Nascap-2k Self-Consistent Simulations of a VLF Plasma Antenna
We simulate the plasma response through tens of cycles of the Demonstration and Science Experiments (DSX) kilovolt near-square-wave very low frequency (VLF) (0.1-50 kHz) antenna in Medium Earth Orbit plasma with Nascap-2k. DSX is an Air Force Research Laboratory experiment that will explore the physics of electromagnetic wave injection from space transmitters, wave propagation, and wave-particle interactions in the magnetosphere. DSX will transmit and receive VLF waves and quantify their effect on the trapped electron populations in the magnetosphere. In these preflight calculations, the plasma is modeled with a hybrid particle-in-cell (PIC) approach with PIC ions and fluid barometric electron densities. The plasma response, collected ion currents, and chassis floating potential are computed self-consistently with a near-square-wave bias applied to the antennas. Particle injection and splitting are used to replenish the plasma depleted at the boundary, represent the thermal distribution, and maintain appropriately sized macroparticles. Therefore, limitation of current due to the thermal distribution of ions and the resulting angular momentum barrier is included. Above the ion plasma frequency, the plasma current lags the voltage by about 10, while below the ion plasma frequency, the current leads the voltage by about 7 . The volume ion current shows periodic launch of blocks of energetic ions radially outward.
High‐voltage interactions in plasma wakes: Simulation and flight measurements from the Charge Hazards and Wake Studies (CHAWS) experiment
The Charge Hazards and Wake Studies (CHAWS) flight experiment flew on the Wake Shield Facility (WSF) aboard STS-60 and STS-69. The experiment studied high-voltage current collection within the spacecraft wake. The wake-side sensor was a 45-cm-long, biasable cylindrical probe mounted on the 3.66-m-diameter WSF. Operations were performed in free flight and at various attitudes while on the shuttle orbiter remote manipulator system (RMS) arm. Preflight and postflight simulations were performed using the programs Potentials of Large Objects in the Auroral Region (POLAR) and Dynamic Plasma Analysis Code (DynaPAC) and are compared here with the flight results. Both programs perform three-dimensional, self-consistent, steady state plasma simulations. During high-voltage operations the wake-side probe collected current consistent with preflight predictions. In both the flight data and the steady state simulations the current collected has a power law dependence on the potential and has a less than linear dependence on density. Growth of the sheath beyond the WSF edge controls the high-voltage current collection, and kinematic and space charge effects both play important roles in attracting ions into the wake region. Measurements made at low voltage differ from the calculations. The preflight calculations for a pure oxygen plasma predict a collection threshold at −100 V bias. The flight data show little or no threshold, implying a source of ions not accounted for in the simulations. Possible sources for these ions are discussed.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.