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.
Controlled precipitation of radiation belt electrons
[1] First-order estimates indicate that the lifetime of energetic (a few MeV) electrons in the inner radiation belts (e.g., near L = 2) may be significantly reduced by in situ injection of whistler mode waves at radiated power levels of a few kW at frequencies of a few kHz. Our estimates are based on previously published results concerning the effect on the electron lifetimes of VLF signals from ground-based VLF transmitters operating in the 17–23 kHz range. Waves at lower frequencies (a few kHz) can drive diffusion rates that are higher by a factor of as much as ∼30 and can also be efficiently stored in the magnetospheric cavity, resulting in additional effective enhancement of wave power density of a factor of ∼16. This wave power enhancement is also expected to enhance the MeV electron diffusion rates.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.