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Preliminary evaluation of a modified Mueller--Hortig geometry negative ion source using a negative ion source test facility

Description: A negative sputter-type ion source of the Mueller-Hortig geometry is described which utilizes a positive surface ionization source. Among the ion beams which have been produced are: Al-0.2 $mu$A; All0$sup -$-3 $mu$A; Au$sup -$- 6 $mu$A; C$sup -$-25 $mu$A; C$sub 2$$sup -$-20$mu$A; Cl$sup -$-100 $mu$A; Cu$sup - $-0.5 $mu$A; CuO$sup -$-0.8 $mu$A; F$sup -$-40 $mu$A; I$sup -$-26 $mu$A; 0$sup -$- 30 $mu$A; Pt$sup -$-3 $mu$A; S$sup -$-44 $mu$A; TaO$sub 2$$sup -$-2 $mu$A. The yields of Cl$sup -$, F$sup -$, O$sup -$, and S$sup -$ produced from gaseous or high vapor pressure compounds are observed to be sensitively dependent on the metallic surface from which they are generated, indicating an intermediate surface chemical effect. While the source produces very intense beams of the halogens, sulfur, and oxygen and relatively intense beams of the metallic oxides, there appears to be a need for additional surface cesium to ensure maximum negative ion yields from many of the elemental materials. (auth)
Date: January 1, 1975
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

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

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

Single and multiple electron loss processes in MeV heavy ion-target collisions

Description: Experimental data, derived from the study of interactions between MeV heavy ions and gaseous targets are presented which illustrate important physical aspects such as the dependence of cross sections on projectile velocity, and projectile and target atomic numbers. Included are data which reflect the importance of the electron binding energy, the existence of shell effects, the possibility of target polarizability, and the presence of non-additivity and density effects in electron loss processes. Charge state yield versus scattering angle, a prescription for relating total single electron loss cross section per atom atomic and molecular target data and formulas which predict electron loss cross sections with reasonable accuracy are also given.
Date: January 1, 1980
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Emittance characteristics of negative ion beams generated by the sputter technique

Description: Average emittance data for ion beams extracted from cesium-sputter negative ion sources equipped with spherical, ellipsoidal, and cylindrical geometry cesium-surface ionizers are presented. The attributes of the respective source geometries are described in terms of their cesium ion optical properties. The results of recent measurement of the emittances of momentum-analyzed beams extracted from the ellipsoidal geometry source are also presented. These measurements indicate the presence of a species-dependent effect. The effect is believed to be attributable to differences in the energy spreads of the respective negative ion beams introduced by the sputter generation process. 11 refs., 8 figs.
Date: January 1, 1989
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

Theoretical considerations on the performance of negative sputter ion sources

Description: Theoretical analyses of experimentally observed negative ion yield data from cesium rich plasma discharge sources such as those based on the University of Aarhus source concept appear to correlate experiment and theory through surface ionization mechanisms for many species. The agreement between experiment and theory is rather remarkable considering the idealistic model used. A few atomic species appear to overproduce relative to the simple theoretical model. These deviations suggest that still other mechanisms may be important for certain elements such as the affinity level mechanism recently reported.
Date: January 1, 1981
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

The emittance and brightness characteristics of negative ion sources suitable for MeV ion implantation

Description: This paper provides the description and beam properties of ion sources suitable for use with ion implantation devices. Particular emphasis is placed on the emittance and brightness properties of state-of-the-art, high intensity, negative ion sources based on the cesium ion sputter principle. (WRF)
Date: January 1, 1987
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Recent advancements in sputter-type heavy negative ion sources

Description: Significant advancement have been made in sputter-type negative ion sources which utilize direct surface ionization, or a plasma to form the positive ion beam used to effect sputtering of samples containing the material of interest. Typically, such sources can be used to generate usable beam intensities of a few ..mu..A to several mA from all chemically active elements, depending on the particular source and the electron affinity of the element in question. The presentation will include an introduction to the fundamental processes underlying negative ion formation by sputtering from a low work function surface and several sources will be described which reflect the progress made in this technology. 21 refs., 9 figs., 1 tab.
Date: January 1, 1989
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

The sputter generation of negative ion beams: Analytical modeling

Description: The secondary negative ion generation process is examined through the use of energy-dependent analytical models. Non-linear least squares fit parameters for the models are determined from fits to the experimental data of Yu. These models are used to illustrate the effect of work function on the energy distributions of negative ions sputter ejected from a polycrystalline molybdenum surface covered with fractional layers of cesium. Predictions are also made of the functional dependence of the probability for negative ion formation on cesium coverage. 33 refs., 6 figs.
Date: January 1, 1988
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Recent negative ion source developments

Description: This report describes recent results obtained from studies associated with the development of negative ion sources which utilize sputtering in a diffuse cesium plasma as a means of ion beam generation. Data are presented which relate negative ion yield and important operational parameters such as cesium oven temperature and sputter probe voltage from each of the following sources: (1) A source based in principle according to the University of Aarhus design and (2) an axial geometry source. The important design aspects of the sources are given--along with a list of the negative ion intensities observed to date. Also a qualitative description and interpretation of the negative ion generation mechanism in sources which utilize sputtering in the presence of cesium is given.
Date: January 1, 1978
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Design aspects for a pulsed-mode, high intensity, heavy negative ion source

Description: A high-intensity, plasma-sputter, negative ion source, which utilizes multi-cusp, magnetic-field, plasma-confinement techniques, has been designed at the Oak Ridge National Laboratory (ORNL). The source is an axial-geometry version of the radial-geometry source which has demonstrated pulsed-mode peak intensity levels of several mA for a wide spectrum of heavy negative ion species. The mechanical design features include provisions for fast interchange of sputter samples, ease of maintenance, direct cooling of the discharge chamber, and the use of easily replaced coaxial LaB{sub 6} cathodes. 13 refs., 3 figs., 1 tab.
Date: January 1, 1990
Creator: Alton, G.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

Pulsed mode evaluation of an axial geometry cesium sputter negative ion source

Description: An axial geometry negative ion source has been evaluated as a source of pulsed negative ion beams for possible future use of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator as a synchrotron injector. During test stand operation and HHIRF tandem accelerator testing, high-intensity, square wave-form, 100 ..mu..s wide, pulsed beams of Ag/sup -/, Au/sup -/, Cu/sup -/, Ni/sup -/, and O/sup -/ were produced at peak intensity levels ranging between 100 and 350 ..mu..A. The beam intensities were observed to increase approximately linearly with pulsed voltage amplitude over a range of voltages between 400 and 2400 V. In most cases, the pulsed and dc beam components were found to be essentially independent of each other, i.e., the dc component could be adjusted without significantly affecting the pulsed component. Pulsed /sup 16/O/sup -/ beams at peak intensities of 100 ..mu..A were injected into the HHIRF tandem accelerator without observable effects on the operational stability of the accelerator.
Date: January 1, 1985
Creator: Alton, G.D. & Jones, C.M.
Partner: UNT Libraries Government Documents Department

Selection of targets and ion sources for RIB generation at the Holifield Radioactive Ion Beam Facility

Description: In this report, the authors describe the performance characteristics for a selected number of target ion sources that will be employed for initial use at the Holifield Radioactive Ion Beam Facility (HRIBF) as well as prototype ion sources that show promise for future use for RIB applications. A brief review of present efforts to select target materials and to design composite target matrix/heat-sink systems that simultaneously incorporate the short diffusion lengths, high permeabilities, and controllable temperatures required to effect fast and efficient diffusion release of the short-lived species is also given.
Date: December 31, 1995
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Broadband frequency ECR ion source concepts with large resonant plasma volumes

Description: New techniques are proposed for enhancing the performances of ECR ion sources. The techniques are based on the use of high-power, variable-frequency, multiple-discrete-frequency, or broadband microwave radiation, derived from standard TWT technology, to effect large resonant ``volume`` ECR sources. The creation of a large ECR plasma ``volume`` permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge state distributions and much higher intensities within a particular charge state than possible in present forms of the ECR ion source. If successful, these developments could significantly impact future accelerator designs and accelerator-based, heavy-ion-research programs by providing multiply-charged ion beams with the energies and intensities required for nuclear physics research from existing ECR ion sources. The methods described in this article can be used to retrofit any ECR ion source predicated on B-minimum plasma confinement techniques.
Date: December 31, 1995
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Targets for ion sources for RIB generation at the Holifield Radioactive Ion Beam Facility

Description: The Holifield Radioactive Ion Beam Facility (HRIBF), now under construction at the Oak Ridge National Laboratory, is based on the use of the well-known on-line isotope separator (ISOL) technique in which radioactive nuclei are produced by fusion type reactions in selectively chosen target materials by high-energy proton, deuteron, or He ion beams from the Oak Ridge Isochronous Cyclotron (ORIC). Among several major challenges posed by generating and accelerating adequate intensities of radioactive ion beams (RIBs), selection of the most appropriate target material for production of the species of interest is, perhaps, the most difficult. In this report, we briefly review present efforts to select target materials and to design composite target matrix/heat-sink systems that simultaneously incorporate the short diffusion lengths, high permeabilities, and controllable temperatures required to effect maximum diffusion release rates of the short-lived species that can be realized at the temperature limits of specific target materials. We also describe the performance characteristics for a selected number of target ion sources that will be employed for initial use at the HRIBF as well as prototype ion sources that show promise for future use for RIB applications.
Date: December 1995
Creator: Alton, G. D.
Partner: UNT Libraries Government Documents Department

Future prospects for ECR ion sources with improved charge state distributions

Description: Despite the steady advance in the technology of the ECR ion source, present art forms have not yet reached their full potential in terms of charge state and intensity within a particular charge state, in part, because of the narrow band width. single-frequency microwave radiation used to heat the plasma electrons. This article identifies fundamentally important methods which may enhance the performances of ECR ion sources through the use of: (1) a tailored magnetic field configuration (spatial domain) in combination with single-frequency microwave radiation to create a large uniformly distributed ECR ``volume`` or (2) the use of broadband frequency domain techniques (variable-frequency, broad-band frequency, or multiple-discrete-frequency microwave radiation), derived from standard TWT technology, to transform the resonant plasma ``surfaces`` of traditional ECR ion sources into resonant plasma ``volume``. The creation of a large ECR plasma ``volume`` permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, thereby producing higher charge state ions and much higher intensities within a particular charge state than possible in present forms of` the source. The ECR ion source concepts described in this article offer exciting opportunities to significantly advance the-state-of-the-art of ECR technology and as a consequence, open new opportunities in fundamental and applied research and for a variety of industrial applications.
Date: December 31, 1995
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Advanced target concepts for RIB generation

Description: In this report, we describe highly permeable composite target matrices that simultaneously incorporate the short diffusion lengths, high permeabilities, and heat removal properties necessary to effect maximum diffusion release rates of short-lived, radioactive species as required for efficient radioactive ion beam (RIB) generation in nuclear physics and astrophysics research programs. The RIB species are generated by either fusion or fission nuclear reactions between high energy {sup 1}H, {sup 2}H, {sup 3}He or {sup 4}He ion beams and specific nuclei which make up the target material. The target materials may be used directly as small diameter particulates coated or uncoated with Re or Ir to minimize adsorption following diffusion release and eliminate sintering of the particulates at elevated temperatures; plated onto both sides of thin disks of C, for example; or plated, in thin layers, onto low density, Ir or Re coated carbon-bonded-carbon-fiber (CBCF) or reticulated-carbon-fiber (RCF) to form sponge-like composite target matrices; or in other cases, where applicable, the target material of interest can be grown in crystalline fibrous form and fabricated in woven mats of the target material to form a highly permeable fibrous structure.
Date: December 1, 1996
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

High-Efficiency Target-Ion sources for RIB Generation

Description: In this report, emphasis is placed on issues related to selection and design of high-temperature, ion sources that have demonstrated the high ionization efficiency, species versatility, and operational reliability required at ISOL based radioactive ion beam facilities. In designing sources for ISOL applications, careful attention must be given to the following: selecting the most appropriate materials of construction, coupling of the vapor transport system, ion optics, operational parameters, thermal transport properties, emittances, ionization efficiencies and engineering details for safe handling in the high-level radioactivity radiation fields incumbent at such facilities. Included in the article are descriptions and performance data for high temperature, positive (electron-impact and surface-ionization) and negative (kinetic-ejection and surface-ionization) ion sources, as well as, low temperature, batch-mode negative-ion sources, developed for processing long-lived isotopes, that have been principal contributors to recent successes held at the Holifield Radioactive Ion Beam Facility.
Date: June 29, 2001
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Design aspects for a pulsed-mode, high-intensity, heavy negative ion source

Description: A high-intensity, plasma-sputter, negative ion source, which utilizes multi-cusp, magnetic-field, plasma-confinement techniques, has been designed at the Oak Ridge National Laboratory (ORNL). The source is an axial-geometry version of the radial-geometry source which has demonstrated pulsed-mode peak intensity levels of several mA for a wide spectrum of heavy negative ion species. The mechanical design features include provisions for fast interchange of sputter samples, ease of maintenance, direct cooling of the discharge chamber, and the use of easily replaced coaxial LaB{sub 6} cathodes. 12 refs.
Date: January 1, 1991
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Negative ion sources equipped with continuous annular and spherical geometry surface ionizers

Description: Axial geometry negative ion sources have been designed, developed, and evaluated for use in conjunction with tandem accelerator applications. These sources utilize continuous surface solid tungsten ionizers in either annular or spherical geometries to effect ionization of cesium vapor, which in turn is used to sputter a negatively biased probe containing the material of interest. The annular ionizer geometry source has been incorporated as an ''on-line'' source for routine operation of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator. Both test stand and tandem accelerator operational experience indicate that such sources are reliable, long lived, stably operating and prolific producers of a wide spectrum of negative ions. To date these sources have been used to produce more than 18 negative ion species including Ag/sup -/, Au/sup -/, B/sup -/, CaH/sub 3//sup -/, Cl/sup -/, CrH/sub 2//sup -/, Cu/sup -/, Lu/sup -/, MgH/sub 3//sup -/, Mo/sup -/, Ni/sup -/, O/sup -/, S/sup -/, Si/sup -/, Sn/sup -/, TiH/sub 3//sup -/, Tm/sup -/, and Yb/sup -/. Details of the mechanical design features and computational techniques utilized in arriving at the final electrode configuration are presented in the text. Examples of data pertinent to source operation, the dependence of negative ion yields on certain source operational parameters and of intensities typical of a particular negative ion source are also given. 12 refs., 10 figs.
Date: January 1, 1985
Creator: Alton, G.D. & Mills, G.D.
Partner: UNT Libraries Government Documents Department

The emittances and brightnesses of high-intensity negative ion sources

Description: The emittances of high-intensity ion beams extracted from cesium sputter negative ion sources equipped with cylindrical and ellipsoidal solid tungsten and spiral-wound tantalum (General Ionex Corporation, Model 860), and cesium surface ionizers have been measured for several ion species, including /sup 12/C/sup -/, /sup 28/Si/sup -/, /sup 58/Ni/sup -/, and /sup 197/Au/sup -/. While certain sets of data from the ellipsoidal and cylindrical geometry ionizer sources suggest a moderate growth in emittance with increasing negative ion beam intensity I over the range of intensities investigated (5 less than or equal to 1 less than or equal to 60 ..mu..A) of perhaps 20%, not all data exhibit this dependence, especially those from the Model 860 source. As well, no evidence of an emittance dependence on ion mass of a monotonic nature was found. The emittances of ion beams at the 80% intensity level from the Model 860 source are found to be higher on the average by factors of 1.8 and 1.7, respectively, than those from sources equipped with ellipsoidal and cylindrical geometry cesium surface ionizers.
Date: January 1, 1987
Creator: Alton, G.D. & McConnell, J.W.
Partner: UNT Libraries Government Documents Department