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  • 1
    Electronic Resource
    Electronic Resource
    Charged particle flow in plasma-filled pinched-electron-beam diodes (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2274-2286 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma-filled pinched-electron-beam diode experiments have been performed on the Gamble II (1.5 MV, 800 kA, 60 ns) pulsed power generator at Naval Research Laboratory. These plasma-filled diode (PFD) experiments show three phases of behavior: a low impedance phase followed by a phase of rapidly increasing impedance that culminates in a relatively constant vacuum impedance phase. The duration of the low impedance phase as well as the final operating impedance depends on the prefill plasma density. The charged particle flow in the PFD is studied with one-dimensional (1-D) and two-dimensional (2-D) simulation models. These simulation models show the formation of growing sheaths at both electrodes during the low impedance phase. The end of the low impedance phase in the simulations coincides with the two sheaths meeting in the center of the anode-cathode (A-K) gap. Based on these observations, an analytic model was developed that treats the low impedance phase as symmetric bipolar sheaths. The analytical model adequately predicts the duration of the low impedance phase predicted by the 1-D simulation model. Differences between the bipolar model and the experiments or 2-D simulations can be explained in terms of magnetized sheaths which enhance the ion current over the bipolar level and cause the sheath to grow faster than the bipolar model. During the rapidly increasing impedance phase, the simulations show that the cathode sheath quickly expands to completely fill the A-K gap. At this time, charged particle flow in the simulation models are consistent with the vacuum gap spacing. Experimentally, the higher density, longer conduction time, PFD shots exhibited a significantly lower final impedances than predicted by 2-D simulations. This difference is probably caused by expanding electrode surface plasmas produced by the interaction of the plasma source with one or both electrode surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354711
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  • 2
    Electronic Resource
    Electronic Resource
    K-shell x-ray yield scaling for aluminum x-pinch plasmas (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8134-8138 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report results from experiments performed to measure and characterize the intense K-shell radiation from aluminum x-pinch plasmas at peak driving currents ranging from 280 kA to 1.0 MA. Single pulse aluminum K-shell (predominantly line radiation at 1.6–2 keV) x-ray yields ranged from 7.6 J at 290 kA to 240 J at 1.0 MA. In the range from 280 to 470 kA, the yield scales with current to the power of 3.6, whereas nonoptimized K-shell yields at 800 kA and 1.0 MA indicate a power of about 3 or higher.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353452
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical modeling and experimental characterization of a rod-pinch diode (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4618-4636 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The rod-pinch diode consists of an annular cathode and a small-diameter anode rod that extends through the hole in the cathode. With high-atomic-number material at the tip of the anode rod, the diode provides a small-area, high-yield x-ray source for pulsed radiography. The diode is operated in positive polarity at peak voltages of 1 to 2 MV with peak total electrical currents of 30–70 kA. Anode rod diameters as small as 0.5 mm are used. When electrode plasma motion is properly included, analysis shows that the diode impedance is determined by space-charge-limited current scaling at low voltage and self-magnetically limited critical current scaling at high voltage. As the current approaches the critical current, the electron beam pinches. When anode plasma forms and ions are produced, a strong pinch occurs at the tip of the rod with current densities exceeding 106 A/cm2. Under these conditions, pinch propagation speeds as high as 0.8 cm/ns are observed along a rod extending well beyond the cathode. Even faster pinch propagation is observed when the rod is replaced with a hollow tube whose wall thickness is much less than an electron range, although the propagation mechanism may be different. The diode displays well-behaved electrical characteristics for aspect ratios of cathode to anode radii that are less than 16. New physics understanding and important properties of the rod-pinch diode are described, and a theoretical diode current model is developed and shown to agree with the experimental results. Results from numerical simulations are consistent with this understanding and support the important role that ions play. In particular, it is shown that, as the ratio of the cathode radius to the anode radius increases, both the Langmuir–Blodgett space-charge-limited current and the magnetically limited critical current increase above previously predicted values. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1403016
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  • 4
    Electronic Resource
    Electronic Resource
    Self-pinched transport of an intense proton beam (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 346-358 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion beam self-pinched transport (SPT) experiments have been carried out using a 1.1-MeV, 100-kA proton beam. A Rutherford scattering diagnostic and a LiF nuclear activation diagnostic measured the number of protons within a 5 cm radius at 50 cm into the transport region that was filled with low-pressure helium. Time-integrated signals from both diagnostics indicate self-pinching of the ion beam in a helium pressure window between 35 and 80 mTorr. Signals from these two diagnostics are consistent with ballistic transport at pressures above and below this SPT pressure window. Interferometric measurements of electron densities during beam injection into vacuum are consistent with ballistic transport with co-moving electrons. Interferometric measurements for beam injection into helium show that the electron density increases quadratically with pressure through the SPT window and roughly linearly with pressure above the SPT window. The ionization fraction of the helium plateaus at about 1.5% for pressures above 80 mTorr. In the SPT window, the electron density is 3 to 20 times the beam density. Numerical simulations of these beam transport experiments produce results that are in qualitative agreement with the experimental measurements. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873803
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  • 5
    Electronic Resource
    Electronic Resource
    Interaction of intense MeV light-ion beams with low-pressure gasesf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1700-1707 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of intense proton beams with low-pressure (0.25 to 4 Torr) background gases is studied to evaluate beam-current neutralization during transport. Electrons to neutralize the beam are provided by beam-induced ionization of the gas. In experiments with 1 MeV, 1 kA/cm2 protons, net currents outside the beam envelope and electron densities within the beam envelope are measured for helium, neon, argon, and air. Net-current fractions are 2% to 8% and ionization fractions are 0.6% to 5% for 5 to 7 kA beams. Simulations of the experiments for helium and argon suggest that fast electrons play an important role in generating a significant fraction of the return current in a halo outside the beam. As a result, net currents inside the beam may be larger than inferred from magnetic-field measurements outside the beam. Ions at the head of the beam are observed to lose more energy than expected from collisional energy losses in the background gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870673
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  • 6
    Electronic Resource
    Electronic Resource
    High-fluence large-area MeV proton-beam diagnostics : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3122-3124 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The spatial distribution of intense MeV pulsed proton beams over 100 cm2 area is measured with two techniques. An array of carbon-activation samples gives fluences of 100–400 J/cm2 with 1–2 cm resolution. Continuous distributions with 3–4 mm resolution are obtained by imaging proton-induced Al K-line x rays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141701
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  • 7
    Electronic Resource
    Electronic Resource
    Erratum: "Theoretical modeling and experimental characterization of a rod-pinch diode" [Phys. Plasmas 8, 4618 (2001)] (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3643-3643 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1493795
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  • 8
    Electronic Resource
    Electronic Resource
    Radiachromic film as a detector for intense MeV proton beams : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1201-1204 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple technique has been developed to image intense pulsed proton beams with radiachromic film and to measure their spatial distribution. The optical density (OD) of 50 μm thick film, sufficient to stop 1.5 MeV protons, is measured to infer the incident beam fluence. The OD increases nearly linearly with fluence up to 0.25 cal/cm2. This film is used to measure the uniformity of large-area beams as well as the detector in a multiple-pinhole camera to determine the source uniformity and divergence of applied-magnetic field and pinched-beam ion diodes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149298
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  • 9
    Electronic Resource
    Electronic Resource
    A Rutherford scattering diagnostic for intense pulsed proton beams transported in low-pressure gases : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 281-284 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Rutherford scattering of pulsed 1 MeV proton beams is developed as a time-resolved fluence diagnostic for proton transport experiments. The incident beam is scattered from a thin aluminum target and recorded with a silicon PIN detector. For a pinched-beam diode, fluences of protons transported in 1 Torr air are consistent with fluences determined with calorimeters, provided the proton energy is smaller than expected from the measured ion current and voltage. Beam bunching is observed as the flight path increases, consistent with reduced proton energy at the head of the beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147823
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  • 10
    Electronic Resource
    Electronic Resource
    Absolute calibration of nuclear activation diagnostics for intense pulsed ion beams (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2182-2188 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Absolute calibration of an annihilation-radiation NaI coincidence detection system for short-lived ion-induced radioactivity is described. Calibration with a 22Na radioactive source is compared with an independent calibration using the 12C(p,γ)13N(β+) reaction with 1 MeV protons from a Van de Graaff accelerator. These calibrations are consistent, provided correction for summing of the 0.51 and 1.27 MeV gamma rays from the 22Na source in the NaI detectors is included. This summing correction depends on the total efficiency for detecting 1.27 MeV gamma rays and can alter the calibration by as much as a factor of 2, depending on the size and separation of the detectors. A procedure to determine this correction using 60Co and 22Na radioactive sources is described. These two calibrations give a thick-target yield for the 12C(p,γ)13N reaction at 1 MeV of (8.0±0.4)×10−10 reactions/proton. Intense pulsed proton fluences of 0.08 to 3.7 cal/cm2, determined by coincidence counting β+ annihilation radiation produced by the 12C(p,γ)13N(β+) reaction, are in agreement with ion-beam fluences measured independently with carbon calorimeters on the same carbon sample. © 1996 American Institute of Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147048
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