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Papers by Eric Pitcher

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

Nuclear Technology, Dec 1, 2009

Radionuclide inventory calculations support design and accident analyses for the Materials Test S... more Radionuclide inventory calculations support design and accident analyses for the Materials Test Station (MTS). MTS is a spallation source facility being designed to irradiate reactor fuels and materials in a fast neutron spectrum. Calculated radionuclide inventories are used to provide decay heat input to cooling system design, decay radiation source terms for hot cell design, and materialat-risk input to accident analyses. CINDER'90 is a transmutation code that uses MCNPX-calculated spallation product yields and neutron fluxes to calculate residual nuclide concentrations based on irradiation history. The code also calculates decay heat and photon spectra for the resulting radionuclide inventories. A total activity of 2ϫ10 17 Bq is created during MTS operation. Decay heat is an important factor since in loss of primary cooling scenarios, this heat must be removed. The major sources at shutdown are 3000 W for the tungsten target plates and 6000 W for fuel pins being irradiated. Decay photon spectra result in unshielded dose rates that hot cell design must accommodate on the order of 1000 Sv/h. The MTS design includes lead-bismuth eutectic (LBE) coolant. For accident analysis 210 Po activity in the LBE is a significant concern. The calculated 210 Po activity following 2.5 yr of operation is 2 ϫ 10 14 Bq. Radionuclide inventory calculations are important for MTS design. The CINDER'90 code is a valuable tool for this purpose.

under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US... more under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for US. Government purposes. The Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. The Los Alamos National Laboratory strongly supports academic freedom and a researcher's rlght to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. Fwm No. 836 R5 ST2629 1W1 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spccific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, rccommendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible electronic image products. Images are produced from the best available original document.

, an affirmative actidequal opptunity employer, Is operated by the University of California for t... more , an affirmative actidequal opptunity employer, Is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonaxclusive, myalty-free license to publish or reproduce the published form of this conttibution, or to allow others to do so, for U.S. Govennnent pmposes. Los Alamos National laboratofy requests that the publisher kkntify this article as wolk performed under the auspices of the U.S. Department of Energy. The Los Alamos National Laborxory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical c m t n e s s. Farm 836 (1 0 6) This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process. or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Nucleation and Atmospheric Aerosols, 1995

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 (&gt;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.

This report was prepared as an account of work sponsored by an agency of the United States Govern... more This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Gwernment nor any agency thereof, nor any of their employees. makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product. or process disclosed, of represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise docs not ncccssarily constitute or imply its endorsement, mommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Review of Scientific Instruments, 1990

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.

Fusion Engineering and Design, Oct 1, 2011

's proposed signature facility , MaRIE, will provide scientists and engineers with new capabiliti... more 's proposed signature facility , MaRIE, will provide scientists and engineers with new capabilities for modeling, synthesizing, examining , and testing materials of the future that will enhance the USA ' s energy security and national security. In the area of fusion power, the development of new structural alloys with better tolerance to the harsh radiation environments expected in fusion reactors will lead to improved safety and lower operating costs. The Fission and Fusion Materials Facility (F 3) , one of three pillars of the proposed MaRIE facility, will offer researchers unprecedented access to a neutron radiation environment so that the effects of radiation damage on materials can be measured in-situ, during irradiation. The calculated radiation damage conditions within the F3 match , in many respects , that of a fusion reactor first wall , making it well suited for testing fusion materials. Here we report in particular on two important characteristics of the radiation environment with relevancy to radiation damage: the primary knock-on atom spectrum and the impact of the pulse structure of the proton beam on temporal characteristics of the atomic displacement rate. With respect to both of these, analyses show the F3 has conditions that are consistent with those of a steady-state fusion reactor first wall.

IEEE Transactions on Nuclear Science, Nov 1, 2020

Problems caused by neutron-induced soft errors in electrical devices are becoming increasingly co... more Problems caused by neutron-induced soft errors in electrical devices are becoming increasingly common in various applications. The neutron-energy-dependent soft-error rate is indispensable for evaluating the frequency of such errors in different neutron fields. We have observed the energy-dependent neutron-induced error rates continuously over the energy range of 1-800 MeV at Los Alamos Neutron Science Center (LANSCE). This was made possible by using extremely fast circuits built into field-programmable gate arrays (FPGAs) for time-of-flight measurement. Current experimental results revealed the overall trend of the error rate, which gradually increases up to 20 MeV. Interestingly, the rate depended on the type of device, and the errors occurred even below the threshold energy of the nuclear cross section of silicon, 2.75 MeV.

Journal of Neutron Research, Nov 1, 1997

There are potential gains of about a factor of seven in the time-average neutron brightness for a... more There are potential gains of about a factor of seven in the time-average neutron brightness for a coupled liquid H2 moderator compared to a decoupled one, and a factor of around five for a H20 moderator. However, these gains come at the expense of putting "tails" on the neutron pulses. The particulars of the neutron pulses from a moderator (e.g., energy-dependent rise times, peak intensities, pulse widths, and decay constant(s) of the tails) are crucial parameters for designing instruments and estimating their performance at an LPSS. The spallation target system designer can alter moderator neutronic performance by: (a) the choice of target material and geometry; (b) proper selection of the moderator material and geometry; (c) varying the target-moderator geometry; (d) the choice of reflector material(s); (e) the presence/ absence of decouplers and liners; and (f) the proton pulse width. A 1-MW Long-Pulse Spallation Source (LPSS) has world-class neutronic performance. We show that the calculated performance of a liquid H2 moderator at a I-MW LPSS is equivalent to one-fourth the calculated performance of the best liquid D2 moderator at the Institut Laue Langevin (ILL) reactor.

Springer eBooks, 2001

Los Alamos National Laboratory, an affirmative aetidequal opportunityemployer, is operated by the... more Los Alamos National Laboratory, an affirmative aetidequal opportunityemployer, is operated by the University of California for the U.S. Department of Energy under eontraetW-7405-ENG-36. By acceptance of thk article, the publisherremgn"kes that the U.S. Government retains a nonexclusive, royalty-free Iiinse to publish or reproduce the publishedform of this contribution,or to allow others to do so, for U.S. Government puqmses. Los Alamos National Laboratory requests that the publisher identifythk article as work performed under the auspices of the U.S. Department of Energy. Los Alamos National Laboratay stronglysupports academic freedom and a researcher's rightto publish;as an institution,however, the Laboratory does not endorse the viewpointof a publicationor guarantee itstechnical correctness. Form 836 (8/00) DISCIAIMER This repofi was prepared as an account of work sponsored by an agency of the United States Government.

Reliability and availability are key metrics for achieving the scientific vision of the ESS. The ... more Reliability and availability are key metrics for achieving the scientific vision of the ESS. The approach taken to analyze and to improve these metrics in order to achieve the goals is described in this contribution. The methodology used to obtain the requirements considers not only the availability and reliability figures but also the specific needs extracted from users expectations from the neutron source in order to succeed in their experiments. A top-down requirements allocation is being developed at the same time that bottom-up reliability and availability analyses is being performed. The experiments expected at ESS and their needs in terms of neutron beam performance (reliability, availability and quality) are described as well as the tools used to analyze it. Moreover, the consequences of these analyses in the design phase are discussed.

AIP Conference Proceedings, 2001

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. .