17 Matching Results

Search Results

Advanced search parameters have been applied.

Ionization phenomena and sources of negative ions

Description: Negative ion source technology has rapidly advanced during the past several years as a direct consequence of the discovery of Krohn that negative ion yields can be greatly enhanced by sputtering in the presence of Group IA elements. Today, most negative ion sources use this discovery directly or the principles implied to effect negative ion formation through surface ionization. As a consequence, the more traditional direct extraction plasma and charge exchange sources are being used less frequently. However, the charge exchange generation mechanism appears to be as universal, is very competitive in terms of efficiency and has the advantage in terms of metastable ion formation. In this review, an attempt has been made to briefly describe the principal processes involved in negative ion formation and sources which are representative of a particular principle. The reader is referred to the literature for specific details concerning the operational characteristics, emittances, brightnesses, species and intensity capabilities of particular sources. 100 references.
Date: January 1, 1983
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

On the current intensity limit of a vacuum arc ion source

Description: The maximum ion current that can be produced as a high energy beam from a metal vapor vacuum arc ion source is considered. Results are presented of measurements of the plasma ion current in the MEVVA II ion source. It is shown that this source is an efficient generator of metal ions, an intense flux of which is efficiently transported to the beam extractor. The maximum metal ion current that is available for extraction at the extractor location is 5% of the arc current. The limitation to the intensity of the metal ion beam that can be produced by this kind of ion source is in the extractor design. 27 refs., 6 figs.
Date: March 1, 1987
Creator: Brown, I.G.
Partner: UNT Libraries Government Documents Department

MEVVA ion source for high current metal ion implantation

Description: The MEVVA (Metal Vapor Vacuum Arc) ion source is a new kind of source which can produce high current beams of metal ions. Beams of a wide range of elements have been produced, spanning the periodic table from lithium up to and including uranium. The source extraction voltage is up to 60 kV, and we are increasing this up to 120 kV. A total ion beam current of over 1 Ampere has been extracted from the present embodiment of the concept, and this is not an inherent limit. The ion charge state distribution varies with cathode material and arc current, and beams like Li/sup +/, Co/sup +,2+,3+/ and U/sup 3+,4+,5+,6+/ for example, are typical; thus the implantation energy can be up to several hundred kilovolts without additional acceleration. The ion source has potential applications for ion implantation and ion beam mixing for achievement of improved corrosion resistance or wear resistance in metals or surface modification of ceramic materials and semiconductors. Here we outline the source and its performance, and describe some very preliminary implantation work using this source.
Date: July 1, 1986
Creator: Brown, I. & Washburn, J.
Partner: UNT Libraries Government Documents Department

Development of a lithium liquid metal ion source for MeV ion beam analysis

Description: Lithium liquid metal ion sources are an attractive complement to the existing gaseous ion sources that are extensively used for ion beam analysis. This is due in part to the high brightness of the liquid metal ion source and in part to the availability of a lithium ion beam. High brightness is of particular importance to MeV ion microprobes which are now approaching current density limitations on targets determined by the ion source. The availability of a lithium beam provides increased capabilities for hydrogen profiling and high resolution Rutherford backscattering spectrometry. This paper describes the design and performance of a lithium liquid metal ion source suitable for use on a 5MV Laddertron accelerator. Operational experience with the source and some of its uses for ion beam analysis are discussed. 8 refs., 2 figs.
Date: January 1, 1988
Creator: Read, P.M.; Maskrey, J.T. & Alton, G.D.
Partner: UNT Libraries Government Documents Department

Electronic excitation and ion source optimization

Description: The electronic excitation cross sections leading to H/sub 2/(v'') molecules are discussed. The effect of shortening the length of the first chamber of a tandem configuration for the purpose of reducing the atomic concentration is shown to enhance the extracted current density.
Date: June 29, 1987
Creator: Hiskes, J.R. & Lietzke, A.F.
Partner: UNT Libraries Government Documents Department

Aspects of the physics, chemistry, and technology of high intensity heavy ion sources

Description: Particular emphasis is placed on the technology of plasma discharge ion sources which utilize solid elemental or molecular compounds to produce vapor for the ionization process. A brief discussion is made of the elementary concepts underlying the formation and extraction of ion beams from plasma discharge sources. A limited review of low charge state positive ion sources suitable for accelerator use is also given.
Date: January 1, 1980
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Recent advancements in high intensity heavy negative ion sources based on the sputter principle

Description: Significant advancements have been recently made in the technology of forming high intensity heavy negative ion beams. Due to their ease of operation, simplicity, long lifetime, and wide range of species capabilities, negative ion sources predicated on the sputter principle are being used for an increasing number of diverse applications, including standard tandem accelerator-based research, high-energy ion implantation, tandem accelerator mass spectrometry, and low-energy atomic physics research. Sources have been developed which utilize either direct surface ionization, or a plasma to form the positive ion beam used to effect sputtering of samples containing the material of interest. This article will include a brief review of the fundamental processes underlying negative ion formation in these sources. Emphasis will be placed on the descriptions and performance characteristics of specific sources based on each of the positive ion formation techniques. 21 refs., 16 figs., 1 tab.
Date: January 1, 1989
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

An improved time-of-flight ion charge state diagnostic

Description: A time-of-flight diagnostic for analysis of relatively low energy ion beams is described. The system incorporates several novel features which improve its performance in a number of ways. The technique is simple and can provide an alternative to magnetic analysis of ion beams for the determination of ion charge state and beam composition.
Date: March 1, 1987
Creator: Brown, I.G.; Galvin, J.E.; MacGill, R.A. & Wright, R.T.
Partner: UNT Libraries Government Documents Department

Dual arc penning ion source gas flow experiments

Description: Support gas, when added directly to an arc or admitted to an auxiliary chamber of a two-arc chamber ion source, increases the beam intensity for multicharged ions such as /sup 16/O/sup 5 +/. To clarify the mechanism of this intensity increase, gas flow rates from the auxiliary chamber to the main chamber have been measured by using the ORIC cyclotron as a mass spectrometer. The results show that only about three percent of the gas admitted to the auxiliary chamber reaches the main chamber. One can then infer that the improved operation probably results from the stabilizing effect of heating the common cathodes with the auxiliary arc and/or the more favorable distribution of the support gas to the part of the main arc close to the cathodes.
Date: January 1, 1984
Creator: Hudson, E.D.; Lord, R.S.; Mallory, M.L. & Antaya, T.A.
Partner: UNT Libraries Government Documents Department

Comparison of convoy electron production in ion-atom and ion-solid collisions

Description: We begin with an overview for the benefit of participants lacking acquaintance with the subject of convoy-electron production, and continue with highlights of developments occurring since a review and a comprehensive article published in 1982. A sharp cusp in the velocity spectrum of electrons, ejected in ion-atom and ion-solid collisions, is observed when the ejected electron velocity vector v/sub e/ matches that of the emergent ion vector v in both speed and direction. In ion-atom collisions, the electrons primarily originate from capture to low-lying projectile-centered continuum states (ECC) for fast bare or nearly bare projectiles, and primarily from loss to low-lying continuum states (ELC) when loosely bound projectile electrons are available. Most investigators now agree that ECC cusps are strongly skewed toward lower velocities and exhibit full widths half maxima roughly proportional to v (neglecting sometimes strong shell effects). Convoy cusps produced in heavy ion-solid collisions at MeV/u energies are slightly skewed toward high electron velocities, but exhibit velocity-independent widths, very similar to ELC cusp widths. While the shape of the convoy peaks is approximately independent of projectile Z, velocity, and target, dependence on projectile Z as Z/sup 2/ /sup 7/ and energy as E/sup -2/ /sup 2/. Attempts have been made to link convoy electron production to binary ECC or ELC processes, sometimes at the last layer, or alternatively to a solid-state wake-riding model, but our measured dependences of cusp shape and yield on heavy projectile charge state q and energy are inconsistent with available theories. These wake-riding theories seek to explain the origin of convoy electrons in terms of electrons trapped into an oscillatory electron density polarization potential trailing each projectile, which are then liberated at the surface.
Date: January 1, 1983
Creator: Sellin, I.A.; Breinig, M.; Elston, S.B. & Berry, S.D.
Partner: UNT Libraries Government Documents Department

Li/Li/sub 2/ supersonic nozzle beam

Description: The characterization of a lithium supersonic nozzle beam was made using spectroscopic techniques. It is found that at a stagnation pressure of 5.3 kPa (40 torr) and a nozzle throat diameter of 0.4 mm the ground state vibrational population of Li/sub 2/ can be described by a Boltzmann distribution with T/sub v/ = 195 +- 30/sup 0/K. The rotational temperature is found to be T/sub r/ = 70 +- 20/sup 0/K by band shape analysis. Measurements by quadrupole mass spectrometer indicates that approximately 10 mole per cent Li/sub 2/ dimers are formed at an oven body temperature of 1370/sup 0/K n the supersonic nozzle expansion. This measured mole fraction is in good agreement with the existing dimerization theory.
Date: January 1, 1977
Creator: Wu, C.Y.R.; Crooks, J.B.; Yang, S.C.; Way, K.R. & Stwalley, W.C.
Partner: UNT Libraries Government Documents Department

Indirect mechanisms in electron-impact ionization of multiply charged ions

Description: The important role of indirect-ionization mechanisms in electron-impact ionization of multiply charged ions has been emphasized by some recent experiments conducted with the ORNL-ECR multicharged ion source. Illustrative examples of investigations of the Mg-isoelectronic and Fe-isonuclear sequences are presented and compared with the results of detailed theoretical calculations. New experimental data is also presented concerning the role of resonance effects in the ionization of Li-like O/sup 5 +/ and Na-like Fe/sup 15 +/ ions.
Date: September 1, 1986
Creator: Phaneuf, R.A. & Gregory, D.C.
Partner: UNT Libraries Government Documents Department

Design and operation of the electron beam ion trap

Description: This report describes the basic features and operating principles of the Electron Beam Ion Trap. The differences between EBIT and other sources of highly charged ions are outlined. Its features and operating parameters are discussed. The report also explains why certain design choices were necessary and the constraints involved in building an electron beam ion trap. EBIT's evaporation cooling system is described in detail. 13 refs., 8 figs.
Date: May 30, 1990
Creator: Vogel, D.
Partner: UNT Libraries Government Documents Department

Negative ion formation processes: A general review

Description: The principal negative ion formation processes will be briefly reviewed. Primary emphasis will be placed on the more efficient and universal processes of charge transfer and secondary ion formation through non-thermodynamic surface ionization. 86 refs., 20 figs.
Date: January 1, 1990
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Generation of vibrationally excited H/sub 2/ molecules by H/sub 2//sup +/ wall collisions

Description: The H/sub 2//sup +/ ions from the volume of a hydrogen discharge will strike the discharge chamber walls with a kinetic energy equivalent to the plasma potential. A three-step process is described in which the H/sub 2//sup +/ ions are neutralized in a two-stage Auger process followed by a third stage wall relaxation collision, with the net result that the incident ions are converted to ground state molecules having a broad vibrational excitation spectrum. For kinetic energies ranging from a few electron volts up to twenty electron volts a substantial fraction, approx. = 2/3, of these ions will reflect as molecules, and of this population a fraction as large as twenty percent will have vibrational excitation of v'' greater than or equal to 6. This large vibrational population will provide a contribution to the total excited level distribution that is comparable to the E-V process. Implications for negative ion generation in an optimized tandem configuration are discussed.
Date: November 11, 1983
Creator: Hiskes, J.R. & Karo, A.M.
Partner: UNT Libraries Government Documents Department

Development of high current low energy H/sup +/ ion source

Description: The ultimate goal of this work is the development of an ion source suitable for double charge exchange of D/sup +/ ions to D/sup -/ ions in cesium or other vapor. Since the fraction of the D/sup +/ which changes to D/sup -/ may be as high as 0.35 in the energy below one keV, the process appears very favorable. What is desired is a source of several hundred cm/sup 2/ area, with a D/sup +/ current density greater than, say 0.2A/cm/sup 2/. Small angular spread is essential with up to about 0.1 radian being acceptable. A simple approach to this problem appears to be through fine mesh extraction electrodes. In this system a single grid facing the ion source plasma constitutes the entire extraction electrode system. If the potential difference between the grid and the source plasma is large compared to the ion energy at the plasma boundary, then the distance s/sub 0/ is just the Child-Langmuir distance corresponding to the ion current density J and the potential difference V/sub 0/ between the plasma and the grid.
Date: January 1, 1978
Creator: Forrester, A.T.; Crow, J.T. & Goebel, D.M.
Partner: UNT Libraries Government Documents Department