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  • 1
    Electronic Resource
    Electronic Resource
    Status of the Oak Ridge 25 URC Accelerator (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 721-722 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Beam from the accelerator for research was available for a total period of 3900 h last year and unscheduled maintenance time was reduced by a factor of almost 2. An arc discharge tube conditioning test was conducted on the top five units of the accelerator and a test with macropulsed beam was accomplished. The main problems during the year were vacuum leaks and voltage "tics.''
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138896
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of a cesium surface ionization source with a porous tungsten ionizer. I (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1039-1044 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A cesium surface ionization source of the type and geometry customarily used in conjunction with sputter-type negative heavy ion sources has been characterized. Measurements have been made of positive-ion production and probabilities of ionization as functions of extraction voltage and cesium oven temperature for ionizer porosities of 0.7 and 0.8. The perveance P of the source, when operated in the space-charge-limited regime with the ρ=0.7ρ0 ionizer, is found from experiment to be 7.61×10−4 μP, while that for the ρ=0.8ρ0 ionizer is 1.92×10−4 μP. These values are lower by factors of 3.88 and 15.53, respectively, than those predicted by numerical solution to Poisson's equation for full area emission from the source. Positive-ion current versus ionizer temperature data are also presented along with mechanical design features of the source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139776
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  • 3
    Electronic Resource
    Electronic Resource
    Aspects of negative-ion generation and extraction from a refocus geometry cesium sputter negative-ion source. II (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1045-1052 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The basic parameters of the refocus geometry cesium sputter ion source for the production of negative ions from a low-sputtering material (carbon) and a high-sputtering material (copper) have been measured. The question of the influence of sample temperature on the negative-ion generation process has been addressed. Negative-ion yields from carbon samples are found to be weakly dependent on temperature over a range from 26° to 400 °C, while those from copper samples are found to be essentially independent of temperature over a range of 26° to 200 °C. The results of these investigations indicate that (1) sample temperature does not strongly influence negative formation in these sources, and (2) the maximum negative-ion yields for a given sample are dependent on both cesium-ion energy and positive-ion current. In addition to these data, the negative-ion extraction optics of the source are briefly discussed and cursory estimates of the probabilities for negative-ion formation presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139777
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  • 4
    Electronic Resource
    Electronic Resource
    Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2305-2312 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. 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 higher intensities within a particular charge state than possible in present forms of the ECR source. The ECR plasma "volumes" of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete-frequency, variable frequency, or broad-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance the performance of a traditional B-minimum ECR ion source, comparative studies were made to assess the relative performances of the Oak Ridge National Laboratory Caprice ECR ion source, in terms of multiply charged ion-beam generation capabilities, when excited with high-power, single-frequency, or multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. These studies demonstrate that the charge-state populations for Ar q+ and Xeq+ move toward higher values when excited with two and three discrete-frequency, microwave power compared to those observed when single-frequency microwave power is used. For example, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge states higher than the most probable are increased by factors of ∼3 compared to those observed for single-frequency plasma excitation. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this report. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148936
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Use of multiple-discrete-frequency microwave radiation to enhance the performances of traditional B-minimum electron cyclotron resonance ion sources : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 652-652 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge-state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The ECR plasma "volumes" of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete frequency, variable frequency, or broad-bandwidth frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). In this work, comparisons were made of the charge-state distributions of Arq+ and Xeq+ extracted from the ORNL Caprice ECR ion source, when excited with single frequency and multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. The charge-state populations for Arq+ and Xeq+ move toward higher values when excited with modest power from two and three discrete frequency, microwave radiation compared to those generated with power from single-frequency radiation. For three-frequency plasma excitation, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge-states higher than the most probable are increased by factors of ∼3 over those for the single frequency plasma case. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this article. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148727
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    A combined thermal dissociation and electron impact ionization source for radioactive ion beam generationa) (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1626-1629 
    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/10.1063/1.1146903
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  • 10
    Electronic Resource
    Electronic Resource
    A high-efficiency positive (negative) surface ionization source for radioactive ion beama) (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1630-1633 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed and fabricated which will have the capability of generating both positive- and negative-ion beams without mechanical changes to the source. The source utilizes a highly permeable, high-work-function Ir ionizer (φ≡5.29 eV) for ionizing highly electropositive atoms/molecules; while for negative-surface ionization, the work function is lowered to φ≡1.43 eV by continually feeding cesium vapor through the ionizer matrix. The use of this technique for negative ion beam generation has the potential of overcoming the chronic poisoning effects experienced with LaB6 while enhancing considerably the efficiency for negative surface ionization of atoms and molecules with intermediate electron affinities. The flexibility of operation in either mode makes it especially attractive for radioactive ion beam applications and, therefore, the source will be used as a complementary replacement for the high-temperature electron impact ionization sources presently in use at the Holifield radioactive beam facility. The design features and operational principles of the source will be described in this report. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146905
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