot mass flow ratio (MFR) of 2.3%, the showerhead jets lead to secondary endwall cooling effectiveness of up to 0.2 in pressure side junction and suction side hot ring when showerhead MFR is 0.36%. With a further increase in the showerhead coolant MFR to 0.77%, the showerhead jets push the horseshoe vortex to reattach on pressure side endwall, and thus a high cooling region is formed on pressure side endwall near the slot edge. At low slot MFR of 1.5%, the slot leakage mainly covers the suction side endwall with a large hot ring. The reattachment of showerhead coolant on endwall is weak when the showerhead MFR is 0.36%. When showerhead MFR increases to 0.77%, the showerhead coolant has an ideal secondary cooling effect on endwall suction side hot ring, pressure side upstream part endwall, and pressure side junction. The heat transfer coefficient within the pressure side hot ring and pressure side junction both reaches 400. This paper can guide the joint design of turbine blade and endwall cooling layouts.

Buoyancy-driven nano-suspension subject to interstitial solid/nanofluid heat transfer coefficient: Role of local thermal non-equilibrium (LTNE)

BackgroundBecause of the prominent temperature discrepancy between fluid and solid in porous material, local thermal equilibrium (LTE) is not suitable in case of high-conductivity foams and electronic equipment. In view of above situation, Darcy-Brinkman-Forchheimer model subject to local thermal non-equilibrium (LTNE) is implemented. LTNE technique finds real world applications include groundwater pollution, geothermal extraction, microwave heating, industrial separation process, and transpiration cooling featuring with porous structure. The present study aims at the investigation of the entropy and hydrothermal characteristics of buoyancy-driven TiO2-H2O nanofluid inside a cross-shaped domain embodying two hot and cold rings influenced by LTNE. MethodsFinite element method (FEM) has been considered to solve the dimensionless form of governing equations. Significant findingsAmplification of interstitial solid/nanofluid heat transfer coefficient accounts for the intensification of streamlines, velocities, and diminution of isothermal lines in both nanofluid and solid matrix phases under the influence of LTNE. Strengthening of medium porosity whittles down entropy due to thermal effects in both nanofluid and solid phases, and that ameliorates entropy due to fluid friction and porous medium irreversibilities. Local and average Nusselt numbers in nanofluid phase reduce by 29.31 %, 20.72 %, 17.16 %, and 14.78 % while that in solid phase decays by 13.18 %, 7.63 %, 4.9 %, and 2.8 % for rise in εfrom 0.1 to 0.3, 0.3 to 0.5, 0.5 to 0.7, and 0.7 to 0.9, respectively. Introduction of Darcy-Brinkman-Forchheimer model subject to LTNE yielded better results in hydrothermal behavior of TiO2-H2O nanofluid inside a cross-shaped domain emplacing two hot and cold rings than earlier published results.

Uncertainty quantification of turbine endwall aero-thermal performance under combustor-turbine interface louver coolant and cavity

The uncertainty characteristics have a significant influence on turbine cooling performance and its reliability, especially for the combustor-turbine interface region which faces more complicated flow interactions. Previous researches under the certainty framework are not able to reflect the realistic cooling characteristics of the interface region under real operation circumstances. Considering the random fluctuations of the major structure and flow parameters, uncertainty quantification of turbine endwall cooling performance under realistic combustor-turbine interface conditions is conducted in this paper using the polynomial chaos expansion method. The mix characteristic of combustor louver coolant and interface cavity leakage in the turbine endwall region is investigated, and the influences of parameter uncertainties on endwall cooling, vane phantom cooling, and cascade aerodynamic characteristics are analyzed. The results indicate that the uncertainties at the combustor-turbine interface largely influence the endwall cooling by modifying the strength and position of the secondary flows. Under the random fluctuations of interface geometry parameters, the local mean value of endwall cooling effectiveness can reach up to 0.25, and the standard deviation of endwall cooling effectiveness can reach 0.1. The geometrical parameters of interface width and misalignment height are the decisive factors for endwall cooling uncertainty. The random fluctuations of interface width and misalignment height separately cause great cooling effectiveness uncertainties on the pressure side endwall and suction side hot ring. The uncertainties in mainstream and structure parameters exhibit a reduced propensity to propagate onto vane phantom cooling. The decisive factors for vane phantom cooling uncertainty are interface width and misalignment height, and the major influenced area is the vane middle part. Four mainstream and structure parameters all make great contributions to the aerodynamic uncertainty at the strong secondary flow region and vane wake flow region. This paper can provide a theoretical basis for the design of combustor-turbine interface cooling structures to accommodate the actual turbine operation uncertainty conditions.

Hot rings on Io observed by Juno/JIRAM

It has been thought that Io’s many paterae may contain lava lakes, but observations by NASA’s Galileo spacecraft at sufficiently high resolution were limited to a few locations, such as Loki Patera. Data acquired by NASA’s Juno mission in May 2023 reveal a common set of thermal characteristics for at least ten paterae on Io, with bright (hot) “thermal rings” around the perimeter of their floors. Loki, Surt, Fuchi, Amaterasu, Mulungu, Chors, and Dazhbog Patera, and four unnamed paterae, all show the same pattern of surface temperature. This new Juno/JIRAM data suggests that hot rings around paterae are a common phenomenon, and that they are indicative of active lava lakes. All the investigated paterae lack recent lava flows on their flanks, suggesting that at the time of observations, the level of the lake was not high enough to overflow the rim. These observations provide insight about the characteristics of paterae’s activity, which may involve either central upwelling of magma, or up-and-down “piston-like” vertical motion of the lake surface. Tidal forces, which are extreme at Io, could play a role as well. Future observations from Juno, particularly during the closest flybys, may indicate which mechanism is more plausible.

A Comparative Study of Lubrication Performance for Bs 080M46 Medium Carbon Steel Using Ring Compression Test and Finite Element Simulation

This study investigates the impact of lubrication on friction factors during the hot ring compression test of BS 080M46 medium carbon steel. Hot forging processes are crucial in industries due to the strength and durability of forged products, but friction-related issues can arise. Four lubrication conditions are focused: dry, oil to black graphite, water to black graphite, and water to colorless graphite. The ring compression test procedure, including sample dimensions and lubrication application, is explained. By employing predictive calibration curves generated through FEM which monitored height and internal diameter changes during compression. The study successfully aligns FEM simulation results with experimental data, thereby enhancing the accuracy of friction factor estimations and visualizing material behavior under various lubrication conditions. Results indicate that lubrication significantly affects friction factors, with oil to black graphite performing the best, yielding a friction factor of 0.15. A comparison between theoretical and experimental friction factors shows varying agreement levels, with water-to-black graphite, and water-to-colorless graphite respectively demonstrating excellent alignment with 0.990% and 0.971%. This study has practical implications for selecting lubricants in industrial applications, potentially enhancing manufacturing processes and product quality.

The CMB Cold Spot as predicted by foregrounds around nearby galaxies

Context. The non-Gaussian Cold Spot surrounded by its hot ring is one of the most striking features of the cosmic microwave background (CMB) and has generated significant attention in the literature. It has been speculated that either new physics or the Integrated Sachs-Wolfe effect induced by the presence of a cosmic void at relatively high redshift could account for the observations. Aims. Here, we investigate if the newly discovered systematic decrease in the CMB temperature in the neighbourhood of nearby galaxies may create such a strong temperature depression. In particular, we note that the largest galaxy group complex in the local Universe, the Eridanus super-group with its neighbouring groups, is in the Cold Spot area. Our goal is to analyse observational galaxy data to characterise the neighbourhood of the Cold Spot, explore the properties of these galaxies, and thereby make a prediction of the galaxy induced CMB temperature decrement in this region. Methods. We used the Planck SMICA maps, and as foreground tracers, galaxies from the publicly available observational catalogues: 2MRS, 6dF, and HIPASS, which include information on redshifts, positions, magnitudes, and other astrophysical characteristics. We applied previously explored mean temperature profile shapes to model the expected temperature decrement from the galaxies in the Cold Spot area. Results. Even after correcting for the mean low temperature of the Cold Spot region, we find that the temperature decrement around galaxies is significantly stronger than the mean decrement in other parts of the sky. We discuss whether this could be attributed to the fact that the Cold Spot area coincides with one of the regions populated by the most HI deficient galaxies. Modeling the foreground temperature profile that is mainly associated with spiral galaxies in this location, we find a particularly strong temperature decrement due to the presence of the late-type overabundant largest group complex in the nearby universe. A Cold Spot shape that largely overlaps with the CMB Cold Spot is observed. Conclusions. We conclude that the coincidence of the only nearby spiral-rich group complex located in the Cold Spot region, and the success of the modelling performed, adds strong evidence to the existence of a local extragalactic foreground that may account for the observed temperature depression, alleviating the tension with the Gaussian field that is otherwise expected in the CMB.

Development of a measurement method for tracking the position of hot steel rings on an industrial radial-axial ring rolling mill

Development of a measurement method for tracking the position of hot steel rings on an industrial radial-axial ring rolling mill

The real-time vision measurement of multi geometric information of the rolled ring in the hot ring rolling process based on deep learning

Hot ring rolling (HRR) is an advanced incremental metal-forming technology to manufacture high-performance rings. Nowadays, the mechanical or laser-sensors measurement methods can only obtain one value of the dimensions on the ring circumference per time unit, the measurement data is single and the information is limited. This paper presents a real-time vision measurement method for multi geometric information of the rolled ring such as ring’s diameter, center position, circularity and growth speed in HRR process. Firstly, the deep learning model is constructed to intelligently and quickly identify rolled ring targets from complex image backgrounds, then the adaptive linear gray scale transformation algorithm is proposed to adjust the gray scale contrast of the image according to changes in ring temperature, the interference of oxide scales and flying chips are eliminated by morphology operation. Finally, the least square method is used to fit the contour points, and further the rolled ring’s geometric information and corresponding variation trend are calculated. Several experiments are conducted on a vertical HRR mill, the geometric information of the rolled ring during the HRR is measured in real-time under the interference of harsh working conditions. For the ring with outer diameter of 350 mm, the measurement error of ring’s outer and inner diameter is less than 0.8 mm, the average processing time per image takes about 80 ms. The research provides a basis for accurate measurement of HRR process.

Determination of the Friction Coefficient in the Ring Test for Selected Lubricants Dedicated to the Hot Forging Process of Precision Steel Products

This paper concerns an analysis of the tribological conditions and the effect of the use of seven lubricating agents dedicated to a process of precision forging on a hammer in multiple systems. In particular, it performs a review of the most popular methods of determining the friction coefficient in the aspect of the obtained results. On this basis, the selected method of friction coefficient determination was a hot ring upsetting test for two forging materials: carbon steel (16MnCrS5) and stainless steel (316Ti). The test samples were prepared in the shape of a ring with precisely defined dimensions, and, next, they were subjected to an upsetting process on a hydraulic hammer under conditions similar to those present in an industrial forging process, and the characteristic geometrical features and friction coefficients were determined. Additionally, measurements of the geometrical changes were made with the use of 3D scanning for the extreme friction coefficient values in order to perform their comparison. The obtained results showed that for carbon steel the lowest achieved value was in the case of Lubrodal F185 (µ = 0.24) A and the highest for Lubr_hot_press 123HD (µ = 0.32); in turn, for stainless steel the lowest value µ = 0.19 was achieved for Graphitex CR 7 and the highest for Graphitex CR720K (µ = 0.29). Moreover, for these conditions, numerical modeling was conducted in the Forge 3.0 NxT program, in order to analyze the obtained results and verify the correctness and agreement of the friction coefficients determined in the ring test, on the basis of the geometrical changes. The data obtained in the computer simulation confirmed the possibility of obtaining a good agreement between the FEM (Finite Elements Method) and experimental trials, as the modeling provides reliable information on the plastic deformations and can be used as an alternative method of examining the friction conditions in industrial forging processes.

Response behavior of grain evolution to forming conditions during hot ring rolling of as-cast 100Cr6 steel

Response behavior of grain evolution to forming conditions during hot ring rolling of as-cast 100Cr6 steel

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector in 2013

AbstractWe investigate the Abnormal Sub‐Auroral Ion Drifts (ASAID) developed in the postmidnight (1–4) magnetic local time sector in 2013. Shown by the Defense Meteorological Satellite Program F15 horizontal ion velocity measurements, we specified 21 antisunward (eastward) ASAID flow channels (FCs) based on their respective underlying polar convections. Overall, the polar convection formed a two‐cell pattern with its convection axis tilted in the morning‐evening direction because of the underlying BY < 0 conditions. Its dawn cell intruded into the duskside from the dawnside where the eastward ASAID flows were streaming antisunward, opposite to the dawn cell sunward convection flows. Mostly, the ASAID FC appeared in the coinciding ring‐current–related ionospheric trough and flow‐stagnation–related main ionospheric trough in the South American sector because of the favorable conditions created by the South Atlantic Magnetic Anomaly promoting also the development of Stable Auroral Red (SAR) arc. Rarely observed, the ASAID FC was associated with the SAR arc detected over Rothera. Detected in the Mid Pacific longitude sector, a pair of northern‐southern ASAID FCs demonstrated northern‐southern conjugacy. With correlated observations, demonstrating magnetosphere‐ionosphere conjugacy, the inward (earthward) ASAID electric (E) field could also be investigated. These reveal the ASAID E field's fast‐time development by short‐circuiting when the hot‐ring‐current—cold‐plasmasphere interface developed and became impacted by finite Larmor radius effects because of the earthward intrusion of hot ring current protons. The ASAID E field's inner‐magnetosphere environment was characterized by the hot zone where heating was generated by low‐frequency waves and auroral kilometric radiations.

Experimental Tests of Conduction/Convection Heat Transfer in Very High Porosity Foams with Lattice Structures, Immersed in Different Fluids

This experimental work presents the results of measurements of thermal conductivity λ and convection heat transfer coefficient h on regular structure PLA and aluminium foams with low density ratio (~0.15), carried out with a TCP (thermal conductivity probe), built by the authors’ laboratory. Measurements were performed with two fluids, water and air: pure fluids, and samples with the PLA and aluminium foams immersed in both fluids have been tested. Four temperatures (10, 20, 30, 40 °C) and various temperature differences during the tests ΔT (between 0.35 and 9 °C) were applied. Also, tests in water mixed with 0.5% of a gel (agar agar) have been run in order to increase the water viscosity and to avoid convection starting. For these tests, at the end of the heating, the temperature of the probe reaches steady-state values, when all the thermal power supplied by the probe is transferred to the cooled cell wall; thermal conductivity was also evaluated through the guarded hot ring (GHR) method. A difference was found between the results of λ in steady-state and transient regimes, likely due to the difference of the sample volume interested by heating during the tests. Also, the effect of the temperature difference ΔT on the behaviour of the pure fluid and foams was outlined. The mutual effect of thermal conductivity and free convection heat transfer results in being extremely important to describe the behaviour of such kinds of composites when they are used to increase or to reduce the heat transfer, as heat conductors or insulators. Very few works are present in the literature about this subject, above all, ones regarding low-density regular structures.

Turbine vane endwall aerothermal and film cooling performance considering realistic swirling inflow conditions

The turbine vane inlet downstream of the lean premixed combustor presents nonuniform distributions of velocity and temperature. For obtaining swirling inflow profiles close to reality, the simulated non-reacting combustor is designed firstly. Applying these profiles as inflow boundary conditions, the effects of realistic swirling inflow on the turbine vane endwall aerothermal characteristics and film cooling performance are numerically investigated through solving the three-dimensional Reynolds-Averaged Navier-Stokes equations coupled with the shear stress transfer ([Formula: see text]) turbulence model. Two swirling orientations (anticlockwise and clockwise) and five swirling core pitch-wise positions (aligned with vane 1 to vane 2) are considered in the current work. The results indicate that the residual vortices in the vane passage are strengthened and move with the swirling core along the pitch-wise direction. The migration of the horseshoe vortex is controlled by this movement. The shrinkage or expansion of the separation line of the horseshoe vortex can be observed under the anticlockwise and clockwise swirling inflow conditions respectively. The anticlockwise swirling inflow results in a larger aerodynamic loss by a 10%–35% increase of the laterally [Formula: see text]. The high Nu region near the pressure side surface enlarges and the area-averaged Nu at [Formula: see text] increases from 2337.9 to 2878.3. For the cases with clockwise swirling inflow, the area of the hot ring is enlarged and the Nu downstream of the row 3 film holes is decreased. As for the film cooling performance, the endwall coverage area shrinks and the phantom cooling area enlarges when the anticlockwise swirling core is aligned with vane 2. The endwall loses the protection from the row 3 film holes and the cooling failure ([Formula: see text]) occurs at [Formula: see text] when the swirling core is aligned with the vane passage. This is an extremely bad phenomenon that should be avoided. Among all cases, the highest endwall area-averaged [Formula: see text] (0.122) is obtained when the clockwise swirling core is aligned with vane 1. The largest endwall coverage area is achieved when the clockwise swirling core is aligned with vane 2.

Multi-Level Process Integration of Heat Pumps in Meat Processing

Many countries across the globe are facing the challenge of replacing coal and natural gas-derived process heat with low-emission alternatives. In countries such as New Zealand, which have access to renewably generated electricity, industrial heat pumps offer great potential to reduce sitewide industrial carbon emissions. In this paper, a new Pinch-based Total Site Heat Integration (TSHI) method is proposed and used to explore and identify multi-level heat pump integration options at a meat processing site in New Zealand. This novel method improves upon standard methods that are currently used in industry and successfully identifies heat pump opportunities that might otherwise be missed by said standard methods. The results of the novel method application suggest that a Mechanical Vapour Recompression (MVR) system in the Rendering plant and a centralized air-source heat pump around the hot water ring main could reduce site emissions by over 50%. Future research will develop these preliminary results into a dynamic emissions reduction plan for the site, the novel methods for which will be transferrable to similar industrial sites.

Investigation on Mechanical Properties and Oxidation Behavior of 1.2 and 1.7 GPa Grades Coating-Free Press-Hardened Steels

Al-Si-coated boron-alloyed steels are the most widely used press-hardened steels (PHSs), which offers good oxidation resistance during hot forming due to the presence of the near eutectic Al-Si coating. In this study, a recently developed novel un-coated oxidation resistant PHS, called coating-free PHS (CF-PHS), is introduced as an alternative to the commercial Al-Si coated PHSs. With tailored additions of Cr, Mn, and Si, the new steel demonstrates superior oxidation resistance with a sub-micron oxide layer after the conventional hot stamping process. Hence, it does not require shot blasting before the subsequent welding and E-coating process. Two CF-PHS grades have been developed with ultimate tensile strengths of approximately 1.2 and 1.7 GPa, respectively. Both grades have a total elongation of 8–9%, exceeding the corresponding Al-Si-coated PHS grades (1.0 GPa/6–7%, 1.5 GPa/6–7%). Furthermore, the bendability of CF-PHS was similar to the corresponding Al-Si PHS grades. On the other hand, performance evaluations relevant to automotive applications, such as weldability, the E-coat adhesion, and tailor-welded hot stamp door ring, were also conducted on the CF-PHS steel to satisfy the requirements of manufacturing.

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in Various Inner‐Magnetosphere Configurations at Geomagnetically Quiet Times

AbstractUtilizing multi‐point observations, we investigate a series of inner‐magnetosphere configurations formed at Kp ≤ 3+ when the magnetosphere‐ionosphere (M‐I) conjugate Abnormal Sub‐Auroral Ion Drifts (ASAID) developed near the plasmapause. We analyze the development of ASAID by adopting the recent theories of (1) fast‐time short‐circuiting explaining SAID development and (2) Larmor radius effects explaining ASAID development. The earthward ASAID electric field developed (1) by short‐circuiting when the reconnection‐related earthbound hot ring current (RC) electrons became stopped and ions kept moving earthward and started their usual Larmor rotations, and (2) because of the larger Larmor radius of the hot RC ions creating excess positive charges in the nearby cold‐inner‐edge plasmasheet plasma and deficit negative charges inside the hot RC region. Respective new findings include the observations of (1a) earthward hot RC ion injections across and near the ASAID channel in the inner magnetosphere and (1b) the localized increase of energetic proton differential fluxes (good proxy for hot RC ions) in the topside ionosphere within the ASAID channel, and (2a) M‐I conjugate ASAID and ASAID‐SAID series created by their respective single intrusion and repeated intrusions of hot RC ions into the cold plasmasheet plasma. New findings also include (3) the specifications of plasma waves such as Kelvin‐Helmholtz surface waves and electromagnetic ion cyclotron (EMIC) waves developed in the inner‐magnetosphere during plasmasheet rippling, and (4) the development of multiple ASAID channels in the hot zone impacted by EMIC waves.

Evaluation of the applicability of the hot ring compression test to determine the coefficient of friction in the ABNT 1045 steel machining test through statistical analysis

RESUMO O atrito nas interfaces ferramenta/cavaco e ferramenta/peça é complexo dificultando a determinação do coeficiente de atrito nos processos de usinagem. Assim, vários ensaios tribológicos foram desenvolvidos para simular as condições de corte e determinar o coeficiente de atrito. Este trabalho apresentou análise comparativa do coeficiente de atrito entre o aço ABNT 1045 e WC-10Co revestido com AlCrN por meio de dois métodos: ensaio de torneamento e ensaio de compressão de anel à quente. O ensaio de torneamento foi realizado com corte oblíquo nas velocidades de corte 150 e 220 m/min. A aquisição dos sinais das componentes de força da usinagem por meio de um dinamômetro. O ensaio de compressão de anel foi realizado nas temperaturas de 200 e 400 °C. Os coeficientes de atrito foram obtidos por meio de modelos matemáticos. A análise estatística do coeficiente de atrito apontou equivalência do coeficiente de atrito no ensaio de torneamento na velocidade de corte 150 m/min com o ensaio de compressão de anel à quente 200 °C. Assim como no ensaio de torneamento na velocidade de corte 220 m/min com o ensaio de compressão de anel à quente 400 °C. A análise macrográfica do anel após a deformação no ensaio de compressão de anel observou a influência da temperatura de ensaio no deslocamento do raio neutro. A análise superficial dos anéis e das matrizes do ensaio de compressão foi realizada por meio de microscopia óptica (MO) e rugosidade Ra, onde observou-se o aumento da rugosidade após o ensaio e a presença de desgaste abrasivo.

Generation of Friction Coefficient Function for Hot Forging with Autopilot FEA and Simultaneous Identification of Friction and Heat Transfer Coefficients

An automatic simultaneous identification method for the friction coefficient and heat transfer coefficient is proposed for accurate hot forging process simulation. We established an autopilot finite element analysis system (autopilot FEA; APFEA) that repeats the FEA of the hot ring compression test, minimizing the errors, defined by the compression load and minimum inner diameter reduction ratio, between results of the experiment and the FEA with a machine-learningbased optimization algorithm. The automatic generation of a surface-pressure-dependent friction coefficient function, the selection of the friction law from Coulomb’s and shear friction lows, and the automatic simultaneous identification of the sigmoid curve friction and heat transfer coefficient functions are performed using the APFEA system and the results of a hot ring compression test performed with a quasi-air-suspended heating tester designed by us. As a result, the optimized friction and heat transfer parameters are identified, and the reasonableness of the friction law is evaluated.

Intricate role of doping with d0 ions (Zr4+, V5+, Mo6+, W6+) on cryptomelane (K-OMS-2) performance in the catalytic soot combustion in presence of NO and SO2

Two series of cryptomelane doped with d0 ions (Zr4+, V5+, Mo6+, W6+) were synthesized by impregnation and coprecipitation methods. The obtained samples were characterized in detail by XRD, RS, TEM/EDX, XRF, XPS, O2-TPD and by the work function measurements. Catalytic tests were performed in tight and loose contacts using various reaction mixtures (O2, O2 + NO, O2 + NO + SO2). The role of dopants was examined and discussed in terms of their influence on the principal catalysts’ functionalities such as catalytic performance, structural and thermal stability and resistance to SO2. The work function was found to be a prime descriptor used for the explanation of the catalytic performance in soot oxidation, taking into account the nature of dopants, the way they were introduced, and the composition of the reaction mixture. Due to the formation of a hot ring at the catalyst-soot interface, the oxidation of soot and NO are coupled and significantly influenced by the presence of SO2. It was found that the catalytic activity of the impregnated samples results from the opposite effects of the work function on soot combustion in NO and on sulfur poisoning of the beneficial NO to NO2 oxidation. It leads to an optimal work function value of 4.04 eV observed for the W-doped catalyst. For the coprecipitated samples, due to the non-monotonous and opposite character of those processes, the effect of doping on the cryptomelane catalytic performance in the presence of SO2 is smeared out.

Neutron-yield reduction in sawtooth crashes from n = 2 resonant magnetic perturbations in EAST

A significant reduction in neutron yield in the plasma core has been observed in EAST neutral beam injection into plasmas with a low-edge safe factor of q95=3.5 and a n = 2 resonant magnetic perturbation (RMP) during a sawtooth crash. Harmonics of the m/n = 1/1 mode (m and n being the poloidal and toroidal mode numbers) develop simultaneously. A sawtooth crash is triggered when the current of the RMP exceeds a critical value; saturated fishbone phase occurs with small RMP currents. Soft x-ray (SXR) tomographic patterns obtained during sawtooth crashes have annular hot-ring shapes outside the q = 1 surface that are similar to those of double tearing modes triggered by off-axis sawtooth crashes in TFTR reversed magnetic shear plasma. M3D nonlinear simulations confirmed the initial penetration of the n = 2 RMP in the plasma core and further demonstrated a complete sawtooth crash with the appearance of a right annular hot ring near the q = 1 surface. Reconstruction of the trajectory of SXR signals before the crash shows chaotic behavior. Moreover, a high-frequency mode was seen to appear just before the sawtooth crash, accompanied by an edge geodesic acoustic mode. This edge mode is free in the saturated fishbone phase. The role of high-frequency mode in the sawtooth crash remains unclear.