Kinetic modeling of the electron current collection to a moving bare electrodynamic tether

Tether electron current collection in the Orbital Motion Limited regime is the key mechanism allowing for power and/or thrust generation applications of space electrodynamic tethers. This paper presents a new approach, based on a kinetic model, for the accurate analysis of the electron collection problem to a bare tether moving in a collisionless plasma. The drift velocity associated with the translational speed of the tether is incompatible with 1-D, cylindrically symmetric models (Laframboise, 1966; Sanmartín and Estes, 1999) and its effects on current collection are not well understood. A kinetic model is developed for the two-dimensional plasma surrounding the tether. It consists in solving, self-consistently, the Vlasov and Poisson equations through a semi-analytical, semi-numerical process. A Maxwellian velocity distribution is assumed for the plasma species (electrons and ions) at the outer boundary of the solution space; no assumption is made regarding the velocity distributions in the vicinity of the tether. Initial results are validated with Langmuir cylindrical probe theory in the ion and electron saturation regimes as well as the electron retardation regime. Work is underway to allow the use of the model for cases with a drifting plasma. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87701/2/526_1.pd

Modélisation de réseaux périodiques multicouches par la méthode des lignes

Structure plane multicouche générale -- Excitation d'une surface à sélection de fréquences -- Excitation d'un réseau périodique d'antennes plaques couplées par fentes -- Formulation générale du problème de structure planaire multicouche -- Principes de base de la méthode des lignes -- Discrétisation de l'équation de Helmholtz -- Diagonalisation de l'équation de Helmholtz -- Calcul des champs discrétisés Ex et Hx à partir de Ez et Hz -- Paramètres hybrides d'une couche diélectrique -- Paramètres Y d'une couche absorbante -- Construction du système d'équations transformé -- Réduction du système d'équations dans le domaine spatiale -- Alternatives dans le choix des inconnues du système d'équations -- Application d'une source de champ ou de courant électrique -- Résolution du système d'équations par méthode itérative -- Analyse de surfaces à sélection de fréquences -- Définition des plans d'incidence -- Formulation de la source à polarisation TE -- Formulation de la source à polarisation TM -- Résultats, validation et convergence -- Analyse de réseaux périodiques d'antennes plaques -- Source de tension idéale distribuée -- Alimentation par fentes couplées -- Exemples de distribution de courants et de champs obtenues

Enhancement of electrodynamic tether electron current collection using radio frequency power

Tether electron current collection in the Orbital Motion Limited regime is one of the limiting factors in power and thrust generation applications of electrodynamic tethers. Injection of radio frequency power along tethers is considered in order to enhance electron current collection. As a basic assessment tool, Particle-In-Cell modeling of the tether system is performed using a 1-d cylindrical code. Comparison of test electron trajectories shows that the time periodic field distribution created by the RF excitation results in electrons being scattered off their usual OML trajectories, which under some conditions increases their probability of being collected by the tether. Analysis of simulation results reveals that large current enhancements can occur at resonance frequencies of the input reactance (where Xin = 0Xin=0), but at the expense of high RF power. Current enhancement is best measured in terms of the relative current variation per unit of RF power dissipated for every 1-meter section of the tether. Optimum enhancements of about 9% per RF watt per meter were obtained by simulation at low frequencies (75 MHz). Similar enhancements were observed during experimental measurements on tether samples. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87358/2/473_1.pd

Laboratory experiments of current collection to long conductors with geometries relevant to bare electrodynamic tethers

We describe chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense, high-speed plasma. The geometries tested and described here were cylindrical and flat-ribbon. Several important conclusions that can be drawn from the tests are as follows: the currents collected by cylinder are close to what would be predicted via orbital-motion-limited (OML) current collection theory. The tape tether had comparable current levels to a theoretical equal area OML cylinder collector. However, I-V behavior clearly is different at nearest distances ( ∼ 16λD∼16λD tape width) as compared to furthest test distances ( ∼ 6λD∼6λD tape width). The tape tether did better than a theoretical equal mass solid cylinder. A “knee” in the I-V curves can be seen in the tape data at a potential that is near the estimated energy of the incoming beam of ions, at least for the closest distances where Debye length is smallest. Below this knee the current increases rapidly as voltage is increased. Above the knee the current increases at a rate near that expected from OML current-collection models depending on the relative width. This likely is an example of high-speed plasma flow effect. Perpendicular tape orientation performed slightly better than parallel. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87700/2/517_1.pd

THEORY AND EXPERIMENTAL EVALUATION OF A CONSISTENT STEADY-STATE KINETIC MODEL FOR 2-D CONDUCTIVE STRUCTURES IN IONOSPHERIC PLASMAS WITH APPLICATION TO BARE ELECTRODYNAMIC TETHERS IN SPACE

2004 À mon amour, Isabelle, pour sa patience et son support, et àlamémoire de ma grand-mère Bernadette. ii ACKNOWLEDGMENTS First, I would like to thank my research advisor and committee chair, Professor Brian Gilchrist, for allowing me on board in September of 1999 when I first stepped foot in his office, for making so many great opportunities happen during my years in Ann Arbor, and for all of his support throughout this exciting, difficult, and rewarding journey. I really appreciate the freedom and trust you have given me throughout the years, as well as the friendly atmosphere that you have fostered within the SETS group. I look forward to collaboration in the future. I would also like to thank the other members of my thesis committee, Prof. Sven Bilén, Prof. Iain Boyd, Prof. Alec Gallimore and Prof. Sarabandi, for accepting to judge this work and for their guidance. Special thanks go to Prof. Bilén for teaching me the ropes of experimental work while he was working as a Postdoc at Michigan, as well as for hi

Electron Collection to Arbitrarily Shaped Space Electrodynamic Tethers: A Kinetic Model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76473/1/AIAA-2002-4050-870.pd