Download or read book Operation of a Segmented Hall Thruster with Low sputtering Carbon velvet Electrodes written by N. J. Fisch and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon fiber velvet material provides exceptional sputtering resistance properties exceeding those for graphite and carbon composite materials. A 2 kW Hall thruster with segmented electrodes made of this material was operated in the discharge voltage range of 200-700 V. The arcing between the floating velvet electrodes and the plasma was visually observed, especially, during the initial conditioning time, which lasted for about 1 h. The comparison of voltage versus current and plume characteristics of the Hall thruster with and without segmented electrodes indicates that the magnetic insulation of the segmented thruster improves with the discharge voltage at a fixed magnetic field. The observations reported here also extend the regimes wherein the segmented Hall thruster can have a narrower plume than that of the conventional nonsegmented thruster.
Download or read book Studies of Non conventional Configuration Closed Electron Drift Thrusters written by Y. Raitses and published by . This book was released on 2001 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of a Plume Reduction in Segmented Electrode Hall Thruster written by Y. Raitses and published by . This book was released on 2000 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Annual Highlights written by Princeton University. Plasma Physics Laboratory and published by . This book was released on 2006 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Variable Operation of Hall Thruster with Multiple Segmented Electrodes written by N. J. Fisch and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Variable Operation of Hall Thruster with Multiple Segmented Electrodes written by N. J. Fisch and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Design and Operations of Hall Thruster with Segmented Electrodes written by N. J. Fisch and published by . This book was released on 1999 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Ein Hochprei lich Corpus Evangelicorum Unterth nigste Anzeig und Bittschrifft Unserer des Evangelischen Lutherischen Pfarrers des Kirchspiels Sien im Westrich zwischen Lauterecken und Kyrn gelegen um kr fftigste und schleunigste Assistenz gegen die Freyherren von Sickingen und Dererselben durch Chur Pf ltzische Mannschafft ausge bte gewaltsame Executiones written by and published by . This book was released on 1736 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Low Power Magnetically Shielded Hall Thrusters written by Ryan Conversano and published by . This book was released on 2015 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents an investigation of the applicability of magnetic shielding to low-power Hall thrusters as a means to significantly improve operational lifetime. The key life-limiting factors of conventional Hall thrusters, including ion-bombardment sputter erosion of the discharge channel and high-energy electron power deposition to the channel walls, have been investigated extensively for a wide range of thruster scales. As thruster power is reduced to the "miniature" (i.e. sub-500 W) power regime, the increased surface-to-volume ratio of the discharge channel and decreased thruster component sizes promotes increased plasma-wall interactions and susceptibility to overheating, thereby reducing thruster operational lifetime and performance. Although methods for compensating for these issues have been investigated, unshielded miniature Hall thrusters are generally limited to sub-45% anode efficiencies and maximum lifetimes on the order of 1,000 h. A magnetically shielded magnetic field topology aims to maintain a low electron temperature along the channel surfaces and a plasma potential near that of the discharge voltage along the entire surface of the discharge channel along its axial length. These features result in a reduction of the kinetic energy of ions that impact the channel surfaces to near to or below the sputtering threshold, thus preventing significant ion-bombardment erosion of the discharge channel. Improved confinement of high-energy electrons is another byproduct of the field structure, aiding in the reduction of electron power deposition to the channel. Magnetic shielding has been shown to dramatically reduce plasma-wall interactions on 4 - 6 kW Hall thrusters, resulting in significant increases in projected operational lifetimes with minimal effects to thruster performance. In an effort to explore the scalability of magnetic shielding to low-power devices, two magnetically shielded miniature Hall thrusters were designed, fabricated and tested. The performance of the first thruster, called the MaSMi 40, was characterized at an operating condition of 275 V and 325 W. A peak thrust of approximately 13 mN with a specific impulse of approximately 1,100 s at an anode efficiency of approximately 22% were measured at the nominal operating point. Observations of the near exit plasma discharge during operation, and the discharge channel after operation, suggested that the outer channel wall of the thruster was well shielded from ion bombardment while the inner channel wall appeared to be weakly shielded. Further analysis concluded that the MaSMi-40 generated a partially-magnetically shielded field topology. However, the shortcomings of the MaSMi-40's magnetic circuit design were investigated in detail and are now well understood. The second design iteration in the development of a low-power magnetically shielded Hall thruster was the MaSMi-60. Magnetic field measurements confirmed that a symmetric and fully shielded magnetic field topology was generated by this device across a wide range of possible operating conditions. At operating powers of 160 W to nearly 750 W, the key performance metrics of the MaSMi-60 included a measured thrust ranging from approximately 8 mN to over 33 mN with anode specific impulses of up to approximately 1370 s at anode efficiencies of over 28%. Downstream plume measurements identified the primary factors contributing to the low anode efficiency. Visual observations of the discharge plasma and channel walls during and after thruster operation offered strong evidence of magnetic shielding. Erosion rates of the channel were approximated using carbon backsputter measurements; the results suggested a 10x - 100x decrease in wall erosion compared to unshielded Hall thrusters, corresponding to an equal increase in discharge channel lifetime compared to conventional miniature unshielded Hall thrusters. The physics and behaviors of the MaSMi-60's plasma discharge upstream of and in the near-field of the thruster exit plane were investigated using Hall2De, the 2-D axisymmetric code developed at the Jet Propulsion Laboratory for the simulation of the partially ionized plasma in Hall thrusters. Simulations of the MaSMi-60 suggested that the thruster achieved the plasma properties required for effective magnetic shielding, including low electron temperatures and a near-constant plasma potential along the channel walls. This was the final piece of evidence suggesting that magnetic shielding was attained at the miniature scale. The experimentally measured performance of the MaSMi-60 was captured by the Hall2De model, offering physical explanations for the low measured anode efficiency and leading to suggestions for improving the performance in future design iterations.
Download or read book Design and Operations of Hall Thruster with Segmented Electrodes written by N. J. Fisch and published by . This book was released on 1999 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Plasma Characterization of Hall Thruster with Active and Passive Segmented Electrodes written by Y. Raitses and published by . This book was released on 2002 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Segmented Electrode Hall Thruster with Reduced Plume written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An apparatus and method for thrusting plasma, utilizing a Hall thruster with segmented electrodes along the channel, which make the acceleration region as localized as possible. Also disclosed are methods of arranging the electrodes so as to minimize erosion and arcing. Also disclosed are methods of arranging the electrodes so as to produce a substantial reduction in plume divergence. The use of electrodes made of emissive material will reduce the radial potential drop within the channel, further decreasing the plume divergence. Also disclosed is a method of arranging and powering these electrodes so as to provide variable mode operation.
Download or read book Secondary Electron Emission from Dielectric Materials of a Hall Thruster with Segmented Electrodes written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The discharge parameters in Hall thrusters depend strongly on the yield of secondary electron emission from channel walls. Comparative measurements of the yield of secondary electron emission at low energies of primary electrons were performed for several dielectric materials used in Hall thrusters with segmented electrodes. The measurements showed that at low energies of primary electrons the actual energetic dependencies of the total yield of secondary electron emission could differ from fits, which are usually used in theoretical models. The observed differences might be caused by electron backscattering, which is dominant at lower energies and depends strongly on surface properties. Fits based on power or linear laws are relevant at higher energies of primary electrons, where the bulk material properties play a decisive role.
Download or read book Effect of a Plume Reduction in Segmented Electrode Hall Thruster written by Y. Raitses and published by . This book was released on 2000 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Deep Space Propulsion written by K. F. Long and published by Springer Science & Business Media. This book was released on 2011-11-25 with total page 379 pages. Available in PDF, EPUB and Kindle. Book excerpt: The technology of the next few decades could possibly allow us to explore with robotic probes the closest stars outside our Solar System, and maybe even observe some of the recently discovered planets circling these stars. This book looks at the reasons for exploring our stellar neighbors and at the technologies we are developing to build space probes that can traverse the enormous distances between the stars. In order to reach the nearest stars, we must first develop a propulsion technology that would take our robotic probes there in a reasonable time. Such propulsion technology has radically different requirements from conventional chemical rockets, because of the enormous distances that must be crossed. Surprisingly, many propulsion schemes for interstellar travel have been suggested and await only practical engineering solutions and the political will to make them a reality. This is a result of the tremendous advances in astrophysics that have been made in recent decades and the perseverance and imagination of tenacious theoretical physicists. This book explores these different propulsion schemes – all based on current physics – and the challenges they present to physicists, engineers, and space exploration entrepreneurs. This book will be helpful to anyone who really wants to understand the principles behind and likely future course of interstellar travel and who wants to recognizes the distinctions between pure fantasy (such as Star Trek’s ‘warp drive’) and methods that are grounded in real physics and offer practical technological solutions for exploring the stars in the decades to come.
Download or read book Anagram Solver written by Bloomsbury Publishing and published by Bloomsbury Publishing. This book was released on 2009-01-01 with total page 719 pages. Available in PDF, EPUB and Kindle. Book excerpt: Anagram Solver is the essential guide to cracking all types of quiz and crossword featuring anagrams. Containing over 200,000 words and phrases, Anagram Solver includes plural noun forms, palindromes, idioms, first names and all parts of speech. Anagrams are grouped by the number of letters they contain with the letters set out in alphabetical order so that once the letters of an anagram are arranged alphabetically, finding the solution is as easy as locating the word in a dictionary.
Download or read book The Dynatron written by Donald Menzies Bennett and published by . This book was released on 1921 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:
