The demand for energetic, high-current H$\sp-$ beams is ever-growing. Because H$\sp-$ is efficien... more The demand for energetic, high-current H$\sp-$ beams is ever-growing. Because H$\sp-$ is efficiently neutralized at high energies, these beams are ideally suited to applications where energetic neutral beams of particles are required to propagate across magnetic fields. Prime examples are neutral-beam heating of magnetic fusion plasmas and directed-energy weapons for ballistic missile defense. Such applications place demanding requirements on sources of H$\sp-$ ions, particularly with respect to the parameters of beam current, brightness, quiescence, reliability, and duty-factor. A class of sources that holds great promise for meeting these stringent requirements is the surface-plasma source (SPS), and in particular, the Penning type of SPS. It has long been conjectured that atomic hydrogen plays an important role in both H$\sp-$ formation and transport in these sources. Understanding the interdependence of atomic hydrogen properties and those of H$\sp-,$ and how this relationship might be exploited to improve source performance is the motivation for this research. An overview of SPS's is presented. Previous measurements on the discharge are reviewed. Absorption spectroscopy, the diagnostic technique used to gather all of the data presented here, is discussed. Techniques that may potentially be used to measure the properties of H$\sp-$ in the discharge are discussed. The two absorption spectrometers used in this experiment are described. Measurements of ground-state atomic hydrogen density and temperature in a Penning SPS are presented. These measurements are the first of this kind for this type of discharge. An upper limit on the H$\sp-$ density in the extraction region of the source is measured by the application of a novel diagnostic technique: the hydrogen atom density following H$\sp-$ photodetachment by a Nd:YAG beam is measured and compared to the equilibrium atomic density. A simple model is derived that describes the dependence of the atomic temperature on the externally-controlled parameters of discharge current and H$\sb2$ gas flow. The measured atomic density is considered in light of the widely-accepted hypothesis of the mechanism for H$\sp-$ formation. The measured upper limit of the H$\sp-$ density is used to infer the potential of the discharge plasma relative to the source anode.Ph.D.Nuclear EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102968/1/9226983.pdfDescription of 9226983.pdf : Restricted to UM users only
Nearly all risks to future generations arising from long-term disposal of used nuclear fuel are a... more Nearly all risks to future generations arising from long-term disposal of used nuclear fuel are attributable to the transuranic elements and long-lived fission products, about 2% of its content. The transuranic elements of concern are plutonium, neptunium, americium, and curium. Long-lived (>100,000-year half-life) isotopes of iodine and technetium are also created by nuclear fission of uranium. We can reduce the
Transport of high-perveance H/sup /minus// ion beams frequently depends on space-charge neutraliz... more Transport of high-perveance H/sup /minus// ion beams frequently depends on space-charge neutralization by a background plasma to reduce or eliminate space-charge defocusing. We have developed a four-grid energy analyzer (FGA) that measures the energy distributions of particles emitted radially from the beam-generated plasma. H/sup /minus// beams of 80- to 90- mA current at 21-keV beam energy (which yields a /minus/400 V potential drop for an unneutralized beam) have been studied in a 55-cm drift region using He and Xe neutralizing gases. At a sufficiently high gas density, ion energy distribution analyses show a several volt positive potential drop across the H/sup /minus// beam, supporting the gas focusing concept of overneutralized H/sup /minus// ion beams. There is a neutralizing gas density threshold below which no radially flowing positive ion current is observed. At low gas density, the GA electron current is noisy (indicating the plasma is unstable) and the measured electron distributions are consistent with an underneutralized beam. With the addition of neutralizing gas, the electron current oscillations and energies decrease. 8 refs., 7 figs., 1 tab.
A four-grid energy analyzer diagnostic has been developed for the study of H− beam space-charge c... more A four-grid energy analyzer diagnostic has been developed for the study of H− beam space-charge compensation, and first measurements have been reported previously. Biased beam-dump measurements were undertaken to clarify the origin of electron currents measured in the FGA because they far exceeded predictions based on H−-beam ionization and stripping processes. This experiment partially explains the anomalously large radial electron current. The FGA observations for negative beam-dump bias suggest electron ionization of the background gas is an additional mechanism for producing positive ions.
The original targeting system used for producing radionuclides via 800-MeV proton-induced spallat... more The original targeting system used for producing radionuclides via 800-MeV proton-induced spallation reactions at Los Alamos has been deactivated while a new 100-MeV targeting facility is being implemented. The feasibility of constructing another facility to retain the capability for 800-MeV proton bombardment has been examined. A new feature is the incorporation of tungsten targets to enhance energetic neutron production. A neutron flux of similar magnitude to the proton flux would result, aided by the placement of reflector shields to reduce escaping energetic particles. Interspersed among the tungsten targets are a total of 25 experimental target irradiation positions. A hydraulic target transfer system facilitates independent target insertion and retrieval. In many cases, this mixed neutron/proton irradiation environment significantly increases the radioisotope production rate above that of using protons alone. As a means of validating predicted isotope production rates for the new facility, predicted yields using the MCNPX and CINDER'90 codes were compared with measured yields obtained prior to the deactivation of the 800-MeV facility. Of the 10 isotopes for which measured data exists, activities at EOB are within 35% of the calculated yields. .
The demand for energetic, high-current H$\sp-$ beams is ever-growing. Because H$\sp-$ is efficien... more The demand for energetic, high-current H$\sp-$ beams is ever-growing. Because H$\sp-$ is efficiently neutralized at high energies, these beams are ideally suited to applications where energetic neutral beams of particles are required to propagate across magnetic fields. Prime examples are neutral-beam heating of magnetic fusion plasmas and directed-energy weapons for ballistic missile defense. Such applications place demanding requirements on sources of H$\sp-$ ions, particularly with respect to the parameters of beam current, brightness, quiescence, reliability, and duty-factor. A class of sources that holds great promise for meeting these stringent requirements is the surface-plasma source (SPS), and in particular, the Penning type of SPS. It has long been conjectured that atomic hydrogen plays an important role in both H$\sp-$ formation and transport in these sources. Understanding the interdependence of atomic hydrogen properties and those of H$\sp-,$ and how this relationship might be exploited to improve source performance is the motivation for this research. An overview of SPS's is presented. Previous measurements on the discharge are reviewed. Absorption spectroscopy, the diagnostic technique used to gather all of the data presented here, is discussed. Techniques that may potentially be used to measure the properties of H$\sp-$ in the discharge are discussed. The two absorption spectrometers used in this experiment are described. Measurements of ground-state atomic hydrogen density and temperature in a Penning SPS are presented. These measurements are the first of this kind for this type of discharge. An upper limit on the H$\sp-$ density in the extraction region of the source is measured by the application of a novel diagnostic technique: the hydrogen atom density following H$\sp-$ photodetachment by a Nd:YAG beam is measured and compared to the equilibrium atomic density. A simple model is derived that describes the dependence of the atomic temperature on the externally-controlled parameters of discharge current and H$\sb2$ gas flow. The measured atomic density is considered in light of the widely-accepted hypothesis of the mechanism for H$\sp-$ formation. The measured upper limit of the H$\sp-$ density is used to infer the potential of the discharge plasma relative to the source anode.Ph.D.Nuclear EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102968/1/9226983.pdfDescription of 9226983.pdf : Restricted to UM users only
Nearly all risks to future generations arising from long-term disposal of used nuclear fuel are a... more Nearly all risks to future generations arising from long-term disposal of used nuclear fuel are attributable to the transuranic elements and long-lived fission products, about 2% of its content. The transuranic elements of concern are plutonium, neptunium, americium, and curium. Long-lived (>100,000-year half-life) isotopes of iodine and technetium are also created by nuclear fission of uranium. We can reduce the
Transport of high-perveance H/sup /minus// ion beams frequently depends on space-charge neutraliz... more Transport of high-perveance H/sup /minus// ion beams frequently depends on space-charge neutralization by a background plasma to reduce or eliminate space-charge defocusing. We have developed a four-grid energy analyzer (FGA) that measures the energy distributions of particles emitted radially from the beam-generated plasma. H/sup /minus// beams of 80- to 90- mA current at 21-keV beam energy (which yields a /minus/400 V potential drop for an unneutralized beam) have been studied in a 55-cm drift region using He and Xe neutralizing gases. At a sufficiently high gas density, ion energy distribution analyses show a several volt positive potential drop across the H/sup /minus// beam, supporting the gas focusing concept of overneutralized H/sup /minus// ion beams. There is a neutralizing gas density threshold below which no radially flowing positive ion current is observed. At low gas density, the GA electron current is noisy (indicating the plasma is unstable) and the measured electron distributions are consistent with an underneutralized beam. With the addition of neutralizing gas, the electron current oscillations and energies decrease. 8 refs., 7 figs., 1 tab.
A four-grid energy analyzer diagnostic has been developed for the study of H− beam space-charge c... more A four-grid energy analyzer diagnostic has been developed for the study of H− beam space-charge compensation, and first measurements have been reported previously. Biased beam-dump measurements were undertaken to clarify the origin of electron currents measured in the FGA because they far exceeded predictions based on H−-beam ionization and stripping processes. This experiment partially explains the anomalously large radial electron current. The FGA observations for negative beam-dump bias suggest electron ionization of the background gas is an additional mechanism for producing positive ions.
The original targeting system used for producing radionuclides via 800-MeV proton-induced spallat... more The original targeting system used for producing radionuclides via 800-MeV proton-induced spallation reactions at Los Alamos has been deactivated while a new 100-MeV targeting facility is being implemented. The feasibility of constructing another facility to retain the capability for 800-MeV proton bombardment has been examined. A new feature is the incorporation of tungsten targets to enhance energetic neutron production. A neutron flux of similar magnitude to the proton flux would result, aided by the placement of reflector shields to reduce escaping energetic particles. Interspersed among the tungsten targets are a total of 25 experimental target irradiation positions. A hydraulic target transfer system facilitates independent target insertion and retrieval. In many cases, this mixed neutron/proton irradiation environment significantly increases the radioisotope production rate above that of using protons alone. As a means of validating predicted isotope production rates for the new facility, predicted yields using the MCNPX and CINDER'90 codes were compared with measured yields obtained prior to the deactivation of the 800-MeV facility. Of the 10 isotopes for which measured data exists, activities at EOB are within 35% of the calculated yields. .
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