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Dive into the research topics where D.L. Johnson is active.

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Featured researches published by D.L. Johnson.


IEEE Transactions on Plasma Science | 2000

Design of a radiographic integrated test stand (RITS) based on a voltage adder, to drive a diode immersed in a high magnetic field

I. Smith; V.L. Bailey; J. Fockler; J.S. Gustwiller; D.L. Johnson; J.E. Maenchen; D.W. Droemer

Recent experiments have adapted existing magnetically insulated induction voltage adders (Sabre, Hermes III) to drive a 10-MV diode immersed in magnetic fields as high as 50 T. In such a diode, an electron beam of tens of kiloamperes can be confined by the magnetic field to a diameter of about 1 mm, and when it strikes a high-Z anode, it can create a bremsstrahlung X-ray source intense enough to radiograph massive objects with high resolution. The radiographic integrated test stand (RITS) is an adder system designed specially to drive such diodes, and it will be used to develop and exploit them. As in other adder-based pulsers, such as Sabre, Hermes III, and Kalif-Helia, the induction cells have amorphous-iron cores, and the pulse-forming system consists of water dielectric pulselines and self-closing water switches that are pulse-charged from Marx-charged intermediate water capacitors through laser-triggered Rimfire switches. An oil prepulse switch in series with each pulseline is designed to reduce cathode prepulse to less than /spl plusmn/5 kV, and a means is provided to bias the cathode and avoid negative prepulse entirely. The RITS pulse-forming system consists of two modules. Each module has one Marx that charges two 3-MV intermediate stores, each of which charges three 7.8 /spl Omega/ pulselines, making six pulselines per module. The two modules in concert can supply 1.35-MV, 50-ns pulses to a 12-cell adder and thus drive a 16-MV diode with a single pulse. The 1,35-MV induction cells each have a single-point feed, from which a single, slotted azimuthal oil transmission line distributes energy uniformly around the cell. The modules can also be pulsed separately at different times, either to power two 8-MV adders that each drive one of two closely spaced cathodes immersed in a common magnetic field or to provide two separate pulses to a common six-cell adder and a single 8-MV diode; in these two-pulse modes, the spacing of the two 50-ns pulses may be chosen to be anything from a few hundred nanoseconds upward. The use of only one pulseline per cell has been shown to increase the extent to which the cell voltages can vary with the timing of closure of the water switches. This and all other functions of RITS have been simulated in detail, and a conservative electrical design has been developed. This will be illustrated, along with the conceptual design of a pulse sorting network that can couple two pulselines efficiently to one cell when the two RITS modules drive a common adder in two-pulse mode.


Journal of Applied Physics | 2002

Coupled particle-in-cell and Monte Carlo transport modeling of intense radiographic sources

D. V. Rose; D.R. Welch; B. V. Oliver; R. E. Clark; D.L. Johnson; J.E. Maenchen; P.R. Menge; C.L. Olson; Dean C. Rovang

Dose-rate calculations for intense electron-beam diodes using particle-in-cell (PIC) simulations along with Monte Carlo electron/photon transport calculations are presented. The electromagnetic PIC simulations are used to model the dynamic operation of the rod-pinch and immersed-B diodes. These simulations include algorithms for tracking electron scattering and energy loss in dense materials. The positions and momenta of photons created in these materials are recorded and separate Monte Carlo calculations are used to transport the photons to determine the dose in far-field detectors. These combined calculations are used to determine radiographer equations (dose scaling as a function of diode current and voltage) that are compared directly with measured dose rates obtained on the SABRE generator at Sandia National Laboratories.


ieee international pulsed power conference | 2006

Design, Simulation, and Fault Analysis of a 6.5-MV LTD for Flash X-Ray Radiography

Joshua J. Leckbee; J.E. Maenchen; D.L. Johnson; S. Portillo; David VanDeValde; D.V. Rose; B.V. Oliver

The design of a 6.5-MV linear transformer driver (LTD) for flash-radiography experiments is presented. The design is based on a previously tested 1-MV LTD and is predicted to be capable of producing diode voltages of 6.5 MV for a 50-Omega radiographic-diode load. Several fault modes are identified, and circuit simulations are used to determine their effect on the output pulse and other components. For all the identified fault modes, the peak load voltage is reduced by less than 5%


ieee international pulsed power conference | 1989

Performance of the hermes-III gamma ray simulator

Juan J. Ramirez; K. R. Prestwich; D.L. Johnson; J.P. Corley; G. J. Denison; J. A. Alexander; T. L. Franklin; P. J. Pankuch; T. W. L. Sanford; T. J. Sheridan; L. L. Torrison; G. A. Zawadzkas

Hermes III is a 22-MV, 730-kA, 40-ns pulsed power accelerator that drives an electron beam diode/converter to generate an intense pulse of bremsstrahlung radiation. In Hermes III, eighty individual 1.1-MV, 220-kA pulses are generated and added in groups of four to develop twenty 1.1-MV, 730-kA pulses which are then fed through inductively isolated cavities and added in series by a magnetically insulated transmission line (MITL). An extension MITL delivers this surnmed output to the electron beam diode. The construction of Hermes III was completed February 1988 and was followed by an accelerator characterization and performance demonstration phase. Hermes III met all of its performance requirements during this testing period and has gone operational one year ahead or schedule. An overview of the Hermes-III design is presented together with details of the performance obtained for the various subsystems. A discussion of future applications of this technology is also presented.


international conference on plasma science | 2001

Design of a driver for the Cygnus X-ray source

D. Weidenheimer; P. Corcoran; R. Altes; J. Douglas; H. Nishimoto; I. Smith; R. Stevens; D.L. Johnson; R. White; J. Gustwiller; J.E. Maenchen; P.R. Menge; R.L. Carlson; R.D. Fulton; G. Cooperstein; E. Hunt

Cygnus is the prototype of a radiographic x-ray source leveraging existing hardware and designs to drive a rod-pinch diode at 2.25 MV. This high-resolution x-ray source is being developed to support the Sub-Critical Experiments Program (SCE) at the Nevada Test Site (NTS), and as such employs a modular technology that is scaleable to higher voltages and can be readily deployed underground. The diode is driven by three Induction Voltage Adder (IVA) cells from the Sandia SABRE [1] accelerator, threaded by a positive polarity vacuum coax that extends 2 meters to the diode and is designed to operate below electron emission on the anodized outer electrode. The /spl sim/40 ohm diode impedance requires a 40/3/sup 2/ or /spl sim/4.5 ohm source to drive the three IVA cavities in parallel; a convenient impedance for a single water coax. The water coax is designed to function as a two-step impedance transformer as well as a long, passive water cable, accommodating several bends along its length. The latter feature allows independent positioning of the pulsed power driver, IVA and diode x-ray source. The long water coax is driven by a PFL originally developed for Sandias Radiographic Integrated Test Stand (RITS) and a low-inductance commercial Marx charges the single PFL. The accelerator design is a result of a cooperative effort by Titan-PSI and Maxwell (now collectively Titan-PSD) SNLA, LANL, NRL, and Bechtel-Nevada.


IEEE Transactions on Plasma Science | 1980

High Power Density Water Dielectric Switching

D.L. Johnson; J. P. Vandevender; T. H. Martin

Pulse forming networks for high current particle beam fusion accelerators must produce fast rise time, low jitter, low prepulse, and high voltage power pulses. Conventional water dielectric switching can provide the required rise time and jitter, but has limitations on prepulse and output voltage. A high power density, low prepulse, pulse forming line (PFL) configuration with self-breakdown water dielectric switches is presented. The design parameters and the results of switching experiments are described.


Review of Scientific Instruments | 2003

Optimization of a rod pinch diode radiography source at 2.3 MV

P.R. Menge; D.L. Johnson; J.E. Maenchen; Dean C. Rovang; B.V. Oliver; D. V. Rose; D.R. Welch

Rod pinch diodes have shown considerable capability as high-brightness flash x-ray sources for penetrating dynamic radiography. The rod pinch diode uses a small diameter (0.4–2 mm) anode rod extended through a cathode aperture. When properly configured, the electron beam born off of the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. Sandia’s SABRE accelerator (2.3 MV, 40 Ω, 70 ns) has been utilized to optimize the source experimentally by maximizing the figure of merit (dose/spot diameter2) and minimizing the diode impedance droop. Many diode parameters have been examined including rod diameter, rod length, rod material, cathode aperture diameter, cathode thickness, power flow gap, vacuum quality, and severity of rod–cathode misalignment. The configuration producing the greatest figure of merit uses a 0.5 mm diameter gold rod, a 6 mm rod extension beyond the cathode aperture (diameter=8 mm), and a 10 cm power flow gap to produce up to 3.5 rad (fi...


ieee international conference on pulsed power | 1991

Sabre, A 10-mv Linear Induction Accelerator

J.P. Corley; S.A. Alexander; P.J. Pankuch; C.E. Heath; D.L. Johnson; Juan J. Ramirez; G.J. Denison

SABRE (Sandia Accelerator and Beam Research Experiment) is a 10-MV, 250-kA, 40-ns linear induction accelerator. It was designed to be used in positive polarity output. Positive polarity accelerators are important for application to Sandias ICF (Inertial Confinement Fusion) and LMF (Laboratory Microfusion Facility) program efforts. SABRE was built to allow a more detailed study of pulsed power issues associated, with positive polarity output machines, MITL (Magnetically Insulated Transmission Line) voltage adder efficiency, extraction ion diode development, and ion beam transport and focusing. The SABRE design allows the system to operate in either positive polarity output for ion extraction applications or negative polarity output for more conventional electron beam loads. Details of the design of SABRE and the results of initial machine performance in negative polarity operation are presented in this paper.


ieee international pulsed power conference | 1999

Design of a radiographic integrated test stand (RITS) based on a voltage adder, to drive a diode immersed in an high magnetic field

I. Smith; V. Bailey; P. Corcoran; J. Kishi; J. Fockler; J. Gustwiller; D.L. Johnson; J.E. Maenchen; D. Droemer

Advanced radiography capabilities can be provided by diodes in which a <1 mm diameter cathode is immersed in a /spl sim/60 T magnetic field and pulsed to /spl sim/16 MV. An electron current of /spl sim/50 kA is constrained by the magnetic field to /spl sim/1 mm at the anode, and produces V 1 krad at 1 m. A 16 MV, 50 ns flat-top voltage adder has been designed that is optimum to develop such diodes. The adder approach is chosen to give a relatively short risetime and low prepulse. It also has the advantage of being re-configurable to provide two 8 MV pulses. The pulser uses standard Marxes, intermediate stores, and water PFLs. Novel features include an oil prepulse switch, an induction cell that is fed from one point, and a blocking network to couple two pulses to one cell. Based on detailed simulations, a design has been completed through detailed drawings and prototype hardware will be tested next year.


international conference on high power particle beams | 2002

The ZR refurbishment project

D. H. McDaniel; M.G. Mazarakis; D.E. Bliss; Juan M. Elizondo; H.C. Harjes; H.C. Ives; D.L. Kitterman; J.E. Maenchen; T.D. Pointon; S. E. Rosenthal; D.L. Smith; K.W. Struve; W. A. Stygar; E.A. Weinbrecht; D.L. Johnson; J.P. Corley

ZR is a refurbished (R) version of Z aiming to improve its overall performance, reliability, precision, pulse shape tailoring and reproducibility. Z, the largest pulsed power machine at Sandia, began in December 1985 as the Particle Beam Fusion Accelerator II (PBFA II). PBFAII was modified in 1996 to a z-pinch driver by incorporating a high-current (20-MA, 2.5-MV) configuration in the inner ∼ 4.5 meter section. Following its remarkable success as z-pinch driver, PBFA II was renamed Z in 1997. Currently Z fires 170 to 180 shots a year with a peak load current of the order of 18–20 MA. The maximum z-pinch output achieved to date is 1.6-MJ, 170-TW radiated energy and power from a single 4-cm diameter, 2-cm tall array, and 215 eV temperature from a dynamic hohlraum. ZR in turn will, operating in double shift, enable 400 shots per year, deliver a peak current of 26 MA into a standard 4cm × 2cm Z-pinch load, and should provide a total radiated x-ray energy and power of 3 MJ and 350 TW, respectively, achieve a maximum hohlraum temperature of 260 eV, and include a pulse-shaping flexibility extending from 100ns to 300ns for equation of state and isentropic compression studies. To achieve this performance ZR will incorporate substantial modifications and upgrades to Marx generator, intermediate store capacitors, gas and water switches, water transmission lines and the laser triggering system. Test beds are already in place, and the new pulsed power components are undergoing extensive evaluation. The Z refurbishment (ZR) will be operational by 2006 and will cost approximately

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J.E. Maenchen

Sandia National Laboratories

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B.V. Oliver

Sandia National Laboratories

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I. Molina

Sandia National Laboratories

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D.R. Welch

Sandia National Laboratories

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Dean C. Rovang

Sandia National Laboratories

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Joshua J. Leckbee

Sandia National Laboratories

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K.W. Struve

Sandia National Laboratories

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J. R. Woodworth

Sandia National Laboratories

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D. H. McDaniel

Sandia National Laboratories

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