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At least 163 records · Page 9

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NASA NTRS2019

Pulsed Plasma Acceleration Modeling in Detonation and Deflagration Modes

Gas-fed electromagnetic pulsed plasma accelerators discharge electrical energy into a gas to ionize and electromagnetically accelerate propellant in the domain. Efforts to model pulsed accelerators have either assumed that the discharge is short and completely tran- sient, accelerating the gas by entraining it in a moving current sheet, or that the discharge is relatively long, establishing a stable quasi-steady current distribution pattern that accel- erates a plasma flowing through it. There have been pulsed plasma accelerator tests that appear to fit somewhere between these two bounds, exhibiting some properties that are associated with the purely transient devices while also showing others that are associated with quasi-steady-state plasma acceleration. A model is presented based upon the premise that all pulsed plasma accelerators first form an accelerating current sheet (detonation mode accelerator). Depending upon the pulse length and the gas conditions in the dis- charge channel, the plasma sheet may reach the end of the accelerator before the discharge has completed a full half-cycle, wherein the proposed model transitions to a quasi-steady description of the acceleration process (deflagration mode accelerator). A review of the entire model is presented, highlighting improvements and upgrades implemented to aid in the stability of the numerical scheme used to model the gas flow in the channel and an im- proved treatment of current sheet mass shedding, which adds gas to the wake of the sheet. The assumptions employed to model the transition from detonation to deflagration mode are presented and used to generate solutions to the governing equations. The modeling of the deflagration-mode under the present assumptions results in very low deflagration im- pulse bits relative to those obtained at the end of the detonation mode, implying that the present assumptions and modeling of the deflagration mode may not represent a fruitful approach.

Polzin, Kurt A.↗

DOE OSTI2017

Numerical Modeling of Ultra Wideband Combined Antennas

With the help of a program we developed, based on the finite difference method in the time domain, we have investigated the characteristics of ultra wideband combined antennas in detail. The antennas were developed to radiate bipolar pulses with durations in the range 0.5–3 ns. Data obtained by numerical modeling are compared with the data of experimental studies on antennas and have been used in the synthesis of electromagnetic pulses with maximum field strength.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS2005

Galium Electromagnetic (GEM) Thruster Concept and Design

We describe the design of a new type of two-stage pulsed electromagnetic accelerator, the gallium electromagnetic (GEM) thruster. A schematic illustration of the GEM thruster concept is given. In this concept, liquid gallium propellant is pumped into the first stage through a porous metal electrode using an electromagnetic pump. At a designated time, a pulsed discharge (approx. 10-50 J) is initiated in the first stage, ablating the liquid gallium from the porous electrode surface and ejecting a dense thermal gallium plasma into the second state. The presence of the gallium plasma in the second stage serves to trigger the high-energy (approx. 500 J), second-stage pulse which provides the primary electromagnetic (j x B) acceleration.

Polzin, Kurt A.↗

DOE OSTI2013

Nonlinear extraordinary wave in dense plasma

Conditions for the propagation of a slow extraordinary wave in dense magnetized plasma are found. A solution to the set of relativistic hydrodynamic equations and Maxwell’s equations under the plasma resonance conditions, when the phase velocity of the nonlinear wave is equal to the speed of light, is obtained. The deviation of the wave frequency from the resonance frequency is accompanied by nonlinear longitudinal-transverse oscillations. It is shown that, in this case, the solution to the set of self-consistent equations obtained by averaging the initial equations over the period of high-frequency oscillations has the form of an envelope soliton. The possibility of excitation of a nonlinear wave in plasma by an external electromagnetic pulse is confirmed by numerical simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Modification of Structural, Chemical and Process Properties of Rare Metal Minerals under Treatment by High-Voltage Nanosecond Pulses

The authors have studied the mechanism of controlled modification of composition, structure, chemistry, physicochemical and process properties of columbite, tantalite, zircon and feldspar at the meso-, micro- and nanoscales after nonthermal treatment by high-voltage nanosecond electromagnetic pulses. The studies used methods: X-ray photoelectron spectroscopy, scanning electron and atomic force microscopy, potentiometric titration, electromigration chromatography, Kelvin probe force microscopy, microhardness metering and assessment of hydrophobic behavior and flotation activity of the minerals. It is found that changes in the chemical state of atoms on the surface of minerals are mainly connected with the sequential transformation of stages in the process of formation and modification of a functional cover of mineral surface, with variation in a ratio of different type hydroxyl groups on the surface of columbite, zircon and feldspar, which conditions contrast physicochemical properties of rare metal minerals and improves selectivity of their separation by flotation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Mesoscopic fluctuations of the population of a qubit in a strong alternating field

Fluctuations of the population of a Josephson qubit in an alternating field, which is a superposition of electromagnetic pulses with large amplitudes, are studied. It is shown that the relative phase of pulses is responsible for the rate of Landau–Zener transitions and, correspondingly, for the frequency of transitions between adiabatic states. The durations of pulses incident on the qubit are controlled with an accuracy of the field period, which results in strong mesoscopic fluctuations of the population of the qubit. Similar to the magnetic field in mesoscopic physics, the relative phase of pulses can destroy the interference pattern of the population of the qubit. The influence of the duration of the pulse and noise on the revealed fluctuation effects is studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Measurement of the target current by inductive probe during laser interaction on terawatt laser system PALS

Measurements of the return-current flowing through a solid target irradiated with the sub-nanosecond kJ-class Prague Asterix Laser System is reported. A new inductive target probe was developed which allows us measuring the target current derivative in a kA/ns range. The dependences of the target current on the laser pulse energy for cooper, graphite, and polyethylene targets are reported. The experiment shows that the target current is proportional to the deposited laser energy and is strongly affected by the shot-to-shot fluctuations. The corresponding maximum target charge exceeded a value of 10 μC. A return-current dependence of the electromagnetic pulse produced by the laser-target interaction is presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2018

Self-Similar Character of Generation of Superradiance Pulses in an Electron–Wave Backward Wave Oscillator

The phenomenon of superradiance of electron bunches provides a promising method for generating high-power ultrashort electromagnetic pulses. In the present paper, it is shown that the equations describing the interaction between an electron beam and an electromagnetic wave in a BWO-type oscillator admit a self-similar solution that describes an amplifying and compressing pulse. It is demonstrated by numerical simulation that the generation of short superradiance pulses is of self-similar character at the initial stage of the transient process. The specific features of the main characteristics of such pulses (the amplitude and width of a pulse and the coordinates of its maximum) are investigated as a function of time and control parameters. It is shown that, after a transient process, the solution reaches the self-similar stage, where the pulse amplitude and the inverse of its squared width grow linearly with time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation

We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domain spectroscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

Tiny Electromagnetic Explosions

This paper considers electromagnetic transients of a modest total energy (E≳10{sup 40} erg) and small initial size (R≳10{sup −1} cm). They could be produced during collisions between relativistic field structures (e.g., macroscopic magnetic dipoles) that formed around or before cosmic electroweak symmetry breaking. The outflowing energy has a dominant electromagnetic component; a subdominant thermal component (temperature >1 GeV) supplies inertia in the form of residual e{sup ±}. A thin shell forms, expanding subluminally and attaining a Lorentz factor ∼10{sup 6--7} before decelerating. Drag is supplied by the reflection of an ambient magnetic field and deflection of ambient free electrons. Emission of low-frequency (GHz–THz) superluminal waves takes place through three channels: (i) reflection of the ambient magnetic field; (ii) direct linear conversion of the embedded magnetic field into a superluminal mode; and (iii) excitation outside the shell by corrugation of its surface. The escaping electromagnetic pulse is very narrow (a few wavelengths), so the width of the detected transient is dominated by propagation effects. GHz radio transients are emitted from (i) the dark matter halos of galaxies and (ii) the near-horizon regions of supermassive black holes that formed via direct gas collapse and now accrete slowly. Brighter and much narrower 0.01–1 THz pulses are predicted at a rate at least comparable to fast radio bursts, experiencing weaker scattering and absorption. The same explosions also accelerate protons up to ∼10{sup 19} eV, and heavier nuclei up to 10{sup 20–21} eV.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Antiferromagnetic resonance excitation by terahertz magnetic field resonantly enhanced with split ring resonator

Excitation of antiferromagnetic resonance (AFMR) in a HoFeO{sub 3} crystal combined with a split ring resonator (SRR) is studied using terahertz (THz) electromagnetic pulses. The magnetic field in the vicinity of the SRR is induced by the incident THz electric field component and excites spin oscillations that correspond to the AFMR, which are directly probed by the Faraday rotation of the polarization of a near-infrared probe pulse. The good agreement of the temperature-dependent magnetization dynamics with the calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms that the AFMR is excited by the THz magnetic field, which is enhanced at the SRR resonance frequency by a factor of 20 compared to the incident magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Size effects on the structural, electronic, and optical properties of (5,0) finite-length carbon nanotube: An ab-initio electronic structure study

We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4–44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

EMP Coupling to a Straight Conductor Above Ground: Transmission Line Formulation Based on Electromagnetic Reciprocity

A simple model for coupling of an electromagnetic plane wave incident on a conductor above ground has been developed using reciprocity theory, providing some advantages as compared to the conventional transmission line approach. The model is developed using a semi-infinitely long single conductor above a lossy ground plane and connected by an arbitrary load impedance to a vertical grounding conductor. This configuration corresponds to the worst-case wave coupling, because it leads to a line induced current larger than in the cases of finite and multiconductor lines. A frequency-domain Thévenin equivalent model is developed to relate the incident wave amplitude to the voltage across a generic load, connected at any point on the vertical conductor. The application to the threat analysis of a high-altitude electromagnetic pulse impact on a power transmission line is discussed by considering the time-domain solution (via inverse Fourier transform) for an incident EMP fast-rise transient (E1) waveshape, following the standard IEC specifications. For typical high-voltage power line load impedances, it is shown that voltage magnitudes in the MV range can be induced across the line termination, in the case of a wave with a near-grazing incidence angle and with wave vector aligned along the horizontal conductor.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2016

Distribution of leakage currents in the cylindrical and conical sections of the magnetically insulated transmission line of the Angara-5-1 facility in experiments with wire arrays

Current leakages in the magnetically insulated transmission lines (MITL) impose restrictions on the transmission of electromagnetic pulses to the load in high-power electrophysical facilities. The multimodule Angara-5-1 facility with an output electric power of up to 6 TW is considered. In this work, the experimental and calculated profiles of leakage currents in two sections of the line are compared when the eight-module facility is loaded by a wire array. The azimuthal distribution of the current in the cylindrical section of the MITL is also considered.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Peculiarities of the coherent spontaneous synchrotron radiation of dense electron bunches

In a short section of homogeneous magnetic field, quasi-plane electron bunches from linear accelerators with laser-driven photo-injectors at moderate particle energies can generate strongly directed, very short and powerful terahertz electromagnetic pulses with a broad frequency spectrum. The formulas for radiation fields, their spectra and efficiency of radiation are presented in a very simple analytical form using expressions for the fields of an arbitrary moving charged plane. The self-action and mutual interaction of thin electron layers are estimated. It is shown that the radiation with frequencies of up to (1–3) THz can be effectively generated by electrons with energies (4–6) MeV in a short and relatively weak magnetic field of (4–10) kOe.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Measurements of Ionizing Radiation Doses Induced by High Irradiance Laser on Targets in LCLS MEC Instrument - Paper 75

High-power laser interaction with targets in vacuum at high laser irradiance levels can generate plasma and, consequently, create ionizing radiation hazards. The theory for ionizing radiation generation from laser-plasma interaction is complicated. The basics of theory and phenomenology are available qualitatively. However, the ionizing radiation yields associated with laser-plasma interaction have not been well quantified. Based on the theoretical analysis and review of the published reports and measurement data, SLAC National Accelerator Laboratory (SLAC) developed an analytic model to estimate conservatively the electron temperature and photon radiation yield (Sv/J) of a laser pulse hitting a solid target at 1 m as a function of laser irradiance between 10{sup 15} and 10{sup 21} W/cm{sup 2}. Ionizing radiation measurements from high-intensity laser-induced plasma interactions on solid targets inside the Al-walled vacuum chamber of the LCLS MEC instrument at SLAC were conducted using passive and active detectors at irradiance between 3x10{sup 16} and 6x10{sup 17} W/cm{sup 2}. Each run of the more than 20 runs had a unique set of laser, optic and target conditions with laser pulses rastering over the target surface mainly perpendicularly at a fixed irradiance. Significant effort was made in characterizing the laser irradiance values for each configuration of laser, focusing mirror, and target; four irradiances with targets of Au foils and copper plate were found to produce good measurement results. Electron doses inside the target chamber were highly anisotropic and peaked at backward direction by several orders of magnitude. Photon doses outside the target chamber were nearly isotropic (a factor of ∼2 higher in backward direction). When considering the large uncertainties of the irradiance (a factor of 2-3) and the potential shielding effects from detectors and target chamber, the measured photon dose rates at 1 m (150 mJ and 10 Hz) outside the target chamber (when averaged over different types of detectors) were in good agreement (a factor of ∼3) with the calculated values of the SLAC model, except at 3.0x10{sup 16} W/cm{sup 2}, which has an electron temperature of only 14 keV. At 6x10{sup 17} W/cm{sup 2}, a low level of ∼0.1 mrem/h from fast neutrons was measured (at 1 m, 150 mJ and 10 Hz) with a neutron-to-photon dose ratio of 0.2%. This is equivalent to a neutron dose yield of 2.8x10{sup -8} mSv/J (to be compared to the LULI measurements of 1x10{sup -4} mSv/J at 3x10{sup 19} W/cm{sup 2}). Both active and passive types of detectors performed well and the dose results were consistent, which is the same as the dose measurements in the Titan laser facility. Active detectors were not affected by the electromagnetic pulses associated with the MEC laser system; this was different from the Titan radiation measurements, in which all active detectors failed to respond, likely due to the high EMP in the Titan's high laser intensity fields. (authors)

43 PARTICLE ACCELERATORS↗

DOE OSTI2015

Determination of energy release zones arising due to current losses in the convolution region of the magnetically insulated transmission lines of the ANGARA-5-1 facility

Among the factors limiting electromagnetic pulse transmission to the load in high-power electro-physical facilities, current losses in magnetically insulated transmission lines (MITLs) are of significant importance. One of such facilities is ANGARA-5-1—a multimodule facility with an output electric power of up to 6 TW. A fairly complicated configuration of the magnetic field in the convolution region of several MITLs makes it difficult to fix the places of current losses there. In this work, these places were determined by detecting the positions of IR sources in the convolution region of the MITLs of the ANGARA-5-1 facility.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Assessing the vulnerability of solar inverters to EMPs: Port testing, PCI modeling, and protection strategies

Renewable energy sources are becoming an ever-larger contributor to the power grid. These renewable energy sources depend upon the power electronic devices, specifically inverters, being essential for connecting Photovoltaic (PV) generation to the grid. However, the Electromagnetic Pulses (EMPs) caused by the high-altitude nuclear explosions can generate fast broad-band pulses with nanosecond rise time, potentially causing damage or destruction to electronic components. To assess the vulnerability of PV inverters to high-altitude EMPs, the port testing and Pulsed Current Injection (PCI) modeling schemes are proposed based on the port impedance analysis. Wide-band frequency measurements are achieved by fusing impedance results from three vector network analyzers. Then, a PCI model is used to simulate the induced response to EMP, with two typical immunity levels of EC5 and EC8 tested. Here, the experiment successfully excites the induced voltage and current under EMP, where the voltage and current can reach 1500V/40A and 8000V/150Aunder EC5 andEC8, respectively. The port vulnerability analysis results demonstrate that only some ports can survive under EC5. To defend against the impact of EMP, three protection strategies are discussed.

42 ENGINEERING↗