The Effects of Space-charge Limited Electron Emission on the Plasma Sheath PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Theory and experiments are presented that explore the space-charge limited regime of plasma sheaths surrounding electron emitting surfaces. The separation point technique and the inflection point probe methods for measuring the plasma potential were compared to the floating potential of a highly emissive probe in a Hall thruster plasma. The inflection point techniques' measurement of the plasma potential was ~2Te/e above the floating potential measurement, supporting fluid theory predictions. The separation point technique was inconsistent with every other technique and did not accurately measure the plasma potential. A virtual cathode was observed in a multidipole chamber plasma sheath near a grounded, metal boundary coated with a dielectric. A combination of secondary electron emission and a relatively high density of primary electrons formed the space-charge limited sheath indicated by the virtual cathode. Low neutral pressure, primary electron energy, and discharge current allowed the virtual cathode to form. The discharge current greatly affected the sheath potential, reducing it as the current increased. A kinetic theory of space-charge limited electron emitting sheaths is presented which accurately treats the loss of plasma electrons to the boundary and the velocity distribution of emitted electrons. By considering those electrons lost to the wall, the predicted sheath potential was reduced by 10%. Using a kinetic description of the emitted electrons, assuming a half-Maxwellian distribution, greatly affects the sheath potential. It is shown that the kinetic theory predicts that the sheath potential goes to zero as the plasma potential. To test this kinetic theory of emissive sheaths, time-resolved measurements of the emissive sheath potential were made in the afterglow of a capacitively coupled plasma. The results showed that as the plasma electron temperature cooled and approached the emitted electron temperature, the normalized sheath potential was drastically reduced and went to zero when the two temperatures were equal, qualitative supporting the emissive sheath kinetic theory. The emissive sheath potential was unexpectedly large when the plasma electron temperature was larger than the emitted electron temperature by a factor of 4.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Theory and experiments are presented that explore the space-charge limited regime of plasma sheaths surrounding electron emitting surfaces. The separation point technique and the inflection point probe methods for measuring the plasma potential were compared to the floating potential of a highly emissive probe in a Hall thruster plasma. The inflection point techniques' measurement of the plasma potential was ~2Te/e above the floating potential measurement, supporting fluid theory predictions. The separation point technique was inconsistent with every other technique and did not accurately measure the plasma potential. A virtual cathode was observed in a multidipole chamber plasma sheath near a grounded, metal boundary coated with a dielectric. A combination of secondary electron emission and a relatively high density of primary electrons formed the space-charge limited sheath indicated by the virtual cathode. Low neutral pressure, primary electron energy, and discharge current allowed the virtual cathode to form. The discharge current greatly affected the sheath potential, reducing it as the current increased. A kinetic theory of space-charge limited electron emitting sheaths is presented which accurately treats the loss of plasma electrons to the boundary and the velocity distribution of emitted electrons. By considering those electrons lost to the wall, the predicted sheath potential was reduced by 10%. Using a kinetic description of the emitted electrons, assuming a half-Maxwellian distribution, greatly affects the sheath potential. It is shown that the kinetic theory predicts that the sheath potential goes to zero as the plasma potential. To test this kinetic theory of emissive sheaths, time-resolved measurements of the emissive sheath potential were made in the afterglow of a capacitively coupled plasma. The results showed that as the plasma electron temperature cooled and approached the emitted electron temperature, the normalized sheath potential was drastically reduced and went to zero when the two temperatures were equal, qualitative supporting the emissive sheath kinetic theory. The emissive sheath potential was unexpectedly large when the plasma electron temperature was larger than the emitted electron temperature by a factor of 4.
Author: W. Lochte-Holtgreven Publisher: American Institute of Physics ISBN: Category : Science Languages : en Pages : 968
Book Description
Market: Plasma physicists and students. Upon publication in 1968, Plasma Diagnostics represented the most up- to-date survey of the experimental methods used in plasma analysis, including the necessary theoretical background. This work emphasizes spectroscopic techniques along with in-depth sections on laser techniques and electric and magnetic probe methods. The evaluation of collision and transport cross sections, heat and electrical conductivity, and viscosity are some of the many applications of plasma diagnostics reviewed as well. This long-awaited reprint volume is of interest to both physicists and students of theoretical physics as it deals with plasma theory from a fundamental point of view, stressing a careful derivation and discussion of the equations.
Author: P.M. Chung Publisher: Springer Science & Business Media ISBN: 3642658865 Category : Science Languages : en Pages : 163
Book Description
The electric probe has long been used as a fundamental diagnostic tool for measuring the local properties of a plasma. Since Langmuir first developed the electric-probe technique in 1924, probes have been used to measure electron densities and temperatures in a wide variety of gaseous ionized media, such as electric discharges, afterglows, ionizing shock waves, flames, MHD, and plasma-jet flows, reentry vehicle flow fields, and atmospheric and space plasmas. The first systematic account of modern theories of electriC-probe behavior was given by Chen (1965), who also provided practical information on experimental techniques. A subsequent survey by Swift and Schwar (1970), which was representative of results contained in the literature through 1969, included additional information on some of the modern theories and on practical details of probe utilization. The purpose of this volume is to supplement the previously mentioned two works by providing an account of a large body of the up-to-date informa tion available on electric probes, particularly in the areas of transitional and continuum-flow phenomena, and by offering, for all domains of probe appli cation, a critical appraisal of the more significant probe theories and experi mental investigations in the literature.
Author: Dirk Naujoks Publisher: Springer Science & Business Media ISBN: 3540321497 Category : Technology & Engineering Languages : en Pages : 279
Book Description
This book deals with the specific contact between the fourth state of matter, i.e. plasma, and the first state of matter, i.e. a solid wall, in controlled fusion experiments. A comprehensive analysis of the main processes of plasma-surface interaction is given together with an assessment of the most critical questions within the context of general criteria and operation limits. It also contains a survey on other important aspects in nuclear fusion.
Author: Kevin L. Jensen Publisher: John Wiley & Sons ISBN: 1119051762 Category : Science Languages : en Pages : 1305
Book Description
A practical, in-depth description of the physics behind electron emission physics and its usage in science and technology Electron emission is both a fundamental phenomenon and an enabling component that lies at the very heart of modern science and technology. Written by a recognized authority in the field, with expertise in both electron emission physics and electron beam physics, An Introduction to Electron Emission provides an in-depth look at the physics behind thermal, field, photo, and secondary electron emission mechanisms, how that physics affects the beams that result through space charge and emittance growth, and explores the physics behind their utilization in an array of applications. The book addresses mathematical and numerical methods underlying electron emission, describing where the equations originated, how they are related, and how they may be correctly used to model actual sources for devices using electron beams. Writing for the beam physics and solid state communities, the author explores applications of electron emission methodology to solid state, statistical, and quantum mechanical ideas and concepts related to simulations of electron beams to condensed matter, solid state and fabrication communities. Provides an extensive description of the physics behind four electron emission mechanisms—field, photo, and secondary, and how that physics relates to factors such as space charge and emittance that affect electron beams. Introduces readers to mathematical and numerical methods, their origins, and how they may be correctly used to model actual sources for devices using electron beams Demonstrates applications of electron methodology as well as quantum mechanical concepts related to simulations of electron beams to solid state design and manufacture Designed to function as both a graduate-level text and a reference for research professionals Introduction to the Physics of Electron Emission is a valuable learning tool for postgraduates studying quantum mechanics, statistical mechanics, solid state physics, electron transport, and beam physics. It is also an indispensable resource for academic researchers and professionals who use electron sources, model electron emission, develop cathode technologies, or utilize electron beams.
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Author: Irving Langmuir
Author: W. Lochte-Holtgreven
Author: P.M. Chung
Author: Michael Matthew Micci
Author: Dirk Naujoks
Author: Kevin L. Jensen
Author: Y. Raitses
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