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ABSTRACT: The lifefimes of the (2p)2P3/2 level in Si XII and the (2p2)3P2,1,0, (2s2p)1P1 and the (2p2)1D2 levels in Si XI have been determined using the beam-foil method. It is proposed that existing discrepancies between experimental and theoretical f values for the (2s2)1S0-(2s2p)1P1 transition in some ions of the Be sequence may be the result of the inability of the experimentalist to account for strong cascading from the (2p2)1S0 level.
Physica Scripta 01/2007; 18(1):18. · 1.20 Impact Factor
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ABSTRACT: As clearly demonstrated at several laboratories, the performances of electron-cyclotron resonance (ECR) ion sources can be enhanced by increasing the physical sizes (volumes) of embedded ECR zones. En-larged ECR zones have been achieved by engineering the central magnetic field region of these sources so they are uniformly-distributed "volumes" in resonance with single-frequency rf power. Alternatively, the number of ECR surfaces in conventional minimum-B geometry sources can be increased by heating their plasmas with multiple, discrete frequency microwave radiation. Broadband rf power offers a simple, low cost and arguably more effective means for increasing the physical sizes of the ECR zones within the latter source type. In this article, theoretical arguments are made in support of the volume effect and the charge-state enhancing ef-fects of broadband microwave radiation (bandwidth: 200MHz) plasma heating are demonstrated by comparing the high-charge-states of Ar ion beams, produced by powering a conventional minimum-B geometry, 6.4GHz ECR ion source, equipped with a biased disk, with those produced by conventional bandwidth (bandwidth: ∼1.5MHz) radiation.
HIGH ENERGY PHYSICS AND NUCLEAR PHYSICS Supp. Jul. 01/2007; 31.
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ABSTRACT: In order to generate useful intensities of short-lived radioactive species at Isotope Separator On-Line (ISOL) based research facilities, species of interest must be diffused from the interior of the production target-material, effusively transported to an ion source, ionized, extracted, mass-analyzed, and accelerated to research energies in times commensurate with their lifetimes. The intensities at such facilities are principally limited by decay losses associated with times required for diffusion-release from target materials and transport from the target to the ion source and by the maximum permissible primary beam power depositional density that can be tolerated without deleteriously affecting target integrity or ion source efficiency. Consequently, it is imperative to minimize delay times associated with the independent diffusion and effusive-flow processes by choosing small dimensioned (short-diffusion length) highly refractory target materials and formatting them in highly permeable mechanically and thermally robust structures that can withstand high-power beam irradiation for extended periods of time. This article provides basic information on methods, procedures and principles for selecting target materials; for designing fast diffusion-release targets; for designing fast effusive-flow vapor transport systems; and introduces methods for controlling target temperatures as required for optimizing intensities of short-lived radioactive ion beams at ISOL based research facilities.
Applied Radiation and Isotopes 01/2007; 64(12):1574-603. · 1.17 Impact Factor
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ABSTRACT: A new ECR ion source geometry has been conceived which uses a minimum-B magnetic mirror geometry consisting of a multi-cusp, 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 for confining the plasma in the axial direction. The magnetic field, designed to achieve an axially symmetric plasma "volume" with constant mod-B, extends over the length of the central field region. This design, which strongly contrasts with "surface" ECR zones characteristic of conventional ECR ion sources, results in dramatic increases in the adsorption of RF power, thereby increasing the electron temperature and "hot" electron population within the ionization volume of the source. The ECR zone is concentrated symmetrically around the axis of symmetry and along the length of the plasma volume rather than in thin surface layers located off-axis as is the case in conventional ECR ion sources. The creation of a "volume" rather than a "surface" ECR zone and its distribution relative to the optical axis where the ions of interest are extracted is commensurate with the generation of higher beam intensities, higher charge states and a higher degree of ionization. The new ECR ion source concept has been computationally designed through the use of magnet design codes, plasma-dispersion sources, and particle-in-cell (PIC) codes. A summary of the design attributes of the source is given in this report.
Physica Scripta 12/2006; 1997(T71):66. · 1.20 Impact Factor
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ABSTRACT: In this report, high-temperature ion sources are described, which have demonstrated the high ionization efficiency, species versatility, and operational reliability required at isotope-separator-online (ISOL) based radioactive ion beam facilities such as the Holifield Radioactive Ion Beam Facility (HRIBF). Specific attention is given to the ion optics, operational parameters, thermal transport properties, emittances, and ionization efficiencies of the HRIBF ion sources that have been carefully designed for safe handling in the high-level 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 the principal contributors to recent successes held at the Holifield Radioactive Ion Beam Facility.
Review of Scientific Instruments 04/2006; 77(3):03A711-03A711-5. · 1.37 Impact Factor
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ABSTRACT: The performances of electron cyclotron resonance ion sources can be enhanced by increasing the physical sizes or numbers of resonant zones embedded within their plasma volumes. Broadband rf power offers a simple, cost effective alternative for increasing the sizes of electron cyclotron resonance (ECR) zones in conventional minimum-B geometry sources over independently powered narrow bandwidth, multiple discrete frequency schemes. In this report, the charge-state enhancing effects of broadband microwave radiation are first demonstrated by comparing the high charge states of Ar ion beams produced by powering a conventional minimum-B geometry, 6.4 GHz ECR ion source with broadband microwave radiation {200 MHz [full width at half maximum (FWHM)]} with those produced by conventional bandwidth [ ∼ 1.5 MHz (FWHM)] radiation. The results of these studies show that high-charge-state beams (e.g., Ar11+) can be enhanced by factors >2 with broadband microwave radiation over those powered with narrow bandwidth radiation at the same power level, with or without voltage applied to the biased disk. The high charge states exhibit an anomalously strong increase in intensity at an optimum pressure with broadband microwave radiation.
Review of Scientific Instruments 03/2006; 77(3):03A331-03A331-3. · 1.37 Impact Factor
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ABSTRACT: Simulation studies with computer models offer cost effective methods for designing targets and vapor transport systems at Isotope Separator On-Line (ISOL)-based radioactive ion beam facilities. A finite difference code, Diffuse II, was developed at the Oak Ridge National Laboratory (ORNL) for studying diffusion-release of short-lived ion species from the three principal target geometries; results derived by use of the code are in close agreement with analytical solutions to Fick’s second equation. A Monte-Carlo code, Effusion, was developed to address issues related to the design of fast vapor transport systems. Results, derived by the use of Effusion closely agree with experimental measurements. These codes and their applications are discussed in this article
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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ABSTRACT: Broadband rf injection offers a low-cost and effective method for increasing the physical sizes of ECR zones within ECR ion sources. Broadband radiation can also be used to ameliorate diamagnetic frequency detune effects that are believed to be problematical in single-frequency plateau ECR sources. An additive white Gaussian noise generator (AWGNG) system for injecting broadband rf power into these sources has been developed in conjunction with a commercial firm. The noise generator, in combination with an external local oscillator and a traveling wave tube amplifier (TWTA), can be used to generate broadband microwave power for ECR ion sources without requirements of modifying the injection system of these sources. The AWGNG and its initial use for powering the all permanent magnet, ORNL plateau ECR ion source will be described in this document.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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ABSTRACT: Worldwide interest in the use of accelerated radioactive ion beams (RIBs) for exploring reactions important in understanding the structure of the nucleus and nuclear astrophysical phenomena has motivated the construction of facilities dedicated to their production and acceleration. Many facilities utilize the isotope-separator-on-line (ISOL) method in which species of interest are generated within a solid or liquid target matrix. Experimentally useful RIBs are often difficult to generate by this technique because of the times required for diffusion from the interior of the target material, and to effusively transport the species of interest to the ion source following diffusion release in relation to its lifetime. Therefore, these delay times must be minimized. We have developed an experimental method that can be used to determine effusive-flow times of arbitrary geometry target/vapor transport systems. The technique utilizes a fast valve to measure effusive-flow times as short as 0.1 ms for any chemically active or inactive species through any target system, independent of size, geometry and materials of construction. In this report, we provide a theoretical basis for effusive flow through arbitrary geometry vapor transport systems, describe a universal experimental apparatus for measuring effusive-flow times, and provide time spectra for noble gases through prototype RIB target/vapor-transport systems. © 2004 American Institute of Physics.
Review of Scientific Instruments 05/2004; 75(5):1613-1613. · 1.37 Impact Factor
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ABSTRACT: An all-permanent-magnet, 6 GHz “volume-type,” flat central-field concept ECR ion source has been constructed and initially evaluated at the Holifield Radioactive Ion Beam Facility, Oak Ridge National Laboratory. The source is designed so that it can be easily converted from a flat-B configuration to the traditional minimum-B configuration and vice versa, so that comparisons can be made of the performances of the source in the “volume” ECR and “surface” ECR modes of operation under the same conditions. Descriptions of the source, the experimental equipment, and the procedures for evaluation are given, and comparisons of the performances of both volume and surface modes of operation are presented with and without gas mixing. The present studies clearly show that the volume ECR configuration is superior to the surface configuration in terms of charge-state distribution and intensity within a particular charge state, under the same operating conditions. © 2004 American Institute of Physics.
Review of Scientific Instruments 05/2004; 75(5):1436-1436. · 1.37 Impact Factor
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ABSTRACT: A multi‐sample Cs‐sputter negative ion source has been evaluated for generating 7BeO− beams for measuring the nuclear‐astrophysically important 7Be(p,γ)8B reaction at the Holifield Radioactive Ion Beam Facility. The design features and operational parameters of the source are described and measured efficiencies for forming beams of Ni−, C− and MgO− and estimated efficiencies for generating beams of BeO− for the proposed experiment are presented in this report. © 2003 American Institute of Physics
AIP Conference Proceedings. 08/2003; 680(1):1017-1021.
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ABSTRACT: An axial injection system has been designed for injection of high intensity beams of H<sup>-</sup>, D<sup>-</sup>, and He<sup>++</sup> into the Oak Ridge Isochronous Cyclotron (ORIC). The device consists of two high-voltage platforms, two external ion sources, a double-drift-tube beam bunching system, a spiral inflector and integrated beam analysis diagnostics and focusing elements. With the axial injection system, it is expected that more than 100 μA of high quality, primary light ion beams will be extracted from the ORIC using either the existing septum extraction system for He<sup>++</sup> beams or a foil stripping extraction system for extracting either H<sup>+</sup> or D<sup>+</sup> beams. In addition, beam scattering and the consequent internal activation problems, endemic with the present short lifetime internal Penning discharge source along with the down times attributable to its maintenance will be dramatically reduced.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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ABSTRACT: The results of numerical studies of the electric field distributions in a spiral inflector, designed for axial injection system of H<sup>-</sup>, D<sup>-</sup> and He<sup>++</sup> beams into the Oak Ridge Isochronous Cyclotron (ORIC), are presented in this report. Discrepancies are found between the electric fields obtained from numerical computations and those derived from theoretical field distributions within the inflector. Fringe fields at the entrance to the inflector, in combination with the field discrepancies, lead to significant deviations in particle trajectories from those derived from analytical expressions for fields within such devices. A method is described for shaping the electrode surfaces of the spiral inflector that is effective in compensating for fringe fields at the entrance to the inflector and a simple solution is introduced that eliminates the seemingly unavoidable shift in the central beam path. As a consequence of these studies, we arrive at a design for a spiral inflector that operates at a low voltage with greatly improved optical properties in which the paths of injected particles are precisely known.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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ABSTRACT: An all-permanent-magnet, 6-GHz "volume-type" ECR ion source has been constructed and evaluated. This source employs a novel magnetic field configuration with an extended central flat region to form a large, on-axis, ECR volume. It can also be converted to a traditional minimum-5 source where the ECR zones are surfaces. Comparisons are made of the performance of the source when operated in both "volume" and "surface" modes. According to the preliminary results, the "volume" mode is superior in terms of ion beam intensities and charge-state distributions.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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ABSTRACT: Studies have been conducted to determine the feasibility of using the collisional cooling technique as a means of reducing energy spreads and emittances of sputter-generated negative-ion beams. A gas-filled rf-quadrupole ion cooler, equipped with provisions for decelerating ion beams to sufficiently low energies prior to cooling and reaccelerating them to high energies following the cooling process, has been designed and used to cool O− and F− ion beams with initial energy spreads, ΔE>10 eV to final energy spreads, ΔE ∼ 2 eV full width half-maximum. Overall transmission efficiencies of ∼14% for F− beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions. © 2002 American Institute of Physics.
Review of Scientific Instruments 01/2002; 73(2):800-802. · 1.37 Impact Factor
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G.D. Alton
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ABSTRACT: 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
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: This paper describes a low-charge-state heavy-ion post-accelerator
system for upgrading the Holifield Radioactive Ion Beam Facility. It is
comprised of a room temperature 12.5-MHz RFQ, followed by a normal
conducting IH linac, a SC IH linac and a SC QWR linac booster. The
system is designed to accelerate ions with mass-to-charge ratio up to
140. The system can be used to accelerate beams directly (bypass the
25-MV tandem) or to post-accelerate beams from the tandem accelerator.
By use of stripping between acceleration stages, low-charge-state
radioactive ion beams of all elements, including uranium, can be
accelerated to energies above the Coulomb barrier
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: This article describes a high-charge-state linear post accelerator
for enhancing the number and intensities of short-lived radioactive
nuclei at the Holifield Radioactive Ion Beam facility (HRIBF). The
system consists of a room temperature RFQ, a normal conducting IH linac
and a SC QWR linac that is designed to either bypass or post accelerate
beams from the 25-MV tandem. The voltage gain of the linac system will
reach 60 MV making possible the acceleration of ions with masses,
M⩽150, above the Coulomb barrier. Since the linac accelerates
positive-ion beams, it will increase the number of elements that can be
delivered for research by a factor of ~3 and the intensity of a given
species by orders of magnitude over those of the present HRIBF
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: In this article, thermal modeling techniques are used to simulate
ISOL targets irradiated with high power proton beams. Beam scattering
effects, nuclear reactions and beam power deposition distributions in
the target were computed with the Monte Carlo simulation code, GEANT4.
The power density information was subsequently used as input to the
finite element thermal analysis code, ANSYS, for extracting temperature
distribution information for a variety of target materials. The
principal objective of the studies was to evaluate techniques for more
uniformly distributing beam deposited heat over the volumes of targets
to levels compatible with their irradiation with the highest practical
primary-beam power, and to use the preferred technique to design high
power ISOL targets. The results suggest that radiation cooling, in
combination, with primary beam manipulation, can be used to control
temperatures in practically sized targets, to levels commensurate with
irradiation with 1 GeV, 100 kW proton beams
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: Investigations have been conducted to determine the feasibility of
using collisional cooling for reducing the energy spreads and,
consequently, the emittances of negative-ion beams. We have designed a
gas-filled RF-quadrupole ion cooler equipped with provisions for
retarding energetic negative ion beams to energies below thresholds for
electron detachment at injection and for reacceleration to high energies
after the cooling process. The device has been used to cool
O<sup>-</sup> and F<sup>-</sup> ion beams with initial energy spreads,
ΔE >10 eV to final energy spreads, ΔE ~2 eV FWHM.
Overall, transmission efficiencies of ~14% for F<sup>-</sup> beams have
been obtained. Experimental results show that electron detachment is the
major loss mechanism for negative ions
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
