There are a number of pressing problems mankind is facing today that could, at least in part, be resolved by space systems. These include capabilities for fast and far-reaching telecommunication, surveying of resources and climate, and sustaining global information networks, to name but a few. Not surprisingly, increasing efforts are now devoted to building a strong near-Earth satellite infrastructure, with plans to extend the sphere of active life to orbital space and, later, to the Moon and Mars if not further. The realization of these aspirations demands novel and more efficient means of propulsion. At present, it is not only the heavy launch systems that are fully reliant on thermodynamic principles for propulsion. Satellites and spacecraft still widely use gas-based thrusters or chemical engines as their primary means of propulsion. Nonetheless, similar to other transportation systems where the use of electrical platforms has expanded rapidly, space propulsion technologies are also experiencing a shift toward electric thrusters that do not feature the many limitations intrinsic to the thermodynamic systems. Most importantly, electric and plasma thrusters have a theoretical capacity to deliver virtually any impulse, the latter being ultimately limited by the speed of light. Rapid progress in the field driven by consolidated efforts from industry and academia has brought all-electric space systems closer to reality, yet there are still obstacles that need addressing before we can take full advantage of this promising family of propulsion technologies. In this paper, we briefly outline the most recent successes in the development of plasma-based space propulsion systems and present our view of future trends, opportunities, and challenges in this rapidly growing field.

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Perspectives, frontiers, and new horizons for plasma-based space electric propulsion

Effect of Ce addition on microstructure evolution and precipitation in Cu-Co-Si-Ti alloy during hot deformation

Optimization of strength, ductility and electrical conductivity of a Cu─Cr─Zr alloy by cold rolling and aging treatment

Effects on microstructure evolution, mechanical and electrical properties of a Cu–Cr–Zr–Ni–Si–Ti alloy via multi-stage rolling and aging were investigated in details. The results showed that the optimal comprehensive performance of tensile strength (649 MPa) and electrical conductivity (65.5 %IACS) was obtained by three-stage rolling and aging (primary 80% room-temperature rolling (RTR) and aging at 450 °C for 2 h + secondary 60%RTR and aging at 300 °C for 1 h + tertiary 50%RTR and at 150 °C aging for 1 h). Through the microstructure characterization, it was found that the orientation relationship between the precipitates and Cu matrix was (001)Cu //(001)Cr // ( 001 ) Ni 2 Si , [011]Cu //[011]Cr // [ 010 ] Ni 2 Si in the investigated Cu–Cr–Zr–Ni–Si–Ti alloy. The increase of yield strength was primarily attributed to fine grain strengthening and precipitation strengthening, and secondly attributed to dislocation strengthening. This work will provide a guideline for the fabrication of high-performance copper alloys.

Microstructure evolution and properties of a Cu–Cr–Zr alloy with high strength and high conductivity

High strength and high conductivity (HSHC) Cu alloys are widely used in many fields, such as high-speed electric railway contact wires and integrated circuit lead frames. Pure Cu is well known to have excellent electrical conductivity but rather low strength. The main concern of HSHC Cu alloys is how to strengthen the alloy efficiently. However, when the Cu alloys are strengthened by a certain method, their electrical conductivity will inevitably decrease to a certain extent. This review introduces the strengthening methods of HSHC Cu alloys. Then the research progress of some typical HSHC Cu alloys such as Cu-Cr-Zr, Cu-Ni-Si, Cu-Ag, Cu-Mg is reviewed according to different alloy systems. Finally, the development trend of HSHC Cu alloys is forecasted. It is pointed out that precipitation and micro-alloying are effective ways to improve the performance of HSHC Cu alloys. At the same time, the production of HSHC Cu alloys also needs to comply with the large-scale, low-cost development trend of industrialization in the future.

High strength and high conductivity Cu alloys: A review

A high performance Cu-Cr-Zr alloy with an ultimate tensile strength of 612 MPa, a uniform elongation of 5% and an electrical conductivity of 84.7% IACS was achieved by the severe rotary swaging and two-step peak-aging treatment. A perfect ultrafine grained microstructure with uniformly distributed nano-precipitates was identified to be responsible for the excellent properties of the studied alloy. The proposed method of rotary swaging in combination with the two-step aging treatment shows good potential for producing the high performance Cu-Cr-Zr alloy, which can not only fulfill the industrial requirement of strength and electrical conductivity, but also is suitable for mass production.

Optimizing the strength, ductility and electrical conductivity of a Cu-Cr-Zr alloy by rotary swaging and aging treatment

The effect of the grain refinement and texture on tensile and fatigue properties in commercially pure titanium (grade 2) processed by rotary swaging (RS) and an annealing treatment is investigated. The as-processed sample consists of band-like grains on the longitudinal section and equiaxed grains on the transversal section and revealed an obvious fiber texture with respect to the rod axis. Through this technique, a sample with a high tensile strength of 870 MPa, a high uniform elongation of 8.5%, and a high fatigue limit of 490 MPa can be achieved, and the tensile and fatigue properties are almost the same as those of a conventional Ti-6Al-4V alloy. The enhanced mechanical properties and plastic deformation mechanism are discussed in terms of the observed ultrafine-grained microstructure and strong fiber texture.

https://www.mdpi.com/1996-1944/11/11/2261/pdf

Promising Tensile and Fatigue Properties of Commercially Pure Titanium Processed by Rotary Swaging and Annealing Treatment.

Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasma-material interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of 0.5 m, and exploring its frequency dependence in the range of 13.56-70 MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important ...

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Coupling of RF antennas to large volume helicon plasma

We present a metasurface consisting of W-shaped resonators to realize broadband reflective linear and circular polarization conversions. We find that the cross polarization conversion ratio for normal incidence is over 0.95 from 9.2 to 18.7 GHz, covering 68.1% of the central frequency. We also show that, the conversion performance is almost insensitive to the angle of incident waves. Furthermore, by simply adjusting the geometrical parameters of the W-shaped metasurface, the broadband circular polarization conversion is also achieved. We emphasize that the bandwidth of axis ratio less than 3.0 dB covers from 10.1 to 17.7 GHz, equivalent to 54.7% relative bandwidth. Due to these broadband and high-efficiency polarization conversion features, our proposal may have a wide application prospect.

Broadband Polarization Manipulation Based on W-Shaped Metasurface

Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasma-material interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of $0.5$~m, and exploring its frequency dependence in the range of $13.56-70$~MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important reference for the experimental design of large volume helicon plasma source with high RF power.

Lei Gao

Papers

Optimizing the strength, ductility and electrical conductivity of a Cu-Cr-Zr alloy by rotary swaging and aging treatment

Promising Tensile and Fatigue Properties of Commercially Pure Titanium Processed by Rotary Swaging and Annealing Treatment.

Coupling of RF antennas to large volume helicon plasma

Broadband Polarization Manipulation Based on W-Shaped Metasurface

Coupling of RF Antennas to Large Volume Helicon Plasma.