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The effect of the magnetic-field intensity near an intermediate electrode in the discharge channel of a Hall thruster with a double-peaked configuration, on the thruster discharge and performance is investigated by applying the particle-in-cell Monte Carlo collision model. The result shows that by increasing the magnetic-field intensity near the intermediate electrode while keeping the magnetic-field peak intensity and position unchanged, the current received by the intermediate electrode is gradually reduced, whereas the propellant utilization and thrust are increased. Thus, the specific impulse and efficiency are improved. The efficiency can be increased by more than 10%. Increasing the magnetic-field strength near the intermediate electrode is conducive to improving the performance of the thruster, which provides a reference for the design of a Hall thruster with a double-peaked magnetic field. [ABSTRACT FROM AUTHOR]

The theoretical specific impulse of Hall thrusters using a krypton propellant is much higher than that of those using xenon. However, the actual benefits of this improvement are limited by the difficulty in achieving krypton atom ionization, and its efficiency is much lower than that of xenon. In this study, the anode specific impulse and anode efficiency of Hall thrusters using krypton propellant were improved by adding a small quantity of xenon. A dual-channel supply of xenon and krypton was achieved by optimizing the discharge channel structure based on the design of the aft-loaded magnetic field. The effects of the xenon and krypton supply method and xenon fraction on the discharge characteristics of the Hall thruster were investigated by conducting discharge experiments using the mixed propellant. The results indicated that injecting a small quantity of xenon significantly improved the ionization of krypton, improved the ionization and acceleration efficiency of the thruster, and fully utilized the high specific impulse characteristics of krypton. Furthermore, the addition of a small quantity of xenon also significantly increased the upper limit of the discharge voltage for stable operation using krypton from 500 V. At the maximum tested xenon fraction, the maximum discharge voltage was loaded to 900 V. At a discharge voltage of 800 V, the optimal anode efficiency and anode specific impulse increased by 4.5 % and 534 s, respectively, compared with those for pure xenon propellant (with an anode efficiency of 54 % and anode specific impulse of 3034 s). The results of this study are of great significance for the design of high-efficiency, high-specific-impulse, and low-cost Hall thrusters. • A dual-channel gas supply structure is proposed, which can supply two kinds of gases into the discharge channel individually. • Thruster performance is optimal when krypton is supplied downstream and auxiliary xenon is supplied upstream. • High-voltage operating ability under krypton is greatly improved with the assistance of a small quantity of xenon. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) honeycomb-like hematite superstructure was successfully fabricated on 100 pixel per inch (ppi) Fe foam scaffold via a straightforward hydrothermal approach. Influencing factors including the reaction temperature, time and the dosage of precipitant were systematically studied. A self-assembly growth mechanism was proposed based on the results of hydrothermal reaction. The powder catalyst in the form of zero-dimensional (0D) hematite nanoparticles acted as a reference sample was also synthesized at the same reaction conditions without Fe foam substrate. The honeycomb-like hematite structure exhibited a higher CO conversion and lower methane selectivity than the traditional powder catalyst for Fischer–Tropsch synthesis (FTS). These enhancements can be mainly attributed to its distinctive structure with high specific surface area, large Fe3O4 content, promoted reducibility and uniform particle size distribution, as well as effective diffusion of feed gas and products. [ABSTRACT FROM AUTHOR]

Using a permanent magnet to realize a design with a large height-radius ratio can effectively reduce the radial size of the thruster. The experimental results show that a Hall thruster with a large height-radius ratio also has significant advantages in its discharge performance. Taking the 1.35 kW Hall thruster HEP-1350PM, which has a large height-radius ratio, as an example, the thrust, specific impulse, and efficiency of HEP-1350PM are increased by up to 4.3%, 10.4%, and 7%, respectively, as compared to SPT-100, while its weight is only 56% of that of SPT-100. Numerical simulations were performed to understand the discharge characteristics of a Hall thruster with a large height-radius ratio and the internal mechanism of its performance improvement. The results show that the small middle diameter and wide channel structure concentrate the distribution of the neutral gas in the channel, accelerate the decrease of the propellant density along the axial direction, and move the main ionization zone closer to the channel upstream. These factors increase the ionization concentration, ionization rate peak, working medium utilization rate, and voltage utilization rate. They also reduce the ion loss on the wall surface and plume divergence, thereby improving the comprehensive discharge performance. This study verifies the feasibility of a large height-radius ratio in the design of a Hall thruster, and demonstrates that the design would not only be valuable for reducing the volume and weight of the thruster, but also has the advantages of enhancing its discharge performance and prolonging its working life. • Large height-radius ratio design can reduce the volume and weight of the thruster. • A large height-radius ratio can improve the discharge performance of the thruster. • Hall thruster with a large height-radius ratio has a higher acceleration efficiency. [ABSTRACT FROM AUTHOR]

The application of photocatalysts on pavement engineering to degrade automobile exhaust has become a hot topic for researchers. However, the effect of photocatalysts on pavement materials has not been fully investigated. The primary purpose of this study is to explore the effect of a typical photocatalyst titanium dioxide (TiO2) on the chemical structure and properties of asphalt through laboratory experiments and molecular dynamics (MD) simulation. Performance tests indicated that the physical properties of asphalt modified by TiO2 changed more significantly compared with that of calcium carbonate (CaCO3) and silica (SiO2), which might be due to the smaller particle size of TiO2. Atomic force microscopy (AFM) and Fourier infrared spectrum (FI-IR) analyses demonstrated that the addition of TiO2 resulted in a smoother asphalt surface and a disappearance of the bee structure. Using TiO2 would not accelerate the aging process of asphalt. Moreover, the MD simulation results indicated that a more significant interaction existed between TiO2 and asphalt than that of CaCO3 and SiO2 , which resulted in a tighter asphalt molecule and smaller free volume distribution in the TiO2-asphalt system. [ABSTRACT FROM AUTHOR]

During a long-term discharge of a Hall thruster, local overheating on the anode surface occurs and its location shifts randomly. The asymmetrical supply of anode potential is thought to be the cause. To investigate their relationship, a bias voltage is applied on one piece of a quartered anode to realize the asymmetrical supply of anode potential. Variations of both the current and temperature of each anode piece are measured and analyzed. The results indicate that the disruption of the anode potential symmetrical supply does not affect the total anode current; however, it enhances the current oscillation. As the bias voltage increases, the current concentrates gradually on the high-potential part of the anode, accompanied by an increase in the local temperature. Changes in the Ez × Br drift direction, magnetic field strength, discharge voltage, and anode flow rate do not affect the above-mentioned laws. Preliminary analysis shows that the formation of a local electric field near the anode and the generation of an extra Eθ × Br drift are the main causes, which can affect the movement of electrons in the near-anode region greatly. [ABSTRACT FROM AUTHOR]

Alkali-activated cementitious material (AACM) based on the utilization of solid waste is a new type of environmentally friendly inorganic material, which has the advantages of early strength, fast hardening, high strength, and better durability. The reactivity of solid waste powder is a key factor for its appropriate utilization in alkali-activated cementitious materials, necessitating a rational evaluation of its reactivity. The reactivity evaluation was conducted on various solid waste powders, including fly ash (FA), red mud (RM), recycled micro-powder (RMP), red brick powder (RBP), coal gangue powder (CGP), and cement kiln dust (CKD). The effects of NaOH concentration, weight ratio of water to solid waste powder (W/P) and curing humidity on the compressive strength were investigated，then the compressive strength under optimal conditions was determined based on response surface analysis. The compressive strength under optimal conditions was used to evaluate the reactivity of solid waste powders. Moreover, microscopic tests (e.g., XPS test, ICP test, and NMR test) were carried to evaluate the reactivity of the solid waste. The relative number of bridging oxygen (RBO) measured by the NMR method in conjunction with chemical composition analysis serves as an effective method for evaluating the reactivity of solid waste powders. The leaching rate of Silicon (Si) and Aluminum (Al) ions in the ICP method depended mainly on the NaOH concentration and the elemental content in the raw material. In addition, the binding energies of O1s, Si 2p, and Al 2p tested by the XPS method had no particular correlation with the compressive strength. • Based on response surface analysis to evaluate the reactivity of solid waste powders. • Compressive strength under optimum conditions was used as criteria for evaluation. • Combining NMR method with chemical composition could assess reactivity effectively. [ABSTRACT FROM AUTHOR]

• On-orbit non-intrusive perturbation measurement of Hall effect thrusters. • 10 kHz to 100 kHz analysis better than full frequency domain. • Perturbation signal amplified by scatter numbers in the far-zero region. • The physical core represented by the scatter numbers is the dwell time. • Dwell time is mainly related to breathing oscillations. The failure of Hall effect thruster (HET) is usually the result of the accumulation of several tiny abnormal disturbances during operation. Timely and accurate early warning of perturbations is an important guarantee for the normal operation of thrusters. In this study, when the perturbation rate of HET signal (anode voltage or anode flow rate) is −4% to 4%, the time scale signal of breathing oscillation (BO) in the frequency range of 10 kHz to 100 kHz is statistically analyzed. Experiments show that when the signal is perturbed, the balance between ionization and acceleration of plasma in the discharge channel is destroyed, resulting in the dwell time of the wave peaks and valleys of BO in the far-zero region with the perturbation law, which visually shows that the number of scattered points at the corresponding current value changes regularly. According to the above statistical characteristics, this paper proposes a new condition monitoring index, namely the number of scattered points in the wave peaks side of the far-zero point area, and designs a perturbation indicator for the operating condition of the HET. Compared with direct monitoring of discharge current in engineering, this indicator can amplify the influence of the perturbation signal on BO, and has better identification and accuracy. Meanwhile, the indicator does not use invasive measurement and complex equipment, and is promising to be applied to the monitoring and diagnosis of the perturbation operation state of the on-orbit thruster. [ABSTRACT FROM AUTHOR]

With the development of electric space propulsion and all-electric propulsion technologies, the application range of the Hall effect thruster (HET) has gradually expanded. As an important part of the HET, the magnetic field plays a decisive role in its performance. In the development of versatile HETs, it is necessary to comprehensively and thoroughly understand the effects of the magnetic field on the HET discharge characteristics. In this paper, a HEP-100X thruster with multiple degrees of freedom in terms of magnetic field control is used to study the effects of the peak magnetic field position on the thruster discharge characteristics. The results indicate that the peak magnetic field position can effectively control the main ionization zone position and affect the ionization rate. The thruster has the best comprehensive discharge performance when the peak magnetic field position is located near the channel exit. Further analysis reveals that the performance improvement is mainly due to the reduced ion loss on the wall surface and plume divergence half-angle, and the increased current utilization efficiency and voltage utilization efficiency. The HEP-100X shows the above trends under various flow conditions, and the anode efficiency is the highest when the anode flow is 50 sccm. In this condition, the propellant is sufficiently ionized and the ion loss on the wall surface is small. This research provides the necessary support for a comprehensive understanding of the role and significance of the magnetic field in the thruster discharge process, and has important significance for the design optimization of multifunctional Hall thrusters and subsequent research. [ABSTRACT FROM AUTHOR]

The use of krypton in the field of electric propulsion has become a key research topic owing to its high specific impulse and high reserves. However, because krypton has features such as a small ionization cross section and high ionization energy, its ionization performance is relatively low, thereby increasing the actual specific impulse loss of the krypton Hall thruster in comparison with its theoretical value. Therefore, to use of krypton as the propellant of the Hall thruster instead of xenon, it is necessary to study the optimization of its ionization process. In this study, a gas distributor with a rotating propellant supply mode is designed, considering factors such as the velocity and density of the velocity of neutral atoms, which affects the ionization process. The distribution of neutral atom parameters in the discharge channel is changed by the rotation; and its influences on the propellant ionization and other performance parameters of the Hall thruster are experimentally analyzed with respect to the magneto-ampere, volt-ampere, and flow rate-ampere characteristics. The results demonstrate that the rotating propellant supply reduces the axial velocity of neutral atoms, increases the density and circumferential motion distance, and thus improves the ionization efficiency of the krypton Hall thruster. Furthermore, the performance parameters, such as thrust and efficiency, are also improved, and the plume divergence angle is reduced. When the discharge voltage is 450 V and the anode flow rate is 60 sccm, the rotating propellant supply can increase the anode efficiency of the axial propellant supply mode from 46.2% to 53.2%. However, the plume divergence half-angle reduces from 39.2° to 35.5°. In addition, an increase in the anode flow rate and discharge voltage continuously increases the performance promotion in the rotating propellant supply mode. • Rotating propellant supply is achieved by a particular gas distributor design. • Rotating propellant supply slows down krypton neutrals inside the channel and improves ionization efficiency. • Performance increment under rotating propellant supply increases with both discharge voltage and krypton flow rate. [ABSTRACT FROM AUTHOR]

This paper experimentally evaluated the effect of the disruption of the symmetrical distribution of the propellant on the characteristics of the anode current. The change in the asymmetry degree of the propellant distribution is achieved by supplying gas with a dual-cavity gas distributor. The results show that as the asymmetry degree increases, the magnitude of the anode current changes monotonically from a slow growth to a rapid growth, while the peak-to-peak value of the anode current exhibits a non-monotonic behavior. A preliminary analysis shows that the asymmetrical distribution of the propellant causes a nonuniform plasma generation along the azimuthal direction and consequently the appearance of an azimuthal electric field. The effect of the azimuthal electric field on the electron azimuthal drift as well as the induction of the electron axial drift are key factors that account for the change of the anode current and its oscillation. • Transition in discharge current occurs as propellant asymmetry degree increases. • Transition point drops down as propellant flow rate or discharge voltage increases. • Azimuthal electric field induced by asymmetrical discharge accounts for transition. [ABSTRACT FROM AUTHOR]

• The behavior of aging degradation and reactive reconstruction for SBS were studied. • The molecular weight of SBS decreased and its rheological properties deteriorated seriously after simulated aging. • The creep recovery ability and medium–high temperature rheological properties of aged SBS can be well restored by reactive reconstruction. • Isocyanate pre-polymer showed the better performance for restoring the molecular weight and the glass transition temperature of aged SBS. Achieving high-performance recycling of aged SBS modified asphalt will help promote the sustainable development of transportation infrastructure. The destruction of the SBS cross-linking network is an important reason for the deterioration of the performance of aged SBS modified asphalt. Scientific reconstruction of aged SBS cross-linked network is the key to achieving the performance recovery of aged modified asphalt. In this research, the evolution of chemical structure, molecular weight, thermodynamic properties, multiple stress creep recovery capability and rheological property of SBS during the process of aging degradation and reactive reconstruction were systematically investigated. The results showed that the molecular weight and creep recovery capability of SBS decreased sharply, and its complex modulus and phase angle exhibited a strong temperature and frequency dependence after aging. While the number average molecular weight of aged SBS increased by over 70% after reactive reconstruction, and its thermal-oxygen stability shown better performance as compared with that of fresh SBS. Meanwhile, the glass transition temperature of aged SBS was restored to −43.8℃ and −54.9℃ after reactive reconstructed by toluene diisocyanate (TDI) and isocyanate pre-polymer. Therefore, isocyanate pre-polymer with flexible long chain structure was more benefit for improving the low-temperature performance of reactive reconstructed aged SBS. Furthermore, the creep recovery ability and complex modulus of aged SBS were all significantly improved, and exhibited dramatically high-elastic properties after reactive reconstruction. And as compared with isocyanate pre-polymer, TDI with benzene ring rigid structure was more conducive to restoring the medium–high temperature rheological properties of aged SBS. Therefore, effective restoration of molecular weight and performance of aged SBS can be achieved by using reaction reconstruction method. This study would provide inspiration and ideas for the high-value recycling of waste polymer modified asphalt. [ABSTRACT FROM AUTHOR]

In this paper, a type of magnetically insulated anode structure is proposed for the design of a low-power cylindrical Hall thruster. The magnetic field distribution in the channel is guided by the magnetically insulated anode, altering the intersection status of the magnetic field line passing through the anode and wall. Experimental and simulation results show that a high potential is formed near the wall by the magnetically insulated anode. As the ionization moves towards the outlet, the energy and flux of the ions bombarding the channel wall can be reduced effectively. Due to the reduction in the bombardment of the wall from high-energy ions, the thrust and specific impulse greatly increase compared with those of the non-magnetically insulated anode. For anode mass flow rates of 0.3 and 0.35 mg s−1 and discharge voltages in the 100–200 V range, the thrust can be increased by more than 33% and the anode efficiency can be improved by more than 7%. Meanwhile, the length of the sputtering area is clearly reduced. The starting position of the sputtering area is in front of the magnetic pole, which can effectively prolong the service life of the thruster. [ABSTRACT FROM AUTHOR]

A type of Hall thruster without wall losses is designed by adding two permanent magnet rings in the magnetic circuit. The maximum strength of the magnetic field is set outside the channel. Discharge without wall losses is achieved by pushing down the magnetic field and adjusting the channel accordingly. The feasibility of the Hall thrusters without wall losses is verified via a numerical simulation. The simulation results show that the ionization region is located in the discharge channel and the acceleration region is outside the channel, which decreases the energy and flux of ions and electrons spattering on the wall. The power deposition on the channel walls can be reduced by approximately 30 times. [ABSTRACT FROM AUTHOR]

Abstract In this experimental study, the ceramics of a cylindrical Hall thruster with a magnetically insulated anode structure at the bottom of a discharge channel was found to be eroded. The potential, distribution of the ion number density, ion velocity in the channel, and the power density into the bottom of the channel were analyzed through a particle-in-cell numerical simulation. The results of this study indicate that the electrons move along the magnetic line to the bottom of the channel where the negative charges accumulated form a negative potential. Under a potential action, some low-energy ions in the channel move toward the bottom of the channel in an accelerating manner, causing an erosion of the ceramic material; the deposition power density reaches the peak value at the bottom center and gradually decreases in a radial direction, which is consistent with the actual erosion occurring at the bottom of the channel. Highlights • Electrons move to the bottom of the channel and form a negative potential. • Low-energy ions cause the erosion of bottom of the channel. • The deposition power density reaches a peak value in the center of the bottom channel and gradually decreases with the radial coordinate. [ABSTRACT FROM AUTHOR]

Abstract The reliability of cathode is critical to electric propulsion systems. Although researchers have carried out many life tests on hollow cathode, the discharge current is almost steady when the cathode is independently tested for life. Actually, when it is coupled with the thruster, the discharge current is with large amplitude low-frequency oscillation. Therefore, we suggest a new external circuit for a cathode-independent life test, which could simulate the characteristics of discharge current oscillation when the cathode is coupled with Hall thruster. We carried out 160 h of life test using the normal external circuit and the new external circuit, and the variation characteristics of the cathode orifice area are also studied during the life test. The results show that under the normal external circuit, the growth rate of the cathode orifice area initially increases and then decreases gradually with the increase of the time of life test, whilst the cathode orifice area in the new external circuit linearly increases. The new external circuit can provide a new method to simulate the discharge current oscillation when the cathode is coupled with Hall thruster during the independent life test of the cathode. [ABSTRACT FROM AUTHOR]

A typical Hall thruster is powered by a constant-voltage power supply. In this study, to ensure the normal operation of Hall thrusters at lower power conditions, we applied pulse modulation technology to supply power to a 600-W Hall thruster. The results show that, when the input power of the thruster was within the rated power range, the thrust and efficiency of the thruster were slightly reduced under pulsating mode compared with those of direct current (DC) operation. However, the thrust-to-power ratio of the thruster under pulsating mode was superior to that under DC operation at low power (<350 W). The thrust-to-power ratio under pulsating mode was improved to 77.5 mN/kW at 210 W compared with that under DC operation (70 mN/kW). Meanwhile, we found that the stable operating boundary of the thruster under pulsating mode significantly widened at high frequencies. A 600-W Hall thruster under pulsating mode can operate at a lowest power of 66.8 W, which is an order of magnitude lower than the rated power. The thrust and anode efficiency under pulsating mode at 68.8 W were 4.3 mN and 7.8%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between the morphology of the cathode crater and plasma ionization between thrusters is studied by adjusting the input energy of the micro-cathode arc thruster (μ CAT). We monitor the morphology of the cathode crater of the μ CAT using scanning electron microscopy and explore the relationship between the crater morphology and the internal energy loss of the cathode crater. This relationship, combined with the numerical simulation results, is used to monitor the ionization between the electrodes of the μ CAT using an enhanced intensified charge coupled device spectrum detector. The effect of cathode crater morphology on the ionization of the propellant during the operation of the μ CAT is determined. The results show that with a change in the input power processing unit voltage, the external profile and depth-to-diameter ratio of the cathode crater change, resulting in a change in the internal energy loss of the thruster cathode crater and then affecting the ionization efficiency of the cathode working fluid in the μ CAT. Under the condition of basically unchanged cathode feed energy flow density, reasonable adjustment of the depth-to-diameter ratio of the cathode crater can effectively improve the ionization efficiency of the cathode working fluid in the μ CAT. [ABSTRACT FROM AUTHOR]

A time-resolved optical measurement method is applied to examine the gas discharge process inside the discharge channel during a Hall thruster ignition. The results show that the excitation and ionization processes in the working gas begin near the exit of the channel and then propagate upstream along the channel. The change in energy of electrons moving toward the anode leads to the alternating dominance of ionization and excitation processes, which is the main reason for the changes in light intensity in different regions of the channel during the thruster startup. [ABSTRACT FROM AUTHOR]

Hall thrusters generally use a U-shaped insulated wall to form an annular discharge channel. As high-power and high-specific-impulse Hall thrusters develop, the disadvantages of this conventional topology—in terms of material and mechanical strength, processing, and manufacturing—are gradually being exposed. Therefore, in this study, a new wall material was employed, and its effects were investigated numerically and experimentally. A boron nitride ceramic wall was retained in the strong discharge area owing to its excellent secondary electron emission characteristics; while a metallic wall was applied upstream of the channel, forming a segmented hybrid wall. A Hall thruster with an aft-loaded magnetic field, which offers a long lifetime, was adopted for this study. The particle-in-cell simulation shows that the length of the metallic wall has a significant impact on thruster performance. The same trend was observed in the experiments. Under the optimal metallic wall length, the anode efficiency is improved by approximately 4% compared to that of the ceramic-wall-only case. The physics involved is analyzed and qualified by comparing the simulated and measured results. The findings of this study provide valuable guidance for the optimal design of high-power, high-specific-impulse Hall thrusters. • Metal-ceramic hybrid channel wall improves high-voltage performance of Hall thrusters. • Optimal length of metallic segment exists and is strongly related to magnetic field. • Too long metallic segment augments electron wall loss and then ionization loss. [ABSTRACT FROM AUTHOR]

• The content of RAP binder availability and blending efficiency are introduced. • The approaches for blending efficiency characterization are summarized. • Factors that affect the blending efficiency are reviewed. • The applications of blending efficiency are described. Use of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) into asphalt mixtures has become more popular from economic and environmental perspective. However, a significant concern arises us to how much of the aged binder in RAP/RAS can be mobilized into virgin binder during mixing and construction. Variation in reclaimed binder availability leads to the variation of effective binder content, as well as the quality of the blended effective binder, hence the engineering properties of asphalt mixtures. Currently, different approaches were proposed to quantify the blending efficiency of reclaimed asphalt. However, the mechanism and application of each method may not be well understood and clarified. This study presented a comprehensive literature review of binder availability and blending efficiency of reclaimed asphalt. Firstly, the concepts of reclaimed binder availability and blending efficiency were introduced. Secondly, different quantification methods were summarized with the understanding of their mechanisms and application. Thirdly, effects of different factors on blending efficiency of reclaimed asphalt were investigated. Lastly, practical applications of blending efficiency were reviewed. [ABSTRACT FROM AUTHOR]

A decoupling method is proposed for micro-Newton thrust measurement with a torsion pendulum. The basic approach is to reduce the influences introduced by the propellant tube and wires of the thruster. A hollow aluminum tube is used to hang the torsion pendulum and is also chosen as the transport pipe for the propellant of the thruster. The electric control box of the thruster is mounted on the pendulum body, which is powered by an externally installed power supply through a liquid metal conductive unit. The control of the electric control box is performed through wireless transmission. With this design, the influences of the propellant tube and connection wires between the torsion pendulum and the outside device are reduced and the stability of the torsion spring constant of the system can be improved. The use of the liquid metal conductive unit reduces the coupling between the wires and the measurement system. The feasibility of the wireless transmission is analyzed. The error sources during the thrust measurement are analyzed, and the expected three σ uncertainty of the thrust is 0.0 3 2 + (0.10 % * F) 2 μ N for the measurement of the cold gas thruster. The scheme provides a thrust measurement with higher precision and stability. [ABSTRACT FROM AUTHOR]

A magnetically shielded Hall thruster (MSHT) has a significantly longer service life than a conventional unshielded Hall thruster (USHT) as it shifts the magnetic field of maximum strength from the channel interior to the exterior. In this study, it was experimentally determined that the influence of the radial position of an externally mounted hollow cathode on the performance of an MSHT is quite different from that of a USHT. The measured plasma parameters demonstrate that in addition to the coupling voltage loss and plume divergence loss, the electron cross-field transport loss (not considered previously and introduced by the outward shifting of the magnetic field) is also important to explaining the performance variation in the MSHT. This study refines the coupling theory between the cathode and Hall thruster and provides a valuable reference for determining the radial position of an externally mounted hollow cathode in an MSHT. [ABSTRACT FROM AUTHOR]

In steady-state operation of Hall thrusters excited by permanent magnets, the existence of temperature difference between the inner and outer permanent magnets will cause the deviation of the magnetic field configuration from the design value, thus affecting the discharge process. The simulation results show that the ion power loss on the inner wall increases by over 7.5% when the temperature difference between the inner and outer permanent magnets reaches to 140 ℃. The main reason is that the coercivity of the inner permanent magnet decreases more at higher temperature, and the magnetic field lines will incline toward the inner wall, resulting in the increment of the radial component of the electric field pointing to the inner wall. An optimized magnetic field, obtained by moving the inner permanent magnet outward in an appropriate manner, is proposed to alleviate the inner wall erosion. The optimized magnetic field has a near-symmetrical configuration, especially the nearly equal length of intersection lines of the magnetic field lines with the inner and outer walls, which is contributed to reduce the radial component of the electric field and preventing the inclination of the main ionization zone toward the inner wall, so that the peak value of ion power deposition on inner wall can be reduced by more than 50%. Based on the illustrated features and mechanism of wall erosion, an effective and easy-to-implement optimization scheme was proposed in this work to provide a useful reference for the design of long-life Hall thrusters with large height-radius ratio. [ABSTRACT FROM AUTHOR]

In this study, the effect of pulse frequency on the discharge and plume characteristics of Hall thrusters under pulsating operation is investigated. The experimental results show that the discharge current and thrust decrease as the frequency increases to the range of 30–90 kHz. The efficiency of the thruster is negatively correlated with the pulse frequency, and the pulse frequency minimally affects the plume divergence angle and ion current. It is found that an increase in the pulse frequency decreases the secondary electron emission flux on the wall and the near-wall conduction rate of electrons in the channel, thus consequently decreasing the electron current. An increase in the electron current share improves the current-utilization efficiency. In addition, as the frequency increases, the ion power loss on wall increases and the ion acceleration becomes less effective, thus resulting in a decrease in thrust. The combined effect of these two factors results in an increase in the anode efficiency as the frequency increases. • The effect of pulse frequency on the discharge and plume characteristics of Hall thrusters under pulsating operation were investigated. • Increasing the pulse frequency decreases the secondary electron emission flux, which reduces the rate of electron-in-wall conduction in the channel, thus resulting in a lower electron current. • As the pulse frequency increases, the ions power loss on wall increases leading to poorer ion acceleration and a reduction in thrust. [ABSTRACT FROM AUTHOR]

Traditional Hall thrusters can ionize gas inside the channel and accelerate ions outside it by moving the peak magnetic field out of the channel, which improves the thruster performance. In this study, the effects of the peak magnetic field location on the discharge characteristics of a 100-W Hall thruster with large-gradient magnetic field were investigated by changing the ratio of the magnetic field intensity at the channel exit to the peak magnetic field intensity (Br exit /Br max). The experimental results show that the discharge performance decreases significantly when Br exit /Br max < 1. Moreover, the PIC numerical simulation and neutral gas simulation results demonstrate that the ionization rate inside the channel reduces and the ionization proportion outside the channel increases when Br exit /Br max decreases, thereby reducing the performance. When Br exit /Br max = 1, under the anode flow of 5.5 sccm and discharge voltage of 250 V, the thrust, anode specific impulse, propellant utilization efficiency, and anode efficiency of the 100-W thruster were 6.4 mN, 1210 s, 68.9%, and 38.5%, respectively, which represent respective improvements of 16.2%, 16.4%, 13.0%, and 30.0% (relative value) compared with the condition when Br exit /Br max = 0.9. These results provide a reference for the performance optimization of 100-W Hall thrusters with a large-gradient magnetic field. • The Effects of peak magnetic field location on performance of a 100W large gradient magnetic field Hall thruster is studied. • The ionization and discharge performance parameters of thruster under different Br exit /Br max conditions are given. • When the value of Br exit /Br max decreases from 1, the overall performance of the thruster decreases significantly. • The decrease of Br exit /Br max worsens the ionization process and reduces the overall performance of the thruster. [ABSTRACT FROM AUTHOR]

In an ATON-type Hall effect thruster, a ring-shaped anode and a cusped magnetic field intersect the match between the anode shape and the field topology thus must be clarified to optimize the electron transport to the anode and consequently the design of a high-efficiency thruster. By changing the match pattern with both the change in the length of the anode ring and the axial displacement of the cusp magnetic field, this study experimentally investigated the influence of the match pattern on the discharge characteristics of an ATON-type thruster—P100—under the condition of a moderate discharge voltage. The experimental results show that there is a match pattern that always optimizes the performance of the P100 thruster. At the rated operation parameters (300 V of discharge voltage and 5 mg/s of propellant mass flow rate) and the rated magnetic field strength, the observed improvements on thrust (∼79 mN to ∼85 mN) and anode efficiency (∼46% to ∼55%) are significant. Through further theoretical analysis, this study revealed that the change in the characteristics of electron momentum and energy transfer in the near-anode region, induced by the change of the match pattern, is the basic reason. The findings of this work are instructive for both understanding the electron motion in a cusp magnetic field and guiding the design of the anode ring intersecting with a cusp magnetic field in an ATON-type Hall effect thruster. [ABSTRACT FROM AUTHOR]

This study proposes a newly designed ignition circuit that does not change the ignition starting parameters of a Hall thruster, reduces the critical ignition voltage, and improves ignition reliability. The complexity and weight of the Hall thruster power supply system are reduced by multiplexing the ignition and discharge power supplies. Under the condition that the design parameters are satisfied, that is, R 3 + R E C 2 is much larger than RCC1, the residual energy in the circuit after the cathode breakdown can be fed into the thruster discharge channel to improve the ignition energy supply. The experimental results show that when the anode voltage is 98 V, only nine of the 100 ignition tests are successful using the traditional ignition circuit, whereas the number of successes using the newly designed ignition circuit is as high as 99, which provides a simple solution method for improving the ignition reliability. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel water-soluble fluorescent chemosensor based on naphthalene derivate was designed. [•] The fluorescent chemosensor for Al3+ could be synthesized simply. [•] The fluorescent sensor exhibited high selectivity for Al3+ in absolute water media (pH=7.0). [ABSTRACT FROM AUTHOR]

Electric propulsion systems with high-specific impulses have replaced chemical propulsion systems in many space missions. The aft-loaded magnetic field technology of Hall thrusters moves the ionization and acceleration processes downstream of the channel by varying the magnetic field distribution. Consequently, ion bombardment of the channel walls is inhibited, and the service life of the Hall thrusters is substantially increased. However, neutral gas leaks because of the rapid diffusion near the channel outlet, where strong ionization occurs. Thus, the propellant atoms are ionized insufficiently, resulting in a decline in the performance. Therefore, an aft-loading design for the neutral gas flow field was developed to optimization distribution of the neutral gas in this study. A 1.5 kW Hall thruster was verified experimentally. The experimental results show that the aft-loaded neutral gas flow field significantly improved the ionization and acceleration processes. The propellant utilization efficiency increased by 4–8% within the discharge voltage range of 300–900 V. The ion energy distribution moved toward the high-energy direction significantly, promoting an overall improvement in the performance, with a thrust increase of 7.3–11.5 %. The anode efficiency increased from 49–57 % to 58–61 %. The results of this study are significant for the design of high-performance, long-life Hall thrusters. • The aft-loading design of gas flow is realized using the special topology of the hybrid-wall Hall thruster. • The ionization distribution of aft-loaded neutral gas flow field is concentrated in higher potential region. • The aft-loaded neutral gas flow moves the ionization region downstream of the channel. [ABSTRACT FROM AUTHOR]

Poor performance limits the wider application of 100-W-power class Hall thrusters. The effects of position matching between the anode and the zero-magnetic-field region (ZMFR) on the discharge process and performance improvement of 100-W Hall thrusters were investigated. The experimental results demonstrate that appropriately widening the ZMFR downstream of the anode improves the ion current and thrust, promotes plume focusing, and optimizes thruster performance. The thrust and anode efficiency is enlarged by 7.6 % and 20 % (relative value), respectively, when the ZMFR downstream of the anode is expanded by 0.2 L (L is the channel length). The simulation results indicated that widening the ZMFR promoted the expansion of the high-ionization zone to the bottom of the channel, and increased the overall ionization rate. Moreover, as the ZMFR increases, the effective ion acceleration voltage increases. However, widening the ZMFR also aggravated the ion-wall interaction and reduced the propellant utilization rate. Therefore, the performance of the thrusters exhibited an optimal range as the length of the ZMFR increased. In addition, increasing the ZMFR did not affect the life of the thrusters. • The effects of position matching between the anode and zero magnetic field region on discharge characteristics are studied. • The discharge characteristic parameters of thruster with different lengths of ZMFR downstream of the anode are given. • Appropriately increasing the ZMFR can improve the ion current and thrust, thereby improving the anode efficiency. • The position matching between the anode and ZMFR affects the ionization process and propellant utilization ratio. [ABSTRACT FROM AUTHOR]

In this study, the material loss relationship between the electrodes of a micro-cathodic arc thruster was investigated by adjusting the input voltage. The crater morphology of the micro-cathodic arc thruster was observed with a scanning electron microscope. The internal crater material was analyzed with an energy spectrum analyzer. On this basis, the arc path is obtained and the material loss of the structure between the electrodes of the micro-cathodic arc thruster was studied through further numerical simulation. The experimental and simulation results show that with a change in the Power processing unit (PPU) input voltage of the micro-cathodic arc thruster, the material distribution in the cathode crater and the discharge channel between the electrodes changed, affecting the bombardment of ions between the electrodes of the thruster on the insulating structure and conductive coating. In engineering applications, regulation of the arc breakdown path can effectively reduce the total energy of ion bombardment on the wall. • Study on micro-morphology and composition distribution characteristics of arc crater of micro-cathode arc thruster. • Study on the distribution characteristics of PPU input voltage and discharge channel between thrusters. • The ion bombardment on the wall under different discharge channels is simulated. • With the increase of PPU input voltage, the dominant factor of inter-electrode structure loss changes. [ABSTRACT FROM AUTHOR]

Abstract: Various n-alkylviologens-intercalated vanadyl-vanadate (RV)V3O8 were synthesized with the combination of redox and ions-exchange methods. The derivative compounds were characterized by X-ray diffraction (XRD), FT infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The XRD results indicate that the interlayer spacing increases with the alkyl chain length of the alkylviologen cations. The FTIR data shows that alkylviologens were inserted into the interlayers of V3O8 2−. XPS data reveals that the vanadium ions in the intercalation compounds are mostly in a pentavalent V5+ state with some partially reduced to the V4+ state. The intercalation compounds have the strong absorption character in the ultraviolet and visible light region. Magnetic susceptibility indicates that the (ethylviologen) V3O8 (EV3) is antiferromagnetic and possesses an ordered magnetic structure below 15K. Above 15K, EV3 exhibits paramagnetic behavior and a disordered magnetic structure. [Copyright &y& Elsevier]

An analysis of the discharge behavior of a symmetrically designed Hall-effect thruster (HET) under an asymmetrical condition will aid the understanding of the working characteristics of HETs from different perspectives. Therefore, in this paper, with experimental methods, the asymmetrical gas distribution inside the channel of a HET was realized by supplying the gas asymmetrically, and changes in both the performance and plume parameters with the degree of asymmetry were measured. Both the discharge current and thrust were found to vary nonlinearly with the degree of asymmetry; moreover, the discharge mode also shifted, as observed from the variations in the discharge current and oscillation. Furthermore, the relationships between the plume ion current and energy distributions and the degree of asymmetry were determined and further used to explain the nonlinear change in the thrust. Overall, the findings of this study strengthen the understanding of the physics of HET discharge. • Variations of performance and plume parameters show consistency as the degree of asymmetrical neutral distribution changes. • Discharge of high-density region under an asymmetrical neutral distribution dominates the overall thruster operation status. • Deflection of plume are the decisive factors for the reduced thrust under an asymmetrical neutral distribution. [ABSTRACT FROM AUTHOR]

Prior experiments have demonstrated that the pole in a magnetically shielded Hall thruster sputters and erodes visibly, in contrast with that in an unshielded thruster. To determine the reason for this, a particle-in-cell simulation was conducted, and the difference between shielded and unshielded thrusters in terms of plasma behavior near the exit plane was studied. The results show that in the case of the magnetically shielded thruster, the ion flux peak is on the magnetic pole face with higher ion energy, indicating severer erosion at the pole. By contrast, the flux peak of the unshielded thruster is on the head face of the channel wall, indicating severer bombardment at the wall and milder erosion at the pole. Therefore, pole erosion occurs in the magnetically shielded thruster, and channel head face erosion can be observed in the unshielded thruster. In addition, the simulation results indicate that the greater the outward shift of the magnetic field, the severer the pole erosion. [ABSTRACT FROM AUTHOR]

In this study, the evolution of the plasma parameters of a Hall thruster under the pulsating operation was investigated using the particle-in-cell (PIC) model. The results show that the current waveform of the simulation results was almost the same as that of the experimental results under the same pulse parameters and working conditions. The average thrust of the simulation results was close to the experimentally measured thrust, so the accuracy of the simulation model was confirmed. The peak thrust of the Hall thruster under pulsating operation was approximately three times that under direct current (DC) operation. The simulation results show that the ionization rate increases rapidly under pulsating operation and is several times higher than that under DC operation. An increase in the number of ions led to an increase in the discharge current. Meanwhile, owing to the increase in the potential drop in the acceleration zone of the Hall thruster under pulsating operation, the ion acceleration effect was improved. These are the main reasons for the rapid increase in the instantaneous thrust during the pulsating operation. • A PIC model for Hall thruster under pulsating operation was proposed. • Comparison of simulation and experimental results of discharge characteristics and thrust verified the accuracy of the model. • The evolution of the plasma parameters of a Hall thruster under the pulsating operation was investigated. • The increase in the potential drop and ionization rate are the main reasons for the rapid increase in the instantaneous thrust. [ABSTRACT FROM AUTHOR]

This study provides insights into the molecular tailoring of DSSC dyes via synthesis/investigation of three new organic dyes with the position engineering of the acceptor moiety. Differences in photophysical, electrochemical and photovoltaic properties are found and interpreted in detail. The excitation-spectrum study shows that the population of the intramolecular charge transfer (ICT) is incident-wavelength dependent; and the ICT excitons originate not only from direct ICT band transition but also from π-π* energy transfer, and the degree of the latter depends much on the position of the anchoring group. The transient photoluminescence discloses that the non-injection quenching of the ortho dye is the most severe possibly due to the instability of the excited state resulting from the hurdling of electron delocalization by the large steric hinderance. Large steric hinderance in the ortho dye also results in the least dye loading on TiO 2 photoanode. Due to broader/stronger absorption, higher dye loading, high injection efficiency and low charge recombination rate, the para -substituted dye DSSC device achieves the best performance with power conversion efficiency of 6.63%; while the ortho dye based device performs the worst with significant lower of photocurrent and photovoltage compared to the para dye. The dye dependent V OC is explained by combination of dipole moment and dye loading. Particularly, the employing of excitation spectrum as tools to investigate the intrinsic photophysical complicity of dyes with D-π-A structure, which is scarcely reported, is proved to be an effective way. Image 1 • Three new organic dyes with acceptor-position engineering were synthesized for dye-sensitized solar cells (DSSCs). • Differences in material properties and photovoltaic properties were systematicaly studied. • The para-substituted dye based DSSC device achieved the best performance with power conversion efficiency of 6.63%. [ABSTRACT FROM AUTHOR]

A two-dimensional particle in cell model is used to simulate the sheath oscillation in stationary plasma thrusters. The embedded secondary electron emission (SEE) submodel is based on that of Morozov but improved by considering the electron elastic reflection effect. The simulation results show that when the SEE coefficient is smaller than one due to the relative low electron temperature, one-dimensional static sheath can be found; as the electron temperature increase, the SEE coefficient approaches to one and temporal oscillation sheath appears; when the electron temperature increases so high that the SEE coefficient is beyond one, the sheath oscillates not only in time but also in space. [ABSTRACT FROM AUTHOR]

It has been recognized that the application of magnetic shielding technology deteriorates the plume divergence efficiency of a Hall thruster. To try to alleviate this effect, three magnetic shielding configurations with different inclination directions of the lines of force in the strong magnetic field region are designed via the introduction of a peripheral coil surrounding the thruster body, and their influence on the performance and plume divergence are experimentally evaluated in this study. The measured results show that the performance and plume distribution vary significantly with the change in the inclination direction of the lines of force. Particularly, different to the unshielded Hall thruster that exhibits the best performance and minimal divergence when the strong magnetic field lines are non-inclined (perpendicular to the thruster axis), the magnetically shielded Hall thruster has the largest thrust and the smallest divergence angle when the strong magnetic field lines are inclined inward. Further theoretical research indicates that this is mainly due to the change in the ion acceleration process under the magnetic shielding discharge. This study is significant and instructive for the optimized design of magnetically shielded Hall thrusters. [ABSTRACT FROM AUTHOR]

Micro-cathode arc thrusters have been widely used in micro-nanosatellites owing to their high specific impact, long lifetime, repeatable startup, low thrust and high control precision. Micro-cathode arc thrusters and their derivatives are currently being developed and optimized. The micro-cathode arc thruster can generate plasma stably and efficiently, and form a thrust force under a magnetic field with very low power in pulsed operation mode. This paper reviews the last 20 years of literature on micro-cathode arc thrusters, with a focus on papers published in this field in the last 5 years. In light of the development of the micro-cathode arc thruster and the latest research, the direction of future development and the application of key technologies are reviewed. Future micro-cathode arc propulsion systems are expected to exhibit higher reliability, longer lifetimes, higher specific impact, greater integration and higher thrust and to be operated in various modes. [ABSTRACT FROM AUTHOR]

The application of photocatalyst in pavements has received comprehensive attention in recent years due to its ability to decontaminate nitrogen oxides (NOx). However, it's remarkable that NOx also accumulated extensively in parking lots. The purpose of this study is to develop a movable photocatalytic plate (remarked photocatalytic KT plates) coupled with high activity to purify NOx. Firstly, the type of photocatalytic KT plates was determined according to NO removal experiment in laboratory. Then the plates were employed in the parking lots for removing NOx. One sample T-test, normality test and paired sample T-test methods for NOx concentration variation were conducted to determine the appropriate comparative means of dates under both dark and illuminated conditions. The difference of NOX concentration between dark and illuminated conditions was obtained to evaluate the photocatalytic removal efficiency. The results indicated that NO removal efficiency in laboratory and parking lots were 51.31% and 9.2%, respectively. [ABSTRACT FROM AUTHOR]

The backpressure in the ground vacuum chamber significantly influences the discharge characteristics and performance of Hall effect thrusters (HETs). In this study, the propellant supplied from the anode and the propellant ingested from the background are treated as two separate components. Their ionization and acceleration processes are then studied numerically with a Particle-in-cell discharge model. It is found that the background propellant is mainly ionized near the outlet of the channel, thus affecting the local electron mobility and potential distribution inside and outside the channel. This results in an improvement in the ionization and acceleration of the anode propellant, an enhancement in the utilization of the propellant, and a reduction in the divergence of the ion beam. Consequently, the performance of the HETs is augmented. In particular, the increment in the thrust caused by the introduction of backpressure is not only due to the ionization and acceleration of the background propellant but also due to the improvement in the anode propellant discharge. [ABSTRACT FROM AUTHOR]

The dielectric properties of a dielectric material significantly affect the gas-solid interface discharge characteristics of the surface dielectric barrier discharge (SDBD) and surface space charge accumulation. In this study, new high dielectric composite dielectrics were prepared from barium calcium zirconate titanate nanoceramic particles (BZCT-NPs) using olyvinylidene luoride (PVDF) as a matrix. The impact of the amount of BZCT-NPs incorporated in the dielectric was investigated, and the influence mechanism of the new dielectric on the performance of SDBD ion wind thrusts was studied. Dielectrics with 3% (v/v) and 5% (v/v) BZCT-NPs/PVDF had significantly higher dielectric constants, 111% ± 2% and 135% ± 5%, respectively, compared to dielectrics made only of PVDF. The loss angle tangent values increased by 673% ± 33% and 707% ± 33%, respectively. The discharge charge increased by 54% ± 4% and 108% ± 13%, and the discharge time in one cycle increased by 23% ± 6% and 13% ± 4%, respectively. The single-point maximum wind speeds increased by 23.2% and 8.7%, respectively. The maximum thrust-to-power ratio of the 0% (v/v), 3% (v/v), and 5% (v/v) BZCT-NP dielectrics were 1060 μN/kW, 3120 μN/kW, and 2436 μN/kW, respectively. Interestingly, the minimum operating voltage of the thrusters decreased with increasing volume fraction of BZCT-NP, while the thrust-to-power ratio of the thruster increased significantly with higher levels of nanoceramic particles. The starting operating voltage of the 3% (v/v) BZCT-NPs/PVDF dielectric decreased by approximately 35% and 50% compared to the 5% (v/v) BZCT-NPs/PVDF and PVDF dielectrics, respectively, while the maximum thrust-to-power ratio increased by 194.3% and 129.8%, respectively. • Compared with PVDF, the discharge charge of 3 vol% BCZT-NPs/PVDF and 5 vol% BCZT-NPs/PVDF increased by 54% ± 4% and 108% ± 13%, respectively, and the discharge time increased by 23% ± 6% and 13% ± 4%, respectively. The addition of nano-ceramics can effectively regulate the space charge accumulation on the dielectric surface. • The maximum wind speed of the three thrusters is 1.12 m/s, 1.38 m/s and 1.27 m/s, respectively. When 3 vol% BCZT-NPs/PVDF acts as dielectric barrier, the wind speed generated by the thruster is the maximum. • The maximum thrust density is about 1080 μN/m, 860 μN/m and 710 μN/m, respectively. The maximum thrust-power ratios were 1060 μN/kW, 3120 μN/kW and 2436 μN/kW, respectively. and the maximum thrust to power ratio is increased by 194.3% and 28.1%, respectively. [ABSTRACT FROM AUTHOR]

Abstract HET72-VC is a kW-class Hall effect thruster with a variable channel characterized by high thrust and power densities. In this work, an experimental study of the effect of magnetic field configuration on the discharge characteristics of HET72-VC is carried out. By separately adjusting the current through the front and rear coils to change the magnetic field configuration inside the channel, a change in the plume is observed and the discharge performance parameters are measured. Experimental results show that the effects of reducing the front coil current and increasing the rear coil current on the thruster discharge are consistent. The plume gradually changes from a hollow cone with a clear boundary into a solid cone, the thrust increases by about 3%, and the anode efficiency increases by about 2.5%. Theoretical analysis shows that the degree of inclination of the magnetic lines of force plays an important role on the electron conduction and ion acceleration. When the angle between the magnetic lines of force and the channel centerline becomes larger, the discharge performance improves. This study helps in providing a deeper understanding of the working characteristics of this type of thruster, and can provide important guidelines for its structure design and optimization. Highlights • Plume shape is strongly modulated by magnetic field configuration. • Plume shape of a solid cone rather than a hollow cone represents good performance. • Magnetic field configuration impeding electrons strongly yields good performance. [ABSTRACT FROM AUTHOR]

To explore the effect of energy input on the discharge characteristics of a micro cathode arc thruster, the relationships between the different input PPU voltages of the micro cathode arc thruster and the plume shape, arc characteristics, thruster propulsion performance, and working fluid ionization are characterized in this research. The results obtained using a high-speed camera indicate that the change in the thruster's energy input affects the plume contraction. Further, the results of spectroscopy and electrical testing analyses show that an increase in the thruster input voltage prolongates the arc duration, ionization rate of the arc, and degree of plume contraction. When the thruster is in a low input voltage state, the arc ionization rate primarily affects thrust-to-power ratio. However, when the thruster is in a high input voltage state, the degree of plume contraction primarily affects propulsion efficiency. • The effect of Energy Input on the Discharge Characteristics of the Thruster is studied. • The electrical and spectroscopic diagnosis results of the micro-cathode arc thruster are given. • Changes in energy input will affect the proportion of high-energy ions, thereby affecting the ion velocity in the plume. • The increase in ion velocity leads to an increase in the radial loss of plume energy. [ABSTRACT FROM AUTHOR]

• The bottom-up crack was more prone to propagate under periodic eccentric load. • The bottom-up crack propagation velocity increases with its crack tip height. • The bottom-up crack propagation acceleration decreases with its crack tip height. • The bottom-up crack propagation life was predicted by simulation and regression. The bottom-up crack (BUC), one kind of reflective crack that initiates at the bottom of asphalt layer and propagates upwards, has become one of the major distresses of asphalt pavement. The Mode Ⅰ dominated bilinear cohesive zone model (CZM) after calibration was introduced into finite element (FE) model to simulate the BUC propagation in asphalt pavement under displacement load. The mechanism of crack propagation under different types of periodic load was analyzed based on two indexes from Mode Ⅰ dominated bilinear CZM. The FE model and corresponding periodic load were modified to limit the occurrence of top-down crack propagation. A combined method based on the developed model was adopted to predict the BUC propagation velocity at varied heights and the remaining life of pavement. The results showed that the acceleration of BUC propagation decreased with the crack tip height. Moreover, the predicted remaining life of pavement based on the proposed method was reasonable referring to the engineering design specifications. [ABSTRACT FROM AUTHOR]

The inward deflection of the excitation magnetic field was found in a Hall thruster voltage-varying experiment. The influence of Hall current magnitude and radial distribution on the total magnetic field was analyzed through magnetic field simulations. The probable reason why the excitation magnetic field deflected inward evidently at high discharge voltages (＞600 V) was obtained by combining the simulation results and theoretical analysis. This study provides qualitative guidance on the design of the excitation magnetic field in high-specific-impulse Hall thrusters. • Hall current induces an outward deflected magnetic field. • Magnitude and asymmetry of Hall current have an equivalent effect on magnetic field deflection. • An inward deflected excitation magnetic field is necessary to obtain a symmetrical total field. [ABSTRACT FROM AUTHOR]

Rapid evolution of miniaturized, automatic, robotized, function-centered devices has redefined space technology, bringing closer the realization of most ambitious interplanetary missions and intense near-Earth space exploration. Small unmanned satellites and probes are now being launched in hundreds at a time, resurrecting a dream of satellite constellations, i.e., wide, all-covering networks of small satellites capable of forming universal multifunctional, intelligent platforms for global communication, navigation, ubiquitous data mining, Earth observation, and many other functions, which was once doomed by the extraordinary cost of such systems. The ingression of novel nanostructured materials provided a solid base that enabled the advancement of these affordable systems in aspects of power, instrumentation, and communication. However, absence of efficient and reliable thrust systems with the capacity to support precise maneuvering of small satellites and CubeSats over long periods of deployment remains a real stumbling block both for the deployment of large satellite systems and for further exploration of deep space using a new generation of spacecraft. The last few years have seen tremendous global efforts to develop various miniaturized space thrusters, with great success stories. Yet, there are critical challenges that still face the space technology. These have been outlined at an inaugural International Workshop on Micropropulsion and Cubesats, MPCS-2017, a joint effort between Plasma Sources and Application Centre/Space Propulsion Centre (Singapore) and the Micropropulsion and Nanotechnology Lab, the G. Washington University (USA) devoted to miniaturized space propulsion systems, and hosted by CNR-Nanotec—P.Las.M.I. lab in Bari, Italy. This focused review aims to highlight the most promising developments reported at MPCS-2017 by leading world-reputed experts in miniaturized space propulsion systems. Recent advances in several major types of small thrusters including Hall thrusters, ion engines, helicon, and vacuum arc devices are presented, and trends and perspectives are outlined. [ABSTRACT FROM AUTHOR]

A kilowatt-order Hall effect thruster with a variable channel, the HET72-VC, is proposed. The discharge channel consists of an inner divergent annular segment and a cylindrical segment near the exit. A discharge comparison experiment was conducted on this thruster, in which the propellant gas is supplied along the axial direction and along the channel centerline. The results show that under the condition of gas supply along the channel centerline, both the current utilization and propellant utilization are higher, the plume divergence angle is smaller, the ion energy distribution curve moves to the high-energy portion, and the overall discharge performance, including the thrust and anode efficiency, is improved. A theoretical analysis shows that these results are attributed to the change in the ionization and acceleration characteristics caused by the different gas supply directions. The HET72-VC is demonstrated to be able to operate stably at an electric power of 2.5 kW; compared with those Hall effect thrusters with the same outer diameter or flow area of the channel, its thrust density and power density are both greatly improved. This provides a new perspective for the development of a high-power Hall effect thruster with a compact structure. [ABSTRACT FROM AUTHOR]