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  • 1
    Electronic Resource
    Electronic Resource
    The electron-beam-plasma ion source as source of negative fluorine : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1327-1331 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Radioactive ion beams (RIBs) of short-lived isotopes of fluorine are in demand for investigating astrophysical phenomena related to the hot CNO cycle and rp processes responsible for stellar nucleosynthesis. Since negative ion beams are required for injection into tandem electrostatic accelerators, such as the 25 MV tandem accelerator used for post acceleration of RIBs for the Holifield radioactive ion beam facility research program at the Oak Ridge National Laboratory, efficient, direct-formation F− ion sources are highly desirable. We have conceived and evaluated a direct extraction F− source for potential RIB applications which is predicated on the reverse polarity operation of a positive electron-beam-plasma target/ion source (EBPTIS) while simultaneously feeding fluorine-rich compounds and Cs vapor into the source. The source is found to operate in two separately distinct temperature regimes for the generation of F−: (1) a high cathode temperature regime or plasma mode and (2) a lower cathode temperature regime or surface ionization mode. For the latter mode of operation, net efficiencies of η=0.2% were attained for the EBPTIS; delay times, τ, attributable to the transport of F and fluoride compounds from the target to the ionization chamber of the source, typically, were found to be τ∼60 s. Brief descriptions of the EBPTIS and experimental techniques used in the studies, as well as net efficiency and effusive flow data for the negative EBPTIS, are presented in this article. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148800
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  • 2
    Electronic Resource
    Electronic Resource
    Design aspects of a compact, single-frequency, permanent-magnet electron cyclotron resonance ion source with a large uniformly distributed resonant plasma volume : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1311-1315 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact, all-permanent-magnet, single-frequency electron cyclotron resonance (ECR) ion source with a large uniformly distributed ECR plasma volume has been designed and is presently under construction at the Oak Ridge National Laboratory. The central region of the field is designed to achieve a flat field (constant mod-B) which extends over the length of the central field region along the axis of symmetry and radially outward to form a uniformly distributed ECR plasma "volume." The magnetic field design strongly contrasts with those used in conventional ECR ion sources where the central field regions are approximately parabolic and the resulting ECR zones are "surfaces." The plasma confinement magnetic field mirror has a mirror ratio Bmax/BECR of slightly greater than 2. The source is designed to operate at a nominal rf frequency of 6 GHz. The central flat magnetic field region can be easily adjusted by mechanical means to tune the source to the resonant conditions within the limits of 5.5–6.8 GHz. The rf injection system is broadband to ensure excitation of transverse electric modes so that the rf power is largely concentrated in the resonant plasma volume which lies along and surrounds the axis of symmetry of the source. Because of the much larger ECR zone, the probability for absorption of microwave power is dramatically increased, thereby increasing the probability for acceleration of electrons, the electron temperature of the plasma, and, consequently, the "hot" electron population within the plasma volume of the source. The creation of an ECR "volume" rather than a "surface" is commensurate with higher charge states and higher beam intensities within a particular charge state. The source has also been designed so that it can be easily converted into a conventional magnetic field geometry source so that comparisons of the performances of the "volume" and "surface" forms of the source can be easily made. The design features of the source and rf injection system will be described in detail in this article. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148798
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  • 3
    Electronic Resource
    Electronic Resource
    The electron-beam-plasma ion source as source of negative fluorine : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 773-773 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Radioactive ion beams (RIBs) of short-lived isotopes of fluorine are in demand for investigating astrophysical phenomena related to the hot CNO cycle and rp processes responsible for stellar nucleosynthesis. Since negative ion beams are required for injection into tandem electrostatic accelerators, such as the 25 MV tandem accelerator used for post acceleration of RIBs for the Holifield radioactive ion beam facility research program at the Oak Ridge National Laboratory, efficient, direct-formation F− ion sources are highly desirable. We have conceived and evaluated a direct extraction F− source for potential RIB applications which is predicated on the reverse polarity operation of a positive electron-beam-plasma target/ion source (EBPTIS) while simultaneously feeding fluorine-rich compounds and Cs vapor into the source. The source is found to operate in two separately distinct temperature regimes for the generation of F−: (1) a high cathode temperature regime or plasma mode and (2) a lower cathode temperature regime or surface ionization mode. For the latter mode of operation, net efficiencies of η=0.2% were attained for the EBPTIS; delay times, τ, attributable to the transport of F and fluoride compounds from the target to the ionization chamber of the source, typically, were found to be τ∼60 s. Brief descriptions of the EBPTIS and experimental techniques used in the studies, as well as net efficiency and effusive flow data for the negative EBPTIS, are presented in this article. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148734
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  • 4
    Electronic Resource
    Electronic Resource
    Prototype negative ion sources for radioactive ion beam generation (abstract) : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 775-775 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Radioactive ion beams (RIBs) of 17F and 18F are of interest for investigation of astrophysical phenomena such as the "hot" CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F−, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. We have conceived and evaluated two prototype negative ion sources for potential use for RIB generation: a direct extraction source and a kinetic ejection source. Both sources utilize Cs vapor to enhance F− formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F− and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency η for formation and extraction of F− for the direct extraction negative ion source is found to be η∼1.0%, while the characteristic delay time τ for transport of F and fluorides through the source is typically, η∼120 s; the analogous efficiencies and delay times for the kinetic ejection negative ion source are, respectively: η=∼3.2% and τ=∼70 s. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148736
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  • 5
    Electronic Resource
    Electronic Resource
    Effusive flow delay times for gaseous species in a compact rf ion source (abstract) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1353-1353 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rf ion source is presently being developed and evaluated as a potential candidate for use in generating radioactive ion beams (RIBs) for the experimental research program at the Holifield Radioactive Ion Beam Facility (HRIBF) now under construction at the Oak Ridge National Laboratory. For this application, any time delays that are excessively long with respect to the half-life of the radioactive species of interest can result in significant losses of the RIB intensity; therefore the times for effusive flow through the ion source are of fundamental importance since they set limits on the minimum half-life of radioactive species that can be processed in the source. Complementary experimental and computational techniques have been developed which can be used to determine the characteristic delay times for gaseous species in low-pressure ion source assemblies. These techniques are used to characterize the effusive delay times for the stable counterparts of various atomic and molecular radioactive species in the ORNL-rf source: He, Ne, Ar, Kr, Xe, H2, CO, CO2, N2, N2O, and O2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147245
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  • 6
    Electronic Resource
    Electronic Resource
    Selection of targets and ion sources for radioactive ion beam generation at the Holifield Radioactive Ion Beam Facility (invited) (abstract)a),b) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 934-934 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this report, we 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 as well as prototype ion sources that show promise for future use for radioactive ion beam 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. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146775
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  • 7
    Electronic Resource
    Electronic Resource
    Computational studies for a multiple-frequency electron cyclotron resonance ion source (abstract) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 989-989 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The number density of electrons, the energy (electron temperature), and energy distribution are three of the fundamental properties which govern the performance of electron cyclotron resonance (ECR) ion sources in terms of their capability to produce high charge state ions. The maximum electron energy is affected by several processes including the ability of the plasma to absorb power. In principle, the performances of an ECR ion source can be realized by increasing the physical size of the ECR zone in relation to the total plasma volume. The ECR zones can be increased either in the spatial or frequency domains in any ECR ion source based on B-minimum plasma confinement principles. The former technique requires the design of a carefully tailored magnetic field geometry so that the central region of the plasma volume is a large, uniformly distributed plasma volume which surrounds the axis of symmetry, as proposed in Ref. . Present art forms of the ECR source utilize single frequency microwave power supplies to maintain the plasma discharge; because the magnetic field distribution continually changes in this source design, the ECR zones are relegated to thin "surfaces'' which surround the axis of symmetry. As a consequence of the small ECR zone in relation to the total plasma volume, the probability for stochastic heating of the electrons is quite low, thereby compromising the source performance. This handicap can be overcome by use of broadband, multiple frequency microwave power as evidenced by the enhanced performances of the CAPRICE and AECR ion sources when two frequency microwave power was utilized. We have used particle-in-cell codes to simulate the magnetic field distributions in these sources and to demonstrate the advantages of using multiple, discrete frequencies over single frequencies to power conventional ECR ion sources. The electron heating rates are found to scale directly in proportion to the resonant plasma "volume.'' © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146792
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  • 8
    Electronic Resource
    Electronic Resource
    Design studies for an advanced ECR ion source (abstract)a) : Proceedings of 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1100-1100 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnet design codes, plasma dispersion solvers, and particle-in-cell (PIC) simulation codes have been used to arrive at the first step in the design of an advanced ion source based on ECR technology. The advanced concept design uses a minimum-B magnetic mirror geometry, which consists of a multicusp magnetic field, to assist in confining the plasma radially, a flat central field for tuning to the ECR resonant condition, and specially tailored mirror fields in the end zones to confine the plasma in the axial direction. The magnetic field is designed to achieve an axially symmetric plasma volume with constant mode-B, which extends over the length of the central field region. The design permits separation of the "tune'' and confinement magnetic fields, thus enabling the use of low-frequency, low-cost microwave power sources; the location and increased physical size of the ECR zone over those in conventional sources is commensurate with the generation of higher beam intensities, higher charge states and a higher degree of ionization. A summary of the results of these studies is presented in this report.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145076
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  • 9
    Electronic Resource
    Electronic Resource
    A combined thermal dissociation and electron impact ionization source for radioactive ion beam generation (abstract)a) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1189-1189 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147233
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  • 10
    Electronic Resource
    Electronic Resource
    Design features of a high-intensity, cesium-sputter/plasma-sputter negative ion sourcea) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2006-2011 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A versatile, high-intensity, negative ion source has been designed and is now under construction which can be operated in either the cesium-sputter or plasma-sputter mode. The cesium-sputter mode can be effected by installation of a newly designed conical-geometry cesium-surface ionizer; for operation in the plasma-sputter mode, the surface ionizer is removed and either a hot filament or rf antenna plasma-discharge igniter is installed. A multicusp magnetic field is specifically provided confining the plasma in the radial direction when the plasma-sputter mode is selected. This arrangement allows comparison of the two modes of operation. Brief descriptions of the design features, ion optics, and anticipated performances of the two source geometries will be presented in this report.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144804
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