The Australian National University and the Laboratoire de Physique et Technologie des Plasmas (LPTP) of Ecole Polytechnique in Palaiseau (France) obtained experimental results of current free helicon double layer originating with electropositive and electronegative gases. The experimental evidence of a current free helicon double layer envisages tantalizing performance of a thruster exploiting this effect. Although some progress has been achieved, at the present time a number of aspects related to this phenomenon are still partially understood. This research report presents the resulted obtained by a deep numerical investigation on Double layer, formation, stability and characteristic and to explore the applicability of this concept to space mission. The analysis has been conducted through a combination of 1-D and 2-D code numerical code. A 1-D code named PPDL was developed specifically for the porpoise of this study. It is a hybrid code with Boltzmann electrons and drift-kinetic ions, inclusion of dominant 2-D effects and high computational efficiency through implicit nonlinear Boltzmann solver. With the hybrid Boltzmann electron/drift-kinetic ion approach, the time step is only limited by ion period which is two orders of magnitude larger than electron plasma period and ion gyro period which can become very short. Simulations have been performed with several models for thrusters to identify the critical parameters. We analyzed the effects of ions and electrons temperatures, magnetic field strength and gradient. The plasma density and plasma source rates have been changed as well. The 2D model adopted in this study is the Object Oriented Particle in Cell Code (OOPIC). The hybrid configuration has been found to not fulfill our requirements therefore we had to use the full PIC method, where electrons are computed as real particles like ions. The geometry has been defined as near as possible to the experimental apparatus, like the properties of electrons and ions that are charged with Maxwellian distributions inside the source tube. The static magnetic field has been reconstructed adopting two coils with shape and current as reported by Charles, in order to have a axial field inside the source with two peaks of almost 150G. We have conducted three campaigns of simulations with growing source rates and ions densities. The first two campaigns shown the main border conditions' effects on the plasma potential and ions velocity distribution. We have changed the electrons and ions temperatures, the electrical properties of the source walls, neutral pressure, magnetic field and plasma production rates and distributions. The third campaign has been devoted to the evaluation of higher densities plasmas with biased left source walls and, enlarging the diffusion chamber length, the thrust and specific impulse. The results show a high energy ions flux at almost two times the ion sound speed. The potential jump is larger than the experimental measurements and, sometimes, lower. The effect of the neutral pressure increase, which...
Safety requirements and the increase in balloon flight duration make a computerized balloon control system essential. Starting with a global thermodynamic model of a stratospheric balloon (NASA-SINBAD) and 48-h wind forecast data, a flexible system can be built to predict its trajectory. In order to increase the trajectory forecast accuracy, the thermodynamic model of SINBAD, related to infrared radiation and albedo, has been improved. The model and the methodology have been evaluated by comparing the altitude excursion of some already flown zero-pressure balloons, with the altitude excursion computed by SINBAD; meteorological and satellite data (METEOSAT) and meteorological forecast data have been used as input. This system, connected during the mission to the balloon's managing unit, will continuously update the forecast trajectory and will enable real and simulated data to be compared. In this way it will also be possible to simulate the balloon flight trajectory in case of any failures. This paper explains the solution adopted for this system and the application that was carried out for the Italian Space Agency's 2002 summer balloon campaign.
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