No abstract

Indium phosphide (InP) has the characteristics of high electron mobility, large band gap, high temperature resistance, and radiation resistance. It is an important material of electronic devices in the space radiation environment. With the miniaturization of electronic devices, the displacement damage (DD) effect caused by a single heavy ion in the device may give rise to permanent failure. Therefore, this paper uses Monte Carlo software Geant4 to simulate the transportation process of space heavy ions(C, N, O, Fe) in InP. The non-ionizing energy loss (NIEL) of heavy ions is calculated for getting the information about displacement damage. Some conclusions are drawn as follows. 1) NIEL is proportional to the square of the atomic number, which means that single Fe can make severe displacement damage in InP. 2) The heavy ions NIEL is 3 to 4 orders of magnitude larger than PKA NIEL. The NIEL is proportional to the non-ionizing damage energy of recoil atoms produced by nuclear elastic collision, which indicates that the primary recoil atoms produced by heavy ions are the main cause of InP DD. 3) The number of heavy ions in space is small, so the proportion of total non-ionizing damage energy produced by heavy ions in 0.0125 mm³ InP is only 2.56% in one year. But the NIEL of heavy ions NIEL is 2–30 times that of protons and α particles, so the DD effect caused by single heavy ion incident on InP electronic device still needs to be considered. 4) NIEL decreases slightly with the increase of material thickness. The reason is that low-energy heavy ions are completely deposited in the front of InP, resulting in a non-uniform distribution of non-ionizing energy deposited in the material. Analyzing the dependence of mean DD energy with depth, we find that mean DD energy decreases with incident depth increasing, which means that the most severe DD region of heavy ions in InP is in the front of material.

Vacuum arc is a special metal vapor discharge phenomenon, because its discharge medium totally comes from the evaporation and ionization of electrode materials. In the case of low current, the vacuum arc is completely composed of plasma jets emitted from discrete cathode spots on the cathode surface and the current carried by each spot depends on the cathode material. When the arc current exceeds a certain value, a certain number of cathode spot plasma jets will appear. Vacuum arcs play a very important role in some industrial applications such as vacuum circuit breakers, vacuum coatings and electric thrusters. As an important plasma control method, the external axial magnetic field (AMF) has an important influence on the macroscopic morphology and microscopic parameter distribution of the vacuum arc. Various studies of vacuum arc under AMF have been carried out and some progress has been made. However, the existing literature about the simulation research of vacuum arc is mostly concentrated in the case of large current, and less attention is paid to the case of small current. The reason is that the traditional methods, magneto-hydrodynamics or particle-in-cell, are limited by either accuracy or efficiency, and cannot be effectively applied to the low current vacuum arc plasma jet simulations. In this paper, we develop a fully three-dimensional hybrid plasma simulation algorithm to study the single cathode spot vacuum arc plasma jet under AMF. In this model, ions are modelled as particles while electrons are treated as massless fluid, and the self-generated magnetic field is also considered. To simplify the condition, the cathode spot in our model only exists as a plasma jet source, thus the detailed mechanism of producing plasmas is neglected. And the movement of the cathode spot is not considered either. The results show that the single cathode spot plasma jet diffuses into the interelectrode in a cone shape after leaving the cathode spot, and the ion density drops rapidly from cathode to anode. Under the simulation conditions in this paper (<i>I</i> ≤ 150 A), the self-generated magnetic field will not have a significant influence on the plasma jet itself in the case of low current. The external AMF has a compressive effect on the diffusion of the vacuum arc plasma jet. Under the AMF, the radial movement of the ions is suppressed, and the decrease of the ion radial velocity leads to a smaller diffusion radius of the jet. This compression effect of the AMF on the plasma jet is related to both the intensity of the external AMF and the magnitude of the arc current. In the case of a constant arc current magnitude, the compression effect gradually increases as the value of the AMF intensity gradually increases; in the case of a constant value of the external AMF, the compression effect gradually decreases as the current gradually becomes larger.

Compared with the traditional ionization sensor, triple electrode ionization gas sensor based on carbon nanotubes features excellent performances of small size and low operation voltage, and plays an important role in developing smart grids and the ubiquitous Internet of Things. However, they exhibit the disadvantages of small collecting current and low sensitivity, and need to be optimized in structure. Based on the Townsend discharge mechanism and three governing equations of particle mass conservation, electron energy conservation and Poisson equations, a two-dimensional plasma discharge fluid simulation model of the sensor is established by using the COMSOL Multiphysics software. According to gas composition, component concentration, structure of the sensor and voltage applied to the electrodes, we determine the chemical reaction, reaction rate coefficient, field control equation, initial values and boundary conditions. In order to calculate the interior distribution of charged particles inside the boundary, the inter-electrode space region is meshed. Initial values of mesh are set, such as a dense mesh of nano-meter length around the electrode having micro-nano structure, and a rough mesh of micro-meter length in the other region of inter-electrode space. The initial values of time-step are set for each mesh grid, and the discharge model of each mesh grid is numerically solved by the finite volume method. The three linkage governing equations are discretized and calculated iteratively in time and space, and the mesh values and time-steps are adjusted to make the results converged. The electrostatic field distribution and the average collecting current density of the eight kinds of sensors are obtained in the background gas of nitrogen. The optimal sensor structure is obtained by comparing the electric field intensities and current densities under different structure parameters. The eight kinds of the sensors are prepared for experimentally verifying the optimization method. The optimal structure of the 7# sensor has the highest collecting current density in the eight kind structures, which is consistent with the simulation results, and proves the feasibility of the structure optimization method proposed in the paper. Based on the optimal structure, the sensors, respectively with the electrode spacings of 100 and 120 μm, are fabricated, and the response characteristics of NO/SO₂ mixture gas are obtained. Compared with other technologies, the sensor with optimal structure exhibits 1－2 orders of sensitivity higher than the others. The optimized triple electrode ionization sensor based on carbon nanotubes exhibits many potential applications.

Capillary discharge based pulsed plasma thrusters have great prospects of applications in in-orbit maneuvering of<bold/> micro-nano satellites. In this paper, the influence of different capillary cavity structure parameters on the thruster's energy deposition process, ablation characteristics, output thrust parameters and plasma plume parameters under an energy level of 5 J were studied. The experimental results indicate that the increase of the inner diameter of the capillary cavity will significantly reduce the discharge current density, which leads the deposition energy and equivalent power to decrease; the increase of the cavity length helps to improve the energy transfer efficiency. The influence of cavity structure on the ablation characteristics is reflected in the influence of deposition energy per unit area on the tube wall temperature. When the inner diameter of the capillary increases from 1 mm to 3 mm, the ablation mass decreases significantly, and then the equivalent ablation mass remains approximately unchanged as the inner diameter of the cavity increases further; the ablation mass continues to increase as the capillary length increases, while the ablation mass per unit area continues to decrease. The impulse bit depends on the ablation mass and plasma plume velocity, and the difference in ablation characteristic further affects the plasma in the cavity. The density and equivalent pressure determine the plasma electrothermal acceleration process. The continuous increase in the diameter and length of the capillary cavity will induce the acceleration process to lag behind the discharge and ablation process. And the decrease of the deposited energy impedes the electrothermal acceleration process, which results in the decrease of the impulse bit, specific impulse, and the overall efficiency. Furthermore, the overall efficiency transfer model analysis indicates the influence of the capillary inner diameter on thruster efficiency is mainly reflected in the energy transfer efficiency, and the capillary length change mainly affects the electrothermal acceleration efficiency. The overall efficiency optimization of the thruster needs to start from increasing both energy deposition efficiency and acceleration efficiency.