Investigation of short-channel design on performance optimization effect of Hall thruster with large height–radius ratio

In this study,the neutral gas distribution and steady-state discharge under different discharge channel lengths were studied via numerical simulations.The results show that the channel with a length of 22 mm has the advantage of comprehensive discharge performance.At this time,the magnetic field intensity at the anode surface is 10%of the peak magnetic field intensity.Further analysis shows that the high-gas-density zone moves outward due to the shortening of the channel length,which optimizes the matching between the gas flow field and the magnetic field,and thus increases the ionization rate.The outward movement of the main ionization zone also reduces the ion loss on the wall surface.Thus,the propellant utilization efficiency can reach a maximum of 96.8%.Moreover,the plasma potential in the main ionization zone will decrease with the shortening of the channel.The excessively short-channel will greatly reduce the voltage utilization efficiency.The thrust is reduced to a minimum of 46.1 m N.Meanwhile,because the anode surface is excessively close to the main ionization zone,the discharge reliability is also difficult to guarantee.It was proved that the performance of Hall thrusters can be optimized by shortening the discharge channel appropriately,and the specific design scheme of short-channel of HEP-1350 PM was defined,which serves as a reference for the optimization design of Hall thruster with large height–radius ratio.The shortchannel design also helps to reduce the thruster axial dimension,further consolidating the advantages of lightweight and large thrust-to-weight ratio of the Hall thruster with large height–radius ratio.

NbB_(2)Modified Al-Cu Alloys Fabricated by Freeze-Ablation Casting under High Cooling Rate Solidification

At present,improving the properties of aluminum alloys is generally achieved by increasing the cooling rate of the melt and adding micro-nano particles.Controlling the cooling rate of the melt to improve the refining effect of grain refiner is still a difficult problem in the aluminum alloy casting industry.An innovative and environmentally friendly casting process,known as freeze ablation,was introduced during the preparation of an Al–NbB_(2) intermediate alloy.This process significantly enhanced the cooling rate of the melt.The results indicated that the Al–NbB_(2) intermediate alloy produced under high cooling rates had a noticeable refining effect on Al–Cu alloys,with smaller NbB2 particles demonstrating superior refining performance.The average grain size of the refined Al–Cu alloy decreased from 154 to 69μm,the tensile strength increased by 12%,the fluidity increased by 18.4%,and the hot tearing index decreased from 144 to 12.The matching degree between NbB_(2) andα-Al was calculated using high-resolution transmission electron microscopy and the edge-to-edge model.It was found that the atomic interplanar spacing and the interatomic spacing mismatch between NbB_(2)’s<1120>plane and Al were both less than 10%,which further proved that NbB2 could serve as an effective nucleation site forα-Al grains to achieve grain refinement.