Thermal Ionization at Hot Metal Surfaces


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Ionization on hot tungsten, tantalum, and rhenium surfaces was studied. An atomic beam of neutral atoms effused from a Knudsen-type effusion vessel and struck a hot filament of the metal being studied. A temperature- dependent fraction of these atoms was ionized. This filament served as the ion source of a 60-degree-sector single-directional focusing mass spectrometer. According to the Saha-Langmuir theory of surface ionization the temperature dependence of ionization is related to the difference between the ionization potential of the impinging atom and the work function of the surface under consideration.




Atomic and Ionic Impact Phenomena on Metal Surfaces


Book Description

The collisions of neutral or charged gaseous particles with solid surfaces govern many physical and chemical phenomena, as has been The gas/solid phenomena in turn depend on a recognized for a long time. great variety of processes such as the charge transfer of the gas/solid interface, adsorption and desorption, the energy transfer between an incident particle and the surface, etc. Our knowledge of these processes, however, is only fragmentary. This is partly due to the difficulty in adequately controlling the ex perimental conditions. Consequently, until recently the data were usually so complex that reliable information about a particular elementary process could not be deduced. Within the last five to ten years, however, the techniques of ultra-high vacuum and surface preparation have developed rapidly and there has been a booming and widespread interest in the role of gas/solid interactions in such diverse fields as plasma physics, thermonuclear reactions, thermionic energy conversion, ion propulsion, sputtering corrosion of the surface of satellites and ion engines, ion getter pumps, deposition of thin films, etc. This led to extensive investigations of numerous gas/solid phenomena, such as surface ionization, sputtering, emission of secondary electrons and ions from surfaces under atom and/or ion impact, ion neutralization, and the thermal accomodation of gaseous particles on surfaces. As a result, it has become possible to gather a variety of valuable information.













Technical News Bulletin


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Dimensions


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Handbook of Ion Sources


Book Description

The Handbook of Ion Sources delivers the data needed for daily work with ion sources. It also gives information for the selection of a suitable ion source and ion production method for a specific application. The Handbook concentrates on practical aspects and introduces the principle function of ion sources. The basic plasma parameters are defined and discussed. The working principles of various ion sources are explained, and examples of each type of ion source are presented with their operational data. Tables of ion current for various elements and charge states summarize the performance of different ion sources. The problems related to the production of ions of non-gaseous elements are detailed, and data on useful materials for evaporation and ion source construction are summarized. Additional chapters are dedicated to extraction and beam formation, ion beam diagnosis, ion source electronics, and computer codes for extraction, acceleration, and beam transport. Emittance and brilliance are described and space charge effects and neutralization discussed. Various methods for the measurement of current, profile, emittance, and time structure are presented and compared. Intensity limits for these methods are provided for different ion energies. Typical problems related to the operation of ion source plasmas are discussed and practical examples of circuits are given. The influence of high voltage on ion source electronics and possibilities for circuit protection are covered. The generation of microwaves and various microwave equipment are described and special problems related to microwave operation are summarized. The Handbook of Ion Sources is a valuable reference on the subject, of benefit to practitioners and graduate students interested in accelerators, ion implantation, and ion beam techniques.




Electricity in Gases


Book Description

Among the topics covered in this edition are the methods of producing ions in gases, the motion of ions in gases, the velocity of ions in an electric field, and the formation of clouds and the determination of the atomic charge.