D. D. Armstrong

Bio: D. D. Armstrong is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Beam (structure) & Linear particle accelerator. The author has an hindex of 4, co-authored 9 publications receiving 42 citations.

The FMIT Accelerator

Abstract: A 35-MeV 100-mA cw linear accelerator is being designed by Los Alamos for use in the Fusion Materials Irradiation Test (FMIT) Facility. Essential to this program is the design, construction, and evaluation of performance of the accelerator's injector, low-energy beam transport, and radio-frequency quadrupole sections before they are shipped to the facility site. The installation and testing of some of these sections have begun as well as the testing of the rf, noninterceptive beam diagnostics, computer control, dc power, and vacuum systems. An overview of the accelerator systems and the performance to date is given.

Electrode Shaping for Ion and Electron Extractors

Abstract: A technique has been developed that defines the shapes of electrodes needed to produce a good-quality cylindrically symmetric beam of ions or electrons. This work was motivated by the need to optimize electrode shapes for a high-brightness, low-energy, deuteron injector. Our experience had indicated that correct shaping of electrodes becomes increasingly important as beam perveance increases. This provided the motivation for developing a computer program that could specify electrodes producing optimum or improved beam quality. Several techniques have been developed and evaluated. The procedure described here has been very successful in meeting our design goals.

Performance Optimization of a Cusp-Field Ion Source and High-Perveance Extractor

Abstract: The injector for the Fusion Materials Irradiation Test (FMIT) Facility must deliver a 110-mA dc beam of deuterons or H2+ ions to the radio-frequency quadrupole (RFQ) accelerator at 75-keV energy. Operational parameters of a hydrogen-fed cusp-field ion source and a high-perveance extractor have been evaluated on a test stand and on the recently completed first stage of the prototype injector (Fig. 1).

Progress Report on Testing of a 100-kV 125-mA Deuteron Injector

Abstract: The Linear Accelerator to be used for the Fusion Materials Irradiation Test Facility (FMIT) will require an injection energy of 100 keV at a dc current level of 125 mA. Studies are being made on a pre-prototype version of this injector, including performance tests of both a single aperture reflexarc ion source and a cusp-field source. A single stage, high-gradient extraction system is used prior to mass analysis in a 90° bending magnet. A two-stage beam steering device to measure beam emittance under full beam power has been designed and constructed. To avoid production of neutrons, all prototype tests are run with H2+ ions rather than D+ ions.

Development of a high-current deuteron injector for the FMIT Facility

Abstract: The injector for the Fusion Materials Irradiation Test (FMIT) Facility has been designed to deliver a 100-keV, 125-mA dc deuteron beam. A prototype injector has been built to run with a H/sub 2//sup +/ ion beam. Two ion sources are being tested - one with magnetic-cusp geometry. The injector transport consists of a single-stage modified-Pierce extractor, a double-focusing 90/sup 0/ analyzing magnet, a high-power emittance scanner, steering and quadrupole focusing magnets, a mechanical beam-current modulator and a deflection type beam pulser. The performance of the prototype injector is discussed.

Negative ion source operation with deuterium

Abstract: When the working gas of a negative ion source is changed from hydrogen to its isotope, deuterium, an 'isotope effect' is observed; namely, several plasma characteristics such as the electron energy distribution, the atomic fraction and the spectra of rovibrationally excited molecules change. The understanding of the effect becomes more important, as research and development aiming at ITER power level operation is being challenged with feeding deuterium to the ion sources. As a historical review of the effort to develop hydrogen/deuterium negative ion sources, several types of negative ion sources designed for the neutral beam plasma heating are described: double charge exchange sources, volume sources and surface-plasma sources. The early results with volume sources operated with and without cesium are introduced. The characteristics of the source charged with deuterium are compared to those of the source charged with hydrogen. The isotope effect did not appear pronounced as the negative ion density was measured in a small source but became more pronounced when the plasma source size was enlarged and the discharge power density was increased to higher values. Surface plasma sources were optimized for deuterium operation but could not achieve the same performance as a source operated with hydrogen at the same power and pressure. The lower velocity of negative deuterium ions leaving the low work function surface seemed to limit the production efficiency. Fundamental processes causing these differences in negative ion source operation are summarized. After explaining the current status of negative ion source research and development, the acquired knowledge is utilized to the development of large negative ion sources for nuclear fusion research and to the development of compact negative ion sources for neutron source applications.

High yield neutron generator based on a high-current gasdynamic electron cyclotron resonance ion source

Abstract: In present paper, an approach for high yield compact D-D neutron generator based on a high current gasdynamic electron cyclotron resonance ion source is suggested. Results on dense pulsed deuteron beam production with current up to 500 mA and current density up to 750 mA/cm2 are demonstrated. Neutron yield from D2O and TiD2 targets was measured in case of its bombardment by pulsed 300 mA D+ beam with 45 keV energy. Neutron yield density at target surface of 109 s−1 cm−2 was detected with a system of two 3He proportional counters. Estimations based on obtained experimental results show that neutron yield from a high quality TiD2 target bombarded by D+ beam demonstrated in present work accelerated to 100 keV could reach 6 × 1010 s−1 cm−2. It is discussed that compact neutron generator with such characteristics could be perspective for a number of applications like boron neutron capture therapy, security systems based on neutron scanning, and neutronography.

Transverse emittance: Its definition, applications, and measurement

Abstract: Transverse emittance of accelerator particle beams is defined. Various techniques for the measurement of emittance are discussed, including both destructive and nondestructive methods. (AIP)

CW operation of the fmit RFQ accelerator

Abstract: Experiences in attaining cw operation of the radio-frequency quadrupole for the fusion materials irradiation test facility are presented. Modifications of the vacuum system, changes in the RF structure, and operational experiences are discussed, as well as preliminary results of initial beam-characterization measurements.