In this paper,we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space-charge-saturated sheath near the insulated wall of the Hall thruster on the near-wall conductivity,by the method of two-dimensional (2D) particle simulation (2D+3V).The results show that due to the sharp increase of collision frequency between the electrons and the wall under the space-charge-saturated sheath,the near-wall transport current under this sheath is remarkably higher than that under a classical sheath,and equals the near-wall transport current under a spatially oscillating sheath in order of magnitude.However,the transport currents under a space-charge-saturated sheath and a spatially oscillating sheath are different in mechanism,causing different current density distributions under the above two sheaths,and a great influence of channel width on the near-wall transport current under a space-charge-saturated sheath.
Electron-wall interaction is always recognized as an important physical problem because of its remarkable influences on thruster discharge and performance. Based on existing theories, an electrode is predicted to weaken electron-wall interaction due to its low secondary electron emission characteristic. In this paper, the electron-wall interaction in an Aton-type Hall thruster with low-emissive electrodes placed near the exit of discharge channel is studied by a fully kinetic particle-incell method. The results show that the electron-wall interaction in the region of segmented electrode is indeed weakened, but it is significantly enhanced in the remaining region of discharge channel. It is mainly caused by electrode conductive property which makes equipotential lines convex toward channel exit and even parallel to wall surface in near-wall region; this convex equipotential configuration results in significant physical effects such as repelling electrons, which causes the electrons to move toward the channel center, and the electrons emitted from electrodes to be remarkably accelerated, thereby increasing electron temperature in the discharge channel, etc. Furthermore, the results also indicate that the discharge current in the segmented electrode case is larger than in the non-segmented electrode case, which is qualitatively in accordance with previous experimental results.
The distribution of magnetic field in Hall thruster channel has significant effect on its discharge process and wall plasma sheath characteristics. By creating physical models for the wall sheath region and adopting two-dimensional particle in cell simulation method,this work aims to investigate the effects of magnitude and direction of magnetic field and ion velocity on the plasma sheath characteristics. The simulation results show that magnetic field magnitudes have small impact on the sheath potential and the secondary electron emission coefficient,magnetic azimuth between the magnetic field direction and the channel radial direction is proportional to the absolute value of the sheath potential,but inversely proportional to the secondary electron emission coefficient. With the increase of the ion incident velocity,secondary electron emission coefficient is enhanced,however,electron density number,sheath potential and radial electric field are decreased. When the boundary condition is determined,with an increase of the simulation area radial scale,the sheath potential oscillation is aggravated,and the stability of the sheath is reduced.
Interaction between high-intensity pulsed ion beam (HIPIB) and a double-layer targetwith titanium film on top of aluminum substrate was simulated. The two-dimensional nonlinearthermal conduction equations, with the deposited energy in the target taken as source term, werederived and solved by finite differential method. As a result, the two-dimensional spatial andtemporal evolution profiles of temperature were obtained for a titanium/aluminum double-layertarget irradiated by a pulse of HIPIB. The effects of ion beam current density on the phase stateof the target materials near the film and substrate interface were analyzed. Both titanium andaluminum were melted near the interface aRer a shot when the ion beam current density fell inthe range of 100 A/cm^2 to 200 A/cm^2.
