On magnetic reconnection as promising driver for future plasma propulsion systems

This work presents a more detailed analysis of the process of magnetic reconnection as promising ion beam accelerator mechanism with possible applications in laboratory plasmas and, more importantly, in the plasma propulsion field. In a previous work, an introductory study on this subject was already carried out, yet under the adoption of relevant approximations, such as the limitation to 2.5D simulations and the especially use of Hydrogen plasma as a propellant, whose element is rarely considered in the real scenario. Also, the analysis mainly focussed on studying the physical content of the outcomes, by leaving out the analysis of more important engineering quantities, such as the mass flow and thrust effectively reached out of such systems. With this work, we intend to fill these gaps in order to provide further insights into the great potentiality of a future technology based on magnetic reconnection. Additionally, one of the possibly limiting features was the inevitable symmetric outflow produced by the reconnection process. Among all the possible solutions adoptable, we propose here a solution based on the particle behavior undertaken in entering the reconnection region according to the initial density profile. We demonstrate that a noticeable net thrust value can be achieved by setting up a longitudinal asymmetric density profile with a relevant drop gradient

Analysis, simulation and testing of advanced electrodynamic systems for space propulsion

Helicon plasma sources are an attractive means of plasma production in advanced applications of space propulsion thanks to their high ionization efficiency. By means of a compact helicon source, it is possible to enhance the performances of a small propulsive apparatus from a range of almost negligible values (few micro-Newton of thrust and few tens of seconds of specific impulse) to a range useful for many applications (thrust of milli-Newton and 1000s seconds of specific impulse). However, the design of such a system is complicated by the great inter-correlations between the involved parameters, and by the complex physical mechanisms involved. Moreover, thruster operation involve physical regimes which are not common in industrial plasma sources. In this research program, helicon physics has been deeply analyzed in a innovative way, not limiting the study to helicon wave analysis with dielctric tensors, but recognizing that the electromagnetic wave propagation must be closely related to macroscopic transport. An equilibrium theory of an helicon discharge has been derived, where both the plasma-wave local coupling of the RF antenna field with the plasma, and the transport of plasma species at the macroscopic level, are considered. The theory has been practically implemented on a code and validated  with experiments in Laboratory. The theory has allowed to close the correlations between the design parameters and to identify preliminary design configurations of helicon thrusters.Grazie alla loro elevata efficienza, le sorgenti al plasma di tipo helicon sono un attraente mezzo di produzione di plasma per applicazioni avanzate di propulsione spaziale. Per mezzo di una compatta sorgente helicon, è possibile incrementare le prestazioni di un piccolo apparato propulsivo, da un range di valori pressoché trascurabili (pochi micro-Newton di spinta e qualche decina di secondi di impulso specifico) ad un range utile per molte applicazioni (spinta del milli-Newton e migliaia di secondi di impulso specifico). Tuttavia il design di un tale sistema è complicato dalla grande inter-correlazione tra i parametri coinvolti, e dai complessi meccanismi fisici coinvolti. Inoltre il regime operativo del thruster avviene in regimi fisici non comuni per plasmi di sorgenti industriali. In questo programma di ricerca la fisica fondamentale degli helicon è stata attentamente studiata, non limitando le analisi al problema di accoppiamento d'onda con tensore dielettrico, ma riconoscendo che il problema elettromagnetico è strettamente connesso al traporto macroscopico. E' stata sviluppata una teoria dell'equilibrio di una scarica helicon, dove sono tenuti in considerazione sia l'accoppiamento locale plasma-onda del campo RF (radiofrequenza) dell'antenna con il plasma, che il trasporto delle specie di plasma a livello macroscopico. La teoria è stata implementata in un codice e validata con esperimenti in Laboratorio. La teoria ha permesso di chiudere le correlazioni fra i parametri di design e di identificare delle configurazioni preliminari di propulsori helicon

Stability of Electrodynamic Tethers in a Three-Body System

Abstract - The dynamics of an electrodynamic tether orbiting in a three-body gravitational field near the equilibrium positions of the system is analyzed. First, the perturbed classical three-body problem is derived in general terms; then, the in-plane force perpendicular to the local vertical is analyzed in more detail because of its relevance to electrodynamic tethers. Because of the presence of electrodynamic forces, the locations of equilibrium points are modified from their classical Lagrangian positions (that are valid for a null electrodynamic force) and finally disrupted as the electrodynamic force increases.Alinear variational analysis is carried out to characterize the motion of the tethered system around the perturbed equilibrium locations and to compute the variation of the eigenfrequencies versus the intensity of the electrodynamic force. The study of small-amplitude motion about the perturbed equilateral positions has shown the existence of in-plane orbits (Lyapunov) and out-of-plane orbits (Lissajous and halo types) around those points. Large-amplitude orbits, which include nonlinear effects, have been studied using numerical integration of the equations of motion. Numerical tests have proven that when the higher of the two eigenfrequencies is excited, the trajectory is stable and converges toward the equilibrium point. The analysis is of immediate use to the orbit design of motion around perturbed Lagrangian points of electrodynamic tethers

Mycoplasmas–Host Interaction: Mechanisms of Inflammation and Association with Cellular Transformation

Mycoplasmas are the smallest and simplest self-replicating prokaryotes. Located everywhere in nature, they are widespread as parasites of humans, mammals, reptiles, fish, arthropods, and plants. They usually exhibiting organ and tissue specificity. Mycoplasmas belong to the class named Mollicutes (mollis = soft and cutis = skin, in Latin), and their small size and absence of a cell wall contribute to distinguish them from other bacteria. Mycoplasma species are found both outside the cells as membrane surface parasites and inside the cells, where they become intracellular residents as “silent parasites”. In humans, some Mycoplasma species are found as commensal inhabitants, while others have a significant impact on the cellular metabolism and physiology. Mollicutes lack typical bacterial PAMPs (e.g., lipoteichoic acid, flagellin, and some lipopolysaccharides) and consequently the exact molecular mechanisms of Mycoplasmas’ recognition by the cells of the immune system is the subjects of several researches for its pathogenic implications. It is well known that several strains of Mycoplasma suppress the transcriptional activity of p53, resulting in reduced apoptosis of damaged cells. In addition, some Mycoplasmas were reported to have oncogenic potential since they demonstrated not just accumulation of abnormalities but also phenotypic changes of the cells. Aim of this review is to provide an update of the current literature that implicates Mycoplasmas in triggering inflammation and altering critical cellular pathways, thus providing a better insight into potential mechanisms of cellular transformation