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Plastic deformation of colliding hemishells. [Steel-ASTM-A 537]

Description: The collision of two hemishells is analyzed where one hemishell is clamped and the other impinges on the inner surface of the clamped hemishell. A model of rigid-perfectly plastic behavior is proposed for the flow of material in the region of contact. An expression relating velocity and deformation is obtained and compared with the results of experiments.
Date: January 1, 1980
Creator: Moir, D.C. & Neal, T.R.
Partner: UNT Libraries Government Documents Department

PHERMEX as an injector to a modified betatron

Description: The PHERMEX accelerator is a pulsed three-cavity, 50-MHz, standing-wave rf linear accelerator. It is used to produce a 30-MeV, 200-ns envelope of electrons for flash radiography and electron beam experiments. The 200-ns electron pulse contains 10 micropulses. The FWHM of a single micropulse is 3.3 ns. Peak micropulse current varies from 350 to 850 A with widths of 3 and 5 ns, respectively. We propose to inject this beam into a solenoidal field with a neutralizing background gas and stack the PHERMEX micropulses in a 28-cm-dia ring to obtain a 3-ns multi-kiloampere beam. Coupled to the background magnetic field will be a ramped field driven by a magnetic flux compression generator. Beam kinetic energy approaching 100 MeV is theoretically possible. Simulations of ring stability with and without the accelerating field are presented. 9 refs., 4 figs.
Date: January 1, 1985
Creator: Moir, D.C. & Gisler, G.R.
Partner: UNT Libraries Government Documents Department

Pulsed magnetic field for PHERMEX-injected circular accelerator

Description: The PHERMEX accelerator is a standing wave, 50 MHz rf linear accelerator. The rf fields in three cavities are pulsed for a period of 3 ms. The experiments described are directed toward studying injection and trapping of electron rings at modes field strengths (approximately 1 T). A single 200 ns beam macropulse is to be injected transverse to a solenoidal field, which is tilted at a small angle relative to the beam normal so that a beam micropulse does not return and strike the injection point. The pulsed field coils and vacuum chamber are reported under construction, and the capacitor bank being tested. (LEW)
Date: January 1, 1986
Creator: Moir, D.C.; Ruhe, J.R. & Armstrong, W.T.
Partner: UNT Libraries Government Documents Department

Rf phase measurement at PHERMEX (Pulsed High Energy Radiographic Machine Emitting X-Rays) using time-to-digital converters

Description: Recent advances in time-to-digital converters (TDCs) have made 50-MHz rf phase measurement possible without the use of double-balanced mixers. These advances allow zero crossing discriminators to be used in conjunction with fast CAMAC TDCs to make amplitude-independent phase measurements. This method uses a time interval proportional to the phase angle, thus eliminating any of the calculations and calibration required with double-balanced mixers. 4 refs., 1 fig., 1 tab.
Date: January 1, 1989
Creator: Watson, S.A.; Jennings, G.R. & Moir, D.C.
Partner: UNT Libraries Government Documents Department

Time-resolved current, current-density, and emittance measurements of the PHERMEX electron beam

Description: The PHERMEX electron-beam pulse is a burst of ten 3.3-ns micropulses separated by 20 ns. Typical accelerator operating parameters produce a mean beam micropulse energy of 26 MeV with peak current of 300-500 A. The purpose of this work is to present experimental measurements of the current, current density, and emittance of a single PHERMEX micropulse. This experiment is part of an effort to completely characterize the PHERMEX electron beam. Understanding the electron-beam parameters is necessary for machine upgrade as related to flash radiography and for both present and future electron-beam experiments.
Date: January 1, 1985
Creator: Moir, D.C.; Builta, L.A. & Starke, T.P.
Partner: UNT Libraries Government Documents Department

Intense electron-beam propagation in low-density gases using PHERMEX

Description: Preliminary propagation experiments have been performed using the LASL-PHERMEX 21-MeV electron beam with current densities of 40 kA/cm/sup 2/. Gas densities are varied from 10-m torr to 580 torr. Results indicate the presence of microinstabilities.
Date: January 1, 1980
Creator: Moir, D.C.; Newberger, B.S. & Thode, L.E.
Partner: UNT Libraries Government Documents Department

Stabilization of electron beam spot size by self bias potential

Description: In high resolution flash x-ray imaging technology the electric field developed between the electron beam and the converter target is large enough to draw ions from the target surface. The ions provide fractional neutralization and cause the electron beam to focus radially inward, and the focal point subsequently moves upstream due to the expansion of the ion column. A self-bias target concept is proposed and verified via computer simulation that the electron charge deposited on the target can generate an electric potential, which can effectively limit the ion motion and thereby stabilize the growth of the spot size. A target chamber using the self bias target concept was designed and tested in the Integrated Test Stand (ITS). The authors have obtained good agreement between computer simulation and experiment.
Date: December 31, 1998
Creator: Kwan, T.J.T.; Moir, D.C.; Snell, C.M. & Kang, M.
Partner: UNT Libraries Government Documents Department

Large area polycrystalline diamond films as high current photocathodes for linear induction accelerators

Description: Investigations are underway at Los Alamos to develop a new generation of high current, low source temperature photo cathodes able to operate in vacuum environments with pressures above 10e-6 torr without poisoning or degradation of emission properties. Polycrystalline diamond films are emerging as the ideal material for these photocathodes. Robustness, high quantum efficiency and high thermal conductivity are fundamental necessary attributes that are found in diamond. The high electron/hole mobility in the boron doped diamond lattice and the ability to create a negative electron affinity surface through downward band bending allow for high current density emission with quantum efficiencies of 0.5% when illuminated by a ArF laser. We report the results to date toward the development of a four kiloampere photocathode with a source temperature below 5eV for the DARHT linear induction Accelerator
Date: August 1, 1997
Creator: Shurter, R.P.; Moir, D.C.; Devlin, D.J. & Springer, R.W.
Partner: UNT Libraries Government Documents Department

Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation

Description: High current photocathodes using bare metal and polycrystalline diamond films illuminated by ultraviolet lasers are being developed at Los Alamos for use in a new generation of linear induction accelerators. These photocathodes must be able to produce multiple 60 ns pulses separated by several to tens of nanoseconds. The vacuum environment in which the photocathodes must operate is 10{sup -5} torr.
Date: July 1, 1996
Creator: Shurter, R.P.; Moir, D.C. & Devlin, D.J.
Partner: UNT Libraries Government Documents Department

PHERMEX electron gun development

Description: The PHERMEX facility is a 50-MHz standing-wave linear accelerator. Electrons are injected, accelerated, and transported to a tungsten target where bremsstrahlung x rays are generated for flash radiography of hydrodynamic systems. The purpose of this article is to describe the progress of PHERMEX electron gun development. The goal of this program is to generate and transport a 200-ns, 1-MV, 1-kA electron beam into the first PHERMEX accelerating cavity. The standard gun is operated at a pulse voltage of 550 kV, which is the limit determined by internal breakdown of the vacuum insulator. This insulator has been redesigned, and the gun has been pulsed at 750 kV without internal breakdown. At present, the current output is not limited by voltage but by a phenomenon called pulse shortening, which occurs at a pulse voltage of approximately 650 kV. The phenomenon has been investigated and the results are presented.
Date: January 1, 1983
Creator: Builta, L.A.; Elliott, J.C.; Moir, D.C.; Starke, T.P. & Vecere, C.A.
Partner: UNT Libraries Government Documents Department

Suitability of high-current standing-wave linac technology for ultra-relativistic electron beam propagation experiments

Description: Near-term development of the existing PHERMEX standing-wave linac would provide a 40 to 60 MeV electron beam with a current of 3 kA capable of answering a number of fundamental issues concerning endoatmospheric, ultra-relativistic electron beam propagation. Inherent high-repetition rate and multiple-pulse capability would allow alternative propagation scenarios to be investigated. Much of the theoretical expertise required to support the technology development and time-resolved beam propagation experiments presently resides within the Theoretical Applications Division.
Date: January 1, 1981
Creator: Moir, D.C.; Faehl, R.J.; Newberger, B.S. & Thode, L.E.
Partner: UNT Libraries Government Documents Department

Trapping of the PHERMEX beam in a mirror field

Description: An experiment is underway at Los Alamos National Laboratory to trap the 1-kA, 30-MeV PHERMEX beam in a magnetic mirror. The eventual aim is to accelerate the beam to 50 MeV by ramping up the magnetic field. Tangential injection of the beam through a soft iron nozzle is employed. Because the nozzle is placed within the magnetic mirror, energy must be extracted from the beam in one bounce time to prevent particles returning to the nozzle. A design to make the bounce time as long as possible is described, and two schemes to damp the axial motion are considered. Numerical simulations of the device show considerable axial spreading of the beam in one bounce time. Estimates are made of negative mass instability growth rates and the damping to be expected from the experimentally measured beam energy spread. Experimental results obtained to date are described.
Date: January 1, 1987
Creator: Hughes, T.P.; Builta, L.A.; Mack, J.M. & Moir, D.C.
Partner: UNT Libraries Government Documents Department

Intense low-emittance-electron-gun development at PHERMEX

Description: Experimental measurements and theoretical calculations have been performed and compared for the PHERMEX standard electron gun. Slight changes in the gun configuration have produced significant changes in beam intensity and quality. It is hoped that the present gun configuration can be extended to even higher perveances (without significant loss of beam quality) through a joint theoretical and experimental effort.
Date: January 1, 1981
Creator: Elliott, J.C.; Faehl, R.J.; Fullbright, H.J.; Moir, D.C. & Swannack, C.E.
Partner: UNT Libraries Government Documents Department

Pulsed 4-MeV electron injector with an excimer laser driven photocathode

Description: The Relativistic Electron-Beam Experiment injector at the Los Alamos National Laboratory is used to generate a 4-MV pulse across an anode-cathode gap. A simple metal photocathode is illuminated by a pulsed excimer laser. Time-resolved measurements of current, voltage, and current density are made. The resulting quantum efficiencies are being used to obtain the required laser power for a multikiloampere, high-brightness electron gun to be used as an injector for a linear induction accelerator. 3 refs., 5 figs.
Date: January 1, 1989
Creator: Kauppila, T.J.; Builta, L.A.; Carlson, R.L.; Moir, D.C. & Ridlon, R.N.
Partner: UNT Libraries Government Documents Department

A pulsed electron injector using a metal photocathode irradiated by an excimer laser

Description: The hot cathode of an electron gun is replaced by a metallic photocathode driven by an excimer laser. The current, current density, and emittance of the 500-kV electron beam produced by the photoelectron source are presented. In addition, the temperature of the photocathode is varied to study the possibility of a hybrid source.
Date: January 1, 1987
Creator: Kauppila, T.J.; Builta, L.A.; Crutcher, J.K.; Elliott, J.C. & Moir, D.C.
Partner: UNT Libraries Government Documents Department

Development and characterization of diamond film and compound metal surface high current photocathodes

Description: High current photocathodes operating in vacuum environments as high as 8xE-5 torr are being developed at Los Alamos for use in a new generation of linear induction accelerators. We report quantum efficiencies in wide bandgap semiconductors, pure metals, and compound metal surfaces photocathode materials illuminated by ultraviolet laser radiation.
Date: September 1, 1997
Creator: Shurter, R.P.; Moir, D.C.; Devlin, D.J.; Springer, R.W. & Archuleta, T.A.
Partner: UNT Libraries Government Documents Department

Electron-beam generation, transport, and transverse oscillation experiments using the REX injector

Description: The REX machine at LANL is being used as a prototype to generate a 4-MV, 4.5-kA, 55-ns flat-top electron beam as a source for injection into a linear induction accelerator of the 16-MeV Dual-Axis Radiographic Hydrotest facility. The pulsed-power sources drives a planar velvet cathode producing a beam that is accelerated through a foilless anode aperture and transported by an air core magnetic lens for injection into the first of 48 linear induction cells. Extensive measurements of the time-resolved (<1-ns) properties of the beam using a streak camera and high-speed electronic diagnostics have been made. These parameters include beam current, voltage, current density, emittance, and transverse beam motion. The effective cathode temperature is 117 eV, corresponding to a Lapostolle emittance of 0.96 mm-rad. Transverse oscillations of the transported beam have been observed via a differenced B-dot technique to be about {plus minus}100 {mu}m at 245 MHz. This beam motion has been correlated via detailed rf measurements of asymmetric transverse cavity modes in the A-K gap. 7 refs., 6 figs.
Date: January 1, 1991
Creator: Carlson, R.L.; Allison, P.W.; Kauppila, T.J.; Moir, D.C. & Ridlon, R.N.
Partner: UNT Libraries Government Documents Department

Simple laser-driven, metal photocathodes as cold, high-current electron sources

Description: Recent developments in excimer laser design have made near ultraviolet light intensities of several MW/cm/sup 2/ possible in unfocused beams. These advances and recent experiments indicate that high-current, simple-metal photoemissive electron guns are now feasible. Producing more than 50 A/cm/sup 2/ of illuminated cathode surface, the guns could operate at vacuums of 10/sup -6/ torr with no complicated system components inside the vacuum enclosure. The electron beam produced by such photoemission guns would have very low emittance and high brightness. This beam would also closely follow the temporal characteristics of the laser pulse, making fast risetime, ultrashort electron beam pulses possible.
Date: January 1, 1987
Creator: Saunders, J.D.; Ringler, T.J.; Builta, L.A.; Kauppila, T.J.; Moir, D.C. & Downey, S.W.
Partner: UNT Libraries Government Documents Department

Pulse-power-induced oscillations of the REX (Relativistic Electron-Beam Experiment) electron beam

Description: The Relativistic Electron-Beam Experiment pulse power generator is used to produce a 4-MeV, 5-kA, 50-ns electron beam. The beam is produced by a planar velvet cathode. Multiple current rise times are used to examine pulse-power-induced beam oscillations. Diagnostics include a streak camera and high-speed electronic probes for monitoring current and voltage. Correlation between beam oscillations and TE/TM cylindrical cavity modes in the anode-cathode gap is examined. 2 refs., 9 figs.
Date: January 1, 1989
Creator: Builta, L.A.; Carlson, R.L.; Kauppila, T.J.; Moir, D.C.; Ridlon, R.N. & Hughes, T.P.
Partner: UNT Libraries Government Documents Department

Status of the Dual-Axis Radiographic Hydrodynamics Test Facility

Description: The Dual-Axis Radiographic Hydrodynamics Test (DARHT) Facility will employ two electron linear induction accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography with sub-millimeter spatial resolution of very dense (attentuations>10{sup 5}), dynamic objects. We will produce an intense x-ray pulse using a 19.75-MeV, 3.5-4 kA, 60-ns flattop electron beam focused on a tungsten target. A 3.75-MeV injector with either a cold velvet cathode or a laser-driven photocathode will produce a beam to be accelerated through a series of 64 ferrite-loaded induction cells with solenoid focusing. Accelerator technology demonstrations have been underway for several years at the DARHT Integrated Test Stand and results including beam energy, emittance, and beam breakup measurements are discussed.
Date: September 1, 1996
Creator: Burns, M.J.; Allison, P.W.; Carlson, R.L.; Downing, J.N.; Moir, D.C. & Shurter, R.P.
Partner: UNT Libraries Government Documents Department

Computational support for ITS and PHERMEX. Final report

Description: This report describes calculations carried out over the past year in support of the ITS and PHERMEX radiographic machines. The forces produced by nonaxisymmetric structures in the ITS linac were calculated using 3-D simulations. The quadrupole magnetic field produced by the drive rods in the accelerating cell was obtained. This force can be corrected by a weak static magnetic quadrupole provided the current in the drive rods is constant. The octopole force produced by a 4-hole diagnostic section was also obtained. A new recessed cathode design was modeled using PBGUNS. For a 2 mm recess, the electrostatic focusing due to the recess is sufficient to stop current loss on the anode. The emitted and transported currents are in good agreement with the measured values. The LAMDA code was compared in detail to the LLNL code BREAKUP. The codes are in close agreement. To get the results to overlay identically, however, the beam voltages have to differ by about 100 kV (out of 3 MV). The source of this discrepancy has not yet been identified. A plotting utility for LAMDA was written in the IDL{reg_sign} language. This allows LAMDA output to be viewed on any platform supported by IDL. Experiments on the flat-cathode injector were modeled. Beam radius as a function of magnet strength was compared in detail with measurements, and good agreement was obtained. The effect of the trim coil on reducing beam emittance was investigated further. The trim coil allows one to correct emittance growth due to spherical aberration in the focusing magnet and nonlinear self forces. The measured calibrations for the bucking, focus and trim coils are now in good agreement with the calculated values. A code which optimizes the transport magnet settings was developed. The code iterates on the magnet settings to obtain a beam envelope with ...
Date: March 1, 1994
Creator: Hughes, T.P.; Clark, R.E.; Allison, P.W.; Moir, D.C.; Kauppila, T.J. & Watson, S.A.
Partner: UNT Libraries Government Documents Department

Induction cell breakdown experiments for the Dual-Axis Radiographic Hydrotest (DARHT) Facility

Description: Linear induction cells for the Dual-Axis Radiographic Hydrotest (DARHT) Facility have been tested to determine their high-voltage breakdown characteristics. A variety of full scale insulators were tested both in actual cells and in fixtures simulating induction cells. All insulators were constructed using cross-linked polystyrene (Rexolite). High-voltage pulses up to 550 kV were applied to the insulators using both a 60-ns pulse Blumlein and a 200-ns pulse cable Marx. Two different vacuum gaps were used in these tests, 1.46 and 1.91 cm. The tests were performed at various vacuum levels ranging from 1 {times} 10{sup {minus}6} to 5 {times} 10{sup {minus}8} torr. Breakdown tests of the insulators were also performed with an electron beam generated in the vacuum gap through the use of a velvet emitter. The gap voltage and current were measured using calibrated E-dot and B-dot probes. 15 refs., 7 figs.
Date: January 1, 1991
Creator: Earley, L.M.; Barnes, G.A.; Eversole, S.A.; Kauppila, T.J.; Keel, G.; Liska, D.J. et al.
Partner: UNT Libraries Government Documents Department

Pulsed power systems for the DARHT accelerators

Description: The Dual-Axis Radiographic Hydro Test (DARHT) Facility is being designed to produce high-resolution flash radiographs of hydrodynamics experiments. Two 16- to 20-MeV linear induction accelerators (LIA), with an included angle of 90{degree}, are used to produce intense bremsstrahlung x-ray pulses of short duration (60-ns flat-top). Each accelerator has a 4-MeV electron source that injects an electron beam into a series of 250-kV induction cells. The three major pulsed-power systems are the injectors, the induction-cell pulsed-power (ICPP) units, and the ICPP trigger systems, and are discussed in this paper. 11 refs., 5 figs, 3 tabs.
Date: January 1, 1991
Creator: Downing, J.N.; Parsons, W.M.; Earley, L.M.; Melton, J.G.; Moir, D.C.; Carlson, R.L. et al.
Partner: UNT Libraries Government Documents Department