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1

Self-similar relativistic blast waves with energy injection

NASA Astrophysics Data System (ADS)

A sufficiently powerful astrophysical source with power-law luminosity in time will give rise to a self-similar relativistic blast wave with a reverse shock travelling into the ejecta and a forward shock moving into the surrounding medium. Once energy injection ceases and the last energy is delivered to the shock front, the blast wave will transit into another self-similar stage depending only on the total amount of energy injected. I describe the effect of limited duration energy injection into environments with density depending on radius as a power law, emphasizing optical/X-ray Gamma-ray Burst afterglows as applications. The blast wave during injection is treated analytically, the transition following last energy injection with one-dimensional simulations. Flux equations for synchrotron emission from the forward and reverse shock regions are provided. The reverse shock emission can easily dominate, especially with different magnetizations for both regions. Reverse shock emission is shown to support both the reported X-ray and optical correlations between afterglow plateau duration and end time flux, independently of the luminosity power-law slope. The model is demonstrated by application to bursts 120521A and 090515, and can accommodate their steep post-plateau light-curve slopes.

van Eerten, Hendrik

2014-08-01

2

Synchrotron signature of a relativistic blast wave with decaying microturbulence

NASA Astrophysics Data System (ADS)

Microphysics of weakly magnetized relativistic collisionless shock waves, corroborated by recent high performance numerical simulations, indicates the presence of a microturbulent layer of large magnetic field strength behind the shock front, which must decay beyond some hundreds of skin depths. This paper discusses the dynamics of such microturbulence, borrowing from these same numerical simulations, and calculates the synchrotron signature of a power law of shock accelerated particles. The decaying microturbulent layer is found to leave distinct signatures in the spectro-temporal evolution of the spectrum F? ? t-??-? of a decelerating blast wave, which are potentially visible in early multiwavelength follow-up observations of gamma-ray bursts. This paper also discusses the influence of the evolving microturbulence on the acceleration process, with particular emphasis on the maximal energy of synchrotron afterglow photons, which falls in the GeV range for standard gamma-ray burst parameters. Finally, this paper argues that the evolving microturbulence plays a key role in shaping the spectra of recently observed gamma-ray bursts with extended GeV emission, such as GRB 090510.

Lemoine, M.

2013-01-01

3

Secondary Waves from Nozzle Blast.

National Technical Information Service (NTIS)

Blast signatures at the gunner's position produced by recoilless rifles and rocket launchers often exhibit a strong secondary wave following chamber blowdown. To identify its source a series of experiments was performed using a helium-driven blast simulat...

G. C. Carofano

1984-01-01

4

Propagation of Nonideal Blast Waves.

National Technical Information Service (NTIS)

The propagation of non-ideal blast waves initiated by finite power density sources has been classified into three regimes. The early-time motion of a non-ideal blast reflects the characteristics of the energy-time profile of the particular initiation ener...

C. M. Guirao G. G. Bach J. H. Lee

1974-01-01

5

Blast waves in rotating media.

NASA Technical Reports Server (NTRS)

The model investigated involves a cylindrically symmetric blast wave generated by an infinitely long line explosion in a cold and homogeneous gas rotating rigidly in its self-gravitational field. It is found that within the context of rotation in a gravitational field a blast wave will not adopt the one-zone form familiar from similarity solutions but, rather, a two-zone form. The inner compression zone arises as a response to the presence of the restoring force, which drives a rarefaction wave into the outer compression zone.

Rossner, L. F.

1972-01-01

6

Laboratory blast wave driven instabilities

NASA Astrophysics Data System (ADS)

This presentation discusses experiments well-scaled to the blast wave driven instabilities during the explosion phase of SN1987A. Blast waves occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 ?m plastic layer that is followed by a low density foam layer. A blast wave structure similar to those in supernovae, is created in the plastic layer. The blast wave crosses a perturbed interface, which produces nonlinear, unstable growth dominated by the Rayleigh-Taylor (RT) instability. Recent experiments have been performed using complex initial conditions featuring a three-dimensional interface structure with a wavelength of 71 ?m in two orthogonal directions, at times supplemented by an additional sinusoidal mode of 212 ?m or 424 ?m. We have detected the interface structure under these conditions, using dual orthogonal radiographs on some shots, and will show some of the resulting data. Recent advancements in our x-ray backlighting techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed. Current simulations do not show this phenomenon. This presentation will discuss the amount of mass in these spike extensions as well as the error analysis of this calculation. Future experiments will also be discussed. They will be focusing on realistic initial conditions based on 3D stellar evolution models. This research was sponsored by the Stewardship Science Academic Alliances Program through DOE Research Grants DE-FG52-07NA28058, DE-FG52-04NA00064, and other grants and contracts.

Kuranz, Carolyn

2008-04-01

7

Laboratory blast wave driven instabilities

NASA Astrophysics Data System (ADS)

This presentation discusses experiments involving the evolution of hydrodynamic instabilities in the laboratory under high-energy-density (HED) conditions. These instabilities are driven by blast waves, which occur following a sudden, finite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. Instabilities evolving under HED conditions are relevant to astrophysics. These experiments include target materials scaled in density to the He/H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 ?m plastic layer that is followed by a low-density foam layer. A blast wave structure similar to those in supernovae is created in the plastic layer. The blast wave crosses an interface having a 2D or 3D sinusoidal structure that serves as a seed perturbation for hydrodynamic instabilities. This produces unstable growth dominated by the Rayleigh-Taylor (RT) instability in the nonlinear regime. We have detected the interface structure under these conditions using x-ray backlighting. Recent advances in our diagnostic techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the RT spike and penetrating further than previously observed or predicted by current simulations. The observed effect is potentially of great importance as a source of mass transport to places not anticipated by current theory and simulation. I will discuss the amount of mass in these spike extensions, the associated uncertainties, and hypotheses regarding their origin We also plan to show comparisons of experiments using single mode and multimode as well as 2D and 3D initial conditions. This work is sponsored by DOE/NNSA Research Grants DE-FG52-07NA28058 (Stewardship Sciences Academic Alliances) and DE-FG52-04NA00064 (National Laser User Facility).

Kuranz, Carolyn

2008-11-01

8

Simulation of Blast Waves with Headwind

NASA Technical Reports Server (NTRS)

The blast wave resulting from an explosion was simulated to provide guidance for models estimating risks for human spacecraft flight. Simulations included effects of headwind on blast propagation, Blasts were modelled as an initial value problem with a uniform high energy sphere expanding into an ambient field. Both still air and cases with headwind were calculated.

Olsen, Michael E.; Lawrence, Scott W.; Klopfer, Goetz H.; Mathias, Dovan; Onufer, Jeff T.

2005-01-01

9

Gamma-ray burst afterglows from transrelativistic blast wave simulations

NASA Astrophysics Data System (ADS)

We present a study of the intermediate regime between ultrarelativistic and non-relativistic flow for gamma-ray burst afterglows. The hydrodynamics of spherically symmetric blast waves is numerically calculated using the AMRVAC adaptive mesh refinement code. Spectra and light curves are calculated using a separate radiation code that, for the first time, links a parametrization of the microphysics of shock acceleration, synchrotron self-absorption and electron cooling to a high-performance hydrodynamic simulation. For the dynamics, we find that the transition to the non-relativistic regime generally occurs later than expected, the Sedov-Taylor solution overpredicts the late-time blast wave radius and the analytical formula for the blast wave velocity from Huang, Dai & Lu overpredicts the late-time velocity by a factor of 4/3. Also, we find that the lab frame density directly behind the shock front divided by the fluid Lorentz factor squared remains very close to four times the unshocked density, while the effective adiabatic index of the shock changes from relativistic to non-relativistic. For the radiation, we find that the flux may differ up to an order of magnitude depending on the equation of state that is used for the fluid and that the counterjet leads to a clear rebrightening at late times for hard-edged jets. Simulating GRB 030329 using predictions for its physical parameters from the literature leads to spectra and light curves that may differ significantly from the actual data, emphasizing the need for very accurate modelling. Predicted light curves at low radio frequencies for a hard-edged jet model of GRB 030329 with opening angle 22° show typically two distinct peaks, due to the combined effect of jet break, non-relativistic break and counterjet. Spatially resolved afterglow images show a ring-like structure.

van Eerten, H. J.; Leventis, K.; Meliani, Z.; Wijers, R. A. M. J.; Keppens, R.

2010-03-01

10

Simple waves in relativistic magnetofluiddynamics

Summary Relativistic magnetofluiddynamics is a subject of importance for astrophysics and laboratory plasma physics. In this paper\\u000a some exact solutions of the full nonlinear equations of relativistic magnetofluiddynamics are studied, which correspond to\\u000a simple waves. The Riemann invariants are explicitly determined for various cases of noticeable physical interest.

A. M. Anile; O. Muscato

1983-01-01

11

Simple waves in relativistic magnetofluiddynamics

NASA Astrophysics Data System (ADS)

Magnetoacoustic simple waves, which show the effect of the breaking and forming of shock waves, are considered in this study of several exact solutions of the full nonlinear equations of relativistic magnetofluid-dynamics. The Riemann invariants are explicitly determined for various cases in characterizing completely the progressive fast simple waves.

Anile, A. M.; Muscato, O.

1983-12-01

12

Blast waves from cylindrical charges

NASA Astrophysics Data System (ADS)

Comparisons of explosives are often carried out using TNT equivalency which is based on data for spherical charges, despite the fact that many explosive charges are not spherical in shape, but cylindrical. Previous work has shown that it is possible to predict the over pressure and impulse from the curved surface of cylindrical charges using simple empirical formulae for the case when the length-to-diameter ( L/ D) ratio is greater or equal to 2/1. In this paper, by examining data for all length-to-diameter ratios, it is shown that it is possible to predict the peak over pressure, P, for any length-to-diameter ratio from the curved side of a bare cylindrical charge of explosive using the equation P=K_PM(L/D)^{1/3}/R^3, where M is the mass of explosive, R the distance from the charge and K_P is an explosive-dependent constant. Further out where the cylindrical blast wave `heals' into a spherical one, the more complex equation P=C_1(Z^' ' })^{-3}+C_2(Z^' ' })^{-2}+C_3(Z^' ' })^{-1} gives a better fit to experimental data, where Z^' ' } = M^{1/3}(L/D)^{1/9}/D and C_1, C_2 and C_3 are explosive-dependent constants. The impulse is found to be independent of the L/ D ratio.

Knock, C.; Davies, N.

2013-07-01

13

On the Propagation and Interaction of Spherical Blast Waves

NASA Technical Reports Server (NTRS)

The characteristics and the scaling laws of isolated spherical blast waves have been briefly reviewed. Both self-similar solutions and numerical solutions of isolated blast waves are discussed. Blast profiles in the near-field (strong shock region) and the far-field (weak shock region) are examined. Particular attention is directed at the blast overpressure and shock propagating speed. Consideration is also given to the interaction of spherical blast waves. Test data for the propagation and interaction of spherical blast waves emanating from explosives placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure.

Kandula, Max; Freeman, Robert

2007-01-01

14

Blast-wave characteristics near Site 300

The blast-wave overpressures propagating in the atmosphere near the Lawrence Livermore National Laboratory (LLNL) Site 300 have been measured at selected locations to determine whether the Site 300 blast operations will be hindered by the proposed construction of a residential development adjacent to its border.We tested high-explosives (HE) weights ranging from 14 to 545 lb under various weather conditions. Although more tests should be conducted before a definitive statement can be made on the blast propagation near Site 300, we offer the following preliminary interpretation of the results obtained to date. The readings at the closest locations show that the blast-wave overpressures exceed the 126-decibel (dB) level established by LLNL at about 250 lb of HE detonation. The weather conditions do not materially affect the pressure levels at these locations. Insufficient test data exist along the Corral Hollow Road perimeter, making it difficult to reasonably predict HE blast effects along the southern border. Therefore, we recommend that additional measurements be made along this and other boundaries in future tests, to provide more comprehensive data to help determine the blast-wave propagation characteristics in the proposed development areas. Blast-wave focusing may occur in the proposed residential development area under certain weather conditions. We recommend that this possibility should be addressed for its potentially adverse impact on the proposed residential area. Because the testing ground controlled by Physics International, Inc. (PI) is adjacent to Site 300, it is important to be aware of PI`s detonation activities. Peak overpressure measurements near PI`s Corral Hollow Road entrance reveal that PI shots over 25 lb HE have exceeded 126 dB, the limit established by LLNL for safe operations.

Kang, Sang-Wook; Kleiber, J.C. Jr.

1993-08-01

15

Strong Blast Wave Computer Programs.

National Technical Information Service (NTIS)

This report describes a computer program package for the computation of the flow field within a strong blast bubble. The programs are based on Sedov-Laporte-Chang formulas and compute any of the following: shock front location and corresponding flow value...

A. Celmins

1980-01-01

16

Reactive Blast Waves from Composite Charges

Investigated here is the performance of composite explosives - measured in terms of the blast wave they drive into the surrounding environment. The composite charge configuration studied here was a spherical booster (1\\/3 charge mass), surrounded by aluminum (Al) powder (2\\/3 charge mass) at an initial density of = 0.604 g\\/cc. The Al powder acts as a fuel but does

A L Kuhl; J B Bell; V E Beckner

2009-01-01

17

Boundary-layer theory for blast waves

NASA Technical Reports Server (NTRS)

It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.

Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.

1975-01-01

18

Blast waves and how they interact with structures.

The paper defines and describes blast waves, their interaction with a structure and its subsequent response. Explosions generate blast waves, which need not be due to explosives. A blast wave consists of two parts: a shock wave and a blast wind. The paper explains how shock waves are formed and their basic properties. The physics of blast waves is non-linear and therefore non-intuitive. To understand how an explosion generates a blast wave a numerical modelling computer code, called a hydrocode has to be employed. This is briefly explained and the cAst Eulerian hydrocode is used to illustrate the formation and propagation of the blast wave generated by a 1 kg sphere of TNT explosive detonated 1 m above the ground. The paper concludes with a discussion of the response of a structure to a blast wave and shows that this response is governed by the structures natural frequency of vibration compared to the duration of the blast wave. The basic concepts introduced are illustrated in a second simulation that introduces two structures into the blast field of the TNT charge. PMID:11307674

Cullis, I G

2001-02-01

19

Significance of blast wave studies to propulsion.

NASA Technical Reports Server (NTRS)

Brief survey of experimental methods currently used for the study of blast wave phenomena with emphasis on high rate exothermic processes. The experimental techniques have used such devices as divergent test sections in shock or detonation tubes, employment of proper test gases, as in marginal detonations, and a variety of explosion systems from finite source explosion apparatus to devices where virtually point explosions are obtained by local breakdown initiated by means of focused laser irradiation. Other methods used are detonation tubes where pressure waves are generated by accelerating flames or by exothermic reactions developed behind reflected shocks, as well as a variety of converging shock and implosion vessels.

Oppenheim, A. K.

1971-01-01

20

Cylindrical blast wave propagation in an enclosure

NASA Astrophysics Data System (ADS)

A numerical study of propagation and interaction of cylindrical blast waves in an enclosure at different blast intensities is presented. The interest to study such flows stems from the need to bring in an updated description of the flow field and to predict the pressure loads on the structure. An implicit-unfactored high-resolution hybrid Riemann solver for the two-dimensional Euler equations is used. The characteristic values at the cell faces are evaluated by a modified MUSCL scheme. Numerical schlieren-type images are used for understanding the flows qualitatively. The investigation indicated that the resulting flow field is dominated by complex interacting shock systems due to the complex series of shock focusing events, shock-structure and shock-shock interactions. The pressure-load distribution and maximum overpressure are estimated.

Bagabir, A. M.

2012-11-01

21

Computation of viscous blast wave flowfields

NASA Technical Reports Server (NTRS)

A method to determine unsteady solutions of the Navier-Stokes equations was developed and applied. The structural finite-volume, approximately factored implicit scheme uses Newton subiterations to obtain the spatially and temporally second-order accurate time history of the interaction of blast-waves with stationary targets. The inviscid flux is evaluated using MacCormack's modified Steger-Warming flux or Roe flux difference splittings with total variation diminishing limiters, while the viscous flux is computed using central differences. The use of implicit boundary conditions in conjunction with a telescoping in time and space method permitted solutions to this strongly unsteady class of problems. Comparisons of numerical, analytical, and experimental results were made in two and three dimensions. These comparisons revealed accurate wave speed resolution with nonoscillatory discontinuity capturing. The purpose of this effort was to address the three-dimensional, viscous blast-wave problem. Test cases were undertaken to reveal these methods' weaknesses in three regimes: (1) viscous-dominated flow; (2) complex unsteady flow; and (3) three-dimensional flow. Comparisons of these computations to analytic and experimental results provided initial validation of the resultant code. Addition details on the numerical method and on the validation can be found in the appendix. Presently, the code is capable of single zone computations with selection of any permutation of solid wall or flow-through boundaries.

Atwood, Christopher A.

1991-01-01

22

3D Tomographic imaging of colliding cylindrical blast waves

The interaction of strong shocks & radiative blast waves is believed to give rise to the turbulent, knotted structures commonly observed in extended astrophysical objects. Modeling these systems is however extremely challenging due to the complex interplay between hydrodynamics, radiation and atomic physics. As a result we have been developing laboratory scale blast wave collision experiments to provide high quality

R. A. Smith; J. Lazarus; M. Hohenberger; J. Robinson; A. Marocchino; J. Chittenden; M. Dunne; A. Moore; E. Gumbrell

2007-01-01

23

Evolution of blast wave profiles in simulated air blasts: experiment and computational modeling

NASA Astrophysics Data System (ADS)

Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90° orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation is sustained which causes tensile loading on the sides of the cylinder. Friedlander waves formed due to field explosives in the intermediate-to far-field ranges are replicated in a narrow test region located deep inside the shock tube.

Chandra, N.; Ganpule, S.; Kleinschmit, N. N.; Feng, R.; Holmberg, A. D.; Sundaramurthy, A.; Selvan, V.; Alai, A.

2012-09-01

24

Reactive Blast Waves from Composite Charges

Investigated here is the performance of composite explosives - measured in terms of the blast wave they drive into the surrounding environment. The composite charge configuration studied here was a spherical booster (1/3 charge mass), surrounded by aluminum (Al) powder (2/3 charge mass) at an initial density of {rho}{sub 0} = 0.604 g/cc. The Al powder acts as a fuel but does not detonate - thereby providing an extreme example of a 'non-ideal' explosive (where 2/3 of the charge does not detonate). Detonation of the booster charge creates a blast wave that disperses the Al powder and ignites the ensuing Al-air mixture - thereby forming a two-phase combustion cloud embedded in the explosion. Afterburning of the booster detonation products with air also enhances and promotes the Al-air combustion process. Pressure waves from such reactive blast waves have been measured in bomb calorimeter experiments. Here we describe numerical simulations of those experiments. A Heterogeneous Continuum Model was used to model the dispersion and combustion of the Al particle cloud. It combines the gasdynamic conservation laws for the gas phase with a dilute continuum model for the dispersed phase, as formulated by Nigmatulin. Inter-phase mass, momentum and energy exchange are prescribed by phenomenological models of Khasainov. It incorporates a combustion model based on mass conservation laws for fuel, air and products; source/sink terms are treated in the fast-chemistry limit appropriate for such gasdynamic fields, along with a model for mass transfer from the particle phase to the gas. The model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the Al particles with air. The model equations were integrated by high-order Godunov schemes for both the gas and particle phases. Adaptive Mesh Refinement (AMR) was used to capture the energy-bearing scales of the turbulent flow on the computational grid, and to track/resolve reaction zones. Numerical simulations of the explosion fields from 1.5-g and 10-kg composite charges were performed. Computed pressure histories (red curve) are compared with measured waveforms (black curves) in Fig. 1. Comparison of these results with a waveform for a non-combustion case in nitrogen (blue curve) demonstrates that a reactive blast wave was formed. Cross-sectional views of the temperature field at various times are presented in Fig. 2, which shows that the flow is turbulent. Initially, combustion occurs at the fuel-air interface, and the energy release rate is controlled by the rate of turbulent mixing. Eventually, oxidizer becomes distributed throughout the cloud via ballistic mixing of the particles with air; energy release then occurs in a distributed combustion mode, and Al particle kinetics controls the energy release rate. Details of the Heterogeneous Continuum Model and results of the numerical simulations of composite charge explosions will be described in the paper.

Kuhl, A L; Bell, J B; Beckner, V E

2009-10-16

25

Unsteady relativistic shock-wave diffraction by cylinders and spheres.

The unsteady relativistic shock-wave diffraction patterns generated by a relativistic blast wave impinging on a circular cylinder and a sphere are numerically simulated using some high-resolution relativistic kinetic beam schemes in a general coordinate system for solving the relativistic Euler equations of gas dynamics. The diffraction patterns are followed through about 6 radii of travel of the incident shock past the body. The complete diffraction patterns, including regular reflection, transition from regular to Mach reflection, slip lines, and the complex shock-on-shock interaction at the wake region resulting from the Mach shocks collision behind the body are reported in detail. Computational results of several incident shock Mach numbers covering the near ultrarelativistic limit are studied. Various contours of flow properties including the Lorentz factor and velocity streamline plots are also presented to add a better understanding of the complex diffraction phenomena. The three-dimensional relieving effects of the sphere cases are evident and can be quantitatively evaluated as compared with the corresponding cylinder cases. PMID:22463327

Tsai, I-Nan; Huang, Juan-Chen; Tsai, Shang-Shi; Yang, J Y

2012-02-01

26

Unsteady relativistic shock-wave diffraction by cylinders and spheres

NASA Astrophysics Data System (ADS)

The unsteady relativistic shock-wave diffraction patterns generated by a relativistic blast wave impinging on a circular cylinder and a sphere are numerically simulated using some high-resolution relativistic kinetic beam schemes in a general coordinate system for solving the relativistic Euler equations of gas dynamics. The diffraction patterns are followed through about 6 radii of travel of the incident shock past the body. The complete diffraction patterns, including regular reflection, transition from regular to Mach reflection, slip lines, and the complex shock-on-shock interaction at the wake region resulting from the Mach shocks collision behind the body are reported in detail. Computational results of several incident shock Mach numbers covering the near ultrarelativistic limit are studied. Various contours of flow properties including the Lorentz factor and velocity streamline plots are also presented to add a better understanding of the complex diffraction phenomena. The three-dimensional relieving effects of the sphere cases are evident and can be quantitatively evaluated as compared with the corresponding cylinder cases.

Tsai, I.-Nan; Huang, Juan-Chen; Tsai, Shang-Shi; Yang, J. Y.

2012-02-01

27

Relativistic electron acceleration by oblique whistler waves

Test-particle simulations of electrons interacting with finite-amplitude, obliquely propagating whistler waves are carried out in order to investigate the acceleration of relativistic electrons by these waves. According to the present findings, an efficient acceleration of relativistic electrons requires a narrow range of oblique propagation angles, close to the whistler resonance cone angle, when the wave amplitude is held constant at relatively low value. For a constant wave propagation angle, it is found that a range of oblique whistler wave amplitudes permits the acceleration of relativistic electrons to O(MeV) energies. An initial distribution of test electrons is shown to form a power-law distribution when plotted in energy space. It is also found that the acceleration is largely uniform in electron pitch-angle space.

Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States) [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Pandey, Vinay S. [National Institute of Technology Delhi, Dwarka, Delhi—110077 (India)] [National Institute of Technology Delhi, Dwarka, Delhi—110077 (India); Lee, Dong-Hun [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of)] [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of)

2013-11-15

28

Evidence for a blast wave from compressed nuclear matter

Central collisions of heavy nuclei at c.m. kinetic energies of a few hundred MeV per nucleon produce fireballs of hot, dense nuclear matter. Each fireball explodes, producing a blast wave of nucleons and pions. Several features of the observed cross sections for pions and protons from Ne on Na F at 0.8 GeV\\/nucleon (lab) are explained by the blast wave,

Philip Siemens; John Rasmussen

1979-01-01

29

Spectroscopic diagnostics in a colliding-blast-wave experiment

Visible spectral lines from [ital n]=3, [Delta][ital n]=0 transitions in N[sup +] and N[sup 2+] ions are used for measuring the plasma electron density and temperature in a region of two colliding blast waves, propagating through a 1.5--10-Torr nitrogen atmosphere. The blast waves originate at the tips of two aluminum rods irradiated with two beams of the Naval Research Laboratory

R. C. Elton; D.-M. Billings; C. K. Manka; H. R. Griem; J. Grun; B. H. Ripin; J. Resnick

1994-01-01

30

No Flares from Gamma-Ray Burst Afterglow Blast Waves Encountering Sudden Circumburst Density Change

NASA Astrophysics Data System (ADS)

Afterglows of gamma-ray bursts are observed to produce light curves with the flux following power-law evolution in time. However, recent observations reveal bright flares at times on the order of minutes to days. One proposed explanation for these flares is the interaction of a relativistic blast wave with a circumburst density transition. In this paper, we model this type of interaction computationally in one and two dimensions, using a relativistic hydrodynamics code with adaptive mesh refinement called RAM, and analytically in one dimension. We simulate a blast wave traveling in a stellar wind environment that encounters a sudden change in density, followed by a homogeneous medium, and compute the observed radiation using a synchrotron model. We show that flares are not observable for an encounter with a sudden density increase, such as a wind termination shock, nor for an encounter with a sudden density decrease. Furthermore, by extending our analysis to two dimensions, we are able to resolve the spreading, collimation, and edge effects of the blast wave as it encounters the change in circumburst medium. In all cases considered in this paper, we find that a flare will not be observed for any of the density changes studied.

Gat, Ilana; van Eerten, Hendrik; MacFadyen, Andrew

2013-08-01

31

NO FLARES FROM GAMMA-RAY BURST AFTERGLOW BLAST WAVES ENCOUNTERING SUDDEN CIRCUMBURST DENSITY CHANGE

Afterglows of gamma-ray bursts are observed to produce light curves with the flux following power-law evolution in time. However, recent observations reveal bright flares at times on the order of minutes to days. One proposed explanation for these flares is the interaction of a relativistic blast wave with a circumburst density transition. In this paper, we model this type of interaction computationally in one and two dimensions, using a relativistic hydrodynamics code with adaptive mesh refinement called RAM, and analytically in one dimension. We simulate a blast wave traveling in a stellar wind environment that encounters a sudden change in density, followed by a homogeneous medium, and compute the observed radiation using a synchrotron model. We show that flares are not observable for an encounter with a sudden density increase, such as a wind termination shock, nor for an encounter with a sudden density decrease. Furthermore, by extending our analysis to two dimensions, we are able to resolve the spreading, collimation, and edge effects of the blast wave as it encounters the change in circumburst medium. In all cases considered in this paper, we find that a flare will not be observed for any of the density changes studied.

Gat, Ilana; Van Eerten, Hendrik; MacFadyen, Andrew [Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

2013-08-10

32

Relativistically modulational instability by strong Langmuir waves

Based on the set of nonlinear coupling equations, which has considered the relativistic effects of electrons, modulational instability by strong Langmuir waves has been investigated in this paper. Both the characteristic scale and maximum growth rate of the Langmuir field will enhance with the increase in the electron relativistic effect. The numerical results indicate that longitudinal perturbations induce greater instability than transverse perturbations do, which will lead to collapse and formation of the pancake-like structure.

Liu, X. L.; Liu, S. Q. [Department of Physics, Nanchang University, Jiangxi, Nanchang 330031 (China); Li, X. Q. [Department of Physics, Nanjing Normal University, Nanjing 210097 (China)

2012-09-15

33

Relativistic helix traveling wave tube amplifiers

A relativistic field theory of a helix traveling wave tube (TWT) is described for the case in which a thin annular beam propagates through a sheath helix enclosed within a loss-free wall. The theory is applied to the study of a TWT with an intense relativistic electron beam. The analysis implicitly includes beam space-charge effects and is valid for arbitrary azimuthal mode number, and the coupled-wave Pierce theory is recovered in the [ital near]-[ital resonant] limit. The results indicate that impressive gains and efficiencies are possible in this regime. In addition, the interaction is relatively insensitive to the effects of a beam energy spread.

Freund, H.P.; Vanderplaats, N.R.; Kodis, M.A. (Naval Research Laboratory, Washington, D.C. 20375 (United States))

1992-07-01

34

Particle Acceleration at Relativistic and Ultra-Relativistic Shock Waves

NASA Astrophysics Data System (ADS)

We perform Monte Carlo simulations using diffusive shock acceleration at relativistic and ultra-relativistic shock waves. High upstream flow gamma factors are used, ?=(1-uup2/c2)-0.5, which are relevant to models of ultra-relativistic particle shock acceleration in the central engines and relativistic jets of Active Galactic Nuclei (AGN) and in Gamma-Ray Burst (GRB) fireballs. Numerical investigations are carried out on acceleration properties in the relativistic and ultra-relativistic flow regime (? ˜ 10-1000) concerning angular distributions, acceleration time scales, particle energy gain versus number of crossings and spectral shapes. We perform calculations for both parallel and oblique sub-luminal and super-luminal shocks. For parallel and oblique sub-luminal shocks, the spectra depend on whether or not the scattering is represented by pitch angle diffusion or by large angle scattering. The large angle case exhibits a distinctive structure in the basic power-law spectrum not nearly so obvious for small angle scattering. However, both cases yield a significant 'speed-up' of acceleration rate when compared with the conventional, non-relativistic expression, tacc=[c/(uup-udown)] (?up/uup+?down/udown). An energization by a factor ?2 for the first crossing cycle and a large energy gains for subsequent crossings as well as the high 'speed-up' factors found, are important in supporting past works, especially the models developed by Vietri and Waxman on ultra-high energy cosmic ray, neutrino and gamma-ray production in GRB. For oblique super-luminal shocks, we calculate the energy gain and spectral shape for a number of different inclinations. For this case the acceleration of particles is 'pictured' by a shock drift mechanism. We use high gamma flows with Lorentz factors in the range 10-40 which are relevant to ultra-relativistic shocks in AGN accretion disks and jets. In all investigations we closely follow the particle's trajectory along the magnetic field lines, constantly measuring its phase space coordinates in the fluid frames where E=0 and transforming to the shock frame to detect shock crossings. We find that a super-luminal 'shock drift' mechanism is less efficient in accelerating particles to the highest energies than compared to the first order Fermi acceleration. This implies that the former mechanism cannot stand as the sole, sufficient acceleration mechanism for the ultra-high energy cosmic rays observed.

Meli, A.

35

Oxyacetylene driven laboratory scale shock tubes for studying blast wave effects

Instrumentation is needed to produce realistic blast waves in a laboratory setting. This paper describes the development and characterization of oxy-acetylene driven, laboratory scale shock tubes for use in studying blast injury, candidate armor materials, and material properties at blast loading rates. The pressure-time profiles show a true shock front and exponential decay characteristic of blast waves and have relevant

Michael Courtney; Amy Courtney

2011-01-01

36

Micro-blast waves using detonation transmission tubing

NASA Astrophysics Data System (ADS)

Micro-blast waves emerging from the open end of a detonation transmission tube were experimentally visualized in this study. A commercially available detonation transmission tube was used (Nonel tube, M/s Dyno Nobel, Sweden), which is a small diameter tube coated with a thin layer of explosive mixture (HMX + traces of Al) on its inner side. The typical explosive loading for this tube is of the order of 18 mg/m of tube length. The blast wave was visualized using a high speed digital camera (frame rate 1 MHz) to acquire time-resolved schlieren images of the resulting flow field. The visualization studies were complemented by computational fluid dynamic simulations. An analysis of the schlieren images showed that although the blast wave appears to be spherical, it propagates faster along the tube axis than along a direction perpendicular to the tube axis. Additionally, CFD analysis revealed the presence of a barrel shock and Mach disc, showing structures that are typical of an underexpanded jet. A theory in use for centered large-scale explosions of intermediate strength (10 < ? {p}/{p}_0 ? 0.02) gave good agreement with the blast trajectory along the tube axis. The energy of these micro-blast waves was found to be 1.25 ± 0.94 J and the average TNT equivalent was found to be 0.3. The repeatability in generating these micro-blast waves using the Nonel tube was very good (± 2 %) and this opens up the possibility of using this device for studying some of the phenomena associated with muzzle blasts in the near future.

Samuelraj, I. Obed; Jagadeesh, G.; Kontis, K.

2013-07-01

37

Blast wave diagnostic for the petawatt laser system

We report on a diagnostic to measure the trajectory of a blast wave propagating through a plastic target 400 {micro}m thick. This blast wave is generated by the irradiation of the front surface of the target with {approximately} 400 J of 1 {micro}m laser radiation in a 20 ps pulse focused to a {approximately} 50 {micro}m diameter spot, which produces an intensity in excess of 1O{sup 18} W/cm{sup 2}. These conditions approximate a point explosion and a blast wave is predicted to be generated with an initial pressure nearing 1 Gbar which decays as it travels approximately radially outward from the interaction region We have utilized streaked optical pyrometry of the blast front to determine its time of arrival at the rear surface of the target Applications of a self-similar Taylor-Sedov blast wave solution allows the amount of energy deposited to be estimated The experiment, LASNEX design simulations and initial results are discussed.

Budil, K. S., LLNL

1998-06-03

38

Blast wave diagnostic for the Petawatt laser system

We report on a diagnostic to measure the trajectory of a blast wave propagating through a plastic target 400 {mu}m thick. This blast wave is generated by the irradiation of the front surface of the target with {approximately}400 J of 1 {mu}m laser radiation in a 20 ps pulse focused to a {approximately}50 {mu}m diameter spot, which produces an intensity in excess of 10{sup 18}thinspW/cm{sup 2}. These conditions approximate a point explosion and a blast wave is predicted to be generated with an initial pressure nearing 1 Gbar which decays as it travels approximately radially outward from the interaction region. We have utilized streaked optical pyrometry of the blast front to determine its time of arrival at the rear surface of the target. Applications of a self-similar Taylor{endash}Sedov blast wave solution allows the amount of energy deposited to be estimated. The experiment, LASNEX design simulations and initial results are discussed. {copyright} {ital 1999 American Institute of Physics.}

Budil, K.S.; Gold, D.M.; Estabrook, K.G.; Remington, B.A.; Kane, J.; Bell, P.M.; Pennington, D.; Brown, C.; Hatchett, S.; Koch, J.A.; Key, M.H.; Perry, M.D. [Lawrence Livermore National Laboratory, P.O. Box 808, L-21, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, P.O. Box 808, L-21, Livermore, California 94550 (United States)

1999-01-01

39

Rapid miniature fiber optic pressure sensors for blast wave measurements

NASA Astrophysics Data System (ADS)

Traumatic brain injury (TBI) is a serious potential threat to soldiers who are exposed to explosions. Since the pathophysiology of TBI associated with a blast wave is not clearly defined, it is crucial to have a sensing system to accurately quantify the blast wave dynamics. This paper presents an ultra-fast fiber optic pressure sensor based on Fabry-Perot (FP) interferometric principle that is capable of measuring the rapid pressure changes in a blast event. The blast event in the experiment was generated by a starter pistol blank firing at close range, which produced a more realistic wave profile compared to using compressed air driven shock tubes. To the authors' knowledge, it is also the first study to utilize fiber optic pressure sensors to measure the ballistics shock wave of a pistol firing. The results illustrated that the fiber optic pressure sensor has a rise time of 200 ns which demonstrated that the sensor has ability to capture the dynamic pressure transient during a blast event. Moreover, the resonant frequency of the sensor was determined to be 4.11 MHz, which agrees well with the specific designed value.

Zou, Xiaotian; Wu, Nan; Tian, Ye; Niezrecki, Christopher; Chen, Julie; Wang, Xingwei

2013-02-01

40

Blast waves in atomic cluster media using intense laser pulses

We report on the progress of experimental and numerical investigations of the dynamics of strong (>Mach 50) blast waves driven by focusing sub-ps laser pulses into an extended medium of atomic clusters. A gas of atomic clusters is an extraordinarily efficient absorber of intense laser light and can be used to create high energy density plasmas with tabletop laser systems.

Roland Smith

2008-01-01

41

Electron cyclotron wave generation by relativistic electrons

NASA Astrophysics Data System (ADS)

We show that an energetic electron distribution which has a temperature anisotropy (T perpendicular to b is greater than T parallel to b), or which is gyrating about a DC magnetic field, can generate electron cyclotron waves with frequencies below the electron cyclotron frequency. Relativistic effects are included in solving the dispersion equation and are shown to be quantitatively important. The basic idea of the mechanism is the coupling of the beam mode to slow waves. The unstable electron cyclotron waves are predominantly electromagnetic and right-hand polarized. For a low-density plasma in which the electron plasma frequency is less than the electron cyclotron frequency, the excited waves can have frequencies above or below the electron plasma frequency, depending upon the parameters of the energetic electron distribution. This instability may account for observed Z mode waves in the polar magnetosphere of the Earth and other planets.

Wong, H. K.; Goldstein, M. L.

1994-01-01

42

Blast wave reflection trajectories from a height of burst

Consideration is given to an explosive charge (TNT) detonated at various heights of burst above a perfect reflecting planar surface in air. Variations of the incident shock Mach number M(s) of the spherical blast wave front as it decays, and the corresponding wedge angle theta(w), are plotted on a two-dimensional shock wave reflection transition map in the M(s), theta(w) plane.

T. C. J. Hu; I. I. Glass

1986-01-01

43

Blast waves produced by interactions of femtosecond laser pulses with water.

The behaviors of the blast waves produced by femtosecond laser-water interactions, and the blast waves induced by laser self-focusing in air, have been investigated using optical shadowgraphy at a maximum intensity of 1 x 10(16) W/cm(2). The temporal evolution of the blast wave launched by the water plasma can be described by a planar blast wave model including source mass. An aneurismlike structure, due to the quick propagation inside a hollow channel formed by laser self-focusing, is observed. The expansion of the channel in air is found to agree with a cylindrical self-similar blast wave solution. PMID:12786283

Li, Y T; Zhang, J; Teng, H; Li, K; Peng, X Y; Jin, Z; Lu, X; Zheng, Z Y; Yu, Q Z

2003-05-01

44

Relativistic nonlinear plasma waves in a magnetic field

NASA Technical Reports Server (NTRS)

Five relativistic plane nonlinear waves were investigated: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an 'electron-positron' plasma leads to equations which have the form of a one-dimensional potential well. The solutions indicate that a large-amplitude superluminous wave determines the average plasma properties.

Kennel, C. F.; Pellat, R.

1975-01-01

45

The Use of Cantilevers as Blast Wave Gauges.

NASA Astrophysics Data System (ADS)

A study has been made of the response of elastic -plastic and brittle cantilevers when subjected to blast wave loading with a view to using such devices as passive blast wave gauges, and of using the deformation of cantilevers to assess the characteristics of accidental explosions. The study was restricted to cantilevers that were circular in cross-section and made of readily available materials. A cantilever, when loaded by a blast wave, either deforms plastically, in which case the amount of deformation is the critical parameter, or fractures, in which case the failing or not failing of the cantilever provides the required information. Two numerical models were developed to describe the deformation of a dynamically loaded cantilever. Both models assume that the plastic deformation is localized in a region near the fixed end, and that the loading force was a function of the dynamic pressure time history and a variable drag coefficient, dependent on the Reynolds number, Mach number and angle of attack. The first numerical model assumed a rigid-plastic response of the cantilevers. The model accurately described the response only of cantilevers made of 50/50 lead/tin alloy. It overestimated the deformation of cantilevers made of other materials exposed in both high explosive and shock tube experiments. The second model assumed an elastic-plastic response for the blast loaded cantilever with strain hardening effects included. The algorithm was based on the premise that the elastic curvature of the cantilever was limited by the plastic yield stress of the material and that as the curvature approached this limit the cantilever was rotated by the necessary amount to keep the curvature constant and equal to this maximum. The amount of rotation was determined by fitting a fourth order polynomial with a constrained second derivative based on the maximum allowed curvature. The rotation angle were found from the angle derived from the slope of the fitted function at the origin. A rotation by this angle yields a minimum in curvature in the rotated reference frame. This model improved the predictions for cantilevers constructed of aluminum and steel. The numerical models were evaluated by studying the response of cantilevers exposed to shock waves produced in a shock tube, and to blast waves produced by the detonation of two large high-explosive chemical sources. The response of the cantilevers to the shock tube flows was recorded by high-speed photography which showed good agreement between the observed modes of deformation and those predicted by the model. The models which were finally developed also provided good predictions of the deformation or fracture of a wide range of cantilevers exposed to the free-field blast waves. These models were also used to detect any non-radial flows and to study the boundary layers in the blast wave over different surfaces. Finally, it is demonstrated how the numerical modelling can be used to determine the type of cantilever that might be used as a passive gauge for monitoring the blast wave from an explosive event, and for evaluating the deformation of a cantilever exposed to the blast wave from an accidental explosion so as to characterize that explosion.

van Netten, Alexander Antony

1995-01-01

46

Simulation of blast-induced, early-time intracranial wave physics leading to traumatic brain injury.

U.S. soldiers are surviving blast and impacts due to effective body armor, trauma evacuation and care. Blast injuries are the leading cause of traumatic brain injury (TBI) in military personnel returning from combat. Understanding of Primary Blast Injury may be needed to develop better means of blast mitigation strategies. The objective of this paper is to investigate the effects of blast direction and strength on the resulting mechanical stress and wave energy distributions generated in the brain.

Taylor, Paul Allen; Ford, Corey C. (University of New Mexico, Albuquerque, NM)

2008-04-01

47

High power microwave generation by relativistic backward wave oscillator

In this paper, a high power relativistic backward wave oscillator (BWO) experiment is reported. A 230 kV, 2 kA, and 150 ns relativistic electron beam source is developed using a Marx generator. The beam is then injected into a hollow rippled wall metallic cylindrical tube that forms a slow wave structure (SWS). A BWO is a slow wave structure in

Lalit Gupta; Y. Choyal; Prasad Deshpande; K. P. Maheshwari; K. C. Mittal

2008-01-01

48

Review of methods to attenuate shock/blast waves

NASA Astrophysics Data System (ADS)

Quick and reliable shock wave attenuation is the goal of every protection facility and therefore it is not surprising that achieving this has drawn much attention during the past hundred years. Different options have been suggested; their usefulness varying from a reasonable protection to the opposite, a shock enhancement. An example for a suggestion for shock mitigation that turned out to be an enhancement of the impinging shock wave was the idea to cover a protected object with a foam layer. While the pressure behind the reflected shock wave from the foam frontal surface was smaller than that recorded in a similar reflection from a rigid wall [25], the pressure on the “protected” surface, attached to the foam's rear-surface, was significantly higher than that recorded in a similar reflection from a bare, rigid wall [11]. In protecting humans and installations from destructive shock and/or blast waves the prime goal is to reduce the wave amplitude and the rate of pressure increase across the wave front. Both measures result in reducing the wave harmful effects. During the past six decades several approaches for achieving the desired protection have been offered in the open literature. We point out in this review that while some of the suggestions offered are practical, others are impractical. In our discussion we focus on recent schemes for shock/blast wave attenuation, characterized by the availability of reliable measurements (notably pressure and optical diagnostics) as well as high-resolution numerical simulations.

Igra, O.; Falcovitz, J.; Houas, L.; Jourdan, G.

2013-04-01

49

Mach reflection from an HE-driven blast wave

NASA Astrophysics Data System (ADS)

Attention is given to a two-dimensional reflection of a spherical, high energy charge-driven blast wave from an ideal plane surface, whose flowfield evolution has been calculated with a nondiffusive numerical algorithm for the accurate solution of the Euler equations. The incident blast wave was accurately captured by a fine-zoned, one-dimensional calculation that was continuously fed into the two-dimensional mesh, which itself possessed a fine-zoned mesh for following the reflection region and accurately resolving the complex flow structure. It is found that portions of the main reflected shock were reflected within the channel formed by the wall and the dense high explosive products, creating additional pressure pulses on the wall.

Colella, P.; Ferguson, R. E.; Glaz, H. M.; Kuhl, A. L.

50

IMAGING HIGH SPEED PARTICLES IN EXPLOSIVE DRIVEN BLAST WAVES

This research describes a new application of a commercially available particle image velocimetry (PIV) instrument adapted for imaging particles in a blast wave. Powder was dispersed through the PIV light sheet using a right circular cylindrical charge containing aluminum powder filled in the annular space between the explosive core and exterior paper tube wall of the charge. Images acquired from each shot showed particle agglomeration and unique structures with the smaller particle diameters having developed structured appearances.

Jenkins, C. M. [Dept. of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611-6450 (United States); Air Force Research Laboratory, Munitions Directorate, Eglin AFB FL 32542 (United States); Horie, Y. [Air Force Research Laboratory, Munitions Directorate, Eglin AFB FL 32542 (United States); Ripley, R. C.; Wu, C.-Y. [Martec Limited, Suite 400-1888 Brunswick Street, Halifax, NS, B3J3J8 (Canada)

2009-12-28

51

Afterglow emission in gamma-ray bursts - I. Pair-enriched ambient medium and radiative blast waves

NASA Astrophysics Data System (ADS)

Forward shocks caused by the interaction between a relativistic blast wave and the circumburst medium are thought to be responsible for the afterglow emission in gamma-ray bursts (GRBs). We consider the hydrodynamics of a spherical relativistic blast wave expanding into the surrounding medium and we generalize the standard theory in order to account for several effects that are generally ignored. In particular, we consider the role of adiabatic and radiative losses in the hydrodynamical evolution of the shock, under the assumption that the cooling losses are fast. Our model can describe adiabatic, fully radiative and semiradiative blast waves, and can describe the effects of a time-varying radiative efficiency. The equations we present are valid for arbitrary density profiles, and also for a circumburst medium enriched with electron-positron pairs. The presence of pairs enhances the fraction of shock energy gained by the leptons, thus increasing the importance of radiative losses. Our model allows us to study whether the high-energy (>0.1 GeV) emission in GRBs may originate from afterglow radiation. In particular, it is suitable to test whether the fast decay of the high-energy light curve observed in several Fermi Large Area Telescope GRBs can be ascribed to an initial radiative phase, followed by the standard adiabatic evolution.

Nava, L.; Sironi, L.; Ghisellini, G.; Celotti, A.; Ghirlanda, G.

2013-08-01

52

Relativistic Wave Packets and delta-Electron Emission.

National Technical Information Service (NTIS)

Relativistic wave packets are explicitly constructed and exploited in calculations of ionization phenomena. Coupling matrix elements between bound states and wave packets are evaluated for radiative transitions as well as for electron excitation processes...

H. J. Baer G. Soff

1984-01-01

53

Study of high Mach number laser driven blast waves in gases

A series of experiments were performed examining the evolution of blast waves produced by laser irradiation of a target immersed in gas. Blast waves were produced by illumination of wires by 1 kJ, 1 ns laser pulses from the Z-Beamlet laser at Sandia National Laboratories. The blast waves were imaged by probe laser pulses at various times to examine the trajectory, radiative precursor, and induced perturbations on the blast wave front. Well defined perturbations were induced on the blast wave front with arrays of wires placed in the gas and the results of the experiments are compared to the theoretical predictions for the Vishniac overstability. It is found that the experimental results are in general agreement with these theoretical predictions on thin blast wave shells and are in quantitative agreement in the simplest case.

Edens, A. D.; Adams, R. G.; Rambo, P.; Ruggles, L.; Smith, I. C.; Porter, J. L. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Ditmire, T. [Department of Physics, Texas Center for High Intensity Laser Science, University of Texas at Austin, Austin, Texas 78712 (United States)

2010-11-15

54

Interactions between Blast Waves and V-Shaped and Cone-Shaped Structures

A 2-D numerical model of interactions between a blast wave and a V-shaped or a cone-shaped structure is developed. The model simulates the blast wave reflection from a V-shaped or a cone-shaped structure, the movement of the structure due to the blast impact and the induced shock wave behind the structure. Elliptic grid generation and coordinate transformation are utilized to

W. Peng; Z. Y. Zhang; G. Gogos; G. Gazonas

2011-01-01

55

Rankine-Hugoniot Relations in Relativistic Combustion Waves

NASA Astrophysics Data System (ADS)

As a foundational element describing relativistic reacting waves of relevance to astrophysical phenomena, the Rankine-Hugoniot relations classifying the various propagation modes of detonation and deflagration are analyzed in the relativistic regime, with the results properly degenerating to the non-relativistic and highly relativistic limits. The existence of negative-pressure downstream flows is noted for relativistic shocks, which could be of interest in the understanding of the nature of dark energy. Entropy analysis for relativistic shock waves is also performed for relativistic fluids with different equations of state (EoS), denoting the existence of rarefaction shocks in fluids with adiabatic index ? < 1 in their EoS. The analysis further shows that weak detonations and strong deflagrations, which are rare phenomena in terrestrial environments, are expected to exist more commonly in astrophysical systems because of the various endothermic reactions present therein. Additional topics of relevance to astrophysical phenomena are also discussed.

Gao, Yang; Law, Chung K.

2012-12-01

56

RANKINE-HUGONIOT RELATIONS IN RELATIVISTIC COMBUSTION WAVES

As a foundational element describing relativistic reacting waves of relevance to astrophysical phenomena, the Rankine-Hugoniot relations classifying the various propagation modes of detonation and deflagration are analyzed in the relativistic regime, with the results properly degenerating to the non-relativistic and highly relativistic limits. The existence of negative-pressure downstream flows is noted for relativistic shocks, which could be of interest in the understanding of the nature of dark energy. Entropy analysis for relativistic shock waves is also performed for relativistic fluids with different equations of state (EoS), denoting the existence of rarefaction shocks in fluids with adiabatic index {Gamma} < 1 in their EoS. The analysis further shows that weak detonations and strong deflagrations, which are rare phenomena in terrestrial environments, are expected to exist more commonly in astrophysical systems because of the various endothermic reactions present therein. Additional topics of relevance to astrophysical phenomena are also discussed.

Gao Yang; Law, Chung K., E-mail: cklaw@princeton.edu [Center for Combustion Energy and Department of Thermal Engineering, Tsinghua University, Beijing 100084 (China)

2012-12-01

57

Pressure measurements in laboratory-scale blast wave flow fields.

The present study examines the effects that temporal and spatial averagings due to finite size and finite response time of pressure transducers have on the pressure measurements in blast wave flow fields generated by milligram charges of silver azide. In such applications, the characteristic time and length scales of the physical process are of the same order of magnitude as the temporal and spatial characteristics of the transducer. The measured pressure values will then be spatially and temporally averaged, and important parameters for the assessment of blast effects may not be properly represented in the measured trace. In this study, face-on and side-on pressure transducer setups are considered. In the experiments, face-on and side-on readings at the same distance from the charge as well as time-resolved optical visualization of the whole flow field are obtained simultaneously for the same explosive event. The procedure of data extraction from the experimental pressure traces is revisited and discussed in detail. In the numerical modeling part of the study, numerical blast flow fields are generated using an Euler flow solver. A numerical pressure transducer model is developed to qualitatively simulate the averaging effects. The experimental and numerical data show that the results of pressure measurements in experiments with small charges must be used with great caution. The effective averaging of the pressure signal may lead to a significant underestimation of blast wave intensities. The side-on setup is especially prone to this effect. The face-on setup provides results close to those obtained from optical records only if the pressure transducer is sufficiently remote from the charge. PMID:18163748

Rahman, S; Timofeev, E; Kleine, H

2007-12-01

58

A study on planar blast waves initiated by gaseous detonations. I - Estimation of initiation energy

An experimental study has been made of the initiation of planar blast waves by gaseous detonations. A gaseous detonation initiated by a DDT process is submitted into a long tube filled with air at various initial pressures. The measurement of the decay process of a produced shock wave indicates that it can be treated as a 'plane source' blast wave,

S. Ohyagi; T. Yoshihashi; Y. Harigaya

1985-01-01

59

Interactions between Blast Waves and V-Shaped and Cone-Shaped Structures

NASA Astrophysics Data System (ADS)

A 2-D numerical model of interactions between a blast wave and a V-shaped or a cone-shaped structure is developed. The model simulates the blast wave reflection from a V-shaped or a cone-shaped structure, the movement of the structure due to the blast impact and the induced shock wave behind the structure. Elliptic grid generation and coordinate transformation are utilized to solve the flow fields in the irregular physical domain. Different types of blast wave reflections, such as normal reflection, oblique reflection and Mach stem reflection, are captured by the numerical model. It is found that the reflected pressure and impulse transmitted to the structure decrease with the increase of incident angle. On the other hand, with the increase of incident angle, the effects of fluid structure interactions (FSI) in reducing the blast loads decreases. The FSI coupled with oblique or Mach stem reflection improves the blast wave mitigation.

Peng, W.; Zhang, Z. Y.; Gogos, G.; Gazonas, G.

2011-09-01

60

Relativistic distorted-wave procedures with pseudostates

NASA Astrophysics Data System (ADS)

The relativistic distorted-wave (RDW) procedures developed by Chen [Phys. Rev. A 53, 3227 (1996)] have been extended to include pseudostates. The RDW procedures with pseudostates are applied to the calculation of electron impact excitation (EIE) of FeXVII . Pseudostates are shown to have a significant effect on the cross sections for important transitions such as 3C (?=15.015Å) and 3D (?=15.262Å) of FeXVII . The convergence of the RDW calculations has been carefully investigated. The present RDW calculations of FeXVII are further compared with our previous close coupling results using the fully relativistic Dirac R -matrix (DRM) method, where resonance and more complete channel coupling effects were included in addition to the background direct excitations. The present RDW calculations are in good agreement to the background cross sections from the DRM calculations. This agreement indicates the mutual confirmation of the validity of both the RDW and the DRM calculations of the direct or background EIE cross sections.

Chen, Guo-Xin

2008-02-01

61

Electromagnetic wave equations for relativistically degenerate quantum magnetoplasmas

A generalized set of nonlinear electromagnetic quantum hydrodynamic (QHD) equations is derived for a magnetized quantum plasma, including collisional, electron spin-(1/2), and relativistically degenerate electron pressure effects that are relevant for dense astrophysical systems, such as white dwarfs. For illustrative purposes, linear dispersion relations are derived for one-dimensional magnetoacoustic waves for a collisionless nonrelativistic degenerate gas in the presence of the electron spin-(1/2) contribution and for magnetoacoustic waves in a plasma containing relativistically degenerate electrons. It is found that both the spin and relativistic degeneracy at high densities tend to slow down the magnetoacoustic wave due to the Pauli paramagnetic effect and relativistic electron mass increase. The present study outlines the theoretical framework for the investigation of linear and nonlinear behaviors of electromagnetic waves in dense astrophysical systems. The results are applied to calculate the magnetoacoustic speeds for both the nonrelativistic and relativistic electron degeneracy cases typical for white dwarf stars.

Masood, Waqas [TPPD, PINSTECH, P. O. Nilore, Islamabad (Pakistan); Eliasson, Bengt [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden); Institut fuer Theoretische Physik IV, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Shukla, Padma K. [Institut fuer Theoretische Physik IV, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2010-06-15

62

Stability of the blast wave in ideal gas

NASA Astrophysics Data System (ADS)

Stability of a point blast wave in an ideal gas is considered in the case when the initial gas density0 is a power function of radius r:0~r-k . We use a technique previously used in /1,2,3/. Small non-radial blast wave perturbations are expanded to spherical harmonics components of expansion being represented in a self-similar form. The cases of a constant initial gas density and of one being power function of radius are considered. Instability region on n- plane (herestands for a gas specific heat ratio and n stands for a harmonic number) is determined in all cases (k=0 - 12) considered. Critical values of c determining the blast wave stability are calculated. The results are calculated numerically in the general case of arbitrary , n and analytically in some special cases: n=1, n>>1, and -1<<1. The considered cases are modeling supernova explosion /4/ as well as simulating astrophysical phenomena in laboratory experiments /5/. REFERENCES 1. V.M.Ktitorov, Voprosy Atomnoi Nauki i Tekhniki, Ser.Teoreticheskaya i Prikladnaya.Fizika (Atomic Science and Technique Issues, Ser. Theoretical and Applied Physics), No2, p.28, (1984); 2. D.Ryu and E.T.Vishniac, Astrophys.J. 313, 820 (1987); 3. V.M.Ktitorov, Khimicheskaya Fizika (Chemical Physics Issues) V.14, No 2-3, p.169, (1995); 4. R.P.Drake et al., Physics of Plasma, V.8, No 5, p.1804, (2001); 5. R.G.Chevalier, Astrophys.J. 259, p.302 (1982);

Ktitorov, V.

63

The blast wave of the Shuttle plume at ionospheric heights

The main engine burn (MEB) of the Space Shuttle deposits {approximately} 2 x 10{sup 12} joules of explosive energy and {approximately} 3 x 10{sup 5} kg of exhaust in almost horizontal flight at 105-110 km altitude during the period 300-550 s into the ascent. This extremely robust perturbation provides a potential active-excitation source for a variety of geophysical processes, including (1) the effects of aurora-like localized heating on the generation of gravity waves in the thermosphere, (2) the ducting mechanisms for long-period infrasound in the upper atmosphere, (3) dynamo effects associated with transient charge separation, (4) interactions with ambient midlatitude current systems at E-layer heights, and (5) effects in the Earth-ionosphere waveguide of transient electron-density perturbations in the D-region. The sine qua non of such an agenda is to gain a quantitative understanding of the near-field behavior of the MEB exhaust-plume`s quasi-cylindrical expansion, which generates a blast wave propagating away from the explosion. The authors report on observed electron-density signatures of this blast wave as manifested on lines-of-sight (LOSs) from a very-long-baseline interferometer (VLBI) illuminated by 137-MHz beacon signals from the MARECS-B satellite. They also compare the observations to a preliminary three-dimensional neutral-air acoustic model coupled to the ionospheric electron density. 7 refs., 5 figs., 1 tab.

Li, Y.Q.; Jacobson, A.R.; Carlos, R.C.; Massey, R.S.; Taranenko, Y.N.; Wu, G. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1994-12-01

64

Experiments on cylindrically converging blast waves in atmospheric air

NASA Astrophysics Data System (ADS)

Cylindrically converging blast waves have been produced in normal atmospheric conditions by the detonation of the explosives, pentaerythritoltetranitrate, (PETN), over cylindrical surfaces. The shocks generated in this way are so strong that the fronts propagating through the air become luminous of themselves. The production and the propagation of the shocks have been monitored with a framing camera and a streak camera, and the time-space relations of the shock propagations have been determined using an electrical ionization probing system. The results have shown that the trajectory of the shock fronts near the axis of the cylinder can be approximately represented by the Guderley's formula.

Matsuo, Hideo; Nakamura, Yuichi

1980-06-01

65

Secondary shock in a homogeneous medium behind a blast wave

NASA Astrophysics Data System (ADS)

Basing on the theory of asymptotic waves, we present a study on the formation of secondary shocks in a gaseous base medium affected by a strong point explosion. Using the leading equation which rules the evolution of a perturbing signal in a gas flow as shown in a previous paper (Eur. Phys. J. Plus 127, 129 (2012)), we discuss the main conditions which allow the formation of secondary shocks in the medium behind the blast front. For the two models considered, one following a power law density, the other with constant density, we give the times and the radial positions at which secondary shocks form by varying the adiabatic index.

Virgopia, N.; Ferraioli, F.

2013-08-01

66

Spike Penetration in Blast-Wave-Driven Instabilities

NASA Astrophysics Data System (ADS)

Recent experiments by C. Kuranz and collaborators, motivated by structure in supernovae, have studied systems in which planar blast waves encounter interfaces where the density decreases. During the Rayleigh-Taylor (RT) phase of such experiments, they observed greater penetration of the RT spikes than tends to be seen in simulations. Here we seek to employ semi-analytic theory to understand the general nature and regimes of spike penetration for blast-wave-driven instabilities. This problem is not trivial as one must account for the initial vorticity deposition at the interface, for its time-dependent deceleration, for the expansion of the shocked material in time and space, and for the drag on the broadened tips of the spikes. We offer here an improved evaluation of the material expansion in comparison to past work. The goal is to use such models to increase our ability to interpret the behavior of simulations of such systems, in both the laboratory and astrophysics. Supported by the US DOE NNSA under the Predictive Sci. Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances program by grant DE-FG52-04NA00064, and the Nat. Laser User Facility by grant DE-FG03-00SF22021.

Drake, R. Paul

2010-05-01

67

Spike penetration in blast-wave-driven instabilities

NASA Astrophysics Data System (ADS)

Recent experiments by C. Kuranz and collaborators, motivated by structure in supernovae, have studied systems in which planar blast waves encounter interfaces where the density decreases. During the Rayleigh-Taylor (RT) phase of such experiments, they observed greater penetration of the RT spikes than tends to be seen in simulations. Here we seek to employ semi-analytic theory to understand the general nature and regimes of spike penetration for blast-wave-driven instabilities. This problem is not trivial as one must account for the initial vorticity deposition at the interface, for its time-dependent deceleration, for the expansion of the shocked material in time and space, and for the drag on the broadened tips of the spikes. One can hope that such models will increase our ability to interpret the behavior of simulations of such systems, in both the laboratory and astrophysics. Supported by the US DOE NNSA under the Predictive Sci. Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances program by grant DE-FG52-04NA00064, and the Nat. Laser User Facility by grant DE-FG03--00SF22021.

Drake, R. P.

2009-11-01

68

High resolution imaging of colliding blast waves in cluster media

NASA Astrophysics Data System (ADS)

Strong shocks and blast wave collisions are commonly observed features in astrophysical objects such as nebulae and supernova remnants. Numerical simulations often underpin our understanding of these complex systems, however modelling of such extreme phenomena remains challenging, particularly so for the case of radiative or colliding shocks. This highlights the need for well-characterized laboratory experiments both to guide physical insight and to provide robust data for code benchmarking. Creating a sufficiently high-energy-density gas medium for conducting scaled laboratory astrophysics experiments has historically been problematic, but the unique ability of atomic cluster gases to efficiently couple to intense pulses of laser light now enables table top scale (1 J input energy) studies to be conducted at gas densities of >1019 particles cm-3 with an initial energy density >5 × 109 J g-1. By laser heating atomic cluster gas media we can launch strong (up to Mach 55) shocks in a range of geometries, with and without radiative precursors. These systems have been probed with a range of optical and interferometric diagnostics in order to retrieve electron density profiles and blast wave trajectories. Colliding cylindrical shock systems have also been studied, however the strongly asymmetric density profiles and radial and longitudinal mass flow that result demand a more complex diagnostic technique based on tomographic phase reconstruction. We have used the 3D magnetoresistive hydrocode GORGON to model these systems and to highlight interesting features such as the formation of a Mach stem for further study.

Smith, Roland A.; Lazarus, James; Hohenberger, Matthias; Marocchino, Alberto; Robinson, Joseph S.; Chittenden, Jeremy P.; Moore, Alastair S.; Gumbrell, Edward T.; Dunne, Mike

2007-12-01

69

Self-similar blast waves incorporating deflagrations of variable speed

NASA Technical Reports Server (NTRS)

The present investigation is concerned with the development of a systematic approach to the problem of self-similar blast waves incorporating nonsteady flames. The regime covered by the presented solutions is bounded on one side by an adiabatic strong explosion and, on the other, by deflagration propagating at an infinite acceleration. Results for a representative set of accelerations are displayed, taking into account the full range of propagation speeds from zero to velocities corresponding to the Chapman-Jouguet deflagration. It is found that the distribution of stored energy in the undisturbed medium determines the acceleration of the deflagration-shock wave system. The obtained results reveal the existence of a simple relation between the location of the deflagration and its Mach number.

Guirguis, R. H.; Kamel, M. M.; Oppenheim, A. K.

1983-01-01

70

Interaction of a Taylor blast wave with isotropic turbulence

NASA Astrophysics Data System (ADS)

Simulations of the Taylor blast wave through a region of compressible isotropic turbulence are carried out. The turbulent fluctuations are either significantly attenuated or unchanged depending on the initial strength of the shock wave. It is shown through Eulerian simulations and Lagrangian tracking of particles that both these effects are primarily related to the vorticity-dilatation term in the vorticity transport equation. The turbulence length scales associated with this problem are defined and the effect on them quantified. Turbulence also distorts the shock, which can lead to substantial local variations in shock strength and asphericity. Transverse vorticity amplification is compared with linear planar shock-turbulence theory. Aspects that distinguish spherical shock-turbulence interaction from the planar case are stressed.

Bhagatwala, Ankit; Lele, Sanjiva K.

2011-03-01

71

Transition from the Sedov-Taylor Blast Wave Solution Up to the Sound Wave

In the case of a spherical blast wave described by the Sedov-Taylor model in an ideal gas, we apply the Vashy-Buckingham theorem (Pi theorem) to take into account the pressure of the medium at rest, and consequently the internal energy of the gas at rest. We obtain a single formula which contains the full time behavior of the explosion from

C. de Izarra; J. Caillard; O. Vallée

2002-01-01

72

Development of a 2 MW relativistic backward wave oscillator

In this paper, a high power relativistic backward wave oscillator (BWO) experiment is reported. A 230 keV, 2 kA, 150 ns relativistic\\u000a electron beam is generated using a Marx generator. The beam is then injected into a hollow rippled wall metallic cylindrical\\u000a tube that forms a slow wave structure. The beam is guided using an axial pulsed magnetic field having

Yaduvendra Choyal; Lalit Gupta; Prasad Deshpande; Krishna Prasad Maheshwari; Kailash Chander Mittal; Suresh Chand Bapna

2008-01-01

73

Cubic dispersion relation for a relativistic backward-wave oscillator

The cubic approximation to the dispersion relation for a relativistic backward-wave oscillator is obtained, and the utility and limits of the approximation are presented. The approximation is obtained by Taylor series expansion of the wave admittance in the dispersion relation for the transverse-magnetic and free-streaming modes of a relativistic, thin, hollow, cylindrical electron beam moving along the axis of a

HOWARD E. BRANDT; HAN S. UHM

1988-01-01

74

On the magnetization of gamma-ray burst blast waves

NASA Astrophysics Data System (ADS)

The origin of magnetic fields that permeate the blast waves of gamma-ray bursts (GRBs) is a long-standing problem. The present paper argues that in four GRBs revealing extended emission at >100 MeV, with follow-up in the radio, optical and X-ray domains at later times, this magnetization can be described as the partial decay of the micro-turbulence that is generated in the shock precursor. Assuming that the bulk of the extended emission >100 MeV can be interpreted as synchrotron emission of shock-accelerated electrons, we model the multi-wavelength light curves of GRB 090902B, GRB 090323, GRB 090328 and GRB 110731A, using a simplified then a full synchrotron calculation with power-law-decaying micro-turbulence ?B ? t?t (t denotes the time since injection through the shock, in the comoving blast frame). We find that these models point to a consistent value of the decay exponent -0.5 ? ?t ? -0.4.

Lemoine, Martin; Li, Zhuo; Wang, Xiang-Yu

2013-11-01

75

Blast Wave Exposure Impairs Memory and Decreases Axon Initial Segment Length

Abstract Exposure to a blast wave has been proposed to cause mild traumatic brain injury (mTBI), with symptoms including altered cognition, memory, and behavior. This idea, however, remains controversial, and the mechanisms of blast-induced brain injury remain unknown. To begin to resolve these questions, we constructed a simple compressed air shock tube, placed rats inside the tube, and exposed them to a highly reproducible and controlled blast wave. Consistent with the generation of a mild injury, 2 weeks after exposure to the blast, we found that motor performance was unaffected, and a panel of common injury markers showed little or no significant changes in expression in the cortex, corpus callosum, or hippocampus. Similarly, we were unable to detect elevated spectrin breakdown products in brains collected from blast-exposed rats. Using an object recognition task, however, we found that rats exposed to a blast wave spent significantly less time exploring a novel object when compared with control rats. Intriguingly, we also observed a significant shortening of the axon initial segment (AIS) in both the cortex and hippocampus of blast-exposed rats, suggesting altered neuronal excitability after exposure to a blast. A computational model showed that shortening the AIS increased both threshold and the interspike interval of repetitively firing neurons. These results support the conclusion that exposure to a single blast wave can lead to mTBI with accompanying cognitive impairment and subcellular changes in the molecular organization of neurons.

Baalman, Kelli L.; Cotton, R. James; Rasband, S. Neil

2013-01-01

76

Blast wave exposure impairs memory and decreases axon initial segment length.

Exposure to a blast wave has been proposed to cause mild traumatic brain injury (mTBI), with symptoms including altered cognition, memory, and behavior. This idea, however, remains controversial, and the mechanisms of blast-induced brain injury remain unknown. To begin to resolve these questions, we constructed a simple compressed air shock tube, placed rats inside the tube, and exposed them to a highly reproducible and controlled blast wave. Consistent with the generation of a mild injury, 2 weeks after exposure to the blast, we found that motor performance was unaffected, and a panel of common injury markers showed little or no significant changes in expression in the cortex, corpus callosum, or hippocampus. Similarly, we were unable to detect elevated spectrin breakdown products in brains collected from blast-exposed rats. Using an object recognition task, however, we found that rats exposed to a blast wave spent significantly less time exploring a novel object when compared with control rats. Intriguingly, we also observed a significant shortening of the axon initial segment (AIS) in both the cortex and hippocampus of blast-exposed rats, suggesting altered neuronal excitability after exposure to a blast. A computational model showed that shortening the AIS increased both threshold and the interspike interval of repetitively firing neurons. These results support the conclusion that exposure to a single blast wave can lead to mTBI with accompanying cognitive impairment and subcellular changes in the molecular organization of neurons. PMID:23025758

Baalman, Kelli L; Cotton, R James; Rasband, S Neil; Rasband, Matthew N

2013-05-01

77

Cubic dispersion relation for a relativistic backward-wave oscillator

The cubic approximation to the dispersion relation for a relativistic backward-wave oscillator is obtained, and the utility and limits of the approximation are presented. The approximation is obtained by Taylor series expansion of the wave admittance in the dispersion relation for the transverse-magnetic and free-streaming modes of a relativistic, thin, hollow, cylindrical electron beam moving along the axis of a disc-loaded waveguide in a strong axial magnetic field. The resulting cubic dispersion relation yields instability growth rates and frequencies which fall off beyond their maxima more sharply with increasing wavenumber than for the complete dispersion relation. However, the approximation is found to be quite good near the operating points of contemporary high-power relativistic backward-wave oscillators, namely, for relatively long wavelength and small ratio of Bjudker's parameter to the relativistic gamma factor of the beam.

Brandt, H.E.; Uhm, H.S.

1988-04-01

78

Investigation of ULF Wave Modulation of Relativistic Electron Precipitation

NASA Astrophysics Data System (ADS)

Loss processes greatly impact the dynamics of Earth's radiation belts. Balloon payloads can provide information about loss to the atmosphere through observations of bremsstrahlung x-rays emitted from precipitating relativistic electrons. The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) provides spatial and temporal information about precipitating electron events through an array of slowly drifting balloons distributed in magnetic local time and L values. Duskside relativistic electron precipitation events observed by previous balloon-borne x-ray detectors have been reported, and frequently show modulation on ULF wave timescales (Foat et al., 1998; Millan et al., 2002). Similar observations were recently made during the 2013 BARREL Campaign. Theoretical studies have suggested ULF waves are capable of precipitating relativistic electrons in the outer radiation belts (Brito et al., 2012). This study takes an observational approach to investigate the relationship between ULF waves and balloon observations of modulated duskside REP events.

Woodger, L. A.; Sample, J. G.; Millan, R. M.

2013-12-01

79

SPIKE PENETRATION IN BLAST-WAVE-DRIVEN INSTABILITIES

The problem of interest is the unstable growth of structure at density transitions affected by blast waves, which arise in natural environments such as core-collapse supernovae and in laboratory experiments. The resulting spikes of dense material, which penetrate the less dense material, develop broadened tips, but the degree of broadening varies substantially across both experiments and simulations. The variable broadening presumably produces variations in the drag experienced by the spike tips as they penetrate the less dense material. The present work has used semianalytic theory to address the question of how the variation in drag might affect the spike penetration, for cases in which the post-shock interface deceleration can be described by a power law in a normalized time variable. It did so by following the evolution of structure on the interface through the initial shock passage, the subsequent small-amplitude phase of Rayleigh-Taylor instability growth, and the later phase in which the spike growth involves the competition of buoyancy and drag. In all phases, the expansion of the system during its evolution was accounted for and was important. The calculated spike length is strongly affected by the drag attributed to spike tip broadening. One finds from such a calculation that it is not unreasonable for narrow spikes to keep up with the shock front of the blast wave. The implication is that the accuracy of prediction of spike penetration and consequent structure by simulations very likely depends on how accurately they treat the broadening of the spike tips and the associated drag. Experimental validation of spike morphology in simulations would be useful.

Drake, R. P., E-mail: rpdrake@umich.edu [Atmospheric, Oceanic, and Space Science, and Applied Physics, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)

2012-01-10

80

Prospects for studying how high-intensity compression waves cause damage in human blast injuries

NASA Astrophysics Data System (ADS)

Blast injuries arising from improvised explosive devices are often complex leading to long-term disability in survivors. There is an urgent need to mitigate against the effects of blast that lead to these injuries, and to also improve post-traumatic therapeutic treatments related to problems associated with damage and healing processes and infections. We have initiated multidisciplinary studies to develop experimental facilities and strategies for analyzing the effects blast waves upon the human body, from cellular through to skeletal functions.

Brown, Katherine; Bo, Chiara; Ramaswamy, Arul; Masouros, Spiros; Newell, Nicolas; Hill, Adam; Clasper, Jon; Bull, Anthony; Proud, William

2011-06-01

81

Spike morphology in blast-wave-driven instability experiments

The laboratory experiments described in the present paper observe the blast-wave-driven Rayleigh-Taylor instability with three-dimensional (3D) initial conditions. About 5 kJ of energy from the Omega laser creates conditions similar to those of the He-H interface during the explosion phase of a supernova. The experimental target is a 150 {mu}m thick plastic disk followed by a low-density foam. The plastic piece has an embedded, 3D perturbation. The basic structure of the pattern is two orthogonal sine waves where each sine wave has an amplitude of 2.5 {mu}m and a wavelength of 71 {mu}m. In some experiments, an additional wavelength is added to explore the interaction of modes. In experiments with 3D initial conditions the spike morphology differs from what has been observed in other Rayleigh-Taylor experiments and simulations. Under certain conditions, experimental radiographs show some mass extending from the interface to the shock front. Current simulations show neither the spike morphology nor the spike penetration observed in the experiments. The amount of mass reaching the shock front is analyzed and potential causes for the spike morphology and the spikes reaching the shock are discussed. One such hypothesis is that these phenomena may be caused by magnetic pressure, generated by an azimuthal magnetic field produced by the plasma dynamics.

Kuranz, C. C.; Drake, R. P.; Grosskopf, M. J.; Fryxell, B.; Budde, A. [Department of Atmospheric, Oceanic and Space Science, Center for Radiative Shock Hydrodynamics, University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States); Hansen, J. F.; Miles, A. R. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States); Plewa, T. [Department of Scientific Computing, Florida State University, 400 Dirac Science Library, Tallahassee, Florida 32306 (United States); Hearn, N. [Center for Astrophysical Thermonuclear Flashes, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States); Knauer, J. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)

2010-05-15

82

Relativistic solitary-wave solutions of the beat-wave equations

The relativistic equations governing the nonlinear interaction of two light waves and a Langmuir wave are shown to admit two classes of solitary-wave solutions. Temporal solitary waves propagate at speeds greater than the speed of light and carry no information. Spatial solitary waves propagate at speeds less than the speed of light and do carry information. The properties of these

C. J. McKinstrie; D. F. DuBois

1986-01-01

83

Pulsewidth limitation in the relativistic backward wave oscillator

Spontaneous pulse shortening occurring in a relativistic backward wave oscillator (BWO) at gigawatt power levels is studied in experiment and theory. It is experimentally demonstrated that this phenomenon is accompanied by formation of an explosive-emission plasma at the surface of the corrugated slow-wave structure (SWS). Termination of microwave emission is explained by the increase of the BWO starting current from

Sergei D. Korovin; Gennady A. Mesyats; Igor V. Pegel; Sergei D. Polevin; Vladimir P. Tarakanov

2000-01-01

84

Progress on pulse lengthening of a relativistic backward wave oscillator

Summary form only given, as follows. Laser interferometry has been used to diagnose plasma formation and evolution in the slow wave structure (SWS) of a relativistic backward wave oscillator (BWO) during the course of microwave generation. The results indicated that plasma from the cutoff neck inlet contributed to the termination of the high power microwave pulse. In an effort to

F. Hegeler; E. Schamiloglu; S. D. Korovin; V.V. Rostov

1999-01-01

85

Saturation of plasma beat waves and detuning of relativistic Langmuir waves

The authors analyse the saturation mechanism for the electrostatic plasma wave excited by two electromagnetic waves, and show that the level is determined not only by the relativistic frequency shift but also by other nonlinear effects which are of the same order. The difference between this and previous results, which suggest that there is only a relativistic frequency shift, arises

R Bingham; R A Cairns; R G Evans

1986-01-01

86

Localized wake-field excitation and relativistic wave-breaking

The localized wake-field behavior behind a short laser pulse is analyzed numerically as well as analytically in one space dimension. A laser pulse propagating in an underdense plasma oscillates in amplitude and width. Within a certain parameter regime, the variations may be near the threshold for wake-field generation. During the times when the width becomes small enough, localized electrostatic wave-packets are generated. The latter may have amplitudes in the relativistic regime. The breaking of the wake-field wave packets is investigated. Known criteria for wave-breaking are generalized to the relativistic and inhomogeneous cases. It is found that relativistic, inhomogeneous packets break without threshold; however, not, in general, on the first oscillation. The time for wave-breaking can be estimated. The numerical findings are proven analytically by making use of a Lagrangian coordinate formulation.

Lehmann, G.; Laedke, E. W.; Spatschek, K. H. [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)

2007-10-15

87

A repetitive X-band relativistic backward-wave oscillator

A repetitive X-band relativistic backward-wave oscillator (BWO) driven by a SINUS-881 accelerator is described. Relativistic electron beams with peak current of 5.4 kA and voltage of 610 kV at a repetition rate of 100 Hz were generated by the SINUS-881 and then guided through the corrugated waveguide by an axial magnetic field of 3.0 T produced by a superconducting magnet.

Changhua Chen; Guozhi Liu; Wenhua Huang; Zhimin Song; Juping Fan; Hongjun Wang

2002-01-01

88

Relativistic electron loss; ULF waves and enhanced outward radial diffusion

In this study, observations from THEMIS and GOES are used to study the relationship between ULF waves and relativistic electron loss through the magnetopause. Around midnight UT on 25 June, 2008 the GOES satellites measured a two orders-of-magnitude drop in relativistic electron (> 1 MeV) fluxes over about 2.5 hours. The flux levels did not return to their previous levels

P. T. Loto'Aniu; H. J. Singer; T. G. Onsager; V. Angelopoulos; K. Glassmeier; D. Larson; I. R. Mann; C. T. Russell

2008-01-01

89

Propagation of linear waves in relativistic anisotropic magnetohydrodynamics.

Gedalin [Phys. Rev. E 47, 4354 (1993)] derived a dispersion relation for linear waves in relativistic anisotropic Magnetohydrodynamics (MHD). This dispersion relation is used to point out the regions where the relativistic anisotropic MHD leads to new results that cannot be obtained using usual collisional relativistic MHD. This is highlighted by plotting a Fresnal ray surface. Conditions for the onset of firehose and mirror instabilities are also indicated. Such a study can be applied to astrophysical features such as pulsar winds, propagation of cosmic rays, etc. PMID:12513643

Gebretsadkan, W B; Kalra, G L

2002-11-01

90

Relativistic electromagnetic waves in an electron-ion plasma

NASA Technical Reports Server (NTRS)

High power laser beams can drive plasma particles to relativistic energies. An accurate description of strong waves requires the inclusion of ion dynamics in the analysis. The equations governing the propagation of relativistic electromagnetic waves in a cold electron-ion plasma can be reduced to two equations expressing conservation of energy-momentum of the system. The two conservation constants are functions of the plasma stream velocity, the wave velocity, the wave amplitude, and the electron-ion mass ratio. The dynamic parameter, expressing electron-ion momentum conversation in the laboratory frame, can be regarded as an adjustable quantity, a suitable choice of which will yield self-consistent solutions when other plasma parameters were specified. Circularly polarized electromagnetic waves and electrostatic plasma waves are used as illustrations.

Chian, Abraham C.-L.; Kennel, Charles F.

1987-01-01

91

On wave stability in relativistic cosmic-ray hydrodynamics

NASA Technical Reports Server (NTRS)

Wave stability of a two-fluid hydrodynamical model describing the acceleration of cosmic rays by the first-order Fermi mechanism in relativistic, cosmic-ray-modified shocks is investigated. For a uniform background state, the short- and long-wavelength wave speeds are shown to interlace, thus assuring wave stability in this case. A JWKB analysis is performed to investigate the stability of short-wavelength thermal gas sound waves in the smooth, decelerating supersonic flow upstream of a relativistic, cosmic-ray-modified shock. The stability of the waves is assessed both in terms of the fluid velocity and density perturbations, as well as in terms of the wave action. The stability and interaction of the short-wavelength cosmic-ray coherent mode with the background flow is also studied.

Webb, G. M.

1989-01-01

92

High-efficiency relativistic backward wave oscillator: theory and design

Backward wave oscillators (BWOs) driven by high-current relativistic electron beams are capable of producing high-power coherent radiation in the centimeter and millimeter wavelength regions. However, the efficiency of these devices is usually limited to 15-20% when a homogeneous slow-wave structure is used. Utilizing a two-section slow-wave structure, where the spatial period of the second section is larger than that of

Baruch Levush; Thomas M. Antonsen; Alexander N. Vlasov; Gregory S. Nusinovich; Susanne M. Miller; Yuval Carmel; Victor L. Granatstein; William W. Destler; A. Bromborsky; C. Schlesiger; D. K. Abe; L. Ludeking

1996-01-01

93

Spatially-resolved X-ray scattering measurements of a planar blast wave

NASA Astrophysics Data System (ADS)

We present X-ray scattering measurements characterizing the spatial temperature and ionization profile of a blast wave driven in a near-solid density foam. Several-keV X-rays scattered from a laser-driven blast wave in a carbon foam. We resolved the scattering in high resolution in space and wavelength to extract the plasma conditions along the propagation direction of the blast wave. We infer temperatures of 20-40 eV and ionizations of 2-4 in the shock and rarefaction regions of the blast wave. This range of measured ionization states allows for a detailed comparison between different models for the bound-free scattering. FLYCHK simulations of the temperature-ionization balance generally agree with the experimental values in the shocked region while consistently underestimating the ionization in the rarefaction.

Gamboa, E. J.; Keiter, P. A.; Drake, R. P.; Falk, K.; Montgomery, D. S.; Benage, J. F.

2014-06-01

94

NASA Astrophysics Data System (ADS)

this paper, the effects of temperature, pressure, winds, moisture, and molecular content on the propagation of blast waves at high altitudes are investigated. These cause refractions and attenuations which modify the recorded ground overpressures from the ideal predictions. By coupling these effects together, the nonideal corrections to the overpressures are estimated by applying approximations which are dependent on the angle of propagation of the blast wave.

Latunde-Dada, Seyi

2013-10-01

95

Transition from the Sedov-Taylor Blast Wave Solution Up to the Sound Wave

NASA Astrophysics Data System (ADS)

In the case of a spherical blast wave described by the Sedov-Taylor model in an ideal gas, we apply the Vashy-Buckingham theorem (Pi theorem) to take into account the pressure of the medium at rest, and consequently the internal energy of the gas at rest. We obtain a single formula which contains the full time behavior of the explosion from the very beginning (Sedov-Taylor solution) up to the sound wave, therefore describing analytically the transition phase from t = 0 until t --> ?.

de Izarra, C.; Caillard, J.; Vallée, O.

96

Multidimensional effects on relativistic electrons in an oblique shock wave

Multidimensional effects on electron motion in a magnetosonic shock wave propagating obliquely to an external magnetic field are studied by means of a two-dimensional (two space coordinates and three velocities) relativistic, electromagnetic particle code. The simulations demonstrate that after trapping and energization in the main pulse of the shock wave, electrons can be detrapped from it keeping their ultrarelativistic energies. This detrapping is caused by magnetic fluctuations propagating along the wave front. Furthermore, some of the detrapped electrons can be accelerated to much higher energies by the shock wave because they can enter and exit the shock wave as a result of their gyromotions.

Shikii, Kenta; Toida, Mieko [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan)

2010-08-15

97

Relativistic description of electron Bernstein waves

The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave

Joan Decker; Abhay K. Ram

2006-01-01

98

We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v={partial_derivative}{sub p}E. The position-velocity uncertainty relation {delta}x{delta}v{>=}1/2 |<{partial_derivative}{sub p}{sup 2}E>| is saturated by minimal uncertainty wave packets {phi}(p)=Aexp(-{alpha}E(p)+{beta}p). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p{sup 2}/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma{sup 2} as well as for the relativistic dispersion relation E(p)={radical}(p{sup 2}+m{sup 2}). The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

Al-Hashimi, M.H. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)], E-mail: hashimi@itp.unibe.ch; Wiese, U.-J. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)

2009-12-15

99

Oscillations in the wake of a flare blast wave

NASA Astrophysics Data System (ADS)

Context. Oscillations of coronal loops in the Sun have been reported in both imaging and spectral observations at the onset of flares. Images reveal transverse oscillations, whereas spectra detect line-of-sight velocity or Doppler-shift oscillations. The Doppler-shift oscillations are commonly interpreted as longitudinal modes. Aims: Our aim is to investigate the relationship between loop dynamics and flows seen in TRACE 195 Å images and Doppler shifts observed by SUMER in Si iii 1113.2 Å and FeXIX 1118.1 Å at the time of a C.8-class limb flare and an associated CME. Methods: We carefully co-aligned the sequence of TRACE 195 Å images to structures seen in the SUMER Si iii, CaX, and FeXIX emission lines. Additionally, H? observations of a lifting prominence associated with the flare and the coronal mass ejection (CME) are available in three bands around 6563.3 Å. They give constraints on the timing and geometry. Results: Large-scale Doppler-shift oscillations in FeXIX and transverse oscillations in intensity images were observed over a large region of the corona after the passage of a wide bright extreme-ultraviolet (EUV) disturbance, which suggests ionization, heating, and acceleration of hot plasma in the wake of a blast wave. The online movie associated to Fig. 2 is available at http://www.aanda.org and at http://www.mps.mpg.de/data/outgoing/tothova/movie.gif

Tothova, D.; Innes, D. E.; Stenborg, G.

2011-04-01

100

Impact! Chandra Images a Young Supernova Blast Wave

NASA Astrophysics Data System (ADS)

Two images made by NASA's Chandra X-ray Observatory, one in October 1999, the other in January 2000, show for the first time the full impact of the actual blast wave from Supernova 1987A (SN1987A). The observations are the first time that X-rays from a shock wave have been imaged at such an early stage of a supernova explosion. Recent observations of SN 1987A with the Hubble Space Telescope revealed gradually brightening hot spots from a ring of matter ejected by the star thousands of years before it exploded. Chandra's X-ray images show the cause for this brightening ring. A shock wave is smashing into portions of the ring at a speed of 10 million miles per hour (4,500 kilometers per second). The gas behind the shock wave has a temperature of about ten million degrees Celsius, and is visible only with an X-ray telescope. "With Hubble we heard the whistle from the oncoming train," said David Burrows of Pennsylvania State University, University Park, the leader of the team of scientists involved in analyzing the Chandra data on SN 1987A. "Now, with Chandra, we can see the train." The X-ray observations appear to confirm the general outlines of a model developed by team member Richard McCray of the University of Colorado, Boulder, and others, which holds that a shock wave has been moving out ahead of the debris expelled by the explosion. As this shock wave collides with material outside the ring, it heats it to millions of degrees. "We are witnessing the birth of a supernova remnant for the first time," McCray said. The Chandra images clearly show the previously unseen, shock-heated matter just inside the optical ring. Comparison with observations made with Chandra in October and January, and with Hubble in February 2000, show that the X-ray emission peaks close to the newly discovered optical hot spots, and indicate that the wave is beginning to hit the ring. In the next few years, the shock wave will light up still more material in the ring, and an inward moving, or reverse, shock wave will heat the material ejected in the explosion itself. "The supernova is digging up its own past," said McCray. The observations were made on October 6, 1999, using the Advanced CCD Imaging Spectrometer (ACIS) and the High Energy Transmission Grating, and again on January 17, 2000, using ACIS. Other members of the team were Eli Michael of the University of Colorado; Dr. Una Hwang, Dr. Steven Holt and Dr. Rob Petre of NASA's Goddard Space Flight Center in Greenbelt, MD; Professor Roger Chevalier of the University of Virginia, Charlottesville; and Professors Gordon Garmire and John Nousek of Pennsylvania State University. The results will be published in an upcoming issue of the Astrophysical Journal. The ACIS instrument was built for NASA by the Massachusetts Institute of Technology, Cambridge, and Pennsylvania State University. The High Energy Transmission Grating was built by the Massachusetts Institute of Technology. NASA's Marshall Space Flight Center in Huntsville, AL, manages the Chandra program. TRW, Inc., Redondo Beach, CA, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, MA. More About SN 1987A Images to illustrate this release and more information on Chandra's progress can be found on the Internet at: http://chandra.harvard.edu/photo/2000/sn1987a/index.html AND http://chandra.nasa.gov More About SN 1987A

2000-05-01

101

Relativistic Particle Motion in Nonuniform Electromagnetic Waves.

National Technical Information Service (NTIS)

It is shown that a charged particle moving in a strong nonuniform electromagnetic wave suffers a net acceleration in the direction of the negative intensity gradient of the wave. Electrons will be expelled perpendicularly from narrow laser beams and vario...

G. Schmidt T. Wilcox

1973-01-01

102

Relativistic backward wave oscillators: Theory and experiment

The linear and nonlinear theory of backward-wave oscillators (BWOs) is developed taking into account reflection of the electromagnetic wave at the boundaries of the slow wave structure. The effects of finite duration and rise time of the electron beam pulse on device operation are discussed. A series of low-current experiments attempting to measure the start current has been conducted. The

B. Levush; A. Bromborsky; W. R. Lou; D. Abe; S. Miller; Y. Carmel; J. Rodgers; V. Granatstein; W. Destler

1991-01-01

103

Blast Shock Wave Mitigation Using the Hydraulic Energy Redirection and Release Technology

A hydraulic energy redirection and release technology has been developed for mitigating the effects of blast shock waves on protected objects. The technology employs a liquid-filled plastic tubing as a blast overpressure transformer to transfer kinetic energy of blast shock waves into hydraulic energy in the plastic tubings. The hydraulic energy is redirected through the plastic tubings to the openings at the lower ends, and then is quickly released with the liquid flowing out through the openings. The samples of the specifically designed body armor in which the liquid-filled plastic tubings were installed vertically as the outer layer of the body armor were tested. The blast test results demonstrated that blast overpressure behind the body armor samples was remarkably reduced by 97% in 0.2 msec after the liquid flowed out of its appropriate volume through the openings. The results also suggested that a volumetric liquid surge might be created when kinetic energy of blast shock wave was transferred into hydraulic energy to cause a rapid physical movement or displacement of the liquid. The volumetric liquid surge has a strong destructive power, and can cause a noncontact, remote injury in humans (such as blast-induced traumatic brain injury and post-traumatic stress disorder) if it is created in cardiovascular system. The hydraulic energy redirection and release technology can successfully mitigate blast shock waves from the outer surface of the body armor. It should be further explored as an innovative approach to effectively protect against blast threats to civilian and military personnel.

Chen, Yun; Huang, Wei; Constantini, Shlomi

2012-01-01

104

Spectral properties of blast-wave models of gamma-ray burst sources

NASA Technical Reports Server (NTRS)

We calculate the spectrum of blast-wave models of gamma-ray burst sources, for various assumptions about the magnetic field density and the relativistic particle acceleration efficiency. For a range of physically plausible models we find that the radiation efficiency is high and leads to nonthermal spectra with breaks at various energies comparable to those observed in the gamma-ray range. Radiation is also predicted at other wavebands, in particular at X-ray, optical/UV, and GeV/TeV energies. We discuss the spectra as a function of duration for three basic types of models, and for cosmological, halo, and galactic disk distances. We also evaluate the gamma-ray fluences and the spectral characteristics for a range of external densities. Impulsive burst models at cosmological distances can satisfy the conventional X-ray paucity constraint S(sub x)/S(sub gamma)less than a few percent over a wide range of durations, but galactic models can do so only for bursts shorter than a few seconds, unless additional assumptions are made. The emissivity is generally larger for bursts in a denser external environment, with the efficiency increasing up to the point where all the energy input is radiated away.

Meszaros, P.; Rees, M. J.; Papathanassiou, H.

1994-01-01

105

Computation of viscous blast wave solutions with an upwind finite volume method

NASA Technical Reports Server (NTRS)

A fully conservative, viscous, implicit, upwind, finite-volume scheme for the thin-layer Navier-Stokes equations is described with application to blast wave flow fields. In this scheme, shocks are captured without the oscillations typical of central differencing techniques and wave speeds are accurately predicted. The finite volume philosophy ensures conservation and since boundary conditions are also treated conservatively, accurate reflections of waves from surfaces are assured. Viscous terms in the governing equations are treated in a manner consistent with the finite volume philosophy, resulting in very accurate prediction of boundary layer quantities. Numerical results are presented for four viscous problems: a steady boundary layer, a shock-induced boundary layer, a blast wave/cylinder interaction and a blast wave/supersonic missile interaction. Comparisons of the results with an established boundary layer code, similarity solution, and experimental data show excellent agreement.

Molvik, Gregory A.

1987-01-01

106

DYNAMICS AND AFTERGLOW LIGHT CURVES OF GAMMA-RAY BURST BLAST WAVES WITH A LONG-LIVED REVERSE SHOCK

We perform a detailed study on the dynamics of a relativistic blast wave with the presence of a long-lived reverse shock (RS). Although a short-lived RS has been widely considered, the RS is believed to be long-lived as a consequence of a stratification expected on the ejecta Lorentz factors. The existence of a long-lived RS causes the forward shock (FS) dynamics to deviate from a self-similar Blandford-McKee solution. Employing the ''mechanical model'' that correctly incorporates the energy conservation, we present an accurate solution for both the FS and RS dynamics. We conduct a sophisticated calculation of the afterglow emission. Adopting a Lagrangian description of the blast wave, we keep track of an adiabatic evolution of numerous shells between the FS and RS. An evolution of the electron spectrum is also followed individually for every shell. We then find the FS and RS light curves by integrating over the entire FS and RS shocked regions, respectively. Exploring a total of 20 different ejecta stratifications, we explain in detail how a stratified ejecta affects its blast wave dynamics and afterglow light curves. We show that, while the FS light curves are not sensitive to the ejecta stratifications, the RS light curves exhibit much richer features, including steep declines, plateaus, bumps, re-brightenings, and a variety of temporal decay indices. These distinctive RS features may be observable if the RS has higher values of the microphysics parameters than the FS. We discuss possible applications of our results in understanding the gamma-ray burst afterglow data.

Uhm, Z. Lucas; Zhang Bing [Department of Physics and Astronomy, University of Nevada-Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154 (United States); Hascoeet, Romain; Daigne, Frederic; Mochkovitch, Robert [Institut d'Astrophysique de Paris, UMR 7095 Universite Pierre et Marie Curie-CNRS, 98 bis Boulevard Arago, F-75014 Paris (France); Park, Il H., E-mail: uhm@physics.unlv.edu [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2012-12-20

107

Experimental investigations into the dynamics of cylindrical, laser-driven, high-Mach-number shocks are used to study the thermal cooling instability predicted to occur in astrophysical radiative blast waves. A streaked Schlieren technique measures the full blast-wave trajectory on a single-shot basis, which is key for observing shock velocity oscillations. Electron density profiles and deceleration parameters associated with radiative blast waves were recorded, enabling the calculation of important blast-wave parameters including the fraction of radiated energy, {epsilon}, as a function of time for comparison with radiation-hydrodynamics simulations.

Moore, A. S.; Gumbrell, E. T.; Lazarus, J.; Hohenberger, M.; Robinson, J. S.; Smith, R. A.; Plant, T. J. A.; Symes, D. R.; Dunne, M. [Plasma Physics Division, AWE Aldermaston, RG7 4PR. United Kingdom (United Kingdom); Laser Consortium, Blackett Laboratory, Imperial College, London SW7 2BZ. United Kingdom (United Kingdom); Ministry of Defence, Foxhill, Bath BA1 5AB. United Kingdom (United Kingdom); Central Laser Facility, Rutherford Appleton Laboratory, Oxfordshire OX11 0QX. United Kingdom (United Kingdom)

2008-02-08

108

Relativistic particle motion in nonuniform electromagnetic waves

NASA Technical Reports Server (NTRS)

A charged particle moving in a strong nonuniform electromagnetic wave which suffers a net acceleration in the direction of the negative intensity gradient of the wave was investigated. Electrons will be expelled perpendicularly from narrow laser beams and various instabilities result.

Schmidt, G.; Wilcox, T.

1973-01-01

109

Relativistic Landau damping of longitudinal waves in isotropic pair plasmas

Landau damping is described in relativistic electron-positron plasmas. Relativistic electron-positron plasma theory contains important new effects when compared with classical plasmas. For example, there are undamped superluminal wave modes arising from both a continuous and discrete mode structure, the former even in the classical limit. We present here a comprehensive analytical treatment of the general case resulting in a compact and useful form for the dispersion relation. The classical pair-plasma case is addressed, for completeness, in an appendix.

Laing, E. W.; Diver, D. A. [Department of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom)

2006-09-15

110

Analysis of reflected blast wave pressure profiles in a confined room

NASA Astrophysics Data System (ADS)

To understand the blast effects of confined explosions, it is necessary to study the characteristic parameters of the blast wave in terms of overpressure, impulse and arrival time. In a previous study, experiments were performed using two different scales of a pyrotechnic workshop. The main purpose of these experiments was to compare the TNT equivalent for solid and gaseous explosives in terms of mass to define a TNT equivalent in a reflection field and to validate the similitude between real and small scales. To study the interactions and propagations of the reflected shock waves, the present study was conducted by progressively building a confined volume around the charge. In this way, the influence of each wall and the origins of the reflected shock waves can be determined. The purpose of this paper is to report the blast wave interactions that resulted from the detonation of a stoichiometric propane-oxygen mixture in a confined room.

Sauvan, P. E.; Sochet, I.; Trélat, S.

2012-05-01

111

Nonlinear relativistic interactions between electromagnetic waves and quantum plasmas

NASA Astrophysics Data System (ADS)

We present models for the nonlinear interaction between a relativistically strong electromagnetic wave and a quantum plasma. The electron dynamics is modeled using collective nonlinear Schrödinger, Klein-Gordon, and Dirac models, which are coupled nonlinearly with the Maxwell equations for the electromagnetic field. We consider the nonlinear propagation of electromagnetic waves, leading to self-induced transparency, as well as parametric instabilities involving Raman and modulational instabilities, and the acceleration of electrons by electrostatic fields and wakes behind short laser pulses. Spin effects lead to frequency upor downshifts depending on the spin polarization of the plasma and the polarization of the electromagnetic wave. The applications include dense astrophysical bodies and free electron lasers in the quantum regime, where relativistic and quantum effects must be taken into account on an equal footing.

Eliasson, B.; Shukla, P. K.

2012-02-01

112

Reduction of optically observed artillery blast wave trajectories using low dimensionality models

Muzzle blast trajectories from firings of a 152 mm caliber gun howitzer were obtained with high-speed optical imagers and used to assess the fidelity with which low dimensionality models can be used for data reduction. Characteristic flow regions were defined for the blast waves. The near-field region was estimated to extend to 0.98 - 1.25 meters from the muzzle and

Bryan J. Steward; Kevin C. Gross; Glen P. Perram

2011-01-01

113

NASA Astrophysics Data System (ADS)

Injuries to the tympanic membrane (ear drum) are particularly common in individuals subjected to blast overpressure such as military personnel engaged in conflict. Here, the interaction between blast wave and reticulated foams of varying density and thickness has been investigated using shock tube apparatus. The degree of mitigation afforded by the foam samples is discussed in relation to an injury threshold which has been suggested by others for the tympanic membrane.

Wilgeroth, J. M.; Nguyen, T.-T. N.; Proud, W. G.

2014-05-01

114

Prediction of the airblast wave effects near a tunnel advanced by drilling and blasting

In this paper, a semi-empirical model for the prediction of the air wave pressure outside a tunnel due to blasting inside is developed. The model reproduces properly the complex phenomenon of the airblast wave propagation, both inside the tunnel and outside, and allows estimating the air pressure level (this is, generally, higher along the axis tunnel direction than in other

Rafael Rodríguez; Javier Toraño; Mario Menéndez

2007-01-01

115

Polycyclic Aromatic Hydrocarbon Processing in the Blast Wave of the Supernova Remnant N132D

NASA Astrophysics Data System (ADS)

We present Spitzer Infrared Spectrograph 14-36 ?m mapping observations of the supernova remnant N132D in the Large Magellanic Cloud. This study focuses on the processing of polycyclic aromatic hydrocarbons (PAHs) that we previously identified in the southern blast wave. The mid-infrared spectra show strong continuum emission from shock-heated dust and a unique, nearly featureless plateau in the 15-20 ?m region, which we attribute to PAH molecules. The typical PAH emission bands observed in the surrounding interstellar medium ahead of the blast wave disappear, which indicates shock processing of PAH molecules. The PAH plateau appears most strongly at the outer edge of the blast wave and coincides with diffuse X-ray emission that precedes the brightest X-ray and optical filaments. This suggests that PAH molecules in the surrounding medium are swept up and processed in the hot gas of the blast wave shock, where they survive the harsh conditions long enough to be detected. We also observe a broad emission feature at 20 ?m appearing with the PAH plateau. We speculate that this feature is either due to FeO dust grains or connected to the processing of PAHs in the supernova blast wave shock.

Tappe, A.; Rho, J.; Boersma, C.; Micelotta, E. R.

2012-08-01

116

POLYCYCLIC AROMATIC HYDROCARBON PROCESSING IN THE BLAST WAVE OF THE SUPERNOVA REMNANT N132D

We present Spitzer Infrared Spectrograph 14-36 {mu}m mapping observations of the supernova remnant N132D in the Large Magellanic Cloud. This study focuses on the processing of polycyclic aromatic hydrocarbons (PAHs) that we previously identified in the southern blast wave. The mid-infrared spectra show strong continuum emission from shock-heated dust and a unique, nearly featureless plateau in the 15-20 {mu}m region, which we attribute to PAH molecules. The typical PAH emission bands observed in the surrounding interstellar medium ahead of the blast wave disappear, which indicates shock processing of PAH molecules. The PAH plateau appears most strongly at the outer edge of the blast wave and coincides with diffuse X-ray emission that precedes the brightest X-ray and optical filaments. This suggests that PAH molecules in the surrounding medium are swept up and processed in the hot gas of the blast wave shock, where they survive the harsh conditions long enough to be detected. We also observe a broad emission feature at 20 {mu}m appearing with the PAH plateau. We speculate that this feature is either due to FeO dust grains or connected to the processing of PAHs in the supernova blast wave shock.

Tappe, A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-72, Cambridge, MA 02138 (United States); Rho, J. [SOFIA Science Mission Operations/USRA, NASA Ames Research Center, MS 211-3, Moffett Field, CA 94035 (United States); Boersma, C. [NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035 (United States); Micelotta, E. R., E-mail: atappe@cfa.harvard.edu [Department of Physics and Astronomy, Western University, 1151 Richmond Street, London, Ontario N6A 3K7 (Canada)

2012-08-01

117

Relativistic wave-particle interaction in magnetospheric plasmas

NASA Astrophysics Data System (ADS)

The interaction between electromagnetic waves and high energy particles both in the magnetosphere of Earth and Jupiter has been investigated in a great detail. Different models for the electron distribution function has been used to determine the synchrotron radiation in the Jovian inner magnetosphere and the growth rate of R- mode waves in a relativistic plasma. Using a bi-loss-cone distribution function (composed of a high anisotropic component and a quasi-isotropic component), the whistler- mode wave growth has been calculated for the interchange events in the Io torus and for chorus emissions during a terrestrial substorm. We demonstrated that the path integrated gain can be dramatically enhanced over quiescent condition; exceed 20 e-foldings in the interchange event or approach 10 e-foldings during the terrestrial substorm. The wave excitation can cause strong pitch angle scattering leading to quasi-isotropic pitch angle distributions during Jovian interchange event and the terrestrial substorm. The relativistic wave- particle resonant diffusion curves for electron cyclotron resonance with both electromagnetic subluminous waves (electromagnetic R mode and L mode) and superluminous waves (R-X mode, L-O mode and L-X mode) have been constructed and their application are studied to electron acceleration in the Earth magnetosphere at the locations both inside and outside the plasmapause.

Xiao, Fuliang

2001-06-01

118

Parametric instability of a relativistically strong electromagnetic wave.

NASA Technical Reports Server (NTRS)

The stability of a circularly polarized electromagnetic wave that is strong enough to make plasma electrons, but not ions, relativistic is studied. Small perturbations are considered which propagate parallel to the large-amplitude driver. A relativistically strong wave can be unstable on time scales as short as twice its own oscillation period, and decays into a forward-going plasma oscillation and either one or two electromagnetic waves. Ion motion introduces an additional instability which can be important at short perturbation wavelengths, where the driver would otherwise be stable. The unstable ion and electron modes both have potential for producing anomalously large acceleration of relativistic particles, as well as significant amounts of backscattered light. These effects may be important in two applications: (1) the use of intense lasers to heat or compress plasma, and (2) the plasma surrounding a pulsar, if the pulsar is losing energy by radiation of electromagnetic waves at its rotation frequency. Instability persists in the nonrelativistic regime, reducing to stimulated Raman scattering as a special case.

Max, C. E.

1973-01-01

119

Simulation of blast-induced early-time intracranial wave physics leading to traumatic brain injury.

The objective of this modeling and simulation study was to establish the role of stress wave interactions in the genesis of traumatic brain injury (TBI) from exposure to explosive blast. A high resolution (1 mm3 voxels) five material model of the human head was created by segmentation of color cryosections from the Visible Human Female data set. Tissue material properties were assigned from literature values. The model was inserted into the shock physics wave code, CTH, and subjected to a simulated blast wave of 1.3 MPa (13 bars) peak pressure from anterior, posterior, and lateral directions. Three-dimensional plots of maximum pressure, volumetric tension, and deviatoric (shear) stress demonstrated significant differences related to the incident blast geometry. In particular, the calculations revealed focal brain regions of elevated pressure and deviatoric stress within the first 2 ms of blast exposure. Calculated maximum levels of 15 KPa deviatoric, 3.3 MPa pressure, and 0.8 MPa volumetric tension were observed before the onset of significant head accelerations. Over a 2 ms time course, the head model moved only 1 mm in response to the blast loading. Doubling the blast strength changed the resulting intracranial stress magnitudes but not their distribution. We conclude that stress localization, due to early-time wave interactions, may contribute to the development of multifocal axonal injury underlying TBI. We propose that a contribution to traumatic brain injury from blast exposure, and most likely blunt impact, can occur on a time scale shorter than previous model predictions and before the onset of linear or rotational accelerations traditionally associated with the development of TBI. PMID:19449961

Taylor, Paul A; Ford, Corey C

2009-06-01

120

Dispersion of waves in relativistic plasmas with isotropic particle distributions

The dispersion laws of Langmuir and transverse waves are calculated in the relativistic nonmagnetized formalism for several isotropic particle distributions: thermal, power law, relativistic Lorentzian {kappa}, and hybrid {beta}. For Langmuir waves the parameters of superluminal undamped, subluminal damped principal, and higher modes are determined for a range of distribution parameters. The undamped and principal damped modes are found to match smoothly. Principal damped and second damped modes are found not to match smoothly. The presence of maximum wavenumber is discovered above that no longitudinal modes formally exist. The higher damped modes are discovered to be qualitatively different for thermal and certain nonthermal distributions. Consistently with the known results, the Landau damping is calculated to be stronger for nonthermal power-law-like distributions. The dispersion law is obtained for the single undamped transverse mode. The analytic results for the simplest distributions are provided.

Shcherbakov, Roman V. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

2009-03-15

121

Theory of relativistic backward-wave oscillators with end reflectors

Microwave sources based on backward-wave oscillators (BWOs) with relativistic electron beams are capable of producing high-power coherent radiation in the centimeter- and millimeter-wavelength regimes. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical

Baruch Levusch; Thomas M. Antonsen; Alan Bromborsky; Wei-Ran Lou; Yuval Carmel

1992-01-01

122

A relativistic backward wave oscillator with a modulating resonance reflector

A high-efficiency relativistic microwave source based on a backward wave oscillator (BWO) with a resonance reflector has been\\u000a studied by experimental and numerical methods. The BWO is capable of generating 12-ns pulses with a carrier frequency of 9.93\\u000a GHz at an output radiation power of 0.75 0.11 GW. For the BWO pumped by a high-current electron beam from a SINUS-6K

S. D. Korovin; V. V. Rostov; E. M. Tot’meninov

2005-01-01

123

Relativistic backward wave oscillator with a discrete resonance reflector

We study, both theoretically and experimentally, a relativistic backward wave oscillator BWO with a discrete resonance reflector.\\u000a It is shown that premodulation of electrons in the reflector region leads to considerable changes in the oscillator characteristics.\\u000a If a homogeneous slowingdown system (SS) is considered and the space charge is neglected, then the calculated maximum efficiency\\u000a of oscillation increases from 15%

S. D. Korovin; I. K. Kurkan; V. V. Rostov; E. M. Tot’meninov

1999-01-01

124

Relativistic backward wave oscillator with multijet electron beam

The influence of the multijet structure of an annular electron beam on the operation of a high-current relativistic backward\\u000a wave oscillator (BWO) has been experimentally studied. Multijet annular electron beams were generated using graphite explosive-emission\\u000a cathodes shaped as tubes with comb-shaped ridges. It is established that the BWO working characteristics are highly stable\\u000a with respect to the multijet beam structure.

M. B. Goykhman; A. V. Gromov; V. V. Kladukhin; S. V. Kladukhin; N. F. Kovalev; S. P. Khramtsov

2011-01-01

125

The application of cylindrical blast waves to impact studies of materials

NASA Astrophysics Data System (ADS)

An exploding wire method is described in which the impact properties of hollow polymeric cylinders are investigated by subjecting them to internal, high-pressure, blast wave loading. Studies of the blast waves themselves, and of the expansion of thin-walled polymer tubes and rings, have been made using high-speed image convertor photography at 10 exp 5 to 10 exp 6 frames/s. Such observations, when combined with strain gauge and pressure measurements where necesary, have enabled the mechanical properties of several polymers to be determined at high strain rates from 10 exp 3 to 10 exp 5/s.

Parry, D. J.; Stewardson, H. R.; Ahmad, S. H.; Al-Maliky, N.

1991-04-01

126

Effects of internal heat transfer on the structure of self-similar blast waves

NASA Technical Reports Server (NTRS)

An analysis of the problem of self-similar, nonadiabatic blast waves, where both conduction and radiation are allowed to take place, show the problem to be reducible to the integration of a system of six coupled nonlinear ordinary differential equations. Consideration of these equations shows that although radiation tends to produce uniform fields through temperature gradient attenuation, all the energy carried by radiation is deposited on the front and the bounding shock becomes increasingly overdriven. When conduction is taken into account, the distribution of gasdynamic parameters in blast waves in the case of Rosseland diffusion radiation is more uniform than in the case of the Planck emission radiation.

Ghoniem, A. F.; Berger, S. A.; Oppenheim, A. K.; Kamel, M. M.

1982-01-01

127

A high-power relativistic backward wave oscillator with a longitudinal slot slow-wave system

NASA Astrophysics Data System (ADS)

It is established that longitudinal slots in the slow-wave system of a high-current relativistic backward wave oscillator (BWO) can be used as additional means of mode selection and effective absorption of near-wall plasma. Using these properties, it is possible to increase the limiting pulse duration and repetition rate of BWO output radiation pulses.

Goykhman, M. B.; Kladukhin, V. V.; Kladukhin, S. V.; Kovalev, N. F.; Kolganov, N. G.; Khramtsov, S. P.

2014-01-01

128

The experimental research presented in this thesis establishes the feasibility of a novel microwave phased antenna array. The outputs of multiple high power Traveling Wave Tube (TWT) amplifiers driven by a single high power Backward Wave Oscillator (BWO) source feed the antenna. To test the concept we drove twin TWTs with a single BWO, simultaneously supplied by three independent relativistic

Jennifer Margaret Butler

1991-01-01

129

Implementation of the exploding wire technique to study blast-wave-structure interaction

NASA Astrophysics Data System (ADS)

The effort invested in improving our understanding of the physics of high-energy explosion events has been steadily increasing since the latter part of the twentieth century. Moreover, the dramatic increase in computer power over the last two decades has made the numerical simulation approach the dominant tool for investigating blast phenomena and their effects. However, field tests, on both large and small scales, are still in use. In the current paper, we present an experimental tool to better resolve and study the blast-structure interaction phenomenon and to help validate the numerical simulations of the same. The experimental tool uses an exploding wire technique to generate small-scale cylindrical and spherical blast waves. This approach permits safe operation, high repeatability, and the use of advanced diagnostic systems. The system was calibrated using an analytical model, an empirical model, and numerical simulation. To insure that spherical blast geometry was achieved, a set of free air blast experiments was done in which high-speed photography was used to monitor the blast structure. A scenario in which an explosion occurred in the vicinity of a structure demonstrated the system's capabilities. Using this simple but not trivial configuration showed unequivocally the effectiveness of this tool. From this comparison, it was found that at early times of blast-structure interaction, the agreement between the two sets of results was very good, but at later times incongruences appeared. Effort has been made to interpret this observation. Furthermore, by using similitude analysis, the results obtained from the small-scale experiments can be applied to the full-scale problem. We have shown that an exploding wire system offers an inexpensive, safe, easy to operate, and effective tool for studying phenomena related to blast-wave-structure interactions.

Ram, O.; Sadot, O.

2012-11-01

130

Chaotic Motion of Relativistic Electrons Driven by Whistler Waves

NASA Technical Reports Server (NTRS)

Canonical equations governing an electron motion in electromagnetic field of the whistler mode waves propagating along the direction of an ambient magnetic field are derived. The physical processes on which the equations of motion are based .are identified. It is shown that relativistic electrons interacting with these fields demonstrate chaotic motion, which is accompanied by the particle stochastic heating and significant pitch angle diffusion. Evolution of distribution functions is described by the Fokker-Planck-Kolmogorov equations. It is shown that the whistler mode waves could provide a viable mechanism for stochastic energization of electrons with energies up to 50 MeV in the Jovian magnetosphere.

Khazanov, G. V.; Telnikhin, A. A.; Kronberg, Tatiana K.

2007-01-01

131

Generalized relativistic wave equations with intrinsic maximum momentum

NASA Astrophysics Data System (ADS)

We examine the nonperturbative effect of maximum momentum on the relativistic wave equations. In momentum representation, we obtain the exact eigen-energies and wave functions of one-dimensional Klein-Gordon and Dirac equation with linear confining potentials, and the Dirac oscillator. Bound state solutions are only possible when the strength of scalar potential is stronger than vector potential. The energy spectrum of the systems studied is bounded from above, whereby classical characteristics are observed in the uncertainties of position and momentum operators. Also, there is a truncation in the maximum number of bound states that is allowed. Some of these quantum-gravitational features may have future applications.

Ching, Chee Leong; Ng, Wei Khim

2014-05-01

132

Relativistic (covariant) kinetic theory of linear plasma waves and instabilities

The fundamental kinetic description is of vital importance in high-energy astrophysics and fusion plasmas where wave phenomena evolve on scales small comparing with binary collision scales. A rigorous relativistic analysis is required even for nonrelativistic plasma temperatures for which the classical theory yielded unphysical results: e.g. collisonless damping of superluminal waves (phase velocity exceeds the speed of light). The existing nonrelativistic approaches are now improved by covariantly correct dispersion theory. As an important application, the Weibel instability has been recently investigated and confirmed as the source of primordial magnetic field in the intergalactic medium.

Lazar, M. [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); 'Alexandru Ioan Cuza' University, Faculty of Physics, 6600 Iasi (Romania); Schlickeiser, R. [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Centre for Plasma Science and Astrophysics, Ruhr-University, D-44780 Bochum (Germany)

2006-06-19

133

Rapidly rotating relativistic stars as sources of gravitational waves

NASA Astrophysics Data System (ADS)

Rapidly rotating relativistic stars can be subject to different kinds of instabilities leading to gravitational wave emission. A instability spins a star down by allowing it to radiate away its angular momentum in gravitational waves. I will overview of stellar instabilities relevant for an old accreting compact star in low mass X-ray binaries (LMXBs). Taking into account actual values of viscosities in strange quark matter and neglecting the magnetic field I will show that in contrast to neutron stars, strange quark stars described by the MIT bag model can be accelerated to very high frequency in LMXBs if the strange quark mass is consistent with values based on particle data tables.

Gondek-Rosinska, D.; Gourgoulhon, E.; Haensel, P.

134

Whistler wave generation by non-gyrotropic, relativistic, electron beams

NASA Astrophysics Data System (ADS)

Particle-in-cell code, EPOCH, is used for studying features of the wave component evident to propagate backwards from the front of the non-gyrotropic, relativistic beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile. According to recent findings presented in Tsiklauri [Phys. Plasmas 18, 052903 (2011)], Schmitz and Tsiklauri [Phys. Plasmas 20, 062903 (2013)], and Pechhacker and Tsiklauri [Phys. Plasmas 19, 112903 (2012)], in a 1.5-dimensional magnetised plasma system, the non-gyrotropic beam generates freely escaping electromagnetic radiation with properties similar to the Type-III solar radio bursts. In this study, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented for the first time. Background magnetic field strength in the system is varied in order to prove that the backwards propagating wave's frequency, prescribed by the whistler wave dispersion relation, is proportional to the specified magnetic field. Moreover, the identified whistlers are shown to be generated by the normal Doppler-shifted relativistic resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves, while a small but sufficient fraction is going into L- and R-electromagnetic modes.

Skender, M.; Tsiklauri, D.

2014-04-01

135

NASA Astrophysics Data System (ADS)

Radiative blast waves were created by irradiating a krypton cluster source from a supersonic jet with a high intensity femtosecond laser pulse. It was found that the radiation from the shock surface is absorbed in the optically thick upstream medium creating a radiative heat wave that travels supersonically ahead of the main shock. As the blast wave propagates into the heated medium, it slows and loses energy, and the radiative heat wave also slows down. When the radiative heat wave slows down to the transonic regime, a secondary shock in the ionization precursor is produced. This paper presents experimental data characterizing both the initial and secondary shocks and numerical simulations to analyze the double-shock dynamics.

Kim, I.; Quevedo, H. J.; Feldman, S.; Bang, W.; Serratto, K.; McCormick, M.; Aymond, F.; Dyer, G.; Bernstein, A. C.; Ditmire, T.

2013-12-01

136

Radiative blast waves were created by irradiating a krypton cluster source from a supersonic jet with a high intensity femtosecond laser pulse. It was found that the radiation from the shock surface is absorbed in the optically thick upstream medium creating a radiative heat wave that travels supersonically ahead of the main shock. As the blast wave propagates into the heated medium, it slows and loses energy, and the radiative heat wave also slows down. When the radiative heat wave slows down to the transonic regime, a secondary shock in the ionization precursor is produced. This paper presents experimental data characterizing both the initial and secondary shocks and numerical simulations to analyze the double-shock dynamics.

Kim, I.; Quevedo, H. J.; Feldman, S.; Bang, W.; Serratto, K.; McCormick, M.; Aymond, F.; Dyer, G.; Bernstein, A. C.; Ditmire, T. [Center for High Energy Density Science, Department of Physics, The University of Texas at Austin, C1510, Austin, Texas 78712 (United States)] [Center for High Energy Density Science, Department of Physics, The University of Texas at Austin, C1510, Austin, Texas 78712 (United States)

2013-12-15

137

Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

Cox, D. P.; Anderson, P. R.

1981-01-01

138

Dual Band Relativistic Backward Wave Oscillator with Gaussian Radiation

NASA Astrophysics Data System (ADS)

Generating dual-band signals using a relativistic backward wave oscillator (RBWO) with a two-section slow wave structure is attractive to many applications such as plasma diagnostics and sounding systems. Using different sections in the RBWO provides a change of the synchronism conditions and as a result two microwave frequencies at C-band and X-band have been produced at the output. The synchronism condition can be provided by variation of the corrugated waveguide period. In this abstract, a two-spiral corrugated and a sinusoidal structures have been used as two sections to produce the frequency bands. The slow wave structures have been designed analytically and the simulation results verified the analytics. The RBWO is generating a microwave signal that propagates backwards, so the two-spiral corrugated structure acts as a reflector. This reflector gives the ability to extract the signals azimuthally. Two dominant frequencies at 7GHz and 10GHz have been found with a microwave power of megawatts and with a Gaussian beam. The simulations show that the two beam-wave interaction regions work independently. The fully electromagnetic, fully relativistic particle-in-cell (PIC) code MAGIC was used to simulate the device with a voltage pulse 460kV and with a 2T axial magnetic field.

Elfrgani, Ahmed; Vadiee, Ehsan; Prasad, Sarita; Fuks, Mikhail; Schamiloglu, Edl

2012-10-01

139

Large-amplitude oblique whistler waves and relativistic electron acceleration

NASA Astrophysics Data System (ADS)

Observation [Cattell et al., 2008] shows that large-amplitude whistler waves propagating in oblique directions with respect to the ambient magnetic field may be responsible for energizing the radiation belt electrons to relativistic energies within a time scale as short as a fraction of a second. Test-particle simulations available in the literature invariably adopt simple model waveforms for the oblique whistlers. Solutions of fully nonlinear warm electron fluid equation show that oblique whistlers not only undergo steepening (Yoon, 2011) but also large-amplitude whistlers are unstable to nonlinear decay instability. The physics of whistler wave steepening and nonlinear decay processes as well as their impact on particle interaction will be discussed. Relativistic test particle simulation shows that a population of initially low energy electrons can be accelerated in a few seconds to O(10) MeV energies. However, it is shown that such an efficient electron acceleration is possible only if the wave propagation angle is sufficiently large and that quasi-parallel propagation of whistler waves cannot accelerate the electrons.

Yoon, P. H.

2012-12-01

140

Quantifying Momentum Transfer Due to Blast Waves from Oxy-Acetylene Driven Shock Tubes.

National Technical Information Service (NTIS)

Shock tubes have been widely used since the 1950s to study physical phenomena such as shock waves, combustion chemistry, and the response of materiel to blast loading. Recently, laboratory-scale shock tubes driven by oxy- acetylene were described. It was ...

A. Courtney H. Her M. Courtney

2012-01-01

141

Blast Wave Measurements from Detonating Spherical 8.4 Kg Comp B Charges.

National Technical Information Service (NTIS)

Air blast wave measurements were made at distances 4 to 17 m from detonating 8.4 kg spherical Comp B charges suspended at 0.75 and 1.0 m over a plain ground surface. Pressure-time histories, peak pressures, durations and impulses are presented. A comparis...

I. Aaseborn

1983-01-01

142

Theoretical analysis of a relativistic travelling wave tube filled with plasma

A cold and uniform plasma-filled travelling wave tube with sinusoidally corrugated slow wave structure is driven by a finite thick annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. By means of the linear field theory, the dispersion relation for the relativistic travelling wave tube (RTWT) is derived. By numerical computation, the dispersion

Hong-Quan Xie; Pu-Kun Liu

2007-01-01

143

Relativistic waves raised by explosions in space as sources of ultra-high-energy cosmic rays

The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under

G. N. Kichigin

144

Particle radiation from relativistic plasmas contained by soliton waves

NASA Astrophysics Data System (ADS)

In the last few years, the Weibel instability has undergone a change from a marginal phenomenon to a more intense field of research especially in astrophysics. The possibility of magnetic field creation in an unmagnetized plasma enables new applications and the explanation of many scenarios that are still intensely debated. In a previous paper (Schaefer-Rolffs and Lerche 2006 Phys. Plasmas 13 062303), the fundamentals of a nonlinear theory of solitary Weibel modes were derived. The main prerequisite is a bulk of charged particles moving conjoined in one direction, while perpendicular small fluctuations are possible. Such a constraint is obviously fulfilled in any relativistic astrophysical jet, e.g. in gamma-ray bursts or in the jets of active galactic nuclei. This paper provides calculations concerning the frequency spectra of radiation produced from relativistic electrons contained by such solitary waves. Furthermore, the influence of polarization and the Faraday effect are considered.

Schaefer-Rolffs, U.; Lerche, I.; Tautz, R. C.

2009-03-01

145

EFFECT OF INTERACTING RAREFACTION WAVES ON RELATIVISTICALLY HOT JETS

The effect of rarefaction acceleration on the propagation dynamics and structure of relativistically hot jets is studied through relativistic hydrodynamic simulations. We emphasize the nonlinear interaction of rarefaction waves excited at the interface between a cylindrical jet and the surrounding medium. From simplified one-dimensional (1D) models with radial jet structure, we find that a decrease in the relativistic pressure due to the interacting rarefaction waves in the central zone of the jet transiently yields a more powerful boost of the bulk jet than that expected from single rarefaction acceleration. This leads to a cyclic in situ energy conversion between thermal and bulk kinetic energies, which induces radial oscillating motion of the jet. The oscillation timescale is characterized by the initial pressure ratio of the jet to the ambient medium and follows a simple scaling relation, {tau}{sub oscillation}{proportional_to}(P{sub jet,0}/P{sub amb,0}){sup 1/2}. Extended two-dimensional simulations confirm that this radial oscillating motion in the 1D system manifests as modulation of the structure of the jet in a more realistic situation where a relativistically hot jet propagates through an ambient medium. We find that when the ambient medium has a power-law pressure distribution, the size of the reconfinement region along the propagation direction of the jet in the modulation structure {lambda} evolves according to a self-similar relation {lambda}{proportional_to}t{sup {alpha}/2}, where {alpha} is the power-law index of the pressure distribution.

Matsumoto, Jin; Shibata, Kazunari [Kwasan and Hida Observatories, Kyoto University, Kyoto (Japan); Masada, Youhei, E-mail: jin@kusastro.kyoto-u.ac.jp [Graduate School of System Informatics, Department of Computational Science, Kobe University, Kobe (Japan)

2012-06-01

146

High efficiency X-band relativistic backward wave oscillator with non-uniform slow wave structures

NASA Astrophysics Data System (ADS)

Backward wave oscillators (BWOs) driven by intense relativistic electron beams are very efficient means of producing high-power microwaves. However, the efficiency of conventional BWO is lower than 30%. An X-band oversized BWO with non-uniform slow wave structure is designed to improve RF output characteristics. In particle-in-cell simulation, a high power microwave with a power of 8.0 GW and efficiency of 40% is obtained, compared with that of 30% obtained in a conventional relativistic BWO.

Wu, Yang; Xu, Zhou; Li, Zheng-Hong; Ma, Qiao-Sheng; Tang, Chuan-Xiang

2012-08-01

147

Particle acceleration in ultra-relativistic oblique shock waves

NASA Astrophysics Data System (ADS)

We perform Monte Carlo simulations of diffusive shock acceleration at highly relativistic oblique shock waves. High upstream flow Lorentz gamma factors ( ?) are used, which are relevant to models of ultra-relativistic particle shock acceleration in active galactic nuclei (AGN) central engines and relativistic jets and gamma ray burst (GRB) fireballs. We investigate numerically the acceleration properties in the relativistic and ultra-relativistic flow regime ( ?˜10-10 3), such as angular distribution, acceleration time constant, particle energy gain versus number of crossings and spectral shapes. We perform calculations for sub-luminal and super-luminal shocks. For the first case, the dependence on whether or not the scattering is pitch angle diffusion or large angle scattering is studied. The large angle model exhibits a distinctive structure in the basic power-law spectrum which is not nearly so obvious for small angle scattering. However, both models yield significant 'speed-up' or faster acceleration rates when compared with the conventional, non-relativistic expression for the time constant, or alternatively with the time scale rg/ c where rg is Larmor radius. The ?2 energization for the first crossing cycle and the significantly large energy gain for subsequent crossings as well as the high 'speed-up' factors found, are important in supporting the Vietri and Waxman work on GRB ultra-high energy cosmic ray, neutrino and gamma-ray output. Secondly, for super-luminal shocks, we calculate the energy gain for a number of different inclinations and the spectral shapes of the accelerated particles are given. In this investigation we consider only large angle scattering, partly because of computational time limitations and partly because this model provides the most favourable situation for acceleration. We use high gamma flows with Lorentz factors in the range 10-40, which are relevant to AGN accretion disks and jet ultra-relativistic shock configurations. We closely follow the particle's trajectory along the magnetic field lines during shock crossings where the equivalent of a guiding centre approximation is inappropriate, constantly measuring its phase space co-ordinates in the fluid frames where E=0 . We find that a super-luminal 'shock drift' mechanism is less efficient in accelerating particles to the highest energies observed, compared to the first order Fermi acceleration applying in the sub-luminal case, suggesting that the former cannot stand as a sole acceleration mechanism for the ultra-high energy cosmic rays observed.

Meli, A.; Quenby, J. J.

2003-08-01

148

High-efficiency relativistic backward wave oscillator: Theory and design

Backward wave oscillators (BWO`s) driven by high-current relativistic electron beams are capable of producing high-power coherent radiation in the centimeter and millimeter wavelength regions. However, the efficiency of these devices is usually limited to 15--20% when a homogeneous slow-wave structure is used. Utilizing a two-section slow-wave structure, where the spatial period of the second section is larger than that of the first section, a BWO efficiency of greater than 50% was calculated. A conceptual design of a high-efficiency S-band BWO driven by a 500-kV 5-kA electron beam has been developed and analyzed.

Levush, B.; Antonsen, T.M. Jr.; Vlasov, A.N. [Univ. of Maryland, College Park, MD (United States)] [and others] [Univ. of Maryland, College Park, MD (United States); and others

1996-06-01

149

Polycyclic Aromatic Hydrocarbon Processing in the Blast Wave of the Supernova Remnant 132D

NASA Astrophysics Data System (ADS)

We present Spitzer Infrared Spectrograph 14-36 micron spectral mapping of the entire supernova remnant N132D in the Large Magellanic Cloud. We show a multi- wavelength study of N132D including archival Chandra X-ray and HST optical maps. This case study focuses on the processing of Polycyclic Aromatic Hydrocarbons (PAHs) that were previously identified in the southeastern blast wave of N132D by Tappe et al. 2006. The mid-infrared spectra trace the strong continuum emission and show a unique, nearly featureless hump in the 15 to 20 micron region. We attribute this emission to PAH molecules and show how the typical PAH emission bands observed in the surrounding medium ahead of the blast wave disappear. We present changes in the PAH emission spectra as a function of the distance from the shock front. The featureless PAH hump appears most strongly at the outer edge of the blast wave and coincides with fainter, diffuse X-ray emission that precedes the brightest X-ray and optical filaments. This suggests that PAH molecules in the surrounding medium are swept up and processed in the hot gas of the blast wave shock, where they survive the harsh conditions long enough to be detected. In addition, a broad emission feature at 20 micron appears together with the PAH hump. We speculate that this feature is connected to the processing of PAH molecules or clusters in the blast wave shock. We find a similarity of this feature to the well-known but as of yet unidentified 20.1 micron feature observed in carbon-rich protoplanetary nebulae and our detection might offer new clues for its identification.

Rho, Jeonghee; Tappe, A.

2012-01-01

150

On Beat Wave Excitation of Relativistic Plasma Waves

The beat wave excitation process is examined analytically in the Eulerian fluid description. The effects of plasma drifts, harmonics, pump rise time, frequency mismatch, phenomenological damping, plasma inhomogeneities, and two dimensions are discussed. The consistency between the Eulerian and Lagrangian fluid descriptions is verified.

W. B. Mori

1987-01-01

151

THE EARLY BLAST WAVE OF THE 2010 EXPLOSION OF U SCORPII

Three-dimensional hydrodynamic simulations exploring the first 18 hr of the 2010 January 28 outburst of the recurrent nova U Scorpii have been performed. Special emphasis was placed on capturing the enormous range in spatial scales in the blast. The pre-explosion system conditions included the secondary star and a flared accretion disk. These conditions can have a profound influence on the evolving blast wave. The blast itself is shadowed by the secondary star, which itself gives rise to a low-temperature bow shock. The accretion disk is completely destroyed in the explosion. A model with a disk gas density of 10{sup 15} cm{sup -3} produced a blast wave that is collimated and with clear bipolar structures, including a bipolar X-ray emitting shell. The degree of collimation depends on the initial mass of ejecta, energy of explosion, and circumstellar gas density distribution. It is most pronounced for a model with the lowest explosion energy (10{sup 43} erg) and mass of ejecta (10{sup -8} M {sub sun}). The X-ray luminosities of three of six models computed are close to, but consistent with, an upper limit to the early blast X-ray emission obtained by the Swift satellite, the X-ray luminosity being larger for higher circumstellar gas density and higher ejecta mass. The latter consideration, together with estimates of the blast energy from previous outbursts, suggests that the mass of ejecta in the 2010 outburst was not larger than 10{sup -7} M {sub sun}.

Drake, J. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Orlando, S. [INAF-Osservatorio Astronomico di Palermo 'G.S. Vaiana', Piazza del Parlamento 1, 90134 Palermo (Italy)

2010-09-10

152

Relativistic waves raised by explosions in space as sources of ultra-high-energy cosmic rays

NASA Astrophysics Data System (ADS)

The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under consideration can be made are studied thoroughly. Ultra-high-energy CRs (up to 1020 eV) are shown to be obtained due to the surfing in relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs).

Kichigin, G. N.

2013-01-01

153

Stimulated Compton conversion of Langmuir waves by relativistic electron beams

NASA Technical Reports Server (NTRS)

The scattering of a Langmuir wave by a relativistic electron to produce a transversely polarized high-frequency EM wave by an inverse Compton process is investigated theoretically. The results of numerical computations are presented in diagrams and graphs, and it is shown that although net growth rates are predicted for several classes of Langmuir spectra, they are at least several orders of magnitude too small to account for the intense high-frequency emission seen in recent beam-plasma experiments (Benford et al., 1980; Kato et al., 1983) unless some unknown coherence mechanism is focusing the inverse-Compton emission. The implications of the mechanism for astrophysical beam-plasma systems such as quasars and radio galaxies are indicated.

Newman, D. L.

1985-01-01

154

Stimulated Compton conversion of Langmuir waves by relativistic electron beams

NASA Astrophysics Data System (ADS)

The scattering of a Langmuir wave by a relativistic electron to produce a transversely polarized high-frequency EM wave by an inverse Compton process is investigated theoretically. The results of numerical computations are presented in diagrams and graphs, and it is shown that although net growth rates are predicted for several classes of Langmuir spectra, they are at least several orders of magnitude too small to account for the intense high-frequency emission seen in recent beam-plasma experiments (Benford et al., 1980; Kato et al., 1983) unless some unknown coherence mechanism is focusing the inverse-Compton emission. The implications of the mechanism for astrophysical beam-plasma systems such as quasars and radio galaxies are indicated.

Newman, D. L.

1985-05-01

155

NASA Astrophysics Data System (ADS)

We obtain renormalized sets of right and left eigenvectors of the flux vector Jacobians of the relativistic MHD equations, which are regular and span a complete basis in any physical state including degenerate ones. The renormalization procedure relies on the characterization of the degeneracy types in terms of the normal and tangential components of the magnetic field to the wave front in the fluid rest frame. Proper expressions of the renormalized eigenvectors in conserved variables are obtained through the corresponding matrix transformations. Our work completes previous analysis that present different sets of right eigenvectors for non-degenerate and degenerate states, and can be seen as a relativistic generalization of earlier work performed in classical MHD. Based on the full wave decomposition (FWD) provided by the renormalized set of eigenvectors in conserved variables, we have also developed a linearized (Roe-type) Riemann solver. Extensive testing against one- and two-dimensional standard numerical problems allows us to conclude that our solver is very robust. When compared with a family of simpler solvers that avoid the knowledge of the full characteristic structure of the equations in the computation of the numerical fluxes, our solver turns out to be less diffusive than HLL and HLLC, and comparable in accuracy to the HLLD solver. The amount of operations needed by the FWD solver makes it less efficient computationally than those of the HLL family in one-dimensional problems. However, its relative efficiency increases in multidimensional simulations.

Antón, Luis; Miralles, Juan A.; Martí, José M.; Ibáñez, José M.; Aloy, Miguel A.; Mimica, Petar

2010-05-01

156

Summary form only given, as follows. The area of relativistic plasma microwave electronics has recently generated renewed interest in the microwave and millimeter-wave device community. The authors have obtained experimental data demonstrating that the presence of a low-density background plasma in a relativistic backward wave oscillator leads to several beneficial effects, including enhanced interaction efficiency (40%), operation at very low

Y. Carmel; W. R. Lou; J. Rodgers; B. Levush; J. Tate; W. W. Destler; V. L. Granatstein

1992-01-01

157

On the Role of Ambient Reactive Particles in the Mixing and Afterburn behind Explosive Blast Waves

A hybrid two-phase numerical methodology is used to study the propagation of explosive blast waves from spherical charges of TNT and their interaction with an ambient dilute distribution of aluminum particles. The presence of these particles is found to cause perturbations at the contact surface between the inner detonation products and the outer shock-compressed air, which results in Rayleigh-Taylor instabilities

K. Balakrishnan; S. Menon

2010-01-01

158

Biomechanical Assessment of Brain Dynamic Responses Due to Blast Pressure Waves

A mechanized and integrated computational scheme is introduced to determine the human brain responses in an environment where\\u000a the human head is exposed to explosions from trinitrotoluene (TNT), or other high-yield explosives, in military applications.\\u000a The procedure is based on a three-dimensional (3-D) non-linear finite element method (FEM) that implements a simultaneous\\u000a conduction of explosive detonation, shock wave propagation, blast–head

M. S. Chafi; G. Karami; M. Ziejewski

2010-01-01

159

Calculation of wing response to gusts and blast waves with vortex lift effect

A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex lattice method, unsteady suction analogy and Pade approximant. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.

Chao, D.C.; Lan, C.E.

1983-04-01

160

NASA Astrophysics Data System (ADS)

We investigate the dynamics and afterglow light curves of gamma-ray burst blast waves that encounter various density structures (such as bumps, voids, or steps) in the surrounding ambient medium. We present and explain the characteristic response features that each type of density structure in the medium leaves on the forward shock (FS) and reverse shock (RS) dynamics for blast waves with either a long-lived or short-lived RS. We show that when the ambient medium density drops, the blast waves exhibit in some cases a period of an actual acceleration (even during their deceleration stage) due to adiabatic cooling of blast waves. Comparing numerical examples that have different shapes of bumps or voids, we propose a number of consistency tests that must be satisfied by correct modeling of blast waves. Our model results successfully pass these tests. Employing a Lagrangian description of blast waves, we perform a sophisticated calculation of afterglow emission. We show that as a response to density structures in the ambient medium, the RS light curves produce more significant variations than the FS light curves. Some observed features (such as rebrightenings, dips, or slow wiggles) can be more easily explained within the RS model. We also discuss the origin of these different features imprinted on the FS and RS light curves.

Uhm, Z. Lucas; Zhang, Bing

2014-07-01

161

Influence of ambient air pressure on the energy conversion of laser-breakdown induced blast waves

NASA Astrophysics Data System (ADS)

Influence of ambient pressure on energy conversion efficiency from a Nd?:?glass laser pulse (? = 1.053 µm) to a laser-induced blast wave was investigated at reduced pressure. Temporal incident and transmission power histories were measured using sets of energy meters and photodetectors. A half-shadowgraph half-self-emission method was applied to visualize laser absorption waves. Results show that the blast energy conversion efficiency ?bw decreased monotonically with the decrease in ambient pressure. The decrease was small, from 40% to 38%, for the pressure change from 101 kPa to 50 kPa, but the decrease was considerable, to 24%, when the pressure was reduced to 30 kPa. Compared with a TEA-CO2-laser-induced blast wave (? = 10.6 µm), higher fraction absorption in the laser supported detonation regime ?LSD of 90% was observed, which is influenced slightly by the reduction of ambient pressure. The conversion fraction ?bw/?LSD?90% was achieved at pressure >50 kPa, which is significantly higher than that in a CO2 laser case.

Wang, Bin; Komurasaki, Kimiya; Arakawa, Yoshihiro

2013-09-01

162

The nonresonant beat-wave excitation of relativistic plasma waves is studied in two-dimensional simulations and experiments. It is shown through simulations that, as opposed to the resonant case, the accelerating electric fields associated with the nonresonant plasmons are always in phase with the beat-pattern of the laser pulse. The excitation of such nonresonant relativistic plasma waves is shown to be possible

C. V. Filip; R. Narang; S. Ya. Tochitsky; C. E. Clayton; P. Musumeci; R. B. Yoder; K. A. Marsh; J. B. Rosenzweig; C. Pellegrini; C. Joshi

2004-01-01

163

Constitutive Modeling for Blast-Induced Wave Propagation.

National Technical Information Service (NTIS)

The description of stress-time history acting on a buried structure is a major source of error in the analysis of underground structures to weapons loadings. The stress wave propagating spherically from the weapon is attenuated as it travels from the sour...

E. C. Drumm

1985-01-01

164

Constitutive modeling for blast-induced wave propagation

The description of stress-time history acting on a buried structure is a major source of error in the analysis of underground structures to weapons loadings. The stress wave propagating spherically from the weapon is attenuated as it travels from the source. This attenuation is a function of the inelastic response of the soil, and results in an increase in the

E. C. Drumm

1985-01-01

165

Strong versus weak wave-turbulence in relativistic field theory

NASA Astrophysics Data System (ADS)

Nonthermal scaling phenomena can exhibit a characteristic dependence on the dimensionality d of space. For d=3 and 4 we simulate a relativistic scalar field theory on a lattice and compute turbulent scaling exponents. We recover Kolmogorov or weak wave-turbulence in the perturbative high-momentum regime, where it exhibits the scaling exponent ?w=d-3/2. In the nonperturbative infrared regime, we find a different scaling exponent ?s=4(5) for d=3(4), which is in agreement with the recently predicted anomalously large values ?s=d+1 of strong turbulence. We show how the latter can be seen to characterize stationary transport of a conserved effective particle number.

Berges, Jürgen; Sexty, Dénes

2011-04-01

166

Whistler wave generation by non-gyrotropic, relativistic, electron beams

NASA Astrophysics Data System (ADS)

Super-thermal electron beams travelling away from the Sun on the open magnetic field lines are widely accepted to be the source of the Type-III bursts. The earliest idea of the generation of the Type-III bursts was based on the plasma emission mechanism. A fast moving electron beam excites Langmuir waves at the local plasma frequency, ?p. The Langmuir waves are partially transformed via scattering at ?p and 2?p, with ion sound and oppositely propagating Langmuir waves, respectively, into electromagnetic waves. As the electron beam propagates away from the Sun, through less dense coronal and interplanetary environment, the frequency of the emitted electromagnetic radiation decreases, because plasma frequency is a function of the square root of the plasma density. Type-III bursts have been subject of theoretical, observational and numerical studies. The first detailed theory of the Type-III emission invoked coherent plasma waves, generated by a stream of fast particles, which are due to Rayleigh and combination scattering at ?p and 2?p subsequently transformed into radio waves. Stochastic growth of the density irregularities was invoked in order to produce stochastically generated clumpy Langmuir waves, where the ambient density perturbations cause the beam to fluctuate around marginal stability. Other theories on the mechanism which generates the Type-III emission include: linear mode conversion of Langmuir waves, Langmuir waves producing electromagnetic radiation as antennas and non-gyroptropic electron beam emission [1] of commensurable properties to the Type-III bursts. In Refs. [2,3] it was found that the non-gyrotropic beam excites electromagnetic radiation by the current transverse to the magnetic field, which results in (?,k)-space drift while propagating along the 1-dimensional spatial domain throughout the decreasing plasma density profile. The role of the electron beam pitch angle and the background density gradient profile was investigated in [4]. In this study [5], for the first time, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented. Features of the wave component propagating backwards from the front of the non-gyrotropic, relativistic, beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile are studied by using the Particle-In-Cell code EPOCH. Magnetic field in the 1.5-dimensional system is varied in order to prove that the backwards propagating wave is harmonic of the electron cyclotron frequency. The analysis has lead to the identification of the backwards travelling waves as whistlers. Moreover, the whistlers are shown to be generated by the normal and anomalous Doppler resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011). [2] D. Tsiklauri, H. Schmitz, Geophys. Res. Abs. 15, EGU2013-5403 (2013). [3] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013). [4] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012). [5] M. Skender, D. Tsiklauri, submitted to Phys. Plasmas (2013): http://astro.qmul.ac.uk/ tsiklauri/

Skender, Marina; Tsiklauri, David

2014-05-01

167

NASA Astrophysics Data System (ADS)

We report on the characterisation of the upstream medium ahead of a radiative cylindrical blast wave launched in an argon cluster gas with a 1 J, 1 ps, 1054 nm Nd:Glass laser system. By launching two perpendicular blast waves and introducing a time delay between the heating beams it is possible to determine the extent of the cluster medium by observing the high energy absorption region associated with clusters, as apposed to the low energy deposition in monatomic gas. It was found that argon ions launched from the initial laser driven cluster ionisation created a ballistic ion wave which sweeps out ahead of the hydrodynamic blast wave at an initial velocity of 1000 kms -1. This ballistic wave disassembles the clusters ahead of the blast wave into a neutral gas medium before the arrival of a radiative precursor. This observation gives us confidence that the dynamics of a radiative blast wave in cluster based experiments is determined primarily by the properties of an upstream atomic gas, and is not significantly influenced by cluster affects on energy transport or other material properties.

Olsson Robbie, S. I.; Doyle, H. W.; Symes, D. R.; Smith, R. A.

2012-03-01

168

Two-dimensional nozzle-generated reactive blast waves

NASA Astrophysics Data System (ADS)

The behavior of the shock front in a detonation cell has been simulated by generating cylindrical shocks in a coverging-diverging nozzle, with a narrow throat, placed in a rectangular shock tube. It is shown that the locus of the reaction zone behind a decaying cylindrical shock may be accurately predicted from the shock velocity profile and the density field in the induction zone. It follows that if the shock front and reaction zone velocities are determined experimentally the technique provides a method of measuring the activation energy of a system under the conditions prevailing in a detonation wave.

Edwards, D. H.; Hooper, G.; Thomas, G. O.

1981-05-01

169

Low-cost rapid miniature optical pressure sensors for blast wave measurements.

This paper presents an optical pressure sensor based on a Fabry-Perot (FP) interferometer formed by a 45° angle polished single mode fiber and an external silicon nitride diaphragm. The sensor is comprised of two V-shape grooves with different widths on a silicon chip, a silicon nitride diaphragm released on the surface of the wider V-groove, and a 45° angle polished single mode fiber. The sensor is especially suitable for blast wave measurements: its compact structure ensures a high spatial resolution; its thin diaphragm based design and the optical demodulation scheme allow a fast response to the rapid changing signals experienced during blast events. The sensor shows linearity with the correlation coefficient of 0.9999 as well as a hysteresis of less than 0.3%. The shock tube test demonstrated that the sensor has a rise time of less than 2 µs from 0 kPa to 140 kPa. PMID:21643336

Wu, Nan; Wang, Wenhui; Tian, Ye; Zou, Xiaotian; Maffeo, Michael; Niezrecki, Christopher; Chen, Julie; Wang, Xingwei

2011-05-23

170

A repetitive 0.14 THz relativistic surface wave oscillator

Preliminary experimental results of a repetitive 0.14 THz overmoded relativistic surface wave oscillator (RSWO) are presented in this paper. The repetitive RSWO is developed by using a rectangularly corrugated slow-wave structure with overmoded ratio of 3 and a foilless diode emitting annular electron beam with thickness of 0.5 mm. The high quality electron beams at the repetition rate of 10 are obtained over a wide range of diode voltage (180 kV < U < 240 kV) and current (700 A < I < 1.2 kA). The generation experiments of RSWO are conducted at an axial pulsed magnetic field whose maximum strength and duration can reach about 2.7 T and 1 s, respectively. The experimental results show that the RSWO successfully produces reasonable uniform terahertz pulses at repetition rate of 10, and the pulse duration, frequency, and power of a single pulse are about 1.5 ns, 0.154 THz, and 2.6 MW, respectively, whereas the dominated radiation mode of the RSWO is TM{sub 02}.

Wang Guangqiang; Tong Changjiang; Li Xiaoze; Wang Xuefeng; Li Shuang; Lu Xicheng [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi'an 710024 (China); Wang Jianguo [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi'an 710024 (China); School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049 (China)

2013-04-15

171

NASA Astrophysics Data System (ADS)

Multiphase flows, which involve compressible or incompressible fluids with linear or nonlinear dynamics, are found in all areas of technology at all length scales and flow regimes. In this contribution, we discuss application of aqueous-foam barriers against blast wave impact. The first experiments demonstrating this behaviour were conducted in the early 1980s in free-field tests. Based on structural requirements, various foams with different blast energy contents were tested with the aim of characterizing the time history of the blast pressure reduction. A number of consistent methodologies for calculating this pressure reduction in foam are based on the effective gas flow model. For estimating the uncertainties of these methodologies, we briefly demonstrate their comparison with existing experimental data. Thereafter, we present various modifications of modelling approaches and their comparison with new results of blast wave experiments.

Britan, A.; Shapiro, H.; Liverts, M.; Ben-Dor, G.; Chinnayya, A.; Hadjadj, A.

2013-02-01

172

NASA Astrophysics Data System (ADS)

We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch-angle scattering of relativistic and ultra-relativistic electrons during the recovery phase of a moderate geomagnetic storm on October 11, 2012. The EMIC wave activity was observed in-situ on the Van Allen Probes and conjugately on the ground across the CARISMA array throughout an extended 18-hour interval. However, neither enhanced precipitation of >0.7 MeV electrons, nor reductions in Van Allen Probe 90o pitch-angle ultra-relativistic electron flux were observed. Computed radiation belt electron pitch-angle diffusion rates demonstrate that rapid pitch-angle diffusion is confined to low pitch angles and cannot reach 90o. For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultra-relativistic (~2-8 MeV) electron loss, but which is confined to pitch angles below around 45 degrees and not affecting the core distribution.

Usanova, Maria; Drozdov, Alexander; Orlova, Ksenia; Mann, Ian; Shprits, Yuri; Robertson, Matthew; Turner, Drew; Milling, David; Kale, Andy; Baker, Dan; Reeves, Geoff; Spence, Harlan; Kletzing, Craig; Wygant, John

2014-05-01

173

The Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure

Blast-wave-driven instabilities play a rich and varied role throughout the evolution of supernovae from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of the stellar systems. We consider the simpler and fundamental hydrodynamic instability problem of a material interface between two constant-density fluids perturbed from spherical and driven by a divergent central Taylor-Sedov blast wave. The existence of unified solutions at high Mach number and small density ratio suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end we apply buoyancy-drag and bubble merger models modified to include the effects of divergence and radial velocity gradients. In general, these effects preclude the true self-similar evolution of classical Raleigh-Taylor, but can be incorporated into a quasi-self-similar growth picture. Loss of memory of initial conditions can occur in the quasi-self-similar model, but requires initial mode numbers higher than those predicted for pre-explosion interfaces in Type II SNe, suggesting that their late-time structure is likely strongly influenced by details of the initial perturbations. Where low-modes are dominant, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, structure observed now contains direct information about the explosion process. When large-amplitude modes are present in the initial conditions, the contribution to the perturbation growth from the Richtmyer-Meshkov instability is significant or dominant compared to Rayleigh-Taylor. Such Richtmyer-Meshkov growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in the Tycho. Laser-driven high-energy-density laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making connections to their astrophysical counterparts.

Miles, A R

2008-05-27

174

THE Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure

NASA Astrophysics Data System (ADS)

Blast-wave-driven instabilities play a rich and varied role in supernovae (SNe) evolution from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of stellar systems. We consider the simpler idealized problem of an interface between two constant-density fluids perturbed from spherical and driven by a central blast wave. Where valid, the existence of unified solutions suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end, we apply buoyancy-drag and bubble merger models that include effects of divergence and compressibility. In general, these effects preclude the true self-similar evolution of classical Rayleigh-Taylor (RT), but can be incorporated into a quasi-self-similar growth model. Loss of memory of initial conditions (ICs) can occur in the model, but requires pre-explosion mode numbers higher than predicted for Type II SNe, suggesting that their late-time structure is influenced by details of the initial perturbations. Where low modes dominate, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, the structure observed now contains direct information about the explosion process. When large-amplitude modes exist in the ICs, the contribution from the Richtmyer-Meshkov (RM) instability is significant compared to RT. Such RM growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in Tycho. Laser-driven laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making connections to their astrophysical counterparts.

Miles, Aaron R.

2009-05-01

175

Biomechanical assessment of brain dynamic responses due to blast pressure waves.

A mechanized and integrated computational scheme is introduced to determine the human brain responses in an environment where the human head is exposed to explosions from trinitrotoluene (TNT), or other high-yield explosives, in military applications. The procedure is based on a three-dimensional (3-D) non-linear finite element method (FEM) that implements a simultaneous conduction of explosive detonation, shock wave propagation, blast-head interactions, and the confronting human head. The processes of blast propagation in the air and blast interaction with the head are modeled by an Arbitrary Lagrangian-Eulerian (ALE) multi-material FEM formulation, together with a penalty-based fluid/structure interaction (FSI) algorithm. Such a model has already been successfully validated against experimental data regarding air-free blast and plate-blast interactions. The human head model is a 3-D geometrically realistic configuration that has been previously validated against the brain intracranial pressure (ICP), as well as shear and principal strains under different impact loadings of cadaveric experimental tests of Hardy et al. [Hardy W. N., C. Foster, M. Mason, S. Chirag, J. Bishop, M. Bey, W. Anderst, and S. Tashman. A study of the response of the human cadaver head to impact. Proc. 51 ( st ) Stapp. Car Crash J. 17-80, 2007]. Different scenarios have been assumed to capture an appropriate picture of the brain response at a constant stand-off distance of nearly 80 cm from the core of the explosion, but exposed to different amounts of a highly explosive (HE) material such as TNT. The over-pressures at the vicinity of the head are in the range of about 2.4-8.7 atmosphere (atm), considering the reflected pressure from the head. The methodology provides brain ICP, maximum shear stresses and maximum principal strain within the milli-scale time frame of this highly dynamic phenomenon. While focusing on the two mechanical parameters of pressure, and also on the maximum shear stress and maximum principal strain to predict the brain injury, the research provides an assessment of the brain responses to different amounts of over-pressure. The research also demonstrates the ability to predict the ICP, as well as the stress and strain within the brain, due to such an event. The research cannot identify, however, the specific levels of ICP, stress and strain that necessarily lead to traumatic brain injury (TBI) because there is no access to experimental data regarding head-blast interactions. PMID:19806456

Chafi, M S; Karami, G; Ziejewski, M

2010-02-01

176

An X-ray-emitting blast wave from the recurrent nova RS Ophiuchi.

Stellar explosions such as novae and supernovae produce most of the heavy elements in the Universe. The onset of a nova is well understood as driven by runaway thermonuclear fusion reactions on the surface of a white dwarf in a binary star system; but the structure, dynamics and mass of the ejecta are not well known. In rare cases, the white dwarf is embedded in the wind nebula of a red-giant companion, and the explosion products plough through the nebula and produce X-ray emission. Here we report X-ray observations of such an event, from the eruption of the recurrent nova RS Ophiuchi. The hard X-ray emission from RS Ophiuchi early in the eruption emanates from behind a blast wave, or outward-moving shock wave, that expanded freely for less than 2 days and then decelerated owing to interaction with the nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from the standard spherical shell structure. The early onset of deceleration indicates that the ejected shell had a low mass, the white dwarf has a high mass, and that RS Ophiuchi is therefore a progenitor of the type of supernova (type Ia) integral to studies of the expansion of the Universe. PMID:16855584

Sokoloski, J L; Luna, G J M; Mukai, K; Kenyon, Scott J

2006-07-20

177

Comparison with experiment for TVD calculations of blast waves from a shock tube

NASA Astrophysics Data System (ADS)

Harten's second-order-accurate total-variation-diminishing (TVD) scheme is applied to calculation of flow from the open end of a shock tube. Comparison of numerical results with available experimental data for overpressure at selected points around the shock tube exit shows good agreement. Numerically indicated positions of the moving shock front and Mach stem also compare well with flow shadowgraph data. Where the problem geometry is sufficiently simple and rectangular gridding can be used, Harten's method affords a good choice for blast wave calculations.

Cooke, Charlie H.; Fansler, Kevin S.

1989-01-01

178

Relativistic backward-wave oscillators operating near cyclotron resonance

Microwave sources based on backward-wave oscillators (BWO's) driven by relativistic electron beams are capable of producing high-power coherent radiation in the cm and mm wavelength region. When the axial magnetic field used in these devices to confine the electron beam satisfies the condition of cyclotron resonance there is a significant modification in the behavior of BWO due to beam coupling to cyclotron modes. In this paper a time-dependent, self-consistent theory of BWO's is developed, taking into account a possible cyclotron interaction. The analysis of the system near the cyclotron resonance yields the power drop due to the cyclotron absorption effect observed in many BWO experiments. In addition, the theory predicts that there exists a region of magnetic field strength, where an increase in power and efficiency is possible. Depending on the value of the magnetic field and beam coupling to cyclotron mode various regimes of BWO operation are possible, including stable single-frequency oscillations, self-modulation, and a succession of microwave bursts.

Vlasov, A.; Nusinovich, G.; Levush, B.; Bromborsky, A.; Lou, W.; Carmel, Y. (Laboratory for Plasma Research, University of Maryland, College Park, Maryland 20742-3511 (United States))

1993-05-01

179

Phase mixing of relativistically intense waves in a cold homogeneous plasma.

We report on spatiotemporal evolution of relativistically intense longitudinal electron plasma waves in a cold homogeneous plasma, using the physically appealing Dawson sheet model. Calculations presented here in the weakly relativistic limit clearly show that under very general initial conditions, a relativistic wave will always phase mix and eventually break at arbitrarily low amplitudes, in a time scale omegapetaumix approximately {3/64(omegape2delta3/c2k2)|Deltak/k|(|1+Deltak/k|)](1+1|1+Deltak/k|)}(-1). We have verified this scaling with respect to amplitude of perturbation delta and width of the spectrum (Deltakk) using numerical simulations. This result may be of relevance to ultrashort, ultraintense laser pulse-plasma interaction experiments where relativistically intense waves are excited. PMID:19391852

Sengupta, Sudip; Saxena, Vikrant; Kaw, Predhiman K; Sen, Abhijit; Das, Amita

2009-02-01

180

NASA Technical Reports Server (NTRS)

We present multi-satellite observations of large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. This evidence of microburst precipitation occurring at the same time and at nearly the same magnetic local time and L-shell with a bursty temporal structure similar to that of the observed large amplitude wave packets suggests a causal connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave.particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

Kersten, K.; Cattell, C. A.; Breneman, A.; Goetz, K.; Kellogg, P. J.; Wygant, J. R.; Wilson, L. B., III; Blake, J. B.; Looper, M. D.; Roth, I.

2011-01-01

181

Spatially-resolved x-ray scattering measurements of a planar blast wave

NASA Astrophysics Data System (ADS)

In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering is a powerful technique for measuring these plasma parameters. However, the scattered signal is typically measured with little or no spatial resolution, which limits the ability to diagnose inhomogeneous plasmas. We report on the development of a new imaging x-ray Thomson spectrometer (IXTS) for the Omega laser facility. The diffraction of x-rays from a toroidally curved crystal creates high-resolution images that are spatially resolved along a one-dimensional profile while spectrally dispersing the radiation. An experiment is described in which we used the IXTS to measure the spatial temperature profile of a novel system. A low-density carbon foam was irradiated with intensities on the order of 10^15 W/cm^2, launching a planar blast wave. After a delay of several nanoseconds, x-rays created from irradiation of a nickel foil, scattered at 90 and were recorded by the IXTS. The resulting spatially resolved scattering spectra were analyzed to extract the temperature profile across the blast wave.

Gamboa, E. J.; Montgomery, D. S.; Benage, J. F.; Falk, K.; Kuranz, C. C.; Keiter, P. A.; Drake, R. P.

2012-10-01

182

TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION

This paper shows results from experiments diagnosing the development of the Rayleigh-Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use {approx}5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 {mu}m and amplitude of 2.5 {mu}m. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer-Meshkov instability followed and then dominated by Rayleigh-Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.

Kuranz, C. C.; Drake, R. P.; Harding, E. C.; Grosskopf, M. J. [University of Michigan, MI (United States); Robey, H. F.; Remington, B. A.; Edwards, M. J.; Miles, A. R.; Perry, T. S. [Lawrence Livermore National Laboratory, University of California, P.O. Box 5508, L-487, Livermore, CA 94550 (United States); Blue, B. E. [General Atomics, San Diego, CA (United States); Plewa, T. [Department of Scientific Computing, Florida State University, Dirac Science Library Tallahassee, FL 32306-4120 (United States); Hearn, N. C. [ASC/Alliances Center for Astrophysical Thermonuclear Flashes, University of Chicago, IL (United States); Knauer, J. P. [Laboratory of Laser Energetics, University of Rochester, Rochester, NY (United States); Arnett, D. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Leibrandt, D. R. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2009-05-01

183

NASA Technical Reports Server (NTRS)

An analysis is conducted regarding the properties of cylindrically symmetric self-similar blast waves propagating away from a line source into a medium whose density and magnetic field (with components in both the phi and z directions) both vary as r to the -(omega) power (with omega less than 1) ahead of the blast wave. The main results of the analysis can be divided into two classes, related to a zero azimuthal field and a zero longitudinal field. In the case of the zero longitudinal field it is found that there are no physically acceptable solutions with continuous postshock variations of flow speed and gas density.

Lerche, I.

1981-01-01

184

Cyclotron wave generation and phase velocity control on an intense relativistic electron beam

The axisymmetric, negative energy branch of the Doppler-shifted electron cyclotron eigenmode has been excited on an unneutralized, 15 kA, 2.25 MV, relativistic electron beam, propagating along a guide magnetic field interior to a vacuum conducting wave guide. Large amplitude waves have been generated by means of a traveling wave interaction with helical slow wave structures. The growth process has been

E. Cornet; H. A. Davis; T. P. Starke; W. W. Rienstra; J. R. Uglum

1981-01-01

185

Projector augmented-wave method: Application to relativistic spin-density functional theory

Applying the projector augmented-wave (PAW) method to relativistic spin-density functional theory (RSDFT) we derive PAW Dirac-Kohn-Sham equations for four-component spinor pseudo-wave-functions. The PAW freedom to add a vanishing operator inside the PAW spheres allows us to transform these PAW Dirac-type equations into PAW Pauli-type equations for two-component spinor pseudo-wave-functions. With these wave functions, we get the frozen-core energy as well

Andrea Dal Corso

2010-01-01

186

Multiwavelength Observations of an Eruptive Flare: Evidence for Blast Waves and Break-Out

NASA Astrophysics Data System (ADS)

Images of an east-limb flare on 3 November 2010 taken in the 131 Å channel of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory provide a convincing example of a long current sheet below an erupting plasmoid, as predicted by the standard magnetic reconnection model of eruptive flares. However, the 171 Å and 193 Å channel images hint at an alternative scenario. These images reveal that large-scale waves with velocity greater than 1000 km s-1 propagated alongside and ahead of the erupting plasmoid. Just south of the plasmoid, the waves coincided with type-II radio emission, and to the north, where the waves propagated along plume-like structures, there was increased decimetric emission. Initially, the cavity around the hot plasmoid expanded. Later, when the erupting plasmoid reached the height of an overlying arcade system, the plasmoid structure changed, and the lower parts of the cavity collapsed inwards. Hot loops appeared alongside and below the erupting plasmoid. We consider a scenario in which the fast waves and the type-II emission were a consequence of a flare blast wave, and the cavity collapse and the hot loops resulted from the break-out of the flux rope through an overlying coronal arcade.

Kumar, Pankaj; Innes, D. E.

2013-11-01

187

Multimegawatt relativistic harmonic gyrotron traveling-wave tube amplifier experiments

The first multimegawatt harmonic relativistic gyrotron traveling-wave tube (gyro-twt) amplifier experiment has been designed, built, and tested. Results from this experimental setup, including the first ever reported third-harmonic gyro-twt results, are presented. Operation frequency is 17.1 GHz. Detailed phase measurements are also presented. The electron beam source is SNOMAD-II, a solid-state nonlinear magnetic accelerator driver with nominal parameters of 400 kV and 350 A. The flat-top pulsewidth is 30 ns. The electron beam is focused using a Pierce geometry and then imparted with transverse momentum using a bifilar helical wiggler magnet. Experimental operation involving both a second-harmonic interaction with the TE{sub 21} mode and a third-harmonic interaction with the TE{sub 31} mode, both at 17 GHz, has been characterized. The third-harmonic interaction resulted in 4-MW output power and 50-dB single-pass gain, with an efficiency of up to {approximately}8%. The best measured phase stability of the TE{sub 31} amplified pulse was {+-}10{degree} over a 9-ns period. The phase stability was limited because the maximum RF power was attained when operating far from wiggler resonance. The second harmonic, TE{sub 21} had a peak amplified power of 2 MW corresponding to 40-dB single-pass gain and 4% efficiency. The second-harmonic interaction showed stronger superradiant emission than the third-harmonic interaction. Characterizations of the second- and third-harmonic gyro-twt experiments presented here include measurement of far-field radiation patterns, gain and phase versus interaction length, phase stability, and output power versus input power.

Menninger, W.L.; Danly, B.G.; Temkin, R.J. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center] [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center

1996-06-01

188

Twin traveling-wave tube amplifiers driven by a relativistic backward-wave oscillator

Experiments demonstrate stable frequency and relative-phase angle output from twin traveling-wave tube (TWT) amplifiers driven with the redirected signal from a high-power backward-wave oscillator (BWO). The experimental X-band apparatus employs a single generator to produce three independent electron beams which simultaneously drive the BWO and TWT sources. The BWO spontaneously generates up to 14.1 MW peak, 25 to 15-ns long pulses over a current-tunable bandwidth of 9.6%. The BWO power extracted upstream is split and redirected into twin TWT`s for amplification. The TWT`s produce up to 9.0 MW pulses over an 800 MHz instantaneous bandwidth. Across the amplifier`s full-width half-maximum pulse duration of 10 to 20 ns, a relative-phase angle of better than 15{degree} is maintained between TWT`s for an 11.0 to 11.7 GHz range. Experiments characterize the gain, relative-phase angle, and efficiency of twin-TWT output as a function of RF-drive frequency and beam current. These experiments are the first to demonstrate the feasibility of relativistic TWT`s for phased-array applications, and increase the limited data base documenting relativistic-TWT operation.

Butler, J.M.; Wharton, C.B. [Cornell Univ., Ithaca, NY (United States). Lab. of Plasma Physics] [Cornell Univ., Ithaca, NY (United States). Lab. of Plasma Physics

1996-06-01

189

In this paper, small but finite amplitude electrostatic solitary waves in a relativistic degenerate magnetoplasma, consisting of relativistically degenerate electrons and non-degenerate cold ions, are investigated. The Zakharov-Kuznetsov equation is derived employing the reductive perturbation technique and its solitary wave solution is analyzed. It is shown that only compressive electrostatic solitary structures can propagate in such a degenerate plasma system. The effects of plasma number density, ion cyclotron frequency, and direction cosines on the profiles of ion acoustic solitary waves are investigated and discussed at length. The relevance of the present investigation vis-a-vis pulsating white dwarfs is also pointed out.

Ata-ur-Rahman,; Qamar, A. [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan) [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan); National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); Masood, W. [National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan) [National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); COMSATS, Institute of Information Technology, Park Road, Chak Shahzad, Islamabad 44000 (Pakistan); Eliasson, B. [Physics Department, University of Strathclyde, Glasgow G4 0NG, Scotland (United Kingdom)] [Physics Department, University of Strathclyde, Glasgow G4 0NG, Scotland (United Kingdom)

2013-09-15

190

Recent advances in the study of a long pulse relativistic backward wave oscillator

Laser interferometry was recently used to diagnose plasma formation and evolution in the slow wave structure (SWS) of a relativistic backward wave oscillator (BWO) during the course of microwave generation. The results indicated that plasma from the cutoff neck inlet contributed to the termination of the high power microwave pulse. In an effort to mitigate this pulse shortening effect, the

F. Hegeler; E. Schamiloglu; S. D. Korovin; V.V. Rostov

1999-01-01

191

Ion motion and finite temperature effect on relativistic strong plasma waves

The influence of motion of ions and electron temperature on nonlinear one-dimensional plasma waves with velocity close to the speed of light in vacuum is investigated. It is shown that although the wave-breaking field weakly depends on the mass of ions, the nonlinear relativistic wavelength essentially changes. The nonlinearity leads to the increase of the strong plasma wavelength, while the

Arsen G. Khachatryan

1998-01-01

192

We report a very efficient process for accelerating high-energy electrons by coherent whistler mode waves in the Earth's dipole magnetic field, which we have found in our recent test particle simulations. The efficient acceleration process takes place for weakly relativistic seed electrons of a few hundred kiloelectronvolts. Under an assumption that the whistler mode wave packets are excited near the

Yoshiharu Omura; Naoki Furuya; Danny Summers

2007-01-01

193

NASA Astrophysics Data System (ADS)

We establish the general form of inelastic scattering amplitudes based on invariance principles and derive simple relations between these amplitudes and spin-transfer observables. We then examine a plane-wave relativistic impulse approximation for (p,p') which is a simple extension of the relativistic impulse approximation for elastic scattering. We show under what approximations this amplitude reduces to the standard (nonrelativistic) impulse approximation and then examine the novel features of the free relativistic impulse approximation which results from less restrictive assumptions. We also derive free relativistic impulse approximation inelastic electron scattering form factors and then use our (p,p') and (e,e') formulations to extract nuclear structure information for the first two 1+ levels in 12C. We consider possible experimental signatures of the strong scalar and timelike vector potentials of modern relativistic theories.

Shepard, J. R.; Rost, E.; McNeil, J. A.

1986-02-01

194

National Technical Information Service (NTIS)

A new protocol was developed for laboratory study of the interaction of hazardous bioaerosols with shock/blast waves. The method determined the viability of endospores as a function of shock strength (post-shock temperature) and used laser-based diagnosti...

J. B. Jeffries K. E. Mortelmans R. K. Hanson

2011-01-01

195

Cyclotron effects in relativistic backward-wave oscillators operating at low magnetic fields

A small-signal theory of a resonant relativistic backward-wave oscillator (BWO) operating at a very low-guiding magnetic field is developed. The theoretical approach is based on the successive iteration method of analytical solution of the exact three dimensional (3-D) equations of electrons motion. It was shown that cyclotron resonance effects in relativistic BWO (400 kV) operating at low-focusing magnetic field can

Alexander N. Vlasov; Anton S. Ilyin; Yuval Carmel

1998-01-01

196

Sensitivity of a Relativistic Backward-Wave Oscillator to Budker's Parameter

Using the self-consistent Vlasov approach, we calculate the sensitivity of the growth rate and frequency of the transverse magnetic modes of a relativistic backward-wave oscillator to Budker's parameter. A closed algebraic dispersion relation is derived, representing the linear stability properties of the free-streaming modes of a relativistic, thin, hollow, cylindrical electron beam moving down the axis of a disc-loaded waveguide

Howard E. Brandt; Han S. Uhm

1985-01-01

197

NASA Astrophysics Data System (ADS)

To combat the problem of traumatic brain injury (TBI), a signature injury of the current military conflicts, there is an urgent need to design head protection systems with superior blast/ballistic impact mitigation capabilities. Toward that end, the blast impact mitigation performance of an advanced combat helmet (ACH) head protection system equipped with polyurea suspension pads and subjected to two different blast peak pressure loadings has been investigated computationally. A fairly detailed (Lagrangian) finite-element model of a helmet/skull/brain assembly is first constructed and placed into an Eulerian air domain through which a single planar blast wave propagates. A combined Eulerian/Lagrangian transient nonlinear dynamics computational fluid/solid interaction analysis is next conducted in order to assess the extent of reduction in intra-cranial shock-wave ingress (responsible for TBI). This was done by comparing temporal evolutions of intra-cranial normal and shear stresses for the cases of an unprotected head and the helmet-protected head and by correlating these quantities with the three most common types of mild traumatic brain injury (mTBI), i.e., axonal damage, contusion, and subdural hemorrhage. The results obtained show that the ACH provides some level of protection against all investigated types of mTBI and that the level of protection increases somewhat with an increase in blast peak pressure. In order to rationalize the aforementioned findings, a shockwave propagation/reflection analysis is carried out for the unprotected head and helmet-protected head cases. The analysis qualitatively corroborated the results pertaining to the blast-mitigation efficacy of an ACH, but also suggested that there are additional shockwave energy dissipation phenomena which play an important role in the mechanical response of the unprotected/protected head to blast impact.

Grujicic, M.; Bell, W. C.; Pandurangan, B.; Glomski, P. S.

2011-08-01

198

Blast-induced traumatic brain injury has emerged as a “signature injury” in combat casualty care. Present combat helmets are designed primarily to protect against ballistic and blunt impacts, but the current issue with helmets is protection concerning blasts. In order to delineate the blast wave attenuating capability of the Advanced Combat Helmet (ACH), a finite element (FE) study was undertaken to evaluate the head response against blast loadings with and without helmet using a partially validated FE model of the human head and ACH. Four levels of overpressures (0.27–0.66?MPa) from the Bowen’s lung iso-damage threshold curves were used to simulate blast insults. Effectiveness of the helmet with respect to head orientation was also investigated. The resulting biomechanical responses of the brain to blast threats were compared for human head with and without the helmet. For all Bowen’s cases, the peak intracranial pressures (ICP) in the head ranged from 0.68 to 1.8?MPa in the coup cortical region. ACH was found to mitigate ICP in the head by 10–35%. Helmeted head resulted in 30% lower average peak brain strains and product of strain and strain rate. Among three blast loading directions with ACH, highest reduction in peak ICP (44%) was due to backward blasts whereas the lowest reduction in peak ICP and brain strains was due to forward blast (27%). The biomechanical responses of a human head to primary blast insult exhibited directional sensitivity owing to the different geometry contours and coverage of the helmet construction and asymmetric anatomy of the head. Thus, direction-specific tolerances are needed in helmet design in order to offer omni-directional protection for the human head. The blasts of varying peak overpressures and durations that are believed to produce the same level of lung injury produce different levels of mechanical responses in the brain, and hence “iso-damage” curves for brain injury are likely different than the Bowen curves for lung injury.

Zhang, Liying; Makwana, Rahul; Sharma, Sumit

2013-01-01

199

Blast-induced traumatic brain injury has emerged as a "signature injury" in combat casualty care. Present combat helmets are designed primarily to protect against ballistic and blunt impacts, but the current issue with helmets is protection concerning blasts. In order to delineate the blast wave attenuating capability of the Advanced Combat Helmet (ACH), a finite element (FE) study was undertaken to evaluate the head response against blast loadings with and without helmet using a partially validated FE model of the human head and ACH. Four levels of overpressures (0.27-0.66?MPa) from the Bowen's lung iso-damage threshold curves were used to simulate blast insults. Effectiveness of the helmet with respect to head orientation was also investigated. The resulting biomechanical responses of the brain to blast threats were compared for human head with and without the helmet. For all Bowen's cases, the peak intracranial pressures (ICP) in the head ranged from 0.68 to 1.8?MPa in the coup cortical region. ACH was found to mitigate ICP in the head by 10-35%. Helmeted head resulted in 30% lower average peak brain strains and product of strain and strain rate. Among three blast loading directions with ACH, highest reduction in peak ICP (44%) was due to backward blasts whereas the lowest reduction in peak ICP and brain strains was due to forward blast (27%). The biomechanical responses of a human head to primary blast insult exhibited directional sensitivity owing to the different geometry contours and coverage of the helmet construction and asymmetric anatomy of the head. Thus, direction-specific tolerances are needed in helmet design in order to offer omni-directional protection for the human head. The blasts of varying peak overpressures and durations that are believed to produce the same level of lung injury produce different levels of mechanical responses in the brain, and hence "iso-damage" curves for brain injury are likely different than the Bowen curves for lung injury. PMID:23935591

Zhang, Liying; Makwana, Rahul; Sharma, Sumit

2013-01-01

200

Blast waves in inhomogeneous atmospheres with counterpressure and heat transfer effects

NASA Astrophysics Data System (ADS)

The study on blast waves in cold exponential atmospheres by Bach, Kuhl, and Oppenheim is extended to provide a uniformly valid numerical solution of a point explosion problem in isothermal exponential atmospheres with finite temperature at the centre. This is achieved initially by solving the equations of motion with the help of a perturbation technique which takes into account thermal radiation and heat conduction. Whereas the extended perturbation solution for the strong shock regime (i.e. short times after initiation) serves as a starting solution for the numerical integration, the solution using the method of characteristics is valid for the whole flow field since counterpressure effects and energy losses at the front are not neglected.

Gretler, W.; Steiner, H.

1993-09-01

201

Effect of plasma on efficiency enhancement in a high power relativistic backward wave oscillator

A linear theory of the excitation of electromagnetic waves in a plasma-filled backward-wave oscillator driven by an intense relativistic electron beam is presented. It is found that the spatial growth rate of backward-wave instability exhibits a resonant increase for a particular value of fill-plasma density. Results are compared to the results of an experiment by K. Minami et al. (1988)

Ranjana Sawhney; K. P. Maheshwari; Y. Choyal

1993-01-01

202

Zero-frequency cyclotron wave on an intense relativistic-electron beam

The zero-frequency cyclotron wave is studied on an unneutralized, magnetized relativistic-electron beam. This stationary mode occurs where the Doppler-shifted beam-cyclotron dispersion branch crosses the wavenumber axis. In this experiment zero-frequency-cyclotron waves have been generated by the injection of foil (and foilless) diode beams into a drift tube. A linear-cyclotron wave-dispersion theory is presented, which includes the radial electron-energy variation gamma(r)

T. P. Starke; H. V. Wong; W. W. Rienstra; B. N. Moore; Edward Cornet; H. A. Davis

1983-01-01

203

ON THE AMPLIFICATION OF MAGNETIC FIELD BY A SUPERNOVA BLAST SHOCK WAVE IN A TURBULENT MEDIUM

We have performed extensive two-dimensional magnetohydrodynamic simulations to study the amplification of magnetic fields when a supernova blast wave propagates into a turbulent interstellar plasma. The blast wave is driven by injecting high pressure in the simulation domain. The interstellar magnetic field can be amplified by two different processes, occurring in different regions. One is facilitated by the fluid vorticity generated by the 'rippled' shock front interacting with the background turbulence. The resulting turbulent flow keeps amplifying the magnetic field, consistent with earlier work. The other process is facilitated by the growth of the Rayleigh-Taylor instability at the contact discontinuity between the ejecta and the shocked medium. This can efficiently amplify the magnetic field and tends to produce the highest magnetic field. We investigate the dependence of the amplification on numerical parameters such as grid-cell size and on various physical parameters. We show that the magnetic field has a characteristic radial profile such that the downstream magnetic field gets progressively stronger away from the shock. This is because the downstream magnetic field needs a finite time to reach the efficient amplification, and will get further amplified in the Rayleigh-Taylor region. In our simulation, we do not observe a systematic strong magnetic field within a small distance to the shock. This indicates that if the magnetic-field amplification in supernova remnants indeed occurs near the shock front, other processes such as three-dimensional instabilities, plasma kinetics, and/or cosmic ray effect may need to be considered to explain the strong magnetic field in supernova remnants.

Guo Fan; Li Shengtai; Li Hui; Li, David [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Giacalone, Joe; Jokipii, J. R. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721 (United States)

2012-03-10

204

We investigate the propagation of electromagnetic waves in resistive e{sup {+-}} pair plasmas using a one-fluid theory derived from the relativistic two-fluid equations. When the resistivity normalized by the electron/positron inertia variable exceeds a critical value, the dispersion relation for electromagnetic waves shows that the group velocity is larger than the light speed in vacuum. However, in such a case, it also is found that the plasma parameter is less than unity: that is, the electron-positron pair medium no longer can be treated as plasma. Thus, the simple two-fluid approximation is invalid. This confirms that superluminal propagation of electromagnetic wave is forbidden in a plasma--a conclusion consistent with the relativistic principle of causality. As an alternative, we propose a new set of equations for ''causal relativistic magnetohydrodynamics,'' which both have nonzero resistivity and yet are consistent with the causality principle.

Koide, Shinji [Faculty of Science, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555 (Japan)

2008-12-15

205

Comparison of weak-shock reflection factors for wedges, cylinders and blast waves

Ernst Mach (1838--1916) was the first to discover an irregular reflection phenomenon of shock waves, as is well known in our community. In fact, this occurred in 1875 -- three years earlier than usually assumed in the literature. A facsimile of the paper in which he mentioned a special shock wave behavior is shown in a figure. However, it is correct that Mach gave the physical interpretation of this phenomenon in 1878. Since Mach`s discovery of an irregular shock reflection pattern 117 years ago, new shock configurations have been discovered -- one of the most recent examples is the so-called {open_quotes}von Neumann reflection{close_quotes} for weak shocks as reported by Colella and Henderson in 1990. Due to active research efforts related to shock reflection, especially in the last two decades, we now have a relatively detailed understanding of reflection phenomena and of transition conditions from one reflection configuration to another. The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: (1) square-wave planar shock reflection from wedges, (2) square-wave planar shock reflection from cylinders and (3) spherical blast wave reflection from a planar surface. The authors restrict themselves to weak shocks. Following Henderson`s definition, shocks with a Mach number of M{sub 0} < 1.56 in air or with an overpressure of {Delta}p{sub I} < 25 psi (1.66 bar) under normal ambient conditions are called weak.

Reichenbach, H. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany); Kuhl, A.L. [Lawrence Livermore National Lab., CA (United States)

1992-07-01

206

Comparison of weak-shock reflection factors for wedges, cylinders and blast waves

Ernst Mach (1838--1916) was the first to discover an irregular reflection phenomenon of shock waves, as is well known in our community. In fact, this occurred in 1875 -- three years earlier than usually assumed in the literature. A facsimile of the paper in which he mentioned a special shock wave behavior is shown in a figure. However, it is correct that Mach gave the physical interpretation of this phenomenon in 1878. Since Mach's discovery of an irregular shock reflection pattern 117 years ago, new shock configurations have been discovered -- one of the most recent examples is the so-called [open quotes]von Neumann reflection[close quotes] for weak shocks as reported by Colella and Henderson in 1990. Due to active research efforts related to shock reflection, especially in the last two decades, we now have a relatively detailed understanding of reflection phenomena and of transition conditions from one reflection configuration to another. The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: (1) square-wave planar shock reflection from wedges, (2) square-wave planar shock reflection from cylinders and (3) spherical blast wave reflection from a planar surface. The authors restrict themselves to weak shocks. Following Henderson's definition, shocks with a Mach number of M[sub 0] < 1.56 in air or with an overpressure of [Delta]p[sub I] < 25 psi (1.66 bar) under normal ambient conditions are called weak.

Reichenbach, H. (Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany)); Kuhl, A.L. (Lawrence Livermore National Lab., CA (United States))

1992-07-01

207

Development of the relativistic backward wave oscillator with a permanent magnet

NASA Astrophysics Data System (ADS)

Firstly, an X-band relativistic backward wave oscillator with a low guiding magnetic field is simulated, whose output microwave power is 520 MW. Then, an experiment is carried out on an accelerator to investigate a relativistic backward wave oscillator with a permanent magnetic field whose strength is 0.46 T. When the energy of the electron is 630 keV and the current of the electron beam is 6.7 kA, a 15 ns width pulsed microwave with 510 MW output power at 8.0 GHz microwave frequency is achieved.

Ma, Qiao-Sheng; Liu, Zhong; Li, Zheng-Hong; Jin, Xiao

2012-08-01

208

Two dimensional electrostatic shock waves in relativistic electron positron ion plasmas

Ion-acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of electrons, positrons and hot ions. In this regard, Kadomtsev-Petviashvili-Burgers (KPB) equation is derived using the small amplitude perturbation expansion method. The dependence of the IASWs on various plasma parameters is numerically investigated. It is observed that ratio of ion to electron temperature, kinematic viscosity, positron concentration, and the relativistic ion streaming velocity affect the structure of the IASW. Limiting case of the KPB equation is also discussed. Stability of KPB equation is also presented. The present investigation may have relevance in the study of electrostatic shock waves in relativistic electron-positron-ion plasmas.

Masood, W.; Rizvi, H. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad 54000 (Pakistan)

2010-05-15

209

NASA Astrophysics Data System (ADS)

We performed test particle simulations where we assumed the dipole geomagnetic field (L=4) and a coherent whistler-mode wave. We found a very efficient acceleration process due to the resonant trapping by a coherent whistler-mode wave propagating away from the equator, which we call relativistic resonant acceleration (RRA). Weakly relativistic electrons of a few hundred keV can be accelerated to the range of a few MeV through a single resonant interaction, if the wave packet is continuously generated near the equator. In reality, however, as is the case with chorus emissions, a whistler-mode wave packet has a finite length. In our simulation, we assumed several wave packets with finite lengths are generated successively and propagate away from the equator. We varied frequency of whistler-mode wave packets to simulate chorus emissions. We also varied wave amplitude which is an important factor for controlling the resonant trapping. We found that electrons are gradually accelerated to a few MeV by interacting with several wave packets. We demonstrate that the RRA plays an important role in the formation of relativistic electron flux in the outer radiation belt.

Furuya, N.; Omura, Y.; Summers, D.

2006-12-01

210

NASA Astrophysics Data System (ADS)

Spatio-temporal evolution of relativistically intense longitudinal space charge waves in a cold homogeneous plasma is studied analytically as well as numerically, as an initial value problem, using Dawson sheet model. It is found that, except for very special initial conditions which generates the well known longitudinal Akhiezer-Polovin mode, for all other initial conditions, the waves break through a novel mechanism called phase mixing at an amplitude well below the Akhiezer-Polovin limit. An immediate consequence of this is, that Akhiezer-Polovin waves break when subjected to arbitrarily small longitudinal perturbations. We demonstrate this by performing extensive numerical simulations. This result may be of direct relevance to ultrashort, ultraintense laser/beam pulse-plasma interaction experiments where relativistically intense waves are routinely excited.

Sengupta, Sudip

2014-02-01

211

From linearity towards chaos: Basic studies of relativistic backward-wave oscillators

Recent experimental studies have revealed for the first time some basic features of pulsed, relativistic (300-600 kV) backward-wave oscillators such as starting current, axial mode locking, and multifrequency operation. Above a critical beam current a gradual degradation of the spectrum purity of the electromagnetic radiation is observed, culminating in the onset of stochastic oscillations.

Y. Carmel; W. R. Lou; J. Rodgers; H. Guo; W. W. Destler; V. L. Granatstein; B. Levush; T. Antonsen Jr.; A. Bromborsky

1992-01-01

212

Two-fluid relativistic waves and free electron lasers in pulsar plasmas

A relativistic two-fluid approach for a streaming magnetized pair plasma is developed. Such a scenario corresponds to secondary plasmas created at the polar caps of pulsar magnetospheres. Recent studies show that the temperature of such plasmas is very close to the rest mass energy of the particles. It is therefore critical to determine the exact properties of waves at such

A. Rualdo Soto-Chavez; Swadesh M. Mahajan; Richard D. Hazeltine

2010-01-01

213

Relativistic travelling-wave-tube-O (TWT-O) with an irregular moderating system

The optimization of the profile of the decelerating system (DS) of a relativistic O-type traveling wave tube (O-TWT) is a very difficult nonlinear problem, which in addition is multidimensional (due to the necessity to apply the method of large particles), The form of the DS boundary surface under optimization is quasiperiodic and, as a rule, has a large number of

V. F. Kravchenko; A. A. Kuraev; A. B. Zakalyukin

1998-01-01

214

Diffraction of non-relativistic electron waves by a cylindrical capacitor

The diffraction of non-relativistic electron waves by a cylindrical capacitor is considered for an electric voltage at the capacitor small compared with the energy of the incident electrons. On the basis of the exact general solution of the Schrodinger equation for an electron in an attractive logarithmic potential, asymptotic solutions inside the capacitor which are similar to JWKB-type solutions, but

F. Gesztesy; L. Pittner

1979-01-01

215

Interaction of coherent electromagnetic waves with relativistic electrons in a medium

A MECHANISM is proposed here for producing coherent photons by the interaction in a medium of relativistic electrons (moving with velocity greater than the electromagnetic phase velocity in the medium) with coherent electromagnetic waves incident in the opposite direction. A new effect of potential use is exhibited; it is a consequence of two distinct physical phenomena acting synergistically to result

S. Schneider; R. Spitzer

1974-01-01

216

Relativistic magneto-acoustic simple wave solutions for a Synge gas

Summary Simple wave solutions for test-relativistic magneto-fluid dynamics in a flat space-time are considered for one-dimensional\\u000a flow. A numerical integration of the equations has been performed and a discussion of the qualitative behaviour of the solution\\u000a is also given.

O. Muscato

1988-01-01

217

The generalized equations of motion for the gyroresonance interaction between energetic electrons and coherent VLF waves in the magnetosphere are employed to study quasi-relativistic electron precipitation. It is suggested that these exact equations be used for particle energies higher than 50 keV (corresponding to a 10% correction in average pitch angle scattering with respect to a nonrelativistic formulation). Based on

H. C. Chang

1983-01-01

218

Enhanced frequency agility of high-power relativistic backward wave oscillators

This paper describes how finite length effects in high-power backward wave oscillators can be exploited in a controlled manner to achieve enhanced frequency agility. Experiments were performed using a Sinus-6 high-power relativistic repetitively pulsed electron beam accelerator. A uniform slow wave structure was used in these studies and its parameters were fixed. Sections of smooth-walled circular waveguide of varying lengths

L. D. Moreland; E. Schamiloglu; R. W. Lemke; A. M. Roitman; S. D. Korovin; V.V. Rostov

1996-01-01

219

A multigigawatt X-Band relativistic backward wave oscillator with a modulating resonant reflector

Effective generation regime with a high output pulse power has been experimentally realized in a relativistic backward wave\\u000a oscillator (RBWO) with a resonant reflector and a slow-wave system having a diameter 1.6 times the radiation wavelength. At\\u000a a guiding magnetic field of 4.5 T, the maximum peak power amounted to 4.3 GW at a frequency of 9.4 GHz, an efficiency

A. I. Klimov; I. K. Kurkan; S. D. Polevin; V. V. Rostov; E. M. Tot’meninov

2008-01-01

220

NASA Astrophysics Data System (ADS)

The possibility of in-phase excitation of two independent nanosecond-pulsed relativistic 37-GHz backward-wave oscillators (BWOs) with high-current electron beams has been studied. This regime can be achieved using BWO switching with a picosecond precision. It is shown that long-term (up to 100-200 periods of the field) phase locking in each channel is stably reproduced from pulse to pulse, which ensures coherent summation of the output wave beams at a megawatt power.

Yalandin, M. I.; Shunailov, S. A.; Ul'maskulov, M. R.; Sharypov, K. A.; Shpak, V. G.; Rostov, V. V.; Romanchenko, I. V.; El'chaninov, A. A.; Klimov, A. I.

2012-10-01

221

Studies of relativistic backward-wave oscillator operation in the cross-excitation regime

We first reported the operation of a relativistic backward-wave oscillator (BWO) in the so-called cross-excitation regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, resulted from the use of a particularly shallow rippled-wall waveguide [slow wave structure (SWS)] that was installed in an experiment to diagnose pulse shortening in a long-pulse electron beam-driven high-power microwave

Frank Hegeler; Michael D. Partridge; Edl Schamiloglu; Chaouki T. Abdallah

2000-01-01

222

Relativistic Landau damping of electron plasma waves in stimulated Raman scattering

A new formulation of the kinetic (collisionless) electron plasma wave (EPW) damping rate in a relativistic thermal equilibrium plasma is presented, and evaluated for such waves in both forward and backward stimulated Raman scattering (SRS) in laser plasma interactions (LPI) in the temperature regime (5-15 keV) of current and near-future deutirium-tritium (DT) fusion plasma experiments. For LPI at typical values

A. Bers; I. P. Shkarofsky; M. Shoucri

2009-01-01

223

Relativistic analysis of a wave packet interacting with a quantum-mechanical barrier

The dynamics of a wave packet incoming on a quantum-mechanical barrier is analyzed in the framework of a fully relativistic model, with particular emphasis on the case of a large spectrum. Some of the characteristic times of tunneling are calculated and compared; they are all of the same order of magnitude and all indicate an apparent superluminal motion, even if causality is maintained. A time-asymptotic expression for the transmitted wave function is derived and its strong validity is shown.

Petrillo, Vittoria; Janner, Davide [Dipartimento di Fisica, Istituto Nazionale di Fisica della Materia, Istituto Nazionale di Fisica Nucleare, Universita degli Studi di Milano, Via Celoria, 16, Milan (Italy)

2003-01-01

224

NASA Astrophysics Data System (ADS)

A compact P-band coaxial relativistic backward wave oscillator with three periods slow wave structure was investigated experimentally. The experimental results show that the frequency of the P-band coaxial relativistic backward wave oscillator is 897 MHz and the microwave power is 1.47 GW with an efficiency of about 32% in the case in which the diode voltage is 572 kV, the beam current is 8.0 kA, and the guide magnetic field is about 0.86 T. In addition, the device can generate a 3.14 GW microwave radiation as the guide magnetic field increases to 1.2 T at the diode voltage of 997 kV and the beam current of 15.3 kA. The experimental results are in good agreement with those obtained earlier by numerical simulations.

Gao, Liang; Qian, Bao-Liang; Ge, Xing-Jun; Zhang, Xiao-Ping; Jin, Zhen-Xing

2012-08-01

225

A compact P-band coaxial relativistic backward wave oscillator with three periods slow wave structure was investigated experimentally. The experimental results show that the frequency of the P-band coaxial relativistic backward wave oscillator is 897 MHz and the microwave power is 1.47 GW with an efficiency of about 32% in the case in which the diode voltage is 572 kV, the beam current is 8.0 kA, and the guide magnetic field is about 0.86 T. In addition, the device can generate a 3.14 GW microwave radiation as the guide magnetic field increases to 1.2 T at the diode voltage of 997 kV and the beam current of 15.3 kA. The experimental results are in good agreement with those obtained earlier by numerical simulations.

Gao Liang; Qian Baoliang; Ge Xingjun; Zhang Xiaoping; Jin Zhenxing [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2012-08-15

226

Colliding Blast Waves Driven by the Interaction of a Short-Pulse Laser with a Gas of Atomic Clusters

Collisions between shocks are commonly found in many astrophysical objects, however robust numerical models or laboratory\\u000a analogues of these complex systems remain challenging to implement. We report on the development of scaled laboratory experiments\\u000a which employ new techniques for launching and diagnosing colliding shocks and high Mach number blast waves, scalable to a\\u000a limited subset of astrophysically-relevant regimes. Use of

Roland A. Smith; James Lazarus; Matthias Hohenberger; Alastair S. Moore; Joseph S. Robinson; Edward T. Gumbrell; Mike Dunne

2007-01-01

227

Colliding Blast Waves Driven by the Interaction of a Short-Pulse Laser with a Gas of Atomic Clusters

Collisions between shocks are commonly found in many astrophysical objects, however robust numerical models or laboratory\\u000a analogues of these complex systems remain challenging to implement. We report on the development of scaled laboratory experiments\\u000a which employ new techniques for launching and diagnosing colliding shocks and high Mach number blast waves, scalable to a\\u000a limited subset of astrophysically-relevant regimes. Use of

Roland A. Smith; James Lazarus; Matthias Hohenberger; Alastair S. Moore; Joseph S. Robinson; Edward T. Gumbrell; Mike Dunne

228

Linear and nonlinear wave propagation in weakly relativistic quantum plasmas

NASA Astrophysics Data System (ADS)

We consider a recently derived kinetic model for weakly relativistic quantum plasmas. We find that that the effects of spin-orbit interaction and Thomas precession may alter the linear dispersion relation for a magnetized plasma in case of high plasma densities and/or strong magnetic fields. Furthermore, the ponderomotive force induced by an electromagnetic pulse is studied for an unmagnetized plasma. It turns out that for this case the spin-orbit interaction always gives a significant contribution to the quantum part of the ponderomotive force.

Stefan, Martin; Brodin, Gert

2013-01-01

229

NASA Astrophysics Data System (ADS)

A high efficient relativistic backward wave oscillator with coaxial nonuniform slow-wave structures (SWSs) and depth-tunable extractor is presented. The physical mechanism to increase the power efficiency is investigated theoretically and experimentally. It is shown that the nonuniform SWSs, the guiding magnetic field distribution, and the coaxial extractor depth play key roles in the enhancement of the beam-wave power conversion efficiency. The experimental results show that a 1.609 GHz, 2.3 GW microwave can be generated when the diode voltage is 890 kV and the beam current is 7.7 kA. The corresponding power efficiency reaches 33.6%.

Ge, Xingjun; Zhong, Huihuang; Zhang, Jun; Qian, Baoliang

2013-02-01

230

The operation in the cross-excitation instability regimes for relativistic backward wave oscillators has been reported and studied in some earlier papers. In the experiment of a relativistic Cerenkov generator with coaxial slow wave structure (CRCG), the cross-excitation instability has also been observed by us. In this paper, experimental results for the CRCG operating in this regime are given, and an explanation is provided to account for the appearance of the instability. Based on this explanation, two types of reflectors, i.e., coaxial Bragg reflectors and cutoff necks, are adopted to restrain the cross-excitation instability by increasing the reflection coefficient at the entrance of the coaxial slow wave structure.

Xiao Renzhen; Zhang Lijun; Liang Tiezhu; Teng Yan; Chen Changhua; Shao Hao; Liu Guozhi [Northwest Institute of Nuclear Technology, Xi'an 710024 (China); Lin Yuzheng [Tsinghua University, Beijing 100084 (China)

2008-05-15

231

Frequency multiplication of light back-reflected from a relativistic wake wave

A method of coherent high-frequency electromagnetic radiation generation, proposed by Bulanov, Esirkepov, and Tajima [Phys. Rev. Lett. 91, 085001 (2003)], is experimentally demonstrated. This method is based on the radiation frequency multiplication during reflection at a mirror flying with relativistic velocity. The relativistic mirror is formed by the electron density modulations in a strongly nonlinear wake wave, excited in an underdense plasma in the wake behind an ultrashort laser pulse. In our experiments, the reflection of a countercrossing laser pulse from the wake wave is observed. The detected frequency multiplication factor is in the range from 55 to 114, corresponding to a reflected radiation wavelength from 7 to 15 nm. This may open a way towards tunable high-intensity sources of ultrashort coherent electromagnetic pulses in the extreme ultraviolet and x-ray spectral regions. Parameters of the reflecting wake wave can be determined using the reflected radiation as a probe.

Pirozhkov, A. S.; Ma, J.; Kando, M.; Esirkepov, T. Zh.; Fukuda, Y.; Chen, L.-M.; Daito, I.; Ogura, K.; Homma, T.; Hayashi, Y.; Kotaki, H.; Sagisaka, A.; Mori, M.; Koga, J. K.; Kawachi, T.; Daido, H.; Bulanov, S. V.; Kimura, T.; Kato, Y.; Tajima, T. [Advanced Photon Research Center, Japan Atomic Energy Agency, 8-1 Umemidai, Kizugawa, Kyoto 619-0215 (Japan)

2007-12-15

232

Frequency multiplication of light back-reflected from a relativistic wake wave

NASA Astrophysics Data System (ADS)

A method of coherent high-frequency electromagnetic radiation generation, proposed by Bulanov, Esirkepov, and Tajima [Phys. Rev. Lett. 91, 085001 (2003)], is experimentally demonstrated. This method is based on the radiation frequency multiplication during reflection at a mirror flying with relativistic velocity. The relativistic mirror is formed by the electron density modulations in a strongly nonlinear wake wave, excited in an underdense plasma in the wake behind an ultrashort laser pulse. In our experiments, the reflection of a countercrossing laser pulse from the wake wave is observed. The detected frequency multiplication factor is in the range from 55 to 114, corresponding to a reflected radiation wavelength from 7 to 15 nm. This may open a way towards tunable high-intensity sources of ultrashort coherent electromagnetic pulses in the extreme ultraviolet and x-ray spectral regions. Parameters of the reflecting wake wave can be determined using the reflected radiation as a probe.

Pirozhkov, A. S.; Ma, J.; Kando, M.; Esirkepov, T. Zh.; Fukuda, Y.; Chen, L.-M.; Daito, I.; Ogura, K.; Homma, T.; Hayashi, Y.; Kotaki, H.; Sagisaka, A.; Mori, M.; Koga, J. K.; Kawachi, T.; Daido, H.; Bulanov, S. V.; Kimura, T.; Kato, Y.; Tajima, T.

2007-12-01

233

Laser driven high energy density radiative blast waves launched in clustered gases

NASA Astrophysics Data System (ADS)

Intense lasers deposit energy efficiently in clustered gases creating hot plasma with low density, conditions ideal for launching radiative blast waves (BWs) of interest for laboratory astrophysics (LA). We report measurements in a range of gases irradiated by the Astra-Gemini laser with energies >10J. Optical imaging, self emission and temporally resolved x-ray spectra are used to characterise BW evolution. The high repetition rate of the laser allows us to explore the influence of atomic number and density on the BW dynamics. Altering the emitted radiation and opacity of the medium has a strong effect on the BW profile and energy loss. Strongly radiative BWs exhibit shell thinning, increasing their susceptibility to instabilities. We have demonstrated the onset of a velocity instability, driven by the exchange of energy between the shock and precursor in krypton BWs. We discuss the threshold conditions for this behaviour and the potential to study spatial shock front instabilities. Our results will be compared to simulations and analytical calculations with a view to designing scalable LA experiments.

Olsson-Robbie, Stefan; Doyle, Hugo; Lowe, Hazel; Price, Chris; Bigourd, Damien; Patankar, Siddharth; Mecseki, Katalin; Booth, Nicola; Scott, Robbie; Moore, Alastair; Hohenberger, Matthias; Rodriguez, Rafael; Gumbrell, Edward; Symes, Daniel; Smith, Roland

2012-10-01

234

We present the effective range expansions for the 1S0 and 3S1 scattering phase shifts, and the relativistic deuteron wave functions that accompany our recent high precision fits (with \\chi^2/N{data} \\simeq 1) to the 2007 world np data below 350 MeV. The wave functions are expanded in a series of analytical functions (with the correct asymptotic behavior at both large and small arguments) that can be Fourier-transformed from momentum to coordinate space and are convenient to use in any application. A fortran subroutine to compute these wave functions can be obtained from the authors.

Franz Gross, Alfred Stadler

2010-09-01

235

Electrostatic ion acoustic solitary waves are studied in a plasma system comprising of relativistic ions, kappa distributed electrons, and positrons. The increase in the relativistic streaming factor and positron and electron kappa parameters cause the soliton amplitude to thrive. However, the soliton amplitude diminishes as the positron concentration is increased in the system. Our results are general and may be helpful, in understanding nonlinear phenomena in the presence of kappa distibuted electrons, positrons, and relativistically streaming ions.

Shah, Asif; Mahmood, S.; Haque, Q. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan)

2011-11-15

236

Head Kinematics Resulting from Simulated Blast Loading Scenarios.

National Technical Information Service (NTIS)

Blast wave overpressure has been associated with varying levels of traumatic brain injury in soldiers exposed to blast loading. In realistic blast loading scenarios, the mechanisms of primary blast injury are not well known due to the complex interactions...

A. Bouamoul D. Singh D. S. Cronin P. A. Lockhart T. N. Haladuick

2012-01-01

237

NASA Astrophysics Data System (ADS)

Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented for plasma parameters representative of the Earth's magnetosphere at locations both inside and outside the plasmapause. The results obtained indicate minimal electron energy change along the diffusion curves for resonant interaction with L mode waves. Intense storm time EMIC waves are therefore ineffective for electron stochastic acceleration, although these waves could induce rapid pitch angle scattering for >~1 MeV electrons near the duskside plasmapause. In contrast, significant energy change can occur along the diffusion curves for interaction between resonant electrons and whistler (R mode) waves. The energy change is most pronounced in regions of low plasma density. This suggests that whistler mode waves could provide a viable mechanism for electron acceleration from energies near 100 keV to above 1 MeV in the region outside the plasmapause during the recovery phase of geomagnetic storms. A model is proposed to account for the observed variations in the flux and pitch angle distribution of relativistic electrons during geomagnetic storms by combining pitch angle scattering by intense EMIC waves and energy diffusion during cyclotron resonant interaction with whistler mode chorus outside the plasmasphere.

Summers, Danny; Thorne, Richard M.; Xiao, Fuliang

1998-09-01

238

In order to clarify the respective roles of stress wave and gas pressure in the fragmentation of an underground blast the fracture process in the zone immediately around the borehole was studied by separating the 2 principal blast forces analytically and experimentally. In model tests the explosion wave was simulated by the pulse generated by an underwater spark discharge, and

H. K. Kutter; C. Fairhurst

1971-01-01

239

Relativistic solitary waves with phase modulation embedded in long laser pulses in plasmas

NASA Astrophysics Data System (ADS)

We investigate the existence of nonlinear phase-modulated relativistic solitary waves embedded in an infinitely long circularly polarized electromagnetic wave propagating through a plasma. These states are exact nonlinear solutions of the 1-dimensional Maxwell-fluid model for a cold plasma composed of electrons and ions. The solitary wave, which consists of an electromagnetic wave trapped in a self-generated Langmuir wave, presents a phase modulation when the group velocity V and the phase velocity Vph of the long circularly polarized electromagnetic wave do not match the condition VVph = c2. The main properties of the waves as a function of their group velocities, wavevectors, and frequencies are studied, as well as bifurcations of the dynamical system that describes the waves when the parameter controlling the phase modulation changes from zero to a finite value. Such a transition is illustrated in the limit of small amplitude waves where an analytical solution for a grey solitary wave exists. The solutions are interpreted as the stationary state after the collision of a long laser pulse with an isolated solitary wave.

Sanchez-Arriaga, G.; Siminos, E.; Lefebvre, E.

2011-08-01

240

Relativistic solitary waves with phase modulation embedded in long laser pulses in plasmas

We investigate the existence of nonlinear phase-modulated relativistic solitary waves embedded in an infinitely long circularly polarized electromagnetic wave propagating through a plasma. These states are exact nonlinear solutions of the 1-dimensional Maxwell-fluid model for a cold plasma composed of electrons and ions. The solitary wave, which consists of an electromagnetic wave trapped in a self-generated Langmuir wave, presents a phase modulation when the group velocity V and the phase velocity V{sub ph} of the long circularly polarized electromagnetic wave do not match the condition VV{sub ph} = c{sup 2}. The main properties of the waves as a function of their group velocities, wavevectors, and frequencies are studied, as well as bifurcations of the dynamical system that describes the waves when the parameter controlling the phase modulation changes from zero to a finite value. Such a transition is illustrated in the limit of small amplitude waves where an analytical solution for a grey solitary wave exists. The solutions are interpreted as the stationary state after the collision of a long laser pulse with an isolated solitary wave.

Sanchez-Arriaga, G.; Siminos, E.; Lefebvre, E. [CEA, DAM, DIF, 91297 Arpajon (France)

2011-08-15

241

Mode selection in an S-band relativistic backward wave oscillator based on a coaxial waveguide

NASA Astrophysics Data System (ADS)

The competition of oscillations in a relativistic backward wave oscillator (RBWO) based on a coaxial waveguide has been studied by theoretical and experimental methods. It is established that the starting current for asymmetric magnetic TE m1 type waves is lower than that for the TEM wave. Predominant excitation of the former waves is confirmed by numerical simulations using the PIC-code KARAT. In an experimental RBWO prototype, the excitation of asymmetric oscillations was suppressed by longitudinal cuts in the central conductor of the coaxial waveguide. As a result, stable generation of the TEM wave has been achieved at a frequency of 1.23 GHz, a peak power of 260 MW, and a 28% efficiency of electron-beam-power conversion into radiation power for a microwave-pulse duration of 33 ns.

Totmeninov, E. M.; Klimov, A. I.; Konev, V. Yu.; Pegel, I. V.; Rostov, V. V.; Tsygankov, R. V.; Tarakanov, V. P.

2014-02-01

242

Solitary and rogue waves in Fermi-Dirac plasmas: relativistic degeneracy effects

NASA Astrophysics Data System (ADS)

Ion acoustic (IA) solitary and rogue waves are studied in an unmagnetized plasma consisting of non-degenerate warm ions, relativistically degenerate electrons and positrons. By using the reductive perturbation technique, the evolution of IA solitary waves is described by the Korteweg-de Vries (KdV) equation. However, when the frequency of the carrier wave is much smaller than the ion plasma frequency then the KdV equation is also used to study the nonlinear evolution of modulationally unstable modified IA wavepackets through the derivation of nonlinear Schrödinger equation. It is found that the characteristics of the IA solitary and rogue waves are substantially influenced by the intrinsic plasma parameters. The relevance of the present investigation involving IA solitary and rogue waves in astrophysical plasma environments is also highlighted.

Rahman, Ata-ur; Ali, S.

2014-05-01

243

Analysis of the Cross-Excitation Instability in a Relativistic Backward Wave Oscillator

NASA Astrophysics Data System (ADS)

The cross-excitation instability in a relativistic backward wave oscillator (BWO) was first observed by our group in 1998.^1 This instability resulted from the use of a particularly shallow rippled-wall waveguide that we had installed in our experiment to accomodate laser interferometry measurements during the course of microwave generation in a high power BWO. Since those early experiments we have analyzed a considerable amount of data to better understand this operating regime. We have invoked joint time-frequency analysis as well as wavelets to interpret the heterodyned signals of the radiated power measurements. We will discuss the interpretation of the data, as well as the methodology used to analyze the data. ^1 C. Grabowski, E. Schamiloglu, C.T. Abdallah, and F. Hegeler, ``Observation of the cross-excitation instability in a relativistic backward wave oscillator,'' Phys. Plasmas 5, 3490 (1998).

Schamiloglu, Edl; Hegeler, Frank; Abdallah, Chaouki; Partridge, Michael

1999-11-01

244

A simple derivation of relativistic full-wave equations at electron cyclotron resonance

NASA Astrophysics Data System (ADS)

When a wave passes through an electron gyroresonance, in a plasma in the presence of a magnetic field gradient, there is a small spread in the resonance due to the electron's Larmor radius. Mathematically this is represented by the inclusion of the so called gyrokinetic term in the resonance condition, Lashmore-Davies and Dendy. The smallness of this term, compared with other effects such as relativistic broadening, suggests that it should be negligible. However, we shall show here, by extending the method of Cairns et al., into the relativistic regime, that its inclusion is vital for producing self consistent full-wave equations which describe electron gyroresonance. The method is considerably simpler than those used previously by Maroli et al., Petrillo et al., and Lampis et al., for obtaining similar equations. As an example we include a calculation for the O-Mode passing perpendicularly through the fundamental.

McDonald, D. C.; Cairns, R. A.; Lashmore-Davies, C. N.

1994-10-01

245

Exact relativistic expressions for wave refraction in a generally moving fluid.

The law for the refraction of a wave when the two fluids and the interface are moving with relativistic velocities is given in an exact form, at the same time correcting a first order error in a previous paper [Cavalleri and Tonni, Phys. Rev. E 57, 3478 (1998)]. The treatment is then extended to a generally moving fluid with variable refractive index, ready to be applied to the refraction of acoustic, electromagnetic, or magnetohydrodynamic waves in the atmosphere of rapidly rotating stars. In the particular case of a gas cloud receding because of the universe expansion, our result can be applied to predict observable micro- and mesolensings. The first order approximation of our exact result for the deviation due to refraction of the light coming from a further quasar has a relativistic dependence equal to the one obtained by Einsteins' linearized theory of gravitation. PMID:23679540

Cavalleri, G; Tonni, E; Barbero, F

2013-04-01

246

NASA Astrophysics Data System (ADS)

This study has concerned the propagation of finite amplitude, i.e. weakly non-linear, acoustical blast waves from explosions over hard and porous media models of outdoor ground surfaces. The nonlinear acoustic propagation effects require a numerical solution in the time domain. To model a porous ground surface, which in the frequency domain exhibits a finite impedance, the linear phenomenological porous model of Morse and Ingard was used. The phenomenological equations are solved in the time domain for coupling with the time domain propagation solution in the air. The numerical solution is found through the method of finite differences. The second-order in time and fourth -order in space MacCormack method was used in the air, and the second-order in time and space MacCormack method was used in the porous medium modeling the ground. Two kinds of numerical absorbing boundary conditions were developed for the air propagation equations to truncate the physical domain for solution on a computer. Radiation conditions first were used on those sides of the domain where there were outgoing waves. Characteristic boundary conditions secondly are employed near the acoustic source. The numerical model agreed well with the Pestorius algorithm for the propagation of electric spark pulses in the free field, and with a result of Pfriem for normal plane reflection off a hard surface. In addition, curves of pressure amplification versus incident angle for waves obliquely incident on the hard and porous surfaces were produced which are similar to those in the literature. The model predicted that near grazing finite amplitude acoustic blast waves decay with distance over hard surfaces as r to the power -1.2. This result is consistent with the work of Reed. For propagation over the porous ground surface, the model predicted that this surface decreased the decay rate with distance for the larger blasts compared to the rate expected in the linear acoustics limit.

Sparrow, Victor Ward

1990-01-01

247

NASA Astrophysics Data System (ADS)

The paper is concerned with the combined effect of a plasma and of a magnetic field on the parametric interaction of two transverse electromagnetic waves with the space charge wave of a relativistic electron flux. It is shown that absolute instability is possible in such a system in addition to convective instability; the instability can be stabilized by selecting approximate parameters. The plasma existing in the drift region of the relativistic electron beam increases the amplification coefficient.

Draganov, A. B.; Kalmykov, A. M.

1985-12-01

248

A High-Power Backward-Wave Oscillator Driven by a Relativistic Electron Beam

A high-power backward-wave oscillator (BWO) has been constructed that is driven by a relativistic electron beam (REB). A typical electron beam of 2-4 kA is accelerated across a diode potential of 650-800 kV and then guided through a section of corrugated transmission line by an axial magnetic field of 5-15 kG. Peak microwave powers of 100-200 MW have been observed

R. Alan Kehs; Alan Bromborsky; B. G. Ruth; S. E. Graybill; W. W. Destler; Y. C. Carmel; M. C. Wang

1985-01-01

249

Scaling studies and time-resolved microwave measurements on a relativistic backward-wave oscillator

A relativistic backward-wave oscillator (BWO) operating at a frequency near 8 GHz has been built. The parameters of the 60-ns electron beam driving this microwave source are varied over the ranges 0.8-1.5 MV and 2-10 kA. Several different annular cathodes for launching the electron beam are tried, varying the outer radius and shape. The axial magnetic field guiding the beam

J. A. Swegle; R. A. Anderson; J. F. Camacho; B. R. Poole; M. A. Rhodes; E. T. Rosenbury; D. L. Shaeffer

1993-01-01

250

Wave propagation through a moving plasma perturbation in a relativistic plasma

NASA Astrophysics Data System (ADS)

We consider wave propagation in a cold and isotropic relativistic plasma, in the presence of a moving density perturbation, which can be created by a particle bunch or by an intense laser pulse. We derive the space and time reflection coefficients and discuss the associated frequency shifts. This work could be useful for the development of radiation sources and new diagnostic techniques for laser and plasma acceleration experiments.

Mendonça, J. T.; Hizanidis, K.

2012-03-01

251

Electron wave-packet dynamics in a relativistic electromagnetic field: 3-D analytical approximation

A solution to the Klein Gordon equation for a laser-driven electron is constructed from a superposition of Volkov states. The time-and space-dependent three-dimensional superposition integral can be evaluated analytically for an initial Gaussian momentum distribution when the expression for relativistic energy is expanded in a Taylor series over the scaled initial momenta. The solution preserves many complicated wave-packet dynamics in

J. Peatross; C. Müller; C. H. Keitel

2007-01-01

252

Relativistic distorted-wave calculation of inelastic electron-alkali atom scattering

The relativistic distorted-wave method was used to perform calculations for electron impact excitation of the first (n${\\\\rm p}) {}^2{\\\\rm P}_{1\\/2,3\\/2}$levels of Na, K and Rb at incident electron energies in the range 20-200 eV. Scattering parameters presented include differential and integrated cross sections, differential and integrated Stokes parameters, generalized STU-parameters and various collisional alignment and orientation parameters. Comparisons with experiment

V. Zeman; R. P. McEachran; A. D. Stauffer

1998-01-01

253

Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented for plasma parameters

Danny Summers; Richard M. Thorne; Fuliang Xiao

1998-01-01

254

Performance of Weakly Relativistic Oversized Backward Wave Oscillators

Performance of oversized backward wave oscillators (BWOs) is investigated. Due to the axial mode operation, there exists a critical value of beam energy for the oscillation, i.e., a starting energy. The output power depends on the beam radius and voltage. The maximum output powers are above 100 kW (K-band) and above 50 kW (Q-band). The corresponding quality factor Pf 2

Kazuo Ogura; Kiyofumi Komiyama; Masakazu Sakai; Daisuke Yamada; Hiroki Saito; Hoshiyuki Yamazaki

2005-01-01

255

Theory of relativistic backward wave oscillators operating near cutoff

A numerical model for analyzing backward-wave oscillators (BWOs) operating near the upper edge of the transmission band is presented. The model is used to calculate starting currents for two finite length devices, an X-band BWO ([ital f]=8.4 GHz) and a J-band BWO ([ital f]=5.5 GHz). The operating frequency and efficiency predicted by the nonlinear numerical simulations are compared with experimental data for each device.

Miller, S.M.; Antonsen, T.M. Jr.; Levush, B.; Bromborsky, A.; Abe, D.K.; Carmel, Y. (Laboratory for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States))

1994-03-01

256

Relativistic Focusing and Beat Wave Phase Velocity Control in the Plasma Beat Wave Accelerator.

National Technical Information Service (NTIS)

Relativistic focusing allows two colinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase vel...

A. Ting E. Esarey P. Sprangle

1988-01-01

257

The klystron-like relativistic backward wave oscillator (RBWO) combines the transition radiation with Cerenkov radiation and has demonstrated microwave output of high power and high efficiency. The coaxial slow wave structure device can produce microwave with a lower frequency in a smaller cross section. For the purpose of high efficiency, low frequency, and miniaturization, a coaxial klystron-like RBWO with a premodulation cavity is presented. Particle-in-cell simulations show that a microwave with power of 1.15 GW and frequency of 2.1 GHz is generated with conversion efficiency of 48%, whereas for the device with a reflector, the efficiency is 38%.

Xiao Renzhen; Teng Yan; Chen Changhua; Sun Jun [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2011-11-15

258

Dispersion of waves in a weakly relativistic quantum plasma and beam of particles

NASA Astrophysics Data System (ADS)

A brief review of works devoted to quantum hydrodynamics is given. A system of quantum hydrodynamics equations is presented for a weakly relativistic system of charged particles described by the Darwin Hamiltonian. This system of equations involves the continuity equation and the momentum balance equation for such system of particles. The role of the quantum terms in the momentum balance equation is analyzed. As an illustration of principally new effects arising in the examined approximation, longitudinal waves in electron quantum plasma and waves in a beam of charged particles are considered.

Ivanov, A. Yu.; Andreev, P. A.

2013-08-01

259

The shock wave generated by an explosion ("blast wave") may cause injury in any or all of the following: (1) direct impact on the tissues of variations in environmental pressure; (2) flying glass and other debris set in motion by it; (3) propulsion of the body. Injuries in the first category affect gas-containing organs (ears, lungs and intestines), and acute death is attributed to air forced into the coronary vessels via damaged pulmonary alveoli. It is estimated that overpressure sufficient to cause lung injury may occur up to five miles from a 20-megaton nuclear explosion. The greatest single hazard from blast is, however, flying glass, and serious wounding from this cause is possible up to 12 miles from an explosion of this magnitude. PMID:6015742

de Candole, C A

1967-01-28

260

General relativistic interaction of massless fields in cylindrical waves

NASA Astrophysics Data System (ADS)

In this paper the problem of finding exact solutions of the combined system of the Einstein-Maxwell-Weyl equations for cylindrical waves is reduced to the solution of two complete singular integral equations in the complex plane of the auxiliary analytical parameter. In the case of the nonsingular symmetry axis the problem further simplifies and requires solving the only integral equation, the expressions for the Ernst potentials on the symmetry axis then defining the group transformations of internal symmetries during the solution generation process. A large class of exact solutions for neutrino electrovacuum is obtained, and the Cauchy problem related to some particular initial data is considered.

Sibgatullin, N. R.; García, A. A.; Manko, V. S.

2003-11-01

261

Enhanced frequency agility of high-power relativistic backward wave oscillators

This paper describes how finite length effects in high-power backward wave oscillators can be exploited in a controlled manner to achieve enhanced frequency agility. Experiments were performed using a Sinus-6 high-power relativistic repetitively pulsed electron beam accelerator. A uniform slow wave structure was used in these studies and its parameters were fixed. Sections of smooth-walled circular waveguide of varying lengths were inserted both before and after the slow wave structure. Variations in the length of smooth-walled waveguide on the order of a quarter-wavelength of the generated electromagnetic radiation were found to significantly affect both microwave frequency and radiation efficiency in a periodic-like manner. The experimental results were reproduced in TWOQUICK electromagnetic particle-in-cell simulations. A bandwidth of about 500 MHz centered around 9.5 GHz at hundreds of MW power levels has been achieved with constant beam and slow wave structure parameters.

Moreland, L.D.; Schamiloglu, E. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering] [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering; Lemke, R.W. [Sandia National Labs., Albuquerque, NM (United States)] [Sandia National Labs., Albuquerque, NM (United States); Roitman, A.M.; Korovin, S.D.; Rostov, V.V. [Russian Academy of Sciences, Tomsk (Russian Federation). High Current Electronics Inst.] [Russian Academy of Sciences, Tomsk (Russian Federation). High Current Electronics Inst.

1996-06-01

262

Rapid startup in relativistic backward wave oscillator by injecting external backward signal

Investigation on accelerating the building up of oscillation and achieving a rapid startup in powerful relativistic backward wave oscillator by injecting a weak external backward signal is carried out in this paper. Synchronizing the signal with the backward wave excited by intense electron beam extracting with slow wave structure, the initial noise is greatly reduced and mode competition is restrained. The analysis is demonstrated by high power X-band backward wave oscillator experiment, in which a plasma switch is designed to realize the backward signal injection. The results show that the significant reduction of microwave output delay is attained and the start time of oscillation is ahead of 10 ns with the energy conversion efficiency increases about 62%.

Song, W.; Teng, Y.; Zhang, Z. Q.; Li, J. W.; Sun, J.; Chen, C. H.; Zhang, L. J. [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an, Shanxi 710024 (China)

2012-08-15

263

Rapid startup in relativistic backward wave oscillator by injecting external backward signal

NASA Astrophysics Data System (ADS)

Investigation on accelerating the building up of oscillation and achieving a rapid startup in powerful relativistic backward wave oscillator by injecting a weak external backward signal is carried out in this paper. Synchronizing the signal with the backward wave excited by intense electron beam extracting with slow wave structure, the initial noise is greatly reduced and mode competition is restrained. The analysis is demonstrated by high power X-band backward wave oscillator experiment, in which a plasma switch is designed to realize the backward signal injection. The results show that the significant reduction of microwave output delay is attained and the start time of oscillation is ahead of 10 ns with the energy conversion efficiency increases about 62%.

Song, W.; Teng, Y.; Zhang, Z. Q.; Li, J. W.; Sun, J.; Chen, C. H.; Zhang, L. J.

2012-08-01

264

RELATIVISTIC JET DYNAMICS AND CALORIMETRY OF GAMMA-RAY BURSTS

We present numerical solutions of the two-dimensional relativistic hydrodynamics equations describing the deceleration and expansion of highly relativistic conical jets, of opening angles 0.05 {<=} {theta}{sub 0} {<=} 0.2, propagating into a medium of uniform density. Jet evolution is followed from a collimated relativistic outflow to the quasi-spherical non-relativistic phase. We show that relativistic sideways expansion becomes significant beyond the radius r{sub {theta}} at which the expansion Lorentz factor drops to {theta}{sup -1}{sub 0}. This is consistent with simple analytic estimates, which predict faster sideways expansion than has been claimed based on earlier numerical modeling. For t > t{sub s} = r{sub {theta}}/c the emission of radiation from the jet blast wave is similar to that of a spherical blast wave carrying the same energy (significant deviations at t {approx} t{sub s} occur only for well off-axis observers, {theta}{sub obs} {approx} 1 >> {theta}{sub 0}). Thus, the total (calorimetric) energy of gamma-ray burst blast waves may be estimated with only a small fractional error based on t > t{sub s} observations.

Wygoda, N.; Waxman, E. [Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Frail, D. A. [National Radio Astronomy Observatory, Array Operations Center, Socorro, NM 87801 (United States)

2011-09-10

265

NASA Astrophysics Data System (ADS)

Radiative shock waves play a pivotal role in the transport energy into the stellar medium. This fact has led to many efforts to scale the astrophysical phenomena to accessible laboratory conditions and their study has been highlighted as an area requiring further experimental investigations. Low density material with high atomic mass is suitable to achieve radiative regime, and, therefore, low density xenon gas is commonly used for the medium in which the radiative shocks such as radiative blast waves propagate. In this work, by means of collisional-radiative steady-state calculations, a characterization and an analysis of microscopic magnitudes of laboratory blast waves launched in xenon clusters are made. Thus, for example, the average ionization, the charge state distribution, the cooling time or photon mean free paths are studied. Furthermore, for a particular experiment, the effects of the self-absorption and self-emission in the specific intensity emitted by the shock front and that is going through the radiative precursor are investigated. Finally, for that experiment, since the electron temperature is not measured experimentally, an estimation of this magnitude is made both for the shock shell and the radiative precursor.

Rodriguez, R.; Espinosa, G.; Gil, J. M.; Florido, R.; Rubiano, J. G.; Mendoza, M. A.; Martel, P.; Minguez, E.; Symes, D. R.; Hohenberger, M.; Smith, R. A.

2013-08-01

266

This paper describes experiments exploring the three-dimensional (3D) Rayleigh-Taylor instability at a blast-wave-driven interface. This experiment is well scaled to the He/H interface during the explosion phase of SN1987A. In the experiments, {approx}5 kJ of energy from the Omega laser was used to create a planar blast wave in a plastic disk, which is accelerated into a lower-density foam. These circumstances induce the Richtmyer-Meshkov instability and, after the shock passes the interface, the system quickly becomes dominated by the Rayleigh-Taylor instability. The plastic disk has an intentional pattern machined at the plastic/foam interface. This perturbation is 3D with a basic structure of two orthogonal sine waves with a wavelength of 71 {mu}m and an amplitude of 2.5 {mu}m. Additional long-wavelength modes with a wavelength of either 212 or 424 {mu}m are added onto the single-mode pattern. The addition of the long-wavelength modes was motivated by the results of previous experiments where material penetrated unexpectedly to the shock front, perhaps due to an unintended structure. The current experiments and simulations were performed to explore the effects of this unintended structure; however, we were unable to reproduce the previous results.

Kuranz, C. C.; Drake, R. P.; Grosskopf, M. J.; Budde, A.; Krauland, C.; Marion, D. C.; Visco, A. J.; Ditmar, J. R. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Robey, H. F.; Remington, B. A.; Miles, A. R.; Cooper, A. B. R.; Sorce, C. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Plewa, T. [Department of Scientific Computing, Florida State University, Tallahassee, Florida 32306 (United States); Hearn, N. C. [ASC Flash Center, University of Chicago, Chicago, Illinois 60637 (United States); Killebrew, K. L. [Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States); Knauer, J. P. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York (United States); Arnett, D. [Steward Observatory, University of Arizona, Tucson, Arizona 85721 (United States); Donajkowski, T. [Jet Propulsion Laboratory, Pasadena, California 91109 (United States)

2009-05-15

267

In core-collapse supernovae, strong blast waves drive interfaces susceptible to Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) instabilities. In addition, perturbation growth can result from material expansion in large-scale velocity gradients behind the shock front. Laser-driven experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen-helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. In this dissertation, we present a computational study of unstable systems driven by high Mach number shock and blast waves. Using multi-physics radiation hydrodynamics codes and theoretical models, we consider the late nonlinear instability evolution of single mode, few mode, and multimode interfaces. We rely primarily on 2D calculations but present recent 3D results as well. For planar multimode systems, we show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions (IC's) by allowing for memory of the initial conditions to be retained in the mix-width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Aspects of the IC's are shown to have a strong effect on the time to transition to the quasi-self-similar regime. With higher-dimensional blast waves, divergence restores the properties necessary for establishment of the self-similar state, but achieving it requires very high initial characteristic mode number and high Mach number for the incident blast wave. We point to recent stellar calculations that predict IC's we find incompatible with self-similarity, and emphasize the consequent importance of developing a sound understanding of the initial modal structure in the supernova progenitor. For divergent and planar systems, the time-dependence of the drive is shown to impose an 'effective box size' on the systems that limits the inverse cascade to large-scales. Our model explains the weak IC-dependence of this scale observed in some supernova calculations.

Miles, A

2004-04-27

268

Blast-wave and piston shocks connected with the formation and propagation of a coronal mass ejection

NASA Astrophysics Data System (ADS)

The solar coronal mass ejection observed on November 3, 2010 is analyzed using AIA/SDO data (images in the 193 and 211 Å channels) and white-corona images obtained with the SOHO LASCO C2 and C3 coronographs. We have succeeded in revealing both piston and blast-wave shocks attributed to the formation and propagation of a coronal mass ejection. Both of these types of shocks could be responsible for type II radio bursts propagating in front of each shock.

Eselevich, V. G.; Eselevich, M. V.; Zimovets, I. V.

2013-02-01

269

Observation of relativistic plasma waves generated by the beat-wave with 1 ?m lasers

An experiment to generate a plasma wave by the beat wave process is described. The beat wave is generated by mixing two copropagating intense laser beams at 1.053 ?m and 1.064 ?m. The plasma wave is observed by monitoring the sideband generated by the interaction of the plasma wave with a third copropagating laser beam at 0.526 ?m. Plasma waves

A E Dangor; A K L Dymoke-Bradshaw; A E Dyson

1990-01-01

270

Beat-Wave Excitation of Plasma Waves Based on Relativistic Bistability

A nonlinear beat-wave regime of plasma wave excitation is considered. Two beat-wave drivers are considered: intensity-modulated laser pulse and density-modulated (microbunched) electron beam. It is shown that a long beat-wave pulse can excite strong plasma waves in its wake even when the beat-wave frequency is detuned from the electron plasma frequency. The wake is caused by the dynamic bistability of

Gennady Shvets

2004-01-01

271

We present the equatorial and bounce-averaged pitch angle diffusion coefficients for the scattering relativistic electrons by He +-mode electromagnetic ion cyclotron waves. Both the model (prescribed) and self-consistent distributions over the wave normal angle are considered. The main results of our calculation can be summarized as follows: First, in comparison with field-aligned waves, intermediate and highly oblique waves decrease the

G. V. Khazanov; K. V. Gamayunov

2007-01-01

272

We present the equatorial and bounce-averaged pitch angle diffusion coefficients for the scattering relativistic electrons by He+-mode electromagnetic ion cyclotron waves. Both the model (prescribed) and self-consistent distributions over the wave normal angle are considered. The main results of our calculation can be summarized as follows: First, in comparison with field-aligned waves, intermediate and highly oblique waves decrease the bounce-averaged

G. V. Khazanov; K. V. Gamayunov

2007-01-01

273

Skull Flexure from Blast Waves: A Mechanism for Brain Injury with Implications for Helmet Design

NASA Astrophysics Data System (ADS)

Traumatic brain injury (TBI) has become a signature injury of current military conflicts, with debilitating, costly, and long-lasting effects. Although mechanisms by which head impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. From numerical hydrodynamic simulations, we have discovered that nonlethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain, even without a head impact. The possibility that this mechanism may contribute to TBI has implications for injury diagnosis and armor design.

Moss, William C.; King, Michael J.; Blackman, Eric G.

2009-09-01

274

Relativistic modulational instability of electron-acoustic waves in an electron-pair ion plasma

The modulational instability of finite amplitude electron-acoustic waves (EAWs) along the external magnetic field is studied in an electron-pair ion plasma. Accounting for the relativistic electron mass variation nonlinearity and the Boltzmann distribution of both positive and negative ions, new regimes for the relativistic modulational instability (MI) for the low frequency (below the electron gyrofrequency) short-wavelength (in comparison with the ion gyroradius) modes are obtained numerically. It is found that the presence of a significant fraction of negative ions suppresses the MI growth/decay rate for the modulated EAW packets. The results could be of important for understanding the origin of amplitude modulated EAW packets in space (e.g., Earth's magnetotail) as well as in laboratory plasmas.

Misra, A. P. [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan-731 235 (India); Shukla, P. K. [Institut fuer Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultaet fuer Physik and Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany and School of Physics, University of KwaZulu-Natal, 4000 Durban (South Africa)

2008-12-15

275

Dispersion of electrostatic and electromagnetic waves in a relativistically drifting plasma

NASA Astrophysics Data System (ADS)

Multi-dimensional electron beam-plasma instabilities in the relativistic regime [1] are of interest in a number of scenarios, such as fast ignition for inertial confinement fusion and generation of cosmic gamma ray. A closely related problem arises for drifting plasmas with relativistic electron and ion velocities typically found in laser ion acceleration [2] and also in numerical simulations with the boosted frame technique [3] for plasma wakefield acceleration. We study the dispersion of the electrostatic and electromagnetic waves in such plasma using a linear analysis in the cold-fluid limit and a kinetic approach. Possible instabilities are analyzed and compared with those found in an electron beam-plasma system. The potential implications for the boosted frame simulation technique will also be discussed. [4pt][1] A. Bret et al., Physics Of Plasmas 17, 120501 (2010). [2] L. Yin et al., Physics Of Plasmas 14, 056706 (2007). [3] J.-L. Vay, Physical Review Letters 98, 130405 (2007).

Huang, C.-K.; Meyers, M. D.; Albright, B. J.

2011-11-01

276

Ion-acoustic solitary waves in ultra-relativistic degenerate pair-ion plasmas

NASA Astrophysics Data System (ADS)

The arbitrary and the small amplitude ion-acoustic solitary waves (IASWs) have been studied. The former is studied by using the Sagdeev pseudo-potential approach in a plasma consisting of the degenerate ultrarelativistic electrons, positrons, and the non-relativistic classical ions. It is seen that only compressive solitary waves can propagate through such plasmas. The numerical calculations show that the region of existence of the ion-acoustic solitary waves depends upon the positron (ion) number density and the plasma thermal temperature. This study is appropriate for applications in inertial confinement fusion laboratory research as well as the study of astrophysical dense objects such as white dwarf and dense neutron stars.

Rasheed, A.; Tsintsadze, N. L.; Murtaza, G.

2011-11-01

277

NASA Astrophysics Data System (ADS)

Optimal design method of high-power microwave source using particle simulation and parallel genetic algorithms is presented in this paper. The output power, simulated by the fully electromagnetic particle simulation code UNIPIC, of the high-power microwave device is given as the fitness function, and the float-encoding genetic algorithms are used to optimize the high-power microwave devices. Using this method, we encode the heights of non-uniform slow wave structure in the relativistic backward wave oscillators (RBWO), and optimize the parameters on massively parallel processors. Simulation results demonstrate that we can obtain the optimal parameters of non-uniform slow wave structure in the RBWO, and the output microwave power enhances 52.6% after the device is optimized.

Chen, Zaigao; Wang, Jianguo; Wang, Yue; Qiao, Hailiang; Zhang, Dianhui; Guo, Weijie

2013-11-01

278

Effects of initially energetic electrons on relativistic laser-driven electron plasma waves

NASA Astrophysics Data System (ADS)

In this paper, using kinetic calculations and accurate 1D2V particle-in-cell simulations, we point out the important role of initially energetic electrons of the distribution tail in the behavior of high amplitude electron plasma waves (EPWs). In the presence of these electrons, the conventional warm fluid theory (WFT) breaks at very high wave amplitudes that are still noticeably lower than the wave breaking amplitude (WBA). The fluid breakdown results in electron super-heating with respect to the adiabatic laws. Indeed, a new kinetic regime of the relativistic EPWs appears below the WBA. It is argued that the mentioned super-heating results in WBA values lower than the corresponding WFT prediction.

Yazdanpanah, J.; Anvari, A.

2014-02-01

279

We present the effective range expansions for the {sup 1}S{sub 0} and {sup 3}S{sub 1} scattering phase shifts, and the relativistic deuteron wave functions that accompany our recent high precision fits (with {chi}{sup 2}/N{sub data{approx_equal}}1) to the 2007 world np data below 350 MeV. The wave functions are expanded in a series of analytical functions (with the correct asymptotic behavior at both large and small arguments) that can be Fourier-transformed from momentum to coordinate space and are convenient to use in any application. A fortran subroutine to compute these wave functions can be obtained from the authors.

Gross, Franz; Stadler, Alfred [College of William and Mary, Williamsburg, Virginia 23185 (United States) and Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Centro de Fisica Nuclear da Universidade de Lisboa, P-1649-003 Lisboa (Portugal) and Departamento de Fisica da Universidade de Evora, P-7000-671 Evora (Portugal)

2010-09-15

280

Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity

NASA Astrophysics Data System (ADS)

We consider cosmological applications of a new self-consistent system of equations, accounting for a non-minimal coupling of the gravitational, electromagnetic and pseudoscalar (axion) fields in a relativistic plasma. We focus on dispersion relations for electromagnetic perturbations in an initially isotropic ultrarelativistic plasma coupled to the gravitational and axion fields in the framework of isotropic homogeneous cosmological model of the de Sitter type. We classify the longitudinal and transversal electromagnetic modes in an axionically active plasma and distinguish between waves (damping, instable or running), and nonharmonic perturbations (damping or instable). We show that for the special choice of the guiding model parameters the transversal electromagnetic waves in the axionically active plasma, non-minimally coupled to gravity, can propagate with the phase velocity smaller than the speed of light in vacuum, thus displaying a possibility for a new type of resonant particle-wave interactions.

Balakin, Alexander B.; Muharlyamov, Ruslan K.; Zayats, Alexei E.

2013-12-01

281

Observation of Self-Sustaining Relativistic Ionization Wave Launched by a Sheath Field

NASA Astrophysics Data System (ADS)

We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115 fs) at a peak intensity of 5×1017 W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma.

McCormick, M.; Arefiev, A. V.; Quevedo, H. J.; Bengtson, R. D.; Ditmire, T.

2014-01-01

282

Causal wave propagation for relativistic massive particles: physical asymptotics in action

NASA Astrophysics Data System (ADS)

Wavepackets representing relativistic quantum particles injected into a half-space, from a source that is switched on at a definite time, are represented by superpositions of plane waves that must include negative frequencies. Propagation is causal: it is a consequence of analyticity that at time t no part of the wave has travelled farther than ct, corresponding to the front of the signal. Nevertheless, interference fringes behind the front travel superluminally. For Klein-Gordon and Dirac wavepackets, the spatially integrated density increases because current is injected at the boundary. Even in the simplest causal model, understanding the shape of the wave after long times is an instructive exercise in the asymptotics of integrals, illustrating several techniques at a level suitable for graduate students; different spatial features involve contributions from a pole and from two saddle points, the uniform asymptotics for the pole close to a saddle, and the coalescence of two saddles into the Sommerfeld precursor immediately behind the front.

Berry, M. V.

2012-03-01

283

The relativistic motion of a charged particle in a superposition of circularly polarized plane electromagnetic waves and a uniform magnetic field is studied by deriving an exact solution to the Lorentz force equation of the charged particle. All of the circularly polarized plane electromagnetic waves propagate parallel to the uniform magnetic field. The explicit expressions of the charged particle position,

Bao-Liang Qian

2000-01-01

284

Versatile gas gun target assembly for studying blast wave mitigation in materials

NASA Astrophysics Data System (ADS)

Traumatic brain injury (TBI) has become a serious problem for military personnel returning from recent conflicts. This has increased interest in investigating blast mitigating materials for use in helmets. In this paper we describe a new versatile target assembly that is used with an existing gas gun for studying these materials.

Bartyczak, S.; Mock, W., Jr.

2012-03-01

285

NASA Astrophysics Data System (ADS)

This paper provides a fresh insight into the effect of non-uniform slow wave structure (SWS) used in a relativistic backward wave oscillator (RBWO) with a resonant reflector. Compared with the uniform SWS, the reflection coefficient of the non-uniform SWS is higher, leading to a lower modulating electric field in the resonant reflector and a larger distance to maximize the modulation current. Moreover, for both types of RBWOs, stronger standing-wave field takes place at the rear part of the SWS. In addition, besides Cerenkov effects, the energy conversion process in the RBWO strongly depends on transit time effects. Thus, the matching condition between the distributions of harmonic current and standing wave field provides a profound influence on the beam-wave interaction. In the non-uniform RBWO, the region with a stronger standing wave field corresponds to a higher fundamental harmonic current distribution. Particle-in-cell simulations show that with a diode voltage of 1.02 MV and beam current of 13.2 kA, a microwave power of 4 GW has been obtained, compared to that of 3 GW in the uniform RBWO.

Chen, Changhua; Xiao, Renzhen; Sun, Jun; Song, Zhimin; Huo, Shaofei; Bai, Xianchen; Shi, Yanchao; Liu, Guozhi

2013-11-01

286

This paper provides a fresh insight into the effect of non-uniform slow wave structure (SWS) used in a relativistic backward wave oscillator (RBWO) with a resonant reflector. Compared with the uniform SWS, the reflection coefficient of the non-uniform SWS is higher, leading to a lower modulating electric field in the resonant reflector and a larger distance to maximize the modulation current. Moreover, for both types of RBWOs, stronger standing-wave field takes place at the rear part of the SWS. In addition, besides Cerenkov effects, the energy conversion process in the RBWO strongly depends on transit time effects. Thus, the matching condition between the distributions of harmonic current and standing wave field provides a profound influence on the beam-wave interaction. In the non-uniform RBWO, the region with a stronger standing wave field corresponds to a higher fundamental harmonic current distribution. Particle-in-cell simulations show that with a diode voltage of 1.02 MV and beam current of 13.2 kA, a microwave power of 4 GW has been obtained, compared to that of 3 GW in the uniform RBWO.

Chen, Changhua; Xiao, Renzhen; Sun, Jun; Song, Zhimin; Huo, Shaofei; Bai, Xianchen; Shi, Yanchao; Liu, Guozhi [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)] [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2013-11-15

287

NASA Technical Reports Server (NTRS)

We consider the effect of oblique EMIC waves on relativistic electron scattering in the outer radiation belt using simultaneous observations of plasma and wave parameters from CRRES. The main findings can be s ummarized as follows: 1. In 1comparison with field-aligned waves, int ermediate and highly oblique distributions decrease the range of pitc h-angles subject to diffusion, and reduce the local scattering rate b y an order of magnitude at pitch-angles where the principle absolute value of n = 1 resonances operate. Oblique waves allow the absolute va lue of n > 1 resonances to operate, extending the range of local pitc h-angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude; 2. The local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Conseq uently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations; 3. In comparison with f ield-aligned waves, intermediate and highly oblique waves decrease th e bounce-averaged scattering rate near the edge of the equatorial lo ss cone by orders of magnitude if the electron energy does not excee d a threshold (approximately equal to 2 - 5 MeV) depending on specified plasma and/or wave parameters; 4. For greater electron energies_ ob lique waves operating the absolute value of n > 1 resonances are more effective and provide the same bounce_averaged diffusion rate near the loss cone as fiel_aligned waves do.

Gamayunov, K. V.; Khazanov, G. V.

2007-01-01

288

Precipitation of relativistic electrons by interaction with electromagnetic ion cyclotron waves

NASA Astrophysics Data System (ADS)

On August 20, 1996, balloon-borne X-ray detectors observed an intense X-ray event as part of a French balloon campaign near Kiruna, Sweden, at 1532 UT (1835 magnetic local time), on an L shell of 5.8. The energy spectrum of this event shows the presence of X rays with energies >1 MeV, which are best accounted for by atmospheric bremsstrahlung from monoenergetic ~1.7 MeV precipitating electrons. Ultraviolet images from the Polar satellite and energetic particle data from the Los Alamos geosynchronous satellites show the onset of a small magnetospheric substorm 24 min before the start of the relativistic electron precipitation event. Since the balloon was south of the auroral oval and there was no associated increase in relativistic electron flux at geosynchronous altitude, the event is interpreted as the result of selective precipitation of ambient relativistic electrons from the radiation belts. Pitch angle scattering caused by resonance with electromagnetic ion cyclotron mode waves is the most likely mechanism for selective precipitation of MeV electrons. A model is presented in which wave growth is driven by temperature anisotropies in the drifting substorm-injected proton population. The model predicts that this wave growth and resonance with ~1.7 MeV electrons will occur preferentially in regions of density >10 cm-3, such as inside the duskside plasmapause bulge or detached plasma regions. The model predictions are consistent with the location of the balloon, the observed energies, and the timing with respect to the substorm energetic particle injection.

Lorentzen, K. R.; McCarthy, M. P.; Parks, G. K.; Foat, J. E.; Millan, R. M.; Smith, D. M.; Lin, R. P.; Treilhou, J. P.

2000-03-01

289

The experimental investigation described in this dissertation demonstrates the feasibility of generating long (greater than or equal to 50 nsec) pulses of high-power (greater than or equal to 100 MW), X-band frequency microwaves. In these experiments, a relativistic Backward Wave Oscillator (BWO) is used in tandem with a Traveling Wave Tube (TWT) amplifier to generate microwave radiation. The tandem BWO

Gilberto Barreto

1992-01-01

290

A modified relativistic (500 kV, 500 A) backward-wave oscillator (BWO) filled with a radially nonuniform preionized plasma of high-peak density (peak plasma frequency>operating frequency) is studied experimentally. The effects of high plasma density in the interaction region as well as the relativistic diode and the output horn regions were studied. By protecting both the diode and output regions against plasma

Anatoly G. Shkvarunets; Satoru Kobayashi; Yuval Carmel; John Rodgers; T. M. Antonsen; L. Duan; V. L. Granatstein

1998-01-01

291

Macro-mechanical modeling of blast-wave mitigation in foams. Part III: verification of the models

NASA Astrophysics Data System (ADS)

Three different approaches to macro-mechanical modeling of blast-wave mitigation in foam namely: the single-phase effective gas flow model, the two-phase mixture model and the single bubble/shock wave interaction model are critically reviewed. The nature and extent of the approximations inherent in the formulation of the first two models were examined in Part I of this study. In this part, the applicability of the aforementioned approaches is verified based on a comparison of experimental pressure records obtained in shock tube tests with the results of numerical predictions that used the models under consideration. Deficiencies and inconsistencies that are found during this comparison are clarified and possible improvements are suggested. It is emphasized that both the single-phase and the two-phase approaches predict well the refraction of the incident shock at the air/foam interface while they do not uniquely determine the relaxation process and the shape of the transmitted shock wave front. Various flexibilities that are exploited to better describe the inter-phase interactions do not improve the results significantly. The single bubble model is examined with particular attention paid to the manner in which it predicts the shape of the shock wave front. Connections between the flow viscosity and the transient dynamics of the bubble compression that occur at scales of the shock wave front thickness are explored.

Britan, A.; Shapiro, H.; Liverts, M.; Ben-Dor, G.

2014-05-01

292

Phase locking of high power relativistic backward wave oscillator using priming effect

NASA Astrophysics Data System (ADS)

The phase-locking approach using the priming effect is developed for high power relativistic backward wave oscillators (RBWO). A plasma switch is conceived to avoid the feedback effect. In experiment, multicavity RBWO of 200 MW with the 73 MHz half power bandwidth is phase-locked under the injection power ratio 0.044 for the frequency separation of 20 MHz. We found that it takes more time to reach stable phase-locking than to achieve saturation of RBWO generation. The external signal of higher power results in the longer time duration of phase locking. Besides phase-locking, the priming effect leads to longer microwave pulse duration.

Teng, Yan; Song, Wei; Sun, Jun; Xiao, Renzhen; Song, Zhimin; Zhang, Ligang; Zhang, Zhiqiang; Zhang, Lijun; Zhang, Yuchuan; Li, Jiawei; Fang, Jinyong

2012-02-01

293

NASA Astrophysics Data System (ADS)

A theory for dressed quantum ion acoustic waves (QIAWs), which includes higher-order corrections when QIAWs are investigated by the reductive perturbation method, is presented for unmagnetized plasmas containing positive and negative ions and weakly relativistic electron beams. The properties of the QIAWs are investigated using a quantum hydrodynamic model, from which a Korteweg-de Vries equation is derived using the reductive perturbation method. An equation including higher-order dispersion and nonlinearity corrections is also derived, and the physical parameter space is discussed for the importance of these corrections.

Wang, Yunliang; Dong, Yushan; Eliasson, B.

2013-11-01

294

NASA Technical Reports Server (NTRS)

By analyzing CRRES and GOES observations on Aug. 27 1991, Tan et al. [2004] reported evidence of magnetospheric relativistic electron acceleration by resonant interactions with PC5 ULF waves. The event showed strong ULF wave activities after a storm sudden commencement (SSC) and energetic electron fluxes were enhanced in 2 hours. The electron flux peak observed in energy channels (0.6 - 1.1 MeV) were modulated by local electric field observed by CRRES. In this study, we set up a drift-resonant interaction model between ULF wave and magnetospheric relativistic electrons to model the observed electron flux in the event. In this model, the poloidal mode wave is concentrated in the dayside and the toroidal mode wave is concentrated in two flanks. The toroidal mode waves in the dawn and dusk flanks are in anti-phase. We found that electron can be accelerated jointly by the poloidal wave in the dayside and toroidal wave in flanks. The dayside poloidal wave serves as the dominant source of electron acceleration. The simulated electron flux variations agree well with observations both in fine details and long period behavior. These agreements in electron behavior indicate that the ULF wave plays an important role in accelerating MeV relativistic electrons around the geosynchronous orbit.

Fung, Shing

2007-01-01

295

A compact P-band coaxial relativistic backward wave oscillator (BWO) with only three periods slow wave structure (SWS) is investigated both theoretically and numerically. The characteristics of the coaxial SWS are analyzed when the SWS is changed from the structure with only outer conductor ripple to the structure with both inner and outer conductor ripples. It is found that the existence of the inner conductor ripple can reduce the period length of coaxial SWS to maintain the same operating frequency of the BWO and can largely increase the temporal growth rate and the spatial growth rate of the device. Then, the effects of SWS period numbers on the generation of the microwave in the P-band relativistic BWO are studied by PIC simulations. The results show that three periods SWS cannot only make the device more compact but also has a wide region of single-frequency operation and relatively large efficiency and output power in a wide range of the diode voltage. Typical simulation results show that, with a 585 kV and 7.85 kA electron beam guided by a 0.8 T solenoidal field, the microwave of 1.65 GW is generated at the frequency of 900 MHz, and the interaction efficiency is about 36%. Compared with the conventional P-band coaxial relativistic BWO with five periods SWS, the axial length of the SWS is reduced by about one half, which is only 38.4 cm, and the saturation time of the microwave signal is reduced by about 10 ns.

Gao Liang; Qian Baoliang; Ge Xingjun [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2011-10-15

296

NASA Astrophysics Data System (ADS)

We report a very efficient acceleration process of high energy electrons by coherent whistler mode waves in the Earth's dipole magnetic field, which we have found in our recent test particle simulations. The efficient acceleration process takes place only for weakly relativistic seed electrons of a few hundred keV. Under an assumption that the whistler mode wave packets are excited near the equatorial plane of the inner magnetosphere and propagate away from the equator, the acceleration process becomes irreversible. With a sufficiently long whistler mode wave packet of the order of a few hundred milliseconds, the energetic electrons are accelerated to a relativistic energy range of a few MeV through a single resonant trapping process. We call this particular acceleration process relativistic resonant acceleration (RRA), which can be the mechanism for formation process of relativistic electron flux in the outer radiation belt. A necessary condition for the RRA is a relatively large amplitude of the whistler mode wave in the range of a few hundred pT, which has been confirmed by recent in situ observations of whistler mode chorus emissions by Cluster satellites. Chorus emissions consist of successive generation of rising tones in a frequency range of 0.2 - 0.5 of the local cyclotron frequency, which can make the RRA more effective in the formation process of the relativistic electron flux in the recovery phase of magnetic storms.

Omura, Y.; Furuya, N.; Summers, D.

2006-12-01

297

Improved Beam Inlet Design in a Relativistic Backward Wave Oscillator for Pulse Lengthening Studies

NASA Astrophysics Data System (ADS)

Laser interferometry was recently used to diagnose plasma formation and evolution in the slow wave structure (SWS) of a relativistic backward wave oscillator (BWO) during the course of microwave generation.(F. Hegeler, C. Grabowski, and E. Schamiloglu, IEEE Trans. Plasma Sci. 26), 275 (1998). In our studies we concluded that plasma from the cutoff neck inlet to the SWS structure was the source of seed electrons that later resulted in a microwave discharge, subsequently terminating BWO operation for the duration of the electron beam pulse. In an effort to mitigate this pulse shortening effect we have designed alternative cutoff neck inlets to the SWS, as well as a Bragg reflector to replace the cutoff neck entirely, as was demonstrated by Gunin et al./(A. V. Gunin et al./), IEEE Trans. Plasma Sci. 26, 326 (1998). Laser interferometry results with these new configurations, as well as microwave generation results, will be presented.

Hegeler, Frank; Schamiloglu, Edl; Korovin, Sergei; Rostov, Vladislav

1998-11-01

298

The postbounce oscillations of newly-born relativistic stars are expected to lead to gravitational-wave emission through the excitation of nonradial oscillation modes. At the same time, the star is oscillating in its radial modes, with a central density variation that can reach several percent. Nonlinear couplings between radial oscillations and polar nonradial modes lead to the appearance of combination frequencies (sums and differences of the linear mode frequencies). We study such combination frequencies using a gauge-invariant perturbative formalism, which includes bilinear coupling terms between different oscillation modes. For typical values of the energy stored in each mode we find that gravitational waves emitted at combination frequencies could become detectable in galactic core-collapse supernovae with advanced interferometric or wideband resonant detectors.

Passamonti, Andrea; Stergioulas, Nikolaos [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Nagar, Alessandro [Dipartimento di Fisica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin (Italy) and INFN, Sezione di Torino, Via Pietro Giuria 1, Turin (Italy)

2007-04-15

299

National Technical Information Service (NTIS)

Air blast wave measurements 1.1 m above ground have been made at distances 5.5 - 25 m from detonating 48 kg spherical Comp B/TNT charges suspended at 1.05 - 1.32 m over a plain ground surface. Pressure-time histories, peak pressures, durations and impulse...

K. Edin I. Aseborn

1988-01-01

300

NASA Astrophysics Data System (ADS)

In this report, we present a dynamical systems approach to study the exact nonlinear wave-particle interaction in relativistic regime. We give particular attention to the effect of wave obliquity on the dynamics of the orbits by studying the specific cases of parallel (?=0) and perpendicular (?=-?/2) propagations in comparison to the general case of oblique propagation ?=]-?/2,0[. We found that the fixed points of the system correspond to Landau resonance and that the dynamics can evolve from trapping to surfatron acceleration for propagation angles obeying a Hopf bifurcations condition. Cyclotron-resonant particles are also studied by the construction of a pseudo-potential structure in the Lorentz factor ?. We derived a condition for which Arnold diffusion results in relativistic stochastic acceleration. Hence, two general conclusions are drawn: (1) The propagation angle ? can significantly alter the dynamics of the orbits at both Landau and cyclotron-resonances. (2) Considering the short-time scales upon which the particles are accelerated, these two mechanisms for Landau and cyclotron resonant orbits could become potential candidates for problems of particle energization in collisionless space and cosmic plasmas.

Osmane, A.; Hamza, A. M.

2012-05-01

301

NASA Astrophysics Data System (ADS)

We study the nonlinear interaction between relativistic electrons and a coherent Electromagnetic Ion Cyclotron (EMIC) wave. We assume a coherent rising-tone emission as found in recent spacecraft observations of EMIC waves[1,2]. Considering the frequency variation, we derive the second-order resonance condition for interaction between a relativistic electron and a coherent EMIC wave[3]. The second-order resonance condition controlling nonlinear wave trapping of resonant electrons depends on an inhomogeneity factor S which is a function of the frequency sweep rate, the gradient of the magnetic field, and the wave amplitude. There occurs nonlinear trappin g of electrons by the wave potential, if |S|<1. A non-zero value of S induces very effective pitch angle scattering. When an EMIC triggered emission is generated near the equator and propagates toward the high latitude, both the spatial inhomogeneity and the rising-tone frequency result in enhanced precipitation of relativistic electrons with the time scale of EMIC triggered emission (tens of seconds), which is a possible cause of the relativistic electron microbursts observed at low altitudes. [1] J. S. Pickett,, B. Grison, Y. Omura, M. J. Engebretson, I. Dandouras, A. Masson, M. L. Adrian, O. Santolik, P. M. E. Decreau, N. Cornilleau-Wehrlin, and D. Constantinescu, Cluster observations of EMIC triggered emissions in association with Pc1 waves near Earth's plasmapause, Geophys. Res. Lett., 37, L09104, doi:10.1029/2010GL042648, 2010. [2] Y. Omura, J. S. Pickett, B. Grison, O. Santolik, I. Dandouras, M. Engebretson, P. M. E. Decreau, A. Masson, Theory and observation of electromagnetic ion cyclotron triggered emissions in the magnetosphere, J. Geophys. Res., 115, A07234, doi:10.1029/2010JA015300, 2010. [3] Y. Omura and Q. Zhao, Nonlinear pitch-angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere, J. Geophys. Res., in press.

Omura, Y.; Zhao, Q.

2012-12-01

302

Specific slow wave structures are needed in order to produce coherent Cherenkov radiation in overmoded relativistic generators. The electromagnetic characteristics of such slow wave, resonant, finite length structures commonly used in relativistic backward wave oscillators have been studied both experimentally and theoretically. In experiments, perturbation techniques were used to study both the fundamental and higher order symmetric transverse magnetic (TM) modes. Finite length effects lead to end reflections and quantization of the wave number. The effects of end reflections in open slow wave structures were found from the spectral broadening of the discrete resonances of the different axial modes. The measured axial and radial field distributions are in excellent agreement with the results of a 2-D code developed for the calculation of the fields in these structures.

Main, W. (ACCURAY, Inc., Santa Clara, CA (United States)); Carmel, Y.; Weaver, J. (Univ. of Maryland, College Park, MD (United States). Inst. for Plasma Research) (and others)

1994-10-01

303

NASA Astrophysics Data System (ADS)

Scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to be a major cause of relativistic electron precipitation (REP). This mechanism has also been proposed as the cause for REP observed by balloon-borne detectors predominantly in the dusk sector. Observations from the recent BARREL balloon campaign, along with simultaneous detailed spacecraft measurements of waves and plasma conditions, give us an unprecedented opportunity to investigate this mechanism. We simulate relativistic electron pitch-angle diffusion by EMIC waves using wave and particle data measured by GOES and the Van Allen Probes, and compare the energy distribution of the resulting precipitation with BARREL observations of precipitation made on January 17, 2013. This comparison sheds light on the role of EMIC waves in causing REP as well as the effectiveness of the quasi-linear model.

Li, Z.; Millan, R. M.; Hudson, M. K.; Woodger, L. A.; Fennell, J. F.; Engebretson, M. J.; MacDonald, E.

2013-12-01

304

0.14THz high power millimeter wave generation from a relativistic surface wave oscillator

In this paper, a novel overmoded surface wave oscillator (SWO) is proposed, and it could deliver an output power around 40 MW under the condition of 370 kV incident voltage at frequency of about 0.14 THz. The characteristics of surface wave and point operation are crucial to avoid the mode competition. Effects of various operating parameters on the device behavior

Hai Zhang; Jianguo Wang; Changjiang Tong

2008-01-01

305

Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A

NASA Technical Reports Server (NTRS)

Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from approx. 1.1 x 10(exp -6) solar mass of silicate grains radiating at a temperature of approx. 180+/-(15-20) K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard LMC dust abundances. This flux ratio has decreased by a factor of approx. 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization fluence of the soft X-ray emission component, and the evolution of IRX suggest that the radiating si1icate grains are immersed in a 3.5 x 10(exp 6) K plasma with a density of (0.3 - 1) x 10(exp 4)/cu cm, and have a size distribution that is confined to a narrow range of radii between 0.02 and 0.2 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.

Dwek, Eliahu; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, John; DeBuizer James M.; Gehrz, Robert D.; Kirshner, Robert P.; McCray, Richard; Park, Sangwok; Polomski, Elisha; Woodward, Charles

2007-01-01

306

Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear contributing little to the aetiology of the injury. PMID:2050704

Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

1991-01-01

307

Twin traveling-wave tube amplifiers driven by a relativistic backward-wave oscillator

Experiments demonstrate stable frequency and relative-phase angle output from twin traveling-wave tube (TWT) amplifiers driven with the redirected signal from a high-power backward-wave oscillator (BWO). The experimental X-band apparatus employs a single generator to produce three independent electron beams which simultaneously drive the BWO and TWT sources. The BWO spontaneously generates up to 14.1 MW peak, 25 to 15-ns long

Jennifer M. Butler; C. B. Wharton

1996-01-01

308

We study self-modulation and chaotic regimes of generation in a relativistic backward-wave oscillator in the presence of reflections of radiation from the boundaries of a slow-wave structure. The onset of self-modulation is examined in detail in the cases of weak and strong reflections. A numerical simulation of transition-to-chaos scenarios is performed over a wide range of parameters. The relation of

N. M. Ryskin; V. N. Titov

2001-01-01

309

During the interaction of a low-frequency relativistic soliton with the electron density modulations of a wake plasma wave, part of the electromagnetic energy of the soliton is reflected in the form of an extremely short and ultraintense electromagnetic pulse. We calculate the spectra of the reflected and of the transmitted electromagnetic pulses analytically. The reflected wave has the form of a single cycle attosecond pulse. PMID:15903585

Isanin, A V; Bulanov, S S; Kamenets, F F; Pegoraro, F

2005-03-01

310

NASA Astrophysics Data System (ADS)

In the new investigation of dust-ion acoustic (DIA) waves with negative dust charges and weakly relativistic ions and electrons in the plasma, compressive and rarefactive DIA solitons of interesting characters are established through the Korteweg-de Vries (KdV) equation. Eventually, the amplitudes of the compressive DIA solitons are found to be constant at some critical temperature ratio ? c (electron to ion temperature ratio) identifying some critical dust charge Z dc . It is predicted, that the reception of dust charges by the plasma particles at the variation of temperature starts functioning to the growth of compressive soliton's constant stage of amplitude after the state of critical ? c . The identification of critical dust charge (Z dc ) which is found to be very great for solitons of constant amplitudes becomes feasible for very small dust to ion density ratio (?). But it can be achieved, we observe, due to the relativistic increase in ion-density as in mass, which is also a salient feature of this investigation.

Kalita, B. C.; Das, Samiran

2014-05-01

311

General Relativistic Radiant Shock Waves in the Post-Quasistatic Approximation

NASA Astrophysics Data System (ADS)

An evolution of radiant shock wave front is considered in the framework of a recently presented method to study self-gravitating relativistic spheres, whose rationale becomes intelligible and finds full justification within the context of a suitable definition of the post-quasistatic approximation. The spherical matter configuration is divided into two regions by the shock and each side of the interface having a different equation of state and anisotropic phase. In order to simulate dissipation effects due to the transfer of photons and/or neutrinos within the matter configuration, we introduce the flux factor, the variable Eddington factor and a closure relation between them. As we expected the strong of the shock increases the speed of the fluid to relativistic ones and for some critical values is larger than light speed. In addition, we find that energy conditions are very sensible to the anisotropy, specially the strong energy condition. As a special feature of the model, we find that the contribution of the matter and radiation to the radial pressure are the same order of magnitude as in the mant as in the core, moreover, in the core radiation pressure is larger than matter pressure.

Rueda H, Jorge A.; Núñez, L. A.

2007-05-01

312

Electron acceleration in relativistic plasma waves generated by a single frequency short-pulse laser

Experimental evidence for the acceleration of electrons in a relativistic plasma wave generated by Raman forward scattering (SRS-F) of a single-frequency short pulse laser are presented. A 1.053 {mu}m, 600 fsec, 5 TW laser was focused into a gas jet with a peak intensity of 8{times}10{sup 17} W/cm{sup 2}. At a plasma density of 2{times}10{sup 19} cm{sup {minus}3}, 2 MeV electrons were detected and their appearance was correlated with the anti-Stokes laser sideband generated by SRS-F. The results are in good agreement with 2-D PIC simulations. The use of short pulse lasers for making ultra-high gradient accelerators is explored.

Coverdale, C.A.; Darrow, C.B.; Decker, C.D. [Lawrence Livermore National Lab., CA (United States); Mori, W.B.; Tzeng, K.C., Clayton, C.E.; Marsh, K.A.; Joshi, C. [California Univ., Los Angeles, CA (United States)

1995-04-27

313

Single-particle resonant states in spherical nuclei are studied by an analytic continuation in the coupling constant (ACCC) method within the framework of the self-consistent relativistic mean field (RMF) theory. Taking the neutron resonant state {nu}1g{sub 9/2} in {sup 60}Ca as an example, we examine the analyticity of the eigenvalue and eigenfunction for the Dirac equation with respect to the coupling constant by means of a Pade approximant of the second kind. The RMF-ACCC approach is then applied to {sup 122}Zr and, for the first time, this approach is employed to investigate both the energies, widths, and wave functions for l{ne}0 resonant states close to the continuum threshold. Predictions are also compared with corresponding results obtained from the scattering phase shift method.

Zhang, S.S. [School of Physics, Peking University, Beijing 100871 (China); Meng, J.; Zhou, S.G. [School of Physics, Peking University, Beijing 100871 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080 (China); Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China); Hillhouse, G.C. [Department of Physics, University of Stellenbosch, Private Bag X1, Matieland 7602 (South Africa); School of Physics, Peking University, Beijing 100871 (China)

2004-09-01

314

Investigation of an improved relativistic backward wave oscillator in efficiency and power capacity

NASA Astrophysics Data System (ADS)

Investigation of relativistic backward wave oscillator with high efficiency and power capacity is presented in this paper. To obtain high power and high efficiency, a TM021 mode resonant reflector is used to reduce the pulse shortening and increase power capacity to about 1.7 times. Meanwhile, an extraction cavity at the end of slow wave structure is employed to improve the efficiency from less than 30% to over 40%, through the beam-wave interaction intensification and better energy conversion from modulated electron beam to the electromagnetic field. Consistent with the numerical results, microwave with a power of 3.2 GW, a frequency of 9.75 GHz, and a pulse width of 27 ns was obtained in the high power microwave generation experiment, where the electron beam energy was configured to be ~910 kV and its current to be ~8.6 kA. The efficiency of the RBWO exceeds 40% at a voltage range of 870 kV-1000 kV.

Song, W.; Chen, C. H.; Sun, J.; Zhang, X. W.; Shao, H.; Song, Z. M.; Huo, S. F.; Shi, Y. C.; Li, X. Z.

2012-10-01

315

Investigation of an improved relativistic backward wave oscillator in efficiency and power capacity

Investigation of relativistic backward wave oscillator with high efficiency and power capacity is presented in this paper. To obtain high power and high efficiency, a TM{sub 021} mode resonant reflector is used to reduce the pulse shortening and increase power capacity to about 1.7 times. Meanwhile, an extraction cavity at the end of slow wave structure is employed to improve the efficiency from less than 30% to over 40%, through the beam-wave interaction intensification and better energy conversion from modulated electron beam to the electromagnetic field. Consistent with the numerical results, microwave with a power of 3.2 GW, a frequency of 9.75 GHz, and a pulse width of 27 ns was obtained in the high power microwave generation experiment, where the electron beam energy was configured to be {approx}910 kV and its current to be {approx}8.6 kA. The efficiency of the RBWO exceeds 40% at a voltage range of 870 kV-1000 kV.

Song, W.; Chen, C. H.; Sun, J.; Zhang, X. W.; Shao, H.; Song, Z. M.; Huo, S. F.; Shi, Y. C.; Li, X. Z. [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024 (China)

2012-10-15

316

Electron acceleration to relativistic energies at a strong quasi-parallel shock wave

NASA Astrophysics Data System (ADS)

Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks. Furthermore, the acceleration led to electrons at relativistic energies (~MeV), comparable to the highest energies ever attributed to shock-acceleration in the solar wind. These observations suggest that at high-Mach numbers, like those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators.

Masters, Adam; Stawarz, Lukasz; Fujimoto, Masaki; Schwartz, Steve; Sergis, Nick; Thomsen, Michelle; Retino, Alessandro; Hasegawa, Hiroshi; Zieger, Bertalan; Lewis, Gethyn; Coates, Andrew; Canu, Patrick; Dougherty, Michele

2013-04-01

317

Electron acceleration to relativistic energies at a strong quasi-parallel shock wave

NASA Astrophysics Data System (ADS)

Electrons can be accelerated to ultrarelativistic energies at strong (high Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock-surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks. Furthermore, the acceleration led to electrons at relativistic energies (about megaelectronvolt), comparable to the highest energies ever attributed to shock acceleration in the solar wind. These observations suggest that at high Mach numbers, such as those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators.

Masters, A.; Stawarz, L.; Fujimoto, M.; Schwartz, S. J.; Sergis, N.; Thomsen, M. F.; Retinò, A.; Hasegawa, H.; Zieger, B.; Lewis, G. R.; Coates, A. J.; Canu, P.; Dougherty, M. K.

2013-03-01

318

The experimental investigation described in this dissertation demonstrates the feasibility of generating long (>=50 nsec) pulses of high-power (>=100 MW), X-band frequency microwaves. In these experiments, a relativistic Backward Wave Oscillator (BWO) is used in tandem with a Traveling Wave Tube (TWT) amplifier to generate microwave radiation. The tandem BWO-TWT system is driven in the TM_{01 } mode by a

Gilberto Barreto

1992-01-01

319

The stationary state with magnetically trapped particles is investigated at the saturation of the relativistic Weibel instability, within the “multiring” model in a Hamiltonian framework. The multistream model and its multiring extension have been developed in Paper I, under the assumption that the generalized canonical momentum is conserved in the perpendicular direction. One dimensional relativistic Bernstein-Greene-Kruskal waves with deeply trapped particles are addressed using similar mathematical formalism developed by Lontano et al.[Phys. Plasmas 9, 2562 (2002); Phys. Plasmas 10, 639 (2003)] using several streams and in the presence of both electrostatic and magnetic trapping mechanisms.

Ghizzo, A. [Institut Jean Lamour UMR 7163, Université de Lorraine, BP 239 F-54506 Vandoeuvre les Nancy (France)] [Institut Jean Lamour UMR 7163, Université de Lorraine, BP 239 F-54506 Vandoeuvre les Nancy (France)

2013-08-15

320

By using a quasi-optical approach, we study propagation of evanescent waves along a periodically corrugated surface and their excitation by relativistic electron beams. Under assumption of a shallow (in the scale of period) corrugation, the dispersion equation for normal waves is derived and two particular cases are studied. In the first case, the wave frequency is far from the Bragg resonance; therefore, the evanescent wave propagation can be described by using the impedance approximation with deceleration of the zeroth spatial harmonic. The second case takes place at the frequencies close to the Bragg resonance. There, the field can be represented as two counter-propagating quasi-optical wave beams, which are coupled on the corrugated surface and form an evanescent normal wave. With regard to the interaction with an electron beam, the first case corresponds to the convective instability that can be used for amplification of radiation, while the second case corresponds to the absolute instability used in surface-wave oscillators. This paper is focused on studying main features of amplifier schemes, such as the increments, electron efficiency, and formation of a self-consistent spatial structure of the radiated field. For practical applications, the feasibility of realization of relativistic surface-wave amplifiers in the submillimeter wavelength range is estimated.

Ginzburg, N. S.; Malkin, A. M.; Zheleznov, I. V.; Sergeev, A. S. [Institute of Applied Physics of the Russian Academy of Sciences, 46, Ul'yanov St., Nizhny Novgorod (Russian Federation)] [Institute of Applied Physics of the Russian Academy of Sciences, 46, Ul'yanov St., Nizhny Novgorod (Russian Federation)

2013-06-15

321

The authors report measurement data on seismic waves in bulk blasting at quarries by using new high-precise electronic and\\u000a pyrotechnic blasting systems. It is proved that both systems are efficient, intensity of seismic waves is much lower in large-scale\\u000a bulk blasting. The authors implemented numerical modeling of seismic wave propagation under a short-delay bulk blast at a\\u000a quarry. Influence of

E. N. Sher; A. G. Chernikov

2009-01-01

322

Why galactic gamma-ray bursts might depend on environment: Blast waves around neutron stars

NASA Technical Reports Server (NTRS)

Although galactic models for gamma-ray bursts are hard to reconcile with the isotropy data, the issue is still sufficiently open that both options should be explored. The most likely 'triggers' for bursts in our Galaxy would be violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to expel magnetic flux and plasma at relativistic speed. Such ejecta would be braked by the interstellar medium (ISM), and a gamma-ray flash may result from this interaction. The radiative efficiency, of this mechanism would depend on the density of the circumstellar ISM. Therefore, even if neutron stars were uniformly distributed in space (at least within 1-2 kpc of the Sun), the observed locations of bursts would correlate with regions of above-average ISM density.

Rees, Martin J.; Meszaros, Peter; Begelman, Mitchell C.

1994-01-01

323

NASA Astrophysics Data System (ADS)

A klystron-like relativistic backward wave oscillator with a ratio of transverse dimension to free-space wavelength being about four is presented. In the beam-wave interaction region, the electron beam interacts with surface wave and volume wave simultaneously. The cathode holder plays an important role in the reflection of backward waves. A guard electrode, an electron collector ring, and a reflection ring are used to optimize the beam-wave interaction. The particle in cell simulation results reveal that microwaves with a power of 2 GW and a frequency of 12.3 GHz are generated with an efficiency of 42% when the diode voltage is 400 kV, the beam current 12 kA, and the magnetic field 0.48 T.

Xiao, Renzhen; Tan, Weibing; Li, Xiaoze; Song, Zhimin; Sun, Jun; Chen, Changhua

2012-09-01

324

In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5-10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.

Xiao Renzhen; Zhang Xiaowei; Zhang Ligang; Li Xiaoze; Zhang Lijun [National Key Laboratory of Science and Technology on High Power Microwave, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2012-07-15

325

A dual-frequency coaxial relativistic backward-wave oscillator with a modulating resonant reflector

NASA Astrophysics Data System (ADS)

An X-band dual-frequency coaxial relativistic backward-wave oscillator with a modulating resonant reflector is presented and investigated in this paper. Through a theoretical study, numerical analysis and particle-in-cell (PIC) simulation, the stationary single-frequency regime is selected as the operation regime, and the high-frequency characteristics of the system, including the unstable beam-wave interaction regions and operation mode of each section, are obtained. The PIC simulation results indicate that an average power of 1.07 GW with a power conversion efficiency of 24.2% is obtained with an electron beam of 520 kV and 8.5 kA guided by an axial magnetic field of 2.4 T, and the two dominant frequencies are 9.43 and 10.30 GHz, respectively. Furthermore, a periodic-like change in the smaller dominant frequency with a frequency agility bandwidth of about 0.40 GHz is acquired.

Tang, Yongfu; Meng, Lin; Li, Hailong; Zheng, Ling; Yin, Yong; Wang, Bin

2012-05-01

326

NASA Astrophysics Data System (ADS)

In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5-10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.

Xiao, Renzhen; Zhang, Xiaowei; Zhang, Ligang; Li, Xiaoze; Zhang, Lijun

2012-07-01

327

On plane-wave relativistic electrodynamics in plasmas and in vacuum

NASA Astrophysics Data System (ADS)

We revisit the exact microscopic equations (in differential, and equivalent integral form) ruling a relativistic cold plasma after the plane-wave Ansatz, without customary approximations. We show that in the Eulerian description the motion of a very diluted plasma initially at rest and excited by an arbitrary transverse plane electromagnetic travelling-wave has a very simple and explicit dependence on the transverse electromagnetic potential; for a non-zero density plasma the above motion is a good approximation of the real one as long as the back-reaction of the charges on the electromagnetic field can be neglected, i.e. for a time lapse decreasing with the plasma density, and can be used as initial step in an iterative resolution scheme. As one of many possible applications, we use these results to describe how the ponderomotive force of a very intense and short plane laser pulse hitting normally the surface of a plasma boosts the surface electrons into the ion background. In response to this penetration, the electrons are pulled back by the electric force exerted by the ions and the other displaced electrons and may leave the plasma with high energy in the direction opposite to that of propagation of the pulse ‘slingshot effect’ (Fiore G et al 2013 arXiv:1309.1400).

Fiore, Gaetano

2014-06-01

328

Dual-band relativistic backward wave oscillators based on a single beam and dual beams

NASA Astrophysics Data System (ADS)

Two types of relativistic backward wave oscillators (RBWOs) used to produce dual-band microwaves are proposed and investigated by use of the particle-in-cell (PIC) simulation code KARAT [V. P. Tarakanov, User's Manual for Code Karat (Berkeley Research Associates, Springfield, VA, 1992)]. The first type of RBWO, for generation of C-band and X-band microwaves, is designed based on a single beam and a sectioned structure. With an electron beam of 650 keV and 5.0 kA guided by a magnetic field of 2.0 T, an average power of 380 MW with a total power conversion efficiency of 11.7% is obtained and the frequencies are 5.48 and 9.60 GHz, respectively. By changing the distance between the two sections, single-band oscillations are realized with higher power conversion efficiency than that of the dual-band oscillation. The second type, based on a coaxial structure and dual parallel annular beams, is a dual-band RBWO designed with separated beam-wave interaction regions for generation of C-band and X-band microwaves. With a dual beam of 650 keV and 11.8 kA (the outer beam current is 6.4 kA and inner beam current is 5.4 kA) guided by a magnetic field of 2.0 T, an output power of 1400 MW with a total power conversion efficiency of 18.3% is generated and the frequencies are 4.60 and 8.40 GHz, respectively. PIC simulations demonstrate that the two beam-wave interaction regions operate independently. The two types of dual-band RBWO are also compared and analyzed.

Ting, Wang; Jian-de, Zhang; Bao-Liang, Qian; Xiao-Ping, Zhang

2010-04-01

329

NASA Astrophysics Data System (ADS)

In this work, we examine the hydrodynamics of high-energy-density (HED) shear flows. Experiments, consisting of two materials of differing density, use the OMEGA-60 laser to drive a blast wave at a pressure of ˜50 Mbar into one of the media, creating a shear flow in the resulting shocked system. The interface between the two materials is Kelvin-Helmholtz unstable, and a mixing layer of growing width develops due to the shear. To theoretically analyze the instability's behavior, we rely on two sources of information. First, the interface spectrum is well-characterized, which allows us to identify how the shock front and the subsequent shear in the post-shock flow interact with the interface. These observations provide direct evidence that vortex merger dominates the evolution of the interface structure. Second, simulations calibrated to the experiment allow us to estimate the time-dependent evolution of the deposition of vorticity at the interface. The overall result is that we are able to choose a hydrodynamic model for the system, and consequently examine how well the flow in this HED system corresponds to a classical hydrodynamic description.

Di Stefano, C. A.; Malamud, G.; Henry de Frahan, M. T.; Kuranz, C. C.; Shimony, A.; Klein, S. R.; Drake, R. P.; Johnsen, E.; Shvarts, D.; Smalyuk, V. A.; Martinez, D.

2014-05-01

330

Gravitational waves and the deformation of compact objects: Topics in relativistic astrophysics

NASA Astrophysics Data System (ADS)

In this dissertation, we present various theoretical investigations of sources of gravitational waves, relevant to interpreting the data from current and planned gravitational wave detectors; an idee fixe is the deformation of compact objects. We begin in the strong field, vacuum regime, with a construction of initial data for the numerical simulation of black hole binaries (specializing to the case of nonspinning holes in a quasicircular orbit). The data we construct contain more of the binary's expected physics than any other current data set. In particular, they contain both the binary's outgoing radiation and the expected tidal deformations of the holes. Such improved initial data will likely be necessary for simulations to achieve the accuracy required to supply advanced gravitational wave detectors with templates for parameter estimation. We end in the weak field, hydrodynamic regime with a calculation of the expected accuracy with which one can combine standard electromagnetic and gravitational wave observations of white dwarf binaries to measure the masses of the binary's components. In particular, we show that this measurement will not be contaminated by finite size effects for realistic sources observed by LISA, though such effects could be important for exceptional sources and/or advanced mHz gravitational wave detectors. In the middle, we make a detour into the messy and poorly constrained realm of the physics of neutron star interiors, calculating the shear modulus of hadron--quark mixed phase in hybrid stars. Here we include a rough treatment of charge screening, dimensional continuation of the lattice, and the contributions from changing the cell volume when shearing lowerdimensional lattices. We find that the last of these contributions is necessary to stabilize the lattice for those dimensions, where it makes a considerable contribution to the shear modulus. We then move back to sounder theoretical footing in making a general relativistic calculation of the maximum elastic quadrupole deformation that could be sustained by a star with a known shear modulus and breaking strain (provided by, e.g., the hadron--quark mixed phase in the core, or the more standard lattice of nuclei in the crust). We find that the standard Newtonian calculation considerably overestimates the quadrupole, particularly for massive, compact stars. We also present the dimensionally continued Poisson summation formula we discovered while performing the shear modulus calculation, and thought interesting enough to prove rigorously. Our method of proof also provides a new way of proving other (Voronoi) summation formulae obtained from functions satisfying modular transformations, and allows one to relax certain of the standard hypotheses.

Johnson-McDaniel, Nathan Kieran

331

Circularly polarized electric fields associated with seismic waves generated by blasting

NASA Astrophysics Data System (ADS)

Electric field variations coincident with the passage of seismic waves are commonly observed irrespective of whether the seismic events are natural or artificial. We present 10 examples of electric field variations obtained for artificial seismic waves whose typical frequency is a few times higher than that of natural seismic waves. In several cases, the electric fields showed left- and/or right-handed circular polarization, indicating the motion of ions with positive and/or negative electric charge, respectively, generated by ground motion in the Earth's magnetic field. In three cases, we have estimated transfer functions relating the electric field to the ground velocity. Furthermore, we have performed time-frequency analysis with the continuous wavelet transform and have constructed spectrograms of the electric field and ground velocity. In both results, we have found some peaks at the specific frequencies where the resonance of the motion of ions in groundwater with the Earth's magnetic field is expected, thereby supporting the proposed mechanism in terms of the seismic dynamo effect.

Matsushima, Masaki; Honkura, Yoshimori; Kuriki, Mayu; Ogawa, Yasuo

2013-07-01

332

A fully relativistic distorted-wave program is developed based on the Grasp92 and Ratip packages to calculate electron impact excitation (EIE) cross sections. As a first application of the program, the EIE cross sections of Be-like C2+ ions from the metastable 1s22s2p 3P to 1s22p2 3P excitation and the inner-shell excitations are calculated systematically. Meanwhile, the correlation effects of target states

Jun Jiang; Chen-Zhong Dong; Lu-You Xie; Jian-Guo Wang; Jun Yan; Fritzsche Stephan

2007-01-01

333

Summary form only given. A great deal has been learned regarding the operation of intense relativistic electron beam-driven backward wave oscillators (BWO's) over the last few years. The issue of pulse shortening seems to be better understood, although its complete remediation has yet to be demonstrated. The energies radiated in X-band have yet to reach the kiloJoule level, although reliable

E. Schamiloglu; F. Hegeler; C. T. Abdallah; K. Hahn; S. Choi

2000-01-01

334

A dual-band relativistic backward wave oscillator with dual electron beams generating C-band and X-band microwaves is investigated experimentally. The frequencies, powers, and radiation patterns of the dual-band microwaves are measured. With the diode voltage of 657 kV and the total beam current of 14 kA guided by a magnetic field of about 1.7 T, the dual-band microwaves are generated with dominant frequencies of 4.58 and 8.30 GHz close to the results from the particle-in-cell simulation. The powers of the C-band and X-band microwaves are 520 and 113 MW, respectively. The effects of variations in the guiding magnetic field and diode voltage on the powers of the dual-band microwaves are presented and discussed. The radiation patterns of the dual-band microwaves from the radiating antenna are tested both corresponding to a TM{sub 01} mode and the independency of the operation processes of them is discussed.

Wang Ting; Qian Baoliang; Zhang Jiande; Zhang Xiaoping; Cao Yibing; Zhang Qiang [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2011-01-15

335

High-power traveling wave tubes powered by a relativistic electron beam

This thesis presents the results of a high power traveling wave tube a high power, rippled wall waveguide TWT powered by a relativistic electron beam. Initially, the amplifiers consisted of a single section of slow wave structure. Two TWT's of this type were used, with lengths of 11 and 22 periods. These single state tubes were linear and operated in the Tm{sub 01} mode at maximum gains of 33 dB and bandwidths on order of 20 MHz centered at 8.76 GHz. The maximum efficiency was 11% corresponding to an output power of 110 MW. Below beam currents of 1.4 kA, the single stage tubes were monochromatic and phase stable to within {plus minus}8{degree}; however, above this current, a sideband-like structure developed in the frequency spectrum. The two sidebands were unequally displaced from the center frequency. As the current was increased still further to 1.6 kA, the single stage amplifier oscillated due to positive feedback arising from reflections at the exit taper of the TWT. At this point, the TWT was no longer useful as an amplifier. To reduce the positive feedback and stop the oscillations, the author severed the amplifier. Two different lengths of sever were used, the shorter of the two having the highest gain. The shorter sever saturated at 975 A, with a total gain of 37 dB and total power output of 410 MW. Beyond this current, the tube was no longer linear with respect to the input power. The bandwidth of severed tube was about 100 MHz centered at 8.76 GHz. The severed amplifiers showed the sideband-like behavior at all the beam currents used. The sideband frequency separation from the center frequency increased with beam current.

Shiffler, D.A. Jr.

1991-01-01

336

NASA Astrophysics Data System (ADS)

In a klystron-like relativistic backward wave oscillator, the velocity modulation is mainly obtained from the resonant reflector. By introducing two pre-modulation cavities between the input cavity and the resonant reflector, the amplitude and phase of density modulation can be adjusted relatively independently, to ensure an improved fundamental harmonic current distribution. Two peaks of harmonic current with high modulation coefficient of 1.2 appear in the second slow wave structure and the dual-cavity extractor and result in large beam energy losses in both regions. Particle-in-cell simulations show that a microwave with power of 11.5 GW and efficiency of 57% can be obtained.

Xiao, Renzhen; Chen, Changhua; Zhang, Xiaowei

2013-04-01

337

Relativistic treatment of pion wave functions in the annihilation pp{yields}{pi}{sup -}{pi}{sup +}

Quark model intrinsic wave functions of highly energetic pions in the reaction pp{yields}{pi}{sup -}{pi}{sup +} are subjected to a relativistic treatment. The annihilation is described in a constituent quark model with A2 and R2 flavor-flux topology, and the annihilated quark-antiquark pairs are in {sup 3}P{sub 0} and {sup 3}S{sub 1} states. We study the effects of pure Lorentz transformations on the antiquark and quark spatial wave functions and their respective spinors in the pion. The modified quark geometry of the pion has considerable impact on the angular dependence of the annihilation mechanisms.

El-Bennich, B.; Kloet, W.M. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019 (United States)

2004-09-01

338

NASA Astrophysics Data System (ADS)

The propagation of small amplitude nonlinear electrostatic waves in weakly relativistic e-p-i plasma is investigated. The basic set of fluid equations are reduced to a Korteweg-de-Vries (K-dV) equation coupled to a linear inhomogeneous equation for the first and second-order perturbed potential corrections, respectively. The system is solved via a renormalization method. It is shown that to increase the ratio of the positron to the electron density (p = np,0/ne,0), the ratio of the ion temperature to the electron temperature (? = Ti/Te) the amplitude and width ion acoustic waves increases. The higher-order nonlinearity effects also investigated.

Mehdipoor, M.

2011-12-01

339

NASA Astrophysics Data System (ADS)

A new concept of the development of plasma compressor for generation of extremely short, relativistically strong femtosecond pulses at a petawatt power level is proposed. The considered compression mechanism is based on the non-stationary self-focusing of a spatially confined wave packet in transparent plasma during the excitation of a plasma wake wave with a period exceeding the laser pulse duration. It is shown that by using appropriately shaped, strong short laser pulses even shorter pulses (with durations up to one optical cycle of the field) can be generated with intensities much greater (>10 times) than the incident pulse with a significant fraction (?25%) of incident pulse energy.

Balakin, A. A.; Litvak, A. G.; Mironov, V. A.; Skobelev, S. A.

2012-11-01

340

NASA Astrophysics Data System (ADS)

The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev's pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters.

Sahu, Biswajit; Singha, Prasenjit

2013-06-01

341

NASA Astrophysics Data System (ADS)

In this communication, the combined effect of relativistic and ponderomotive nonlinearities on the generation of electron plasma wave by cross focusing of two intense laser beams at difference frequency ( ?? ? ? 1 - ? 2 ? ? p) and acceleration of electrons in laser produced homogeneous plasma is analysed in the non-paraxial region. On account of these nonlinearities, two laser beams affect the dynamics of each other, and cross focusing takes place. It is observed that the focusing of laser beams becomes fast in the non-paraxial region by expanding the eikonal and other relevant quantities up to the fourth power of the radial distance ( r). Modified coupled equations for the beam width of laser beams, electric field amplitude of the excited electron plasma wave and energy gain at beat wave frequency are derived, when relativistic and ponderomotive nonlinearities are operative. These coupled equations are solved analytically and numerically to study the cross focusing of two intense laser beams in plasma and its effect on the variation of the amplitude of the electron plasma wave and energy gain. It is observed from the results that both nonlinearities significantly affect the amplitude of plasma wave excitation and particle acceleration in the non-paraxial region in comparison to the paraxial region.

Rawat, Priyanka; Singh, Ram Kishor; Sharma, Ram Pal; Purohit, Gunjan

2014-03-01

342

Controlling blast wave generation in a shock tube for biological applications

NASA Astrophysics Data System (ADS)

The shock tube is a versatile apparatus used in a wide range of scientific research fields. In this case, we are developing a system to use with biological specimens. The process of diaphragm rupture is closely linked to the shock wave generated. Experiments were performed on an air-driven shock tube with Mylar® and aluminium diaphragms of various thicknesses, to control the output. The evolution of shock pressure was measured and the diaphragm rupture process investigated. Single-diaphragm and double-diaphragm configurations were employed, as were open or closed tube configurations. The arrangement was designed to enable high-speed photography and pressure measurements. Overall, results are highly reproducible, and show that the double-diaphragm system enables a more controllable diaphragm burst pressure. The diaphragm burst pressure was linearly related to its thickness within the range studied. The observed relationship between the diaphragm burst pressure and the generated shock pressure presents a noticeable difference compared to the theoretical ideal gas description. Furthermore, the duration of the primary shock decreased proportionally with the length of the high-pressure charging volume. Computational modelling of the diaphragm breakage process was carried out using the ANSYS software package.

Nguyen, T.-T. N.; Wilgeroth, J. M.; Proud, W. G.

2014-05-01

343

NASA Astrophysics Data System (ADS)

study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of >0.7 MeV electrons nor reductions in Van Allen Probe 90° pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90°. For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultrarelativistic (~2-8 MeV) electron loss but which is confined to pitch angles below around 45° and not affecting the core distribution.

Usanova, M. E.; Drozdov, A.; Orlova, K.; Mann, I. R.; Shprits, Y.; Robertson, M. T.; Turner, D. L.; Milling, D. K.; Kale, A.; Baker, D. N.; Thaller, S. A.; Reeves, G. D.; Spence, H. E.; Kletzing, C.; Wygant, J.

2014-03-01

344

Filamentation Instability of Ion Acoustic Waves Driven by a Scattered Relativistic Beam.

National Technical Information Service (NTIS)

Ion-acoustic instability driven by a scattered relativistic beam propagating in a plasma of hot electrons and cold ions is investigated. We have derived a fully electromagnetic dispersion relation and its cold beam limit and discussed the general features...

H. Lee M. E. Jones

1983-01-01

345

The effect of an electric field E{sub ||} parallel to the magnetic field B on particle acceleration in shock waves is studied. With test particle calculations, for which the electromagnetic fields of shock waves are obtained from one-dimensional, fully kinetic, electromagnetic, particle simulations, the motions of relativistic ions, electrons, and positrons are analyzed. In these simulations, the shock speed v{sub sh} is taken to be close to c cos {theta}, where {theta} is the angle between the external magnetic field and wave normal, and thus strong particle acceleration takes place. Test particle motions calculated in two different methods are compared: In the first method the total electric field E is used in the equation of motion, while in the second method E{sub ||} is omitted. The comparison confirms that in the acceleration of relativistic ions E{sub ||} is unimportant for high-energy particles. For the acceleration of electrons and positrons, however, E{sub ||} is essential.

Takahashi, Seiichi; Kawai, Hiromasa; Ohsawa, Yukiharu [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan); Usami, Shunsuke [National Institute for Fusion Science, Toki 509-5292 (Japan); Chiu, Charles; Horton, Wendell [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2009-11-15

346

NASA Astrophysics Data System (ADS)

The effect of passive compression of frequency-modulated pulses in dispersive media is used to raise the microwave radiation peak power to a multigigawatt level. A waveguide with a helically corrugated surface is applied as a dispersive medium, and a relativistic 3-cm backward-wave oscillator with an accelerating voltage decaying within the pulse duration serves as a source of frequency-modulated pulses. The compression of pulses to an FWHM of 2.2 ns attended by a rise in the peak power by a factor of 4.5 (to 3.2 GW) is demonstrated with a SINUS-6 accelerator.

Bratman, V. L.; Denisov, G. G.; Kolganov, N. G.; Mishakin, S. V.; Samsonov, S. V.; Sobolev, D. I.

2011-02-01

347

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.

Moir, D.C.; Faehl, R.J.; Newberger, B.S.; Thode, L.E.

1981-01-01

348

NASA Astrophysics Data System (ADS)

We present results from a new set of three-dimensional general-relativistic hydrodynamic simulations of rotating iron core collapse. We assume octant symmetry and focus on axisymmetric collapse, bounce, the early postbounce evolution, and the associated gravitational wave (GW) and neutrino signals. We employ a finite-temperature nuclear equation of state, parametrized electron capture in the collapse phase, and a multispecies neutrino leakage scheme after bounce. The latter captures the important effects of deleptonization, neutrino cooling and heating and enables approximate predictions for the neutrino luminosities in the early evolution after core bounce. We consider 12-M? and 40-M? presupernova models and systematically study the effects of (i) rotation, (ii) progenitor structure, and (iii) postbounce neutrino leakage on dynamics, GW, and neutrino signals. We demonstrate that the GW signal of rapidly rotating core collapse is practically independent of progenitor mass and precollapse structure. Moreover, we show that the effects of neutrino leakage on the GW signal are strong only in nonrotating or slowly rotating models in which GW emission is not dominated by inner core dynamics. In rapidly rotating cores, core bounce of the centrifugally deformed inner core excites the fundamental quadrupole pulsation mode of the nascent protoneutron star. The ensuing global oscillations (f˜700-800Hz) lead to pronounced oscillations in the GW signal and correlated strong variations in the rising luminosities of antineutrino and heavy-lepton neutrinos. We find these features in cores that collapse to protoneutron stars with spin periods ?2.5ms and rotational energies sufficient to drive hyperenergetic core-collapse supernova explosions. Hence, GW or neutrino observations of a core-collapse event could deliver strong evidence for or against rapid core rotation. Joint GW+neutrino observations would allow one to make statements with high confidence. Our estimates suggest that the GW signal should be detectable throughout the Milky Way by advanced laser-interferometer GW observatories, but a water-Cherenkov neutrino detector would have to be of near-megaton size to observe the variations in the early neutrino luminosities from a core collapse event at 1 kpc.

Ott, C. D.; Abdikamalov, E.; O'Connor, E.; Reisswig, C.; Haas, R.; Kalmus, P.; Drasco, S.; Burrows, A.; Schnetter, E.

2012-07-01

349

NASA Astrophysics Data System (ADS)

Within the framework of a quasi-optical approach, we develop 2D and 3D self-consistent theory of relativistic surface-wave oscillators. Presenting the radiation field as a sum of two counter-propagating wavebeams coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Dispersion characteristics of the evanescent wave following from this method are in good compliance with those found from the direct cst simulations. Considering excitation of the slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction, which allows us to determine oscillation threshold conditions, electron efficiency, and output coupling. The transition from the model of surface-wave oscillator operating in the ?-mode regime to the canonical model of relativistic backward wave oscillator is considered. We also described a modified scheme of planar relativistic surface-wave oscillators exploiting two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from a wide sheet rectilinear electron beam allowing realization of a Cherenkov millimeter-wave oscillators with subgigawatt output power level.

Ginzburg, N. S.; Malkin, A. M.; Sergeev, A. S.; Zaslavsky, V. Yu.

2013-11-01

350

Within the framework of a quasi-optical approach, we develop 2D and 3D self-consistent theory of relativistic surface-wave oscillators. Presenting the radiation field as a sum of two counter-propagating wavebeams coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Dispersion characteristics of the evanescent wave following from this method are in good compliance with those found from the direct cst simulations. Considering excitation of the slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction, which allows us to determine oscillation threshold conditions, electron efficiency, and output coupling. The transition from the model of surface-wave oscillator operating in the ?-mode regime to the canonical model of relativistic backward wave oscillator is considered. We also described a modified scheme of planar relativistic surface-wave oscillators exploiting two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from a wide sheet rectilinear electron beam allowing realization of a Cherenkov millimeter-wave oscillators with subgigawatt output power level.

Ginzburg, N. S.; Zaslavsky, V. Yu. [Nizhny Novgorod State University, 23 Gagarin Ave., Nizhny Novgorod 603950 (Russian Federation) [Nizhny Novgorod State University, 23 Gagarin Ave., Nizhny Novgorod 603950 (Russian Federation); Institute of Applied Physics of Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod 603950 (Russian Federation); Malkin, A. M.; Sergeev, A. S. [Institute of Applied Physics of Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod 603950 (Russian Federation)] [Institute of Applied Physics of Russian Academy of Sciences, 46 Ulyanov St., Nizhny Novgorod 603950 (Russian Federation)

2013-11-15

351

BlastSim — Multi agent simulation of suicide bombing

This paper introduces BlastSim - physics based stationary multi-agent simulation of blast waves and its impact on human body. The agents are constrained by physical characteristics and mechanics of blast wave. The simulation is capable of assessing the impact of crowd formation patterns on the magnitude of injury and number of casualties during a suicide bombing attack. It also examines

Zeeshan-ul-hassan Usmani; Fawzi A. Alghamdi; Daniel Kirk

2009-01-01

352

Note: A table-top blast driven shock tube

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient

Michael W. Courtney; Amy C. Courtney

2010-01-01

353

NASA Astrophysics Data System (ADS)

With the efficiency increase of a klystron-like relativistic backward wave oscillator, the maximum axial electric field and harmonic current simultaneously appear at the end of the beam-wave interaction region, leading to a highly centralized energy exchange in the dual-cavity extractor and a very high electric field on the cavity surface. Thus, we present a method of distributed energy extraction in this kind of devices. Particle-in-cell simulations show that with the microwave power of 5.1 GW and efficiency of 70%, the maximum axial electric field is decreased from 2.26 MV/cm to 1.28 MV/cm, indicating a threefold increase in the power capacity.

Xiao, Renzhen; Chen, Changhua; Cao, Yibing; Sun, Jun

2013-12-01

354

NASA Astrophysics Data System (ADS)

A solution is given for the problem of the angular and spectral distributions of incoherent radiation emitted by relativistic charges that are driven by a strong, plane electromagnetic vacuum wave of elliptic polarization, using the asymptotic technique of Bleistein (1967) and Ursell (1972) to yield an approximation to the pertinent cross section that is uniformly valid for (1) arbitrary charged particle initial momentum, (2) arbitrary intensity and polarization of the incident strong wave, (3) arbitrary observational direction, and (4) over the entire range of the incident frequency's high harmonics. A reexamination of the main steps of the method's derivation shows that the method holds promise for the quantitative analysis of astrophysical radiation processes more general than the one considered.

Leubner, C.

1982-02-01

355

NASA Astrophysics Data System (ADS)

Previous studies on electromagnetic ion cyclotron (EMIC) waves as a possible cause of relativistic electron precipitation (REP) mainly focus on the time evolution of the trapped electron flux. However, directly measured by balloons and many satellites is the precipitating flux as well as its dependence on both time and energy. Therefore, to better understand whether pitch angle scattering by EMIC waves is an important radiation belt electron loss mechanism and whether quasi-linear theory is a sufficient theoretical treatment, we simulate the quasi-linear wave-particle interactions for a range of parameters and generate energy spectra, laying the foundation for modeling specific events that can be compared with balloon and spacecraft observations. We show that the REP energy spectrum has a peaked structure, with a lower cutoff at the minimum resonant energy. The peak moves with time toward higher energies and the spectrum flattens. The precipitating flux, on the other hand, first rapidly increases and then gradually decreases. We also show that increasing wave frequency can lead to the occurrence of a second peak. In both single- and double-peak cases, increasing wave frequency, cold plasma density or decreasing background magnetic field strength lowers the energies of the peak(s) and causes the precipitation to increase at low energies and decrease at high energies at the start of the precipitation.

Li, Zan; Millan, Robyn M.; Hudson, Mary K.

2013-12-01

356

Relativistic distorted-wave calculation of electron scattering from alkali atoms

In electron scattering from alkali atom systems, the distortion of the target atom by the incident electron plays a important role and is represented by a polarization potential. The perturbative formulation (Temkin 1959) works well for systems with moderate polarizability such as the ground states of noble gases. A simple non-relativistic non-perturbative method was developed for the alkali atoms and

Weixing Ji

2002-01-01

357

Relativistic Distorted-Wave Calculation of Electron Impact Excitation of Xenon

It is generally expected that relativistic effects become important in electron-atom scattering as the atomic number of the target increases. For electron impact excitation of atoms, experimental techniques for observations of, in coincidence, both the scattered electron and the emitted photon when the excited atom decays, have been growing rapidly. Collisional alignment and orientation parameters determined by these electron-photon coincidence

Tao Zuo

1991-01-01

358

NASA Technical Reports Server (NTRS)

We have used the Spitzer satellite to monitor the laid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output, is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from approximately 180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of 5 x 10(exp 6) K and approximately 3 x 10(exp 4) per cubic centimeter, respectively. The mass of the radiating dust is approximately 1.2 x 10(exp -6) solar mass on day 7554, and scales linearly with IR flux. Comparison of the IR data with the soft X-ray flux derived from Chandra observations shows that the IR-to-X-ray flux ratio, IRX, is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of IRX is most consistent with the scenario that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased by a factor of approximately 5 with a time dependence of t(sup '0.87 plus or minus 0.20), t' being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER, as also suggested by X-ray observations. The constant spectral shape of they IR, emission provides strong constraints on the density and temperature of the shocked gas in which the interaction takes place. The IR spectra also suggest the presence of a secondary population of very small, hot (T greater than or equal to 350 K), featureless dust. If these grains spatially coexists with the silicates, then they must have shorter lifetimes. The data show slightly different rates of increase of their respective fluxes, lending some support to this hypothesis. However, the origin of this emission component and the exact nature of its relation to the silicate emission is still a major unsolved puzzle.

Dwek, Eli; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, I. John; De Buizer, James M.; Gehrz, Robert D.; Park, Sangwook; Polomski, Elisha F.; Slavin, Jonathan D.; Woodward, Charles E.

2010-01-01

359

NASA Astrophysics Data System (ADS)

Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3-12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (?e/?B ˜ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R-2. Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s-1, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (˜1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ?e/?B.

Horesh, Assaf; Stockdale, Christopher; Fox, Derek B.; Frail, Dale A.; Carpenter, John; Kulkarni, S. R.; Ofek, Eran O.; Gal-Yam, Avishay; Kasliwal, Mansi M.; Arcavi, Iair; Quimby, Robert; Cenko, S. Bradley; Nugent, Peter E.; Bloom, Joshua S.; Law, Nicholas M.; Poznanski, Dovi; Gorbikov, Evgeny; Polishook, David; Yaron, Ofer; Ryder, Stuart; Weiler, Kurt W.; Bauer, Franz; Van Dyk, Schuyler D.; Immler, Stefan; Panagia, Nino; Pooley, Dave; Kassim, Namir

2013-12-01

360

We consider the nonlinear propagation of electrostatic wave packets in an ultra-relativistic (UR) degenerate dense electron-ion plasma, whose dynamics is governed by the nonlocal two-dimensional nonlinear Schroedinger-like equations. The coupled set of equations is then used to study the modulational instability (MI) of a uniform wave train to an infinitesimal perturbation of multidimensional form. The condition for the MI is obtained, and it is shown that the nondimensional parameter, {beta}{proportional_to}{lambda}{sub C}n{sub 0}{sup 1/3} (where {lambda}{sub C} is the reduced Compton wavelength and n{sub 0} is the particle number density) associated with the UR pressure of degenerate electrons, shifts the stable (unstable) regions at n{sub 0{approx}}10{sup 30}cm{sup -3} to unstable (stable) ones at higher densities, i.e., n{sub 0} > or approx. 7x10{sup 33}. It is also found that the higher the values of n{sub 0}, the lower is the growth rate of MI with cut-offs at lower wave numbers of modulation. Furthermore, the dynamical evolution of the wave packets is studied numerically. We show that either they disperse away or they blowup in a finite time, when the wave action is below or above the threshold. The results could be useful for understanding the properties of modulated wave packets and their multidimensional evolution in UR degenerate dense plasmas, such as those in the interior of white dwarfs and/or pre-Supernova stars.

Misra, Amar Prasad [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden); Shukla, Padma Kant [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden); RUB International Chair, International Centre for Advanced Studies in Physical Sciences, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum (Germany)

2011-04-15

361

We study the generation of electromagnetic pulses with a carrier frequency of 3.7 GHz in a relativistic backward-wave oscillator\\u000a with a long slow-wave system in the superradiance regime of super-radiation for a magnetic induction of 0.2 T (below the cyclotron\\u000a resonance). To decrease transverse velocities of the electrons, we use decompression of a hollow electron beam. Decompression\\u000a in combination with

K. V. Afanasyev; N. M. Bykov; V. P. Gubanov; A. A. Elchaninov; A. I. Klimov; S. D. Korovin; V. V. Rostov; A. S. Stepchenko

2006-01-01

362

NASA Astrophysics Data System (ADS)

We investigate the structural and thermodynamic properties of cerium in ? phase by using the first-principles plane wave method with a relativistic analytic pseudopotential of Hartwigsen, Goedcker and Hutter (HGH) scheme in the frame of local density approximation (LDA). The obtained lattice constant and bulk modulus are consistent with the available experimental data. Moreover, dependences of the normalized primitive volume V/V0 on pressure and the thermodynamic quantities (including the Grüneisen constant ? and thermal expansion ?) on temperature and pressure are obtained. The obtained linear thermal expansion parameter ? (9.857 × 10-6 K-1 at 293.15K and 0GPa) is slightly larger than the experimental value (6.3 × 10-6 K-1). All the results indicate that we provide an effective method to deal with the ground properties of the strongly interacting d- and/or f-electron systems.

Sun, Li-Li; Ji, Guang-Fu; Chen, Xiang-Rong; Gou, Qing-Quan

2009-01-01

363

Neurological effects of blast injury.

Over the last few years, thousands of soldiers and an even greater number of civilians have suffered traumatic injuries due to blast exposure, largely attributed to improvised explosive devices in terrorist and insurgent activities. The use of body armor is allowing soldiers to survive blasts that would otherwise be fatal due to systemic damage. Emerging evidence suggests that exposure to a blast can produce neurologic consequences in the brain but much remains unknown. To elucidate the current scientific basis for understanding blast-induced traumatic brain injury (bTBI), the NIH convened a workshop in April 2008. A multidisciplinary group of neuroscientists, engineers, and clinicians were invited to share insights on bTBI, specifically pertaining to: physics of blast explosions, acute clinical observations and treatments, preclinical and computational models, and lessons from the international community on civilian exposures. This report provides an overview of the state of scientific knowledge of bTBI, drawing from the published literature, as well as presentations, discussions, and recommendations from the workshop. One of the major recommendations from the workshop was the need to characterize the effects of blast exposure on clinical neuropathology. Clearer understanding of the human neuropathology would enable validation of preclinical and computational models, which are attempting to simulate blast wave interactions with the central nervous system. Furthermore, the civilian experience with bTBI suggests that polytrauma models incorporating both brain and lung injuries may be more relevant to the study of civilian countermeasures than considering models with a neurologic focus alone. PMID:20453776

Hicks, Ramona R; Fertig, Stephanie J; Desrocher, Rebecca E; Koroshetz, Walter J; Pancrazio, Joseph J

2010-05-01

364

Neurological Effects of Blast Injury

Over the last few years, thousands of soldiers and an even greater number of civilians have suffered traumatic injuries due to blast exposure, largely attributed to improvised explosive devices in terrorist and insurgent activities. The use of body armor is allowing soldiers to survive blasts that would otherwise be fatal due to systemic damage. Emerging evidence suggests that exposure to a blast can produce neurological consequences in the brain, but much remains unknown. To elucidate the current scientific basis for understanding blast-induced traumatic brain injury (bTBI), the NIH convened a workshop in April, 2008. A multidisciplinary group of neuroscientists, engineers, and clinicians were invited to share insights on bTBI, specifically pertaining to: physics of blast explosions, acute clinical observations and treatments, preclinical and computational models, and lessons from the international community on civilian exposures. This report provides an overview of the state of scientific knowledge of bTBI, drawing from the published literature, as well as presentations, discussions, and recommendations from the workshop. One of the major recommendations from the workshop was the need to characterize the effects of blast exposure on clinical neuropathology. Clearer understanding of the human neuropathology would enable validation of preclinical and computational models, which are attempting to simulate blast wave interactions with the central nervous system. Furthermore, the civilian experience with bTBI suggests that polytrauma models incorporating both brain and lung injuries may be more relevant to the study of civilian countermeasures than considering models with a neurological focus alone.

Hicks, Ramona R.; Fertig, Stephanie J.; Desrocher, Rebecca E.; Koroshetz, Walter J.; Pancrazio, Joseph J.

2010-01-01

365

Dependence of relativistic backward wave oscillator properties on effective beam gamma

The operation of a backward wave oscillator (BWO) is shown to be critically dependent on the energy of the slow space-charge wave of the electron beam. Experimental work parameterizing the dependence of microwave frequency on effective beam energy, ?beam, reveals that through an understanding of electron-beam dynamics, a BWO could be systematically tuned through a desired frequency range while maintaining

JENNIFER M. BUTLER; CHARLES B. WHARTON; SHIGEHARU FURUKAWA

1990-01-01

366

The Relativistic Transformation for an Electromagnetic Plane Wave with General Time Dependence

ERIC Educational Resources Information Center

In special relativity, the transformation between inertial frames for an electromagnetic plane wave is usually derived for the time-harmonic case (the field is a sinusoid of infinite duration), even though all practical waves are of finite duration and may not even contain a dominant sinusoid. This paper presents an alternative derivation in which…

Smith, Glenn S.

2012-01-01

367

Photoemission by Large Electron Wave Packets in a Relativistic Laser Focus

NASA Astrophysics Data System (ADS)

We measure the radiation emitted from an electron whose wave packet has a size comparable to the wavelength of a driving laser. Such electrons are naturally produced during the ionization process in a high-intensity laser focus, where the sharp field gradients force portions of the wave packet over a large area. Using semi-classical quantum theory it is predicted that photoemission will be strongly suppressed as the wave packet size increases. However, fully quantized quantum theory predicts that radiation should be independent of the wave packet size. In this experimental work, we seek to confirm this fully quantized prediction by direct observation. We present our experimental design and noise floor results.

Coburn, Caleb; Cunningham, Eric; Ware, Michael; Peatross, Justin

2012-10-01

368

NASA Technical Reports Server (NTRS)

It is well known that the effects of EMIC waves on RC ion and RB electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. Therefore, realistic characteristics of EMIC waves should be properly determined by modeling the RC-EMIC waves evolution self-consistently. Such a selfconsistent model progressively has been developing by Khaznnov et al. [2002-2006]. It solves a system of two coupled kinetic equations: one equation describes the RC ion dynamics and another equation describes the energy density evolution of EMIC waves. Using this model, we present the effectiveness of relativistic electron scattering and compare our results with previous work in this area of research.

Khazanov, G. V.; Gallagher, D. L.; Gamayunov, K.

2007-01-01

369

Spinless relativistic particle in energy-dependent potential and normalization of the wave function

NASA Astrophysics Data System (ADS)

The problem of normalization related to a Klein-Gordon particle subjected to vector plus scalar energydependent potentials is clarified in the context of the path integral approach. In addition the correction relating to the normalizing constant of wave functions is exactly determined. As examples, the energy dependent linear and Coulomb potentials are considered. The wave functions obtained via spectral decomposition, were found exactly normalized.

Benchikha, Amar; Chetouani, Lyazid

2014-05-01

370

Precipitation of trapped relativistic electrons by amplified whistler waves in the magnetosphere

Numerical study of a loss-cone negative mass instability to amplify whistler waves by energetic electrons in the radiation belts is presented. The results show that a very low intensity whistler wave can be amplified by 50 keV electrons more than 25 dB, consistent with the Siple experimental result [Helliwell et al., J. Geophys. Res. 85, 3360 (1980)]. The dependencies of the amplification factor on the energetic electron density and on the initial wave intensity are evaluated. It is shown that the amplification factor decreases as the initial wave intensity increases. However, this gain can still exceed 15 dB for a 30 dB increase of the initial wave intensity, which is needed for the purpose of precipitating MeV electrons in the radiation belts. We then show that there exists a double resonance situation, by which, as an example, a wave is simultaneously in cyclotron resonance with 50 keV electrons as well as with 1.5 MeV electrons; the wave is first amplified by 50 keV electrons and then precipitates 1.5 MeV electrons. With the aid of the cyclotron resonance, the threshold field for the commencement of chaos in the electron trajectories is reduced considerably from that for a general case. Pitch angle scattering of 1.5 MeV electrons is demonstrated. The results show that a whistler wave with magnetic field amplitude of 0.08% of the background magnetic field can scatter electrons from an initial pitch angle of 86.5 deg. to a pitch angle <50 deg.

Kuo, S. P.; Kuo, Steven S.; Huynh, James T.; Kossey, Paul [Department of Electrical and Computer Engineering, Polytechnic University, Six MetroTech Center, New York, New York 11201 (United States); Northrop Grumman Space Technology, One Space Park, Redondo Beach, California 90278 (United States); Raytheon Space and Airborne Systems, El Segundo, California 90245 (United States); Air Force Research Laboratory/Space Vehicle Branch, Hanscom Air Force Base, Massachusetts 01731 (United States)

2007-06-15

371

Klystronlike relativistic backward wave oscillator (RBWO) can produce microwave power exceeding 5 GW with a high efficiency larger than 40%. In the experiment of klystronlike RBWO, for about 1 MV peak diode voltages, increasing magnetic field from 1.43 to 1.89 T slowed the impedance collapse until it was suppressed completely. The introduction of a stainless steel obstructing ring aggravated the impedance collapse, whereas replacing the stainless steel obstructing ring with a flat stainless steel provided a more stable impedance variation during the pulse duration. These impedance collapses did not affect microwave generation seriously and may be attributed to the radial expansion of cathode plasma initialing from the cathode shank so that part of reverse currents were collected at the anode wall, contributing to the measured diode current. On the other hand, it was found that microwave generation shot-to-shot reproducibility was closely related to the diode impedance variation. When there was no or very low microwave measured, diode impedance collapse appeared at the latter of the pulse. The microwave generation shot-to-shot reproducibility was improved greatly after the electron collector was enlarged on radius with 1 mm. A possible explanation is that the anode plasma produced from electron collector expands axially and enters the diode region at a very high velocity of several mm/ns. The movement of the anode plasma in the beam-wave interaction region affects the microwave generation, which reduces the microwave power during the whole pulse duration significantly.

Xiao Renzhen; Sun Jun; Huo Shaofei; Li Xiaoze; Zhang Ligang; Zhang Xiaowei; Zhang Lijun [Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2010-12-15

372

Explosive overpressure brain injury (OBI) impacts the lives of both military and civilian population. We hypothesize that a single exposure to OBI results in increased hypothalamic expression of oxidative stress and activation of the sympatho-adrenal medullary axis. Since a key component of blast-induced organ injury is the primary overpressure wave, we assessed selective biochemical markers of autonomic function and oxidative stress in male Sprague Dawley rats subjected to head-directed overpressure insult. Rats were subjected to single head-directed OBI with a 358kPa peak overpressure at the target. Control rats were exposed to just noise signal being placed at ~2m distance from the shock tube nozzle. Sympathetic nervous system activation of the adrenal medullae (AM) was evaluated at 6h following blast injury by assessing the expression of catecholamine biosynthesizing enzymes, tyrosine hydroxylase (TH), dopamine-? hydroxylase (D?H), neuropeptide Y (NPY) along with plasma norepinephrine (NE). TH, D?H and NPY expression increased 20%, 25%, and 91% respectively, following OBI (P<0.05). Plasma NE was also significantly elevated by 23% (P<0.05) following OBI. OBI significantly elevated TH (49%, P<0.05) in the nucleus tractus solitarius (NTS) of the brain stem while AT1 receptor expression and NADPH oxidase activity, a marker of oxidative stress, was elevated in the hypothalamus following OBI. Collectively, the increased levels of TH, D?H and NPY expression in the rat AM, elevated TH in NTS along with increased plasma NE suggest that single OBI exposure results in increased sympathoexcitation. The mechanism may involve the elevated AT1 receptor expression and NADPH oxidase levels in the hypothalamus. Taken together, such effects may be important factors contributing to pathology of brain injury and autonomic dysfunction associated with the clinical profile of patients following OBI. PMID:23570732

Tümer, Nihal; Svetlov, Stanislav; Whidden, Melissa; Kirichenko, Nataliya; Prima, Victor; Erdos, Benedek; Sherman, Alexandra; Kobeissy, Firas; Yezierski, Robert; Scarpace, Philip J; Vierck, Charles; Wang, Kevin K W

2013-06-01

373

NASA Astrophysics Data System (ADS)

We calculated synchrotron radio emission and ?-ray emission due to bremsstrahlung, inverse-Compton scattering, and ?0-decay from the remnant of supernova that exploded in the circumstellar matter (CSM) formed by the progenitor's stellar wind. This sort of situation is a possible origin of mixed-morphology supernova remnants (SNRs), like W 49B, which exhibit recombination-radiation spectra in X-ray emission. We assumed that the CSM of 1.5 M? exists at 0.07-3 pc away from the supernova in the interstellar medium (ISM) of density 0.016 cm-3. When the blast wave breaks out of the CSM into the ISM, its velocity rapidly increases, and hence particle acceleration is enhanced. The maximum energy of protons reaches ˜1300 TeV just after the break-out with ˜0.5% of the explosion energy. We considered the non-thermal emission from the blast-shocked ISM shell after the break-out. Synchrotron radio flux at 1 GHz is tens of Jy, comparable to that observed from mixed-morphology SNRs. Because of low density, the ?-ray luminosity is dominated by inverse-Compton scattering, which is higher than the ?0-decay luminosity by an order of magnitude. The total ?-ray luminosity, including bremsstrahlung, is on the order of 1033 erg s-1 lower than the typical value of 1035-1036 erg s-1 observed from mixed-morphology SNRs. However, if, e.g., ˜10% of accelerated protons interact with some matter of density of 100 cm-3, the ?0-decay ?-ray luminosity would be enhanced to be comparable with the observed value.

Shimizu, Takafumi; Masai, Kuniaki; Koyama, Katsuji

2013-06-01

374

NASA Astrophysics Data System (ADS)

Chorus waves have been suggested to be effective in acceleration of radiation belt electrons. Here we perform gyro-averaged test-particle simulations to calculate the bounce-averaged pitch angle and energy diffusion coefficients for parallel-propagating monochromatic chorus waves, and perform a comparison of test-particle (TP) model with quasi-linear (QL) theory to evaluate the influence of nonlinear processes. For small amplitude chorus waves, the diffusion coefficients of TP and QL models are in good agreement. As the wave amplitude reaches a threshold value, two nonlinear processes (phase trapping and phase bunching) start to occur, especially at large equatorial pitch angles. Phase trapping yields rapid increases in pitch angle and kinetic energy. In contrast, phase bunching causes overall decreases in pitch angle and kinetic energy. For the waves with amplitudes slightly above the threshold value, the average behavior is dominated by the phase trapping, and TP diffusion coefficients are larger than QL ones. As wave amplitude increases, TP diffusion coefficients become smaller than QL ones, indicating that phase trapping gradually reduces the dominance over phase bunching.

Gao, Zhonglei; Zhu, Hui; Zhang, Lewei; Zhou, Qinghua; Yang, Chang; Xiao, Fuliang

2014-06-01

375

NASA Astrophysics Data System (ADS)

The nonlinear propagation of ion acoustic waves in electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries-Burger equation has been derived by reductive perturbation technique, and its shock like solution is determined analytically through tangent hyperbolic method. The effect of various plasma parameters on strength and structure of shock wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that strength and steepness of the shock wave enervate with an increase in the ion temperature, relativistic streaming factor, positron concentrations, electron temperature and they accrue with an increase in coefficient of kinematic viscosity. The convective, dispersive, and dissipative properties of the plasma are also discussed. It is determined that the electron temperature has remarkable influence on the propagation and structure of nonlinear wave in such relativistic plasmas. The numerical analysis has been done based on the typical numerical data from a pulsar magnetosphere.

Saeed, R.; Shah, Asif

2010-03-01

376

The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM{sub 01}, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.

Ge Xingjun; Zhong Huihuang; Qian Baoliang; Zhang Jun; Fan Yuwei; Shu Ting; Liu Jinliang [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2009-11-15

377

A linear theory of resonant backward-wave oscillators (BWOs) that takes into account the zero spatial harmonic is developed. It is shown that, depending on the phase shift, this harmonic can either increase or decrease the starting current of the device. The nonlinear theory shows the same effect of the phase shift on the maximum efficiency of the BWO. The numerical analysis of nonstationary processes has also demonstrated the effect of the phase shift on the range of beam current values in which the BWO operates in a steady-state single-frequency regime. The effect of boundary conditions at the cathode end of the slow-wave structure on the phase shift between harmonics is also analyzed. {copyright} {ital 1997 American Institute of Physics.}

Vlasov, A.N.; Nusinovich, G.S. [Institute for Plasma Research, University of Maryland, College Park, Maryland 20742-3511 (United States)] [Institute for Plasma Research, University of Maryland, College Park, Maryland 20742-3511 (United States); Levush, B. [Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)

1997-05-01

378

We develop a Markov process theory of charged particle scattering from stationary, transverse, magnetic waves. We examine approximations that lead to quasilinear theory, in particular the resonant diffusion approximation. We find that, when appropriate, the resonant diffusion approximation simplifies the result of the weak turbulence approximation without significant further restricting the regime of applicability. We also explore a theory generated by expanding drift and diffusion rates in terms of a presumed small correlation time. This small correlation time expansion leads to results valid for relatively small pitch angle and large wave energy density - a regime that may govern pitch angle scattering of high-energy electrons into the geomagnetic loss cone.

Lemons, Don S. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-01-15

379

We present a new periodic all-metal slow wave structure, a coaxial step-disc-loaded system and the dispersion characteristics of the structure. By using the field-matching method, the dispersion equation and the coupling impedance of this structure are obtained. The coaxial structure makes the bandwidth broader than that of the non-coaxial one. Compared with the coaxial disc-loaded and ridged-disc-loaded structures, the pass-band

Ling-Na Yue; Wen-Xiang Wang; Yan-Yu Wei; Yu-Bin Gong

2005-01-01

380

A computational model of blast loading on the human eye.

Ocular injuries from blast have increased in recent wars, but the injury mechanism associated with the primary blast wave is unknown. We employ a three-dimensional fluid-structure interaction computational model to understand the stresses and deformations incurred by the globe due to blast overpressure. Our numerical results demonstrate that the blast wave reflections off the facial features around the eye increase the pressure loading on and around the eye. The blast wave produces asymmetric loading on the eye, which causes globe distortion. The deformation response of the globe under blast loading was evaluated, and regions of high stresses and strains inside the globe were identified. Our numerical results show that the blast loading results in globe distortion and large deviatoric stresses in the sclera. These large deviatoric stresses may be indicator for the risk of interfacial failure between the tissues of the sclera and the orbit. PMID:23591604

Bhardwaj, Rajneesh; Ziegler, Kimberly; Seo, Jung Hee; Ramesh, K T; Nguyen, Thao D

2014-01-01

381

Rodent model of direct cranial blast injury.

Traumatic brain injury resulting from an explosive blast is one of the most serious wounds suffered by warfighters, yet the effects of explosive blast overpressure directly impacting the head are poorly understood. We developed a rodent model of direct cranial blast injury (dcBI), in which a blast overpressure could be delivered exclusively to the head, precluding indirect brain injury via thoracic transmission of the blast wave. We constructed and validated a Cranium Only Blast Injury Apparatus (COBIA) to deliver blast overpressures generated by detonating .22 caliber cartridges of smokeless powder. Blast waveforms generated by COBIA replicated those recorded within armored vehicles penetrated by munitions. Lethal dcBI (LD(50) ? 515?kPa) was associated with: (1) apparent brainstem failure, characterized by immediate opisthotonus and apnea leading to cardiac arrest that could not be overcome by cardiopulmonary resuscitation; (2) widespread subarachnoid hemorrhages without cortical contusions or intracerebral or intraventricular hemorrhages; and (3) no pulmonary abnormalities. Sub-lethal dcBI was associated with: (1) apnea lasting up to 15?sec, with transient abnormalities in oxygen saturation; (2) very few delayed deaths; (3) subarachnoid hemorrhages, especially in the path of the blast wave; (4) abnormal immunolabeling for IgG, cleaved caspase-3, and ?-amyloid precursor protein (?-APP), and staining for Fluoro-Jade C, all in deep brain regions away from the subarachnoid hemorrhages, but in the path of the blast wave; and (5) abnormalities on the accelerating Rotarod that persisted for the 1 week period of observation. We conclude that exposure of the head alone to severe explosive blast predisposes to significant neurological dysfunction. PMID:21639724

Kuehn, Reed; Simard, Philippe F; Driscoll, Ian; Keledjian, Kaspar; Ivanova, Svetlana; Tosun, Cigdem; Williams, Alicia; Bochicchio, Grant; Gerzanich, Volodymyr; Simard, J Marc

2011-10-01

382

NASA Astrophysics Data System (ADS)

First it is shown that "Liouville's theorem" on integrability still holds in the case of time-dependent Hamiltonian systems; when they have n independent, possibly time-dependent, invariants the solution can be found with quadratures and no chaos can take place. Such a system is called "integrable"[1]. This is applied to the problem of the motion of a particle in an electromagnetic field which is studied. The wave is assumed to be circularly polarized first, then an almost circularly polarized wave is considered. The situation when the wave propagates along a constant magnetic field is also studied. In a first part the magnetic field is assumed to be homogeneous [2], then magnetic field gradients are taken into consideration. Trajectories are studied. An equation for the particle energy is found, in one case an exact and simple solution is given, in an other case an approximate expression for the maximum energy is derived. A new way to create a magnetic field with an electromagnetic wave is discussed, a new concept of accelerator is described, some of our results are used to interpret experimental results concerning an X-ray source [3]. [1] S. Bouquet and A. Bourdier,Phys. Rev. 57,1273 (1998). [2] A. Bourdier, M. Valentini, and J. Valat, Phys. Lett. A 215, 219 (1996); Phys. Rev. E 54,5681 (1996). [3] M. Bacal, C. Gaudin, A. Bourdier et al., Nature 384, 421 (1996).

Bourdier, Alain

1998-11-01

383

Relativistic particle acceleration in the process of whistler-mode chorus wave generation

We have found that efficient acceleration of resonant electrons takes place in a self-consistent particle simulation reproducing whistler-mode chorus emissions. While the majority of electrons lose energy contributing to the generation of chorus emissions, a fraction of resonant electrons having large pitch angle are simultaneously energized through nonlinear wave trapping by the generated chorus emissions. A small fraction of energetic

Yuto Katoh; Yoshiharu Omura

2007-01-01

384

Experimental work is underway by a SLAC-LLNL-LBL collaboration to investigate the feasibility of using relativistic klystrons as a power source for future high gradient accelerators. Two different relativistic klystron configurations have been built and tested to date: a high grain multicavity klystron at 11.4 GHz and a low gain two cavity subharmonic buncher driven at 5.7 GHz. In both configurations power is extracted at 11.4 GHz. In order to understand the basic physics issues involved in extracting RF from a high power beam, we have used both a single resonant cavity and a multi-cell traveling wave structure for energy extraction. We have learned how to overcome our previously reported problem of high power RF pulse shortening, and have achieved peak RF power levels of 170 MW with the RF pulse of the same duration as the beam current pulse. 6 refs., 3 figs., 3 tabs.

Allen, M.A.; Azuma, O.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fant, K.S.; Fowkes, W.R.; Herrmannsfeldt, W.B.; Hoag, H.A.; Koontz, R.F.

1989-03-01

385

The phenomenon of passive compression of frequency-modulated (FM) pulses in a dispersive media (DM) was used to increase the peak microwave power up to the multigigawatt level. A helically corrugated waveguide was used as the DM, while a relativistic X-band backward-wave oscillator (RBWO) with a descending-during-the-pulse accelerating voltage served as a source of FM pulses. Compression of pulses down to

V. L. Bratman; G. G. Denisov; N. G. Kolganov; S. V. Mishakin; S. V. Samsonov; A. W. Cross; W. He; L. Zhang; M. McStravick; C. G. Whyte; A. R. Young; K. Ronald; C. W. Robertson; A. D. R. Phelps

2010-01-01

386

We show theoretically that the use of a circular oversized waveguide with a helically corrugated internal surface as a dispersive\\u000a medium ensures efficient compression of frequency-modulated microwave pulses up to peak powers of about 10 GW. According to\\u000a the calculations, a pulse with the required frequency modulation can be obtained in a relativistic backward-wave oscillator\\u000a operated in the 3-cm wavelength

V. L. Bratman; G. G. Denisov; S. V. Samsonov; A. W. Cross; K. Ronald; A. D. R. Phelps

2007-01-01

387

Initial studies of a long-pulse relativistic backward-wave oscillator utilizing a disk cathode

One of the major issues in high-power microwave device operation is pulse shortening, which often limits microwave pulses to less than 100 ns. This has been the focus of many studies on the long-pulse backward-wave oscillator (BWO) at the University of New Mexico. Previous diagnostics have indicated that significant plasma is produced by a graphite knife-edge or \\

Kelly Hahn; Mikhail I. Fuks; Edl Schamiloglu

2002-01-01

388

A numerical simulation of the ablation of a planar, aluminum-foil target by a neodymium laser in the presence of a 2.5 Torr nitrogen background gas is presented. The simulation includes inverse-bremsstrahlung absorption during the laser pulse, the cold isotherm in the equation of state for solid aluminum, non-equilibrium chemistry for both the target material and the background gas, radiation transport of the continuum, ion and electron energy equations, and blast-wave formation in the background gas. The simulation is followed out to > 50 nsec from the peak of the laser pulse. Although the Lagrangian code is 1-D, the divergence of the ablated target material expanding toward the laser (forward) as well as the rearward acceleration of the remaining target is accounted for by using an oblate spheroidal-coordinate system. The primary results of the simulations are as follows: (i), by about 50 nsec a cavity with T/sub e/ about 60 ev and ne about 2 x 10/sup 17//cc has formed behind the denser and cooler forward-moving blast wave; (ii), this cavity is not in chemical equilibrium but highly overionized for its temperature with predominantly Al(+9),Al(+10),Al(+11),N(+5) and N(+6); and (iii), the conditions for a deceleration-driven Rayleigh-Taylor instability are satisfied at the rear blast wave near one equal mass radius. This last feature may account for the experimentally observed floculli on the rearward side.

Giuliani, J.L.

1986-05-09

389

NASA Astrophysics Data System (ADS)

Relativistic distorted-wave collision strengths have been calculated for the 49 ?n=0 optically allowed transitions with n=2 in the 67 B-like ions with nuclear charge number Z in the range 26?Z?92. The calculations were made for the four final, or scattered, electron energies E?=0.20, 0.42, 0.80, and 1.40, where E? is in units of Zeff2 Ry with Z=Z-3.33. In the present calculations, an improved “top-up” method, which employs relativistic plane waves, was used to obtain the high partial-wave contribution for each transition, in contrast to the partial-relativistic Coulomb-Bethe approximation used in previous work by Zhang and Sampson [H.L. Zhang and D.H. Sampson, At. Data Nucl. Data Tables 56 (1994) 41]. In that earlier work, collision strengths were also provided for B-like ions, but for a more comprehensive data set consisting of all 105 ?n=0 transitions, six scattered energies and the 85 ions with Z in the range 8?Z?92. The collision strengths covered in the present work should be more accurate than the corresponding data given by Zhang and Sampson [H.L. Zhang and D.H. Sampson, At. Data Nucl. Data Tables 56 (1994) 41] and are presented here to replace those earlier results.

Fontes, Christopher J.; Zhang, Hong Lin

2014-05-01

390

POES satellite observations of EMIC-wave driven relativistic electron precipitation during 1998-2010

NASA Astrophysics Data System (ADS)

Using six Polar Orbiting Environmental Satellites (POES) satellites that have carried the Space Environment Module-2 instrument package, a total of 436,422 individual half-orbits between 1998 and 2010 were inspected by an automatic detection algorithm searching for electromagnetic ion cyclotron (EMIC) driven relativistic electron precipitation (REP). The algorithm searched for one of the key characteristics of EMIC-driven REP, identified as the simultaneity between spikes in the P1 (52 keV differential proton flux channel) and P6 (>800 keV electron channel). In all, 2331 proton precipitation associated REP (PPAREP) events were identified. The majority of events were observed at L-values within the outer radiation belt (3 < L < 7) and were more common in the dusk and night sectors as determined by magnetic local time. The majority of events occurred outside the plasmasphere, at L-values ~1 Re greater than the plasmapause location determined from two different statistical models. The events make up a subset of EMIC-driven proton spikes investigated by Sandanger et al. (2009), and potentially reflect different overall characteristics compared with proton spikes, particularly when comparing their location to that of the plasmapause, i.e., EMIC-driven proton precipitation inside the plasmapause, and potentially EMIC-driven REP outside the plasmapause. There was no clear relationship between the location of plasmaspheric plumes and the locations of the PPAREP events detected. Analysis of the PPAREP event occurrence indicates that high solar wind speed and high geomagnetic activity levels increase the likelihood of an event being detected. The peak PPAREP event occurrence was during the declining phase of solar cycle 23, consistent with the 2003 maximum in the geomagnetic activity index, Ap.

Carson, Bonar R.; Rodger, Craig J.; Clilverd, Mark A.

2013-01-01

391

NASA Astrophysics Data System (ADS)

A detailed theoretical analysis is carried out of the hose instability of relativistically strong laser pulses propagating in a plasma, whose duration is less than the period of a plasma wake wave. An analytic expression is obtained for the displacement of the mass center of a wave pulse, and the effect of this instability on the modification of the spectrum of laser radiation is analyzed for a wide range of initial parameters. It is shown that the development of instability is characterized by a power-law (rather than exponential) time dependence along the propagation path and does not deteriorate the self-compression of laser pulses.

Balakin, A. A.; Litvak, A. G.; Mironov, V. A.; Skobelev, S. A.

2014-04-01

392

It is shown that (a) both the dispersion relations between the mean frequency 0 and the mean wave number k\\u000a0\\u000a are invariant under the Lorentz transformation; and (b) the relativistic Doppler effects on \\u000a0\\u000a and k\\u000a0\\u000a differ. In the suboptic packet there is anomalous red shift in the mean wave number k'\\u000a0\\u000a received from a source receding

William Band

1988-01-01

393

Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional (3D) numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] are presented. Using the multiphysics, adaptive mesh refinement, higher order Godunov Eulerian hydrocode, Raptor [L. H. Howell and J. A. Greenough, J. Comput. Phys. 184, 53 (2003)], the late nonlinear instability evolution, including transition to turbulence, is considered for various multimode perturbation spectra. The 3D post-transition state differs from the 2D result, but the process of transition proceeds similarly in both 2D and 3D. The turbulent mixing transition results in a reduction in the growth rate of the mixing layer relative to its pretransition value and, in the case of the bubble front, relative to the 2D result. The post-transition spike front velocity is approximately the same in 2D and 3D. Implications for hydrodynamic mixing in core-collapse supernovae are discussed.

Miles, A.R.; Blue, B.; Edwards, M.J.; Greenough, J.A.; Hansen, J.F.; Robey, H.F.; Drake, R.P.; Kuranz, C.; Leibrandt, D.R. [Lawrence Livermore National Laboratory, L-021, 7000 East Avenue, P.O. Box 808, Livermore, California 94551 (United States); University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States)

2005-05-15

394

Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, we present the first results from a computational study of such a system under drive conditions to be attainable on the National Ignition Facility. Using the multiphysics, AMR, higher order Godunov Eulerian hydrocode, Raptor, we consider the late nonlinear instability evolution for multiple amplitude and phase realizations of a variety of multimode spectral types. We show that compressibility effects preclude the emergence of a regime of self-similar instability growth independent of the initial conditions by allowing for memory of the initial conditions to be retained in the mix width at all times. The loss of transverse spectral information is demonstrated, however, along with the existence of a quasi-self-similar regime over short time intervals. Certain aspects of the initial conditions, including the rms amplitude, are shown to have a strong effect on the time to transition to the quasi-self-similar regime.

Miles, A R; Edwards, M J; Greenough, J A

2004-03-26

395

NASA Astrophysics Data System (ADS)

The detailed mechanism of blast-induced traumatic brain injury (bTBI) has not been revealed yet. Thus, reliable laboratory animal models for bTBI are needed to investigate the possible diagnosis and treatment for bTBI. In this study, we used laser-induced shock wave (LISW) to induce TBI in rats and investigated the histopathological similarities to actual bTBI. After craniotomy, the rat brain was exposed to a single shot of LISW with a diameter of 3 mm at various laser fluences. At 24 h after LISW exposure, perfusion fixation was performed and the extracted brain was sectioned; the sections were stained with hematoxylin-eosin. Evans blue (EB) staining was also used to evaluate disruption of the blood brain barrier. At certain laser fluence levels, neural cell injury and hemorrhagic lesions were observed in the cortex and subcortical region. However, injury was limited in the tissue region that interacted with the LISW. The severity of injury increased with increasing laser fluence and hence peak pressure of the LISW. Fluorescence originating from EB was diffusively observed in the injuries at high fluence levels. Due to the grade and spatial controllability of injuries and the histological observations similar to those in actual bTBI, brain injuries caused by LISWs would be useful models to study bTBI.

Hatano, Ben; Matsumoto, Yoshihisa; Otani, Naoki; Saitoh, Daizoh; Tokuno, Shinichi; Satoh, Yasushi; Nawashiro, Hiroshi; Matsushita, Yoshitaro; Sato, Shunichi

2011-02-01

396

Nonlinear model and simulation technique of the interaction and energy transfer between a fast wave and a large-orbit relativistic electron beam in a coaxial electrostatic wiggler are presented. Unlike the situations in a magnetostatic-wiggler free-electron laser (MWFEL) and in an electron cyclotron maser (ECM), the electrostatic potential of the electrons plays an important role and participates in the energy exchange between the wave and the electron beam. Compared to MWFEL and ECM, the coaxial electrostatic-wiggler configuration has a distinguishing peculiarity that besides the electron-beam's kinetic energy, its electrostatic potential energy can be effectively transferred to the fast wave. Simulation shows that wave could be amplified with ultrahigh gain by extracting both the kinetic energy and electrostatic potential energy of the electron beam.

Zhang Shichang [Institute of Photoelectronics, Campus Mail Box 50, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China)

2010-05-15

397

NASA Astrophysics Data System (ADS)

Preface; Prologue: Conference overview Bernard Carr; Part I. The Universe At Large and Very Large Redshifts: 2. The size and age of the Universe Gustav A. Tammann; 3. Active galaxies at large redshifts Malcolm S. Longair; 4. Observational cosmology with the cosmic microwave background George F. Smoot; 5. Future prospects in measuring the CMB power spectrum Philip M. Lubin; 6. Inflationary cosmology Michael S. Turner; 7. The signature of the Universe Bernard J. T. Jones; 8. Theory of large-scale structure Sergei F. Shandarin; 9. The origin of matter in the universe Lev A. Kofman; 10. New guises for cold-dark matter suspects Edward W. Kolb; Part II. Physics and Astrophysics Of Relativistic Compact Objects: 11. On the unification of gravitational and inertial forces Donald Lynden-Bell; 12. Internal structure of astrophysical black holes Werner Israel; 13. Black hole entropy: external facade and internal reality Valery Frolov; 14. Accretion disks around black holes Marek A. Abramowicz; 15. Black hole X-ray transients J. Craig Wheeler; 16. X-rays and gamma rays from active galactic nuclei Roland Svensson; 17. Gamma-ray bursts: a challenge to relativistic astrophysics Martin Rees; 18. Probing black holes and other exotic objects with gravitational waves Kip Thorne; Epilogue: the past and future of relativistic astrophysics Igor D. Novikov; I. D. Novikov's scientific papers and books.

Jones, Bernard J. T.; Markovic, Dragoljub

1997-06-01

398

Preliminary performance of the MKII 17 GHz traveling wave relativistic klystron

Initial test results are presented of an upgraded RF source developed for high peak power 17 GHz linear accelerator applications. The objectives of this upgrade program were (a) to increase the output capability of the existing vacuum demountable prototype tube so that RF power could also be supplied to a future 2 MeV photoinjector system without appreciable loss of input power to the 17 GHz linac and (b) to investigate the performance of a new design traveling wave output circuit incorporating a racetrack shaped dual output coupler with 5{percent} bandwidth high peak power ceramic RF windows. These recently installed devices are presently being conditioned and tested at the MIT Plasma Science and Fusion Center. {copyright} {ital 1999 American Institute of Physics.}

Haimson, J.; Mecklenburg, B.; Stowell, G. [Haimson Research Corporation, 3350 Scott Blvd., Building 60, Santa Clara, California 95054-3104 (United States); Kreischer, K.E.; Mastovsky, I. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4294 (United States)

1999-05-01

399

NASA Astrophysics Data System (ADS)

Transport properties of massive Dirac particles are investigated through an oscillating barrier. The Floquet quasienergies related to the time-dependent potential appear both in transmission and reflection as sidebands around the incoming electron's energy. We take all relevant sidebands into account and present time averaged transmission and reflection probabilities in a wide energy range. Most qualitative features of scattering on a static barrier—like Klein paradox—are still visible, but the transmission probability in the evanescent regime observably increases due to the oscillation of the potential. The strongly inelastic scattering process is shown to lead to multiple Fano-type resonances and temporal trapping of the particles inside the oscillating potential. We also present a detailed study of the time evolution of the wave packets generated in the scattering process. Our results can be relevant for graphene with an induced energy gap.

Szabó, Lóránt Zs.; Benedict, Mihály G.; Czirják, Attila; Földi, Péter

2013-08-01

400

BLAST EFFECTS ON AN AIR-CLEANING SYSTEM. Preliminary Report

A study was made on the effect of shock waves on various types of air ; cleaning equipment. Shock waves generated by nuclear or high-explosive blasts ; which impact upon air-cleaning devices in a direction opposite to that of normal ; air flow were investigated. Major blast effects studied include destruction or ; damage to aircleaning equipment designed to collect

R. Dennis; C. E. Billings

1957-01-01

401

Monte Carlo Simulations of Nonlinear Particle Acceleration in Parallel Trans-relativistic Shocks

NASA Astrophysics Data System (ADS)

We present results from a Monte Carlo simulation of a parallel collisionless shock undergoing particle acceleration. Our simulation, which contains parameterized scattering and a particular thermal leakage injection model, calculates the feedback between accelerated particles ahead of the shock, which influence the shock precursor and "smooth" the shock, and thermal particle injection. We show that there is a transition between nonrelativistic shocks, where the acceleration efficiency can be extremely high and the nonlinear compression ratio can be substantially greater than the Rankine-Hugoniot value, and fully relativistic shocks, where diffusive shock acceleration is less efficient and the compression ratio remains at the Rankine-Hugoniot value. This transition occurs in the trans-relativistic regime and, for the particular parameters we use, occurs around a shock Lorentz factor ?0 = 1.5. We also find that nonlinear shock smoothing dramatically reduces the acceleration efficiency presumed to occur with large-angle scattering in ultra-relativistic shocks. Our ability to seamlessly treat the transition from ultra-relativistic to trans-relativistic to nonrelativistic shocks may be important for evolving relativistic systems, such as gamma-ray bursts and Type Ibc supernovae. We expect a substantial evolution of shock accelerated spectra during this transition from soft early on to much harder when the blast-wave shock becomes nonrelativistic.

Ellison, Donald C.; Warren, Donald C.; Bykov, Andrei M.

2013-10-01

402

Gravitational-Wave Memory from the Relativistic Jet of Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

The gravitational-wave (GW) memory from a radiating and decelerating point mass is studied in detail. It is found that for isotropic photon emission the memory generated from the photons is essentially the same as the memory from the point mass that radiated the photons, so that it is anti-beamed. On the other hand, for anisotropic emission the memory from the photons may have a non-vanishing amplitude, even if it is seen at small viewing angles. In the decelerating phases of gamma-ray burst (GRB) jets the kinetic energy of the jet is converted into the energy of gamma-ray photons. It would then be possible to observe a variation in the GW memory associated with GRB jets on the timescale of the gamma-ray emission if the emission is partially anisotropic. Such anisotropy in gamma-ray emission has been suggested by polarizations detected in recent observations of GRBs. The GW memory from GRB jets would provide clues for clarifying the geometry of the jets and the emission mechanism in GRBs. Thus, it will be an interesting target for the next-generation detectors of GWs.

Akiba, Shota; Nakada, Megumi; Yamaguchi, Chiyo; Iwamoto, Koichi

2013-06-01

403

Conversion of piston-driven shocks from powerful solar flares to blast waves in the solar wind

NASA Technical Reports Server (NTRS)

Published observational data on 39 combined type-II/type-IV solar radio bursts from the period 1972-1982 are analyzed, with a focus on the potential use of the type-IV burst duration to predict the time of arrival at earth of piston-driven shock waves (extending and modifying the prediction method proposed by Smart and Shea, 1985). The data and analysis results are presented in tables and graphs and characterized in detail. It is found that a typical shock of this type leaves the solar flare at velocity 1560 km/sec and continues for a distance of 0.12 AU, decelerates as it is convected by the solar wind, and has a travel time of about 48.5 h. The mean deviation between predicted and measured arrival times is 1.40 h, with standard deviation 1.25 h.

Pinter, S.; Dryer, M.

1990-01-01

404

NASA Astrophysics Data System (ADS)

The giant, superfast, interplanetary coronal mass ejection, detected by STEREO A on 2012 July 23, well away from Earth, appears to have reached 1 AU with an unusual set of leading bow waves resembling in some ways a subsonic interaction, possibly due to the high pressures present in the very energetic particles produced in this event. Eventually, a front of record high-speed flow reached STEREO. The unusual behavior of this event is illustrated using the magnetic field, plasma, and energetic ion observations obtained by STEREO. Had the Earth been at the location of STEREO, the large southward-oriented magnetic field component in the event, combined with its high speed, would have produced a record storm.

Russell, C. T.; Mewaldt, R. A.; Luhmann, J. G.; Mason, G. M.; von Rosenvinge, T. T.; Cohen, C. M. S.; Leske, R. A.; Gomez-Herrero, R.; Klassen, A.; Galvin, A. B.; Simunac, K. D. C.

2013-06-01

405

A detailed treatment of a confined relativistic atom, needed as an initial step for the parametrization of the self-consistent-charge density-functional tight-binding method, is presented and discussed. The required one-component quantities, i.e., orbital energies, orbital wave functions, and Hubbard parameters, are obtained by weighted averaging of the corresponding numbers determined for the atomic spinors. The wave function and density confinement is achieved by introducing the Woods-Saxon potential in the atomic four-component Dirac-Kohn-Sham problem. The effect of the additional confining potential on energy eigenvalues and the shape of atomic wave functions and densities is discussed and numerical examples are presented for the valence spinors of carbon, germanium, and lead. PMID:17567112

Witek, Henryk A; Köhler, Christof; Frauenheim, Thomas; Morokuma, Keiji; Elstner, Marcus

2007-07-01

406

The concentrations of wave functions about classical periodic orbits, or quantum scars, are a fundamental phenomenon in physics. An open question is whether scarring can occur in relativistic quantum systems. To address this question, we investigate confinements made of graphene whose classical dynamics are chaotic and find unequivocal evidence of relativistic quantum scars. The scarred states can lead to strong conductance fluctuations in the corresponding open quantum dots via the mechanism of resonant transmission.

Huang, Liang [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Lai Yingcheng [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Ferry, David K.; Goodnick, Stephen M. [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Center for Solid State Electronics Research, Arizona State University, Tempe, Arizona 85287 (United States); Akis, Richard [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Center for Solid State Electronics Research, Arizona State University, Tempe, Arizona 85287 (United States)

2009-07-31

407

Relativistic quantum revivals.

Quantum revivals are now a well-known phenomena within nonrelativistic quantum theory. In this Letter we display the effects of relativity on revivals and quantum carpets. It is generally believed that revivals do not occur within a relativistic regime. Here we show that while this is generally true, it is possible, in principle, to set up wave packets with specific mathematical properties that do exhibit exact revivals within a fully relativistic theory. PMID:20366519

Strange, P

2010-03-26

408

Note: A table-top blast driven shock tube.

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer that explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test. PMID:21198058

Courtney, Michael W; Courtney, Amy C

2010-12-01

409

Note: A table-top blast driven shock tube

NASA Astrophysics Data System (ADS)

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer that explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

Courtney, Michael W.; Courtney, Amy C.

2010-12-01

410

NASA Technical Reports Server (NTRS)

Understanding the origin and acceleration of magnetospheric relativistic electrons (MREs) in the Earth's radiation belt during geomagnetic storms is an important subject and yet one of outstanding questions in space physics. It has been statistically suggested that during geomagnetic storms, ultra-low-frequency (ULF) Pc-5 wave activities in the magnetosphere are correlated with order of magnitude increase of MRE fluxes in the outer radiation belt. Yet, physical and observational understandings of resonant interactions between ULF waves and MREs remain minimum. In this paper, we show two events during storms on September 25, 2001 and November 25, 2001, the solar wind speeds in both cases were > 500 km/s while Cluster observations indicate presence of strong ULF waves in the magnetosphere at noon and dusk, respectively, during a approx. 3-hour period. MRE observations by the Los Alamos (LANL) spacecraft show a quadrupling of 1.1-1.5 MeV electron fluxes in the September 25, 2001 event, but only a negligible increase in the November 2.5, 2001 event. We present a detailed comparison between these two events. Our results suggest that the effectiveness of MRE acceleration during the September 25, 2001 event can be attributed to the compressional wave mode with strong ULF wave activities and the physical origin of MRE acceleration depends more on the distribution of toroidal and poloidal ULF waves in the outer radiation belt.

Shao, X.; Fung, S. F.; Tan, L. C.; Sharma, A. S.

2010-01-01

411

Nineteen-Foot Diameter Explosively Driven Blast Simulator

This report describes the 19-foot diameter blast tunnel at Sandia National Laboratories. The blast tunnel configuration consists of a 6 foot diameter by 200 foot long shock tube, a 6 foot diameter to 19 foot diameter conical expansion section that is 40 feet long, and a 19 foot diameter test section that is 65 feet long. Therefore, the total blast tunnel length is 305 feet. The development of this 19-foot diameter blast tunnel is presented. The small scale research test results using 4 inch by 8 inch diameter and 2 foot by 6 foot diameter shock tube facilities are included. Analytically predicted parameters are compared to experimentally measured blast tunnel parameters in this report. The blast tunnel parameters include distance, time, static, overpressure, stagnation pressure, dynamic pressure, reflected pressure, shock Mach number, flow Mach number, shock velocity, flow velocity, impulse, flow duration, etc. Shadowgraphs of the shock wave are included for the three different size blast tunnels.

VIGIL,MANUEL G.

2001-07-01

412

Electrocardiographic changes following primary blast injury to the thorax.

Profound physiological changes occur following primary blast exposure but the contribution of cardiac arrhythmias is unknown. Thirteen rats, under intravenous anaesthesia, were exposed to a blast wave directed at the thorax (Group II); 10 other animals underwent abdominal blast (Group III) and nine animals acted as controls (Group I). Animals were monitored before, during and after blast exposure. Group II animals demonstrated apnoea, bradycardia and hypotension. No significant physiological changes were seen in Groups I or III. Group II displayed a variety of ECG disturbances, from ventricular extrasystoles to ventricular fibrillation. All abnormalities reverted to sinus rhythm within minutes except in fatally injured animals. These ECG changes probably result from stress wave injury. Significant disturbances might account for some fatalities following primary blast exposure and may exacerbate the triad of apnoea, bradycardia and hypotension. Such observations may have important consequences for the management of blast casualties. PMID:11346922

Guy, R J; Watkins, P E; Edmondstone, W M

2000-01-01

413

Using the data from neutron monitors and applying various techniques, the parameters of relativistic solar protons (RSPs) outside the magnetosphere are currently being derived by several research groups. Such data, together with direct proton measurements from balloons and spacecraft, allow the determination of particle energy spectra near the Earth's orbit in successive moments of time. Spectra of RSPs in a number of large solar events tend to indicate the existence of multistep acceleration at/near the Sun. In this paper, we study the generation of RSP by neutral current sheet, stochastic, and shock-wave acceleration, within the framework of two-component concepts for ground level enhancements (GLEs) of solar cosmic rays (SCRs). Our analysis is extended to large solar events (GLEs) of 1989 September 29, 2000 July 14, 2003 October 28, and 2005 January 20. We found two different particle populations (components) in the relativistic energy range: a prompt component (PC), characterized by an early impulselike intensity increase, hard spectrum and high anisotropy, and a delayed component, presenting a gradual late increase, soft spectrum and low anisotropy. Based on a two-source model for SCR spectrum formation at the Sun, we carried out theoretical calculations of spectra in the sources for both components. We conclude that the processes in neutral current sheet, together with stochastic acceleration in expanding magnetic trap in the solar corona, are able to explain the production of two different relativistic components. Shock acceleration in the presence of coronal mass ejection (CME) fits fairly only the nonrelativistic range of the SCR spectrum, but fails in the description of relativistic proton spectra, especially for the PC.

Perez-Peraza, J. [Instituto de GeofIsica, UNAM, C.U., Coyoacan, 04510, Mexico, D.F. (Mexico); Vashenyuk, E. V.; Balabin, Yu. V. [Polar Geophysical Institute, Apatity, Murmansk Region, 184209 (Russian Federation); Miroshnichenko, L. I. [N.V. Pushkov Institute IZMIRAN, Moscow Region, 142190 (Russian Federation); Gallegos-Cruz, A. [UPIICSA, I.P.N., Depto. de Ciencias Basicas, Te 950, Iztacalco, 08400, Mexico D.F. (Mexico)

2009-04-20

414

Modelling of blast loading on aboveground structures - II. Internal blast and ground shock

NASA Astrophysics Data System (ADS)

Recent studies of the nature and structural effects of confined explosions, contact blast and explosion-induced ground shock are presented. High explosive blast is distinguished from that due to a gaseous deflagration. The effects of confinement and venting are considered in the evaluation of dynamic loads. Maxima for the initial internal blast pressure can be estimated from the scaled blast data or theoretical analyses of normal blast wave reflection from a rigid wall. Semi-empirical relations and prediction methods for gas pressures for many types of internal explosions including high explosives, gas mixtures and dust suspensions are given on the basis of pseudo-static character. The loading of a contact explosion and the associated effects on a concrete target are determined as functions of charge weight, concrete strength and member thickness. In the final part, the evaluation of both airblast-induced ground shock and directly transmitted motion are included in simple form without considering the soil-structure interaction.

Beshara, F. B. A.

1994-06-01

415

NASA Astrophysics Data System (ADS)

The Basic Local Alignment Search Tool (BLAST) is arguably the most widely used program in bioinformatics. By sacrificing sensitivity for speed, it makes sequence comparison practical on huge sequence databases currently available. The original version of BLAST was developed in 1990. Since then it has spawned a variant of specialized programs. This chapter surveys the development of BLAST and BLAST-like programs for homology search, discusses alignment statistics that are used in assessment of reported matches in BLAST, and provides the reader with guidance to select appropriate programs and set proper parameters to match research requirements.

Ma, Jian; Zhang, Louxin

416

The application of magnetized, intense, relativistic-electron beams to the generation of electromagnetic radiation at wavelengths ranging from 10 cm down to a fraction of a millimeter has enabled significant advances to be made in peak power capabilities. The physical mechanisms are conveniently divided into three categories according to the experimental feature which determines the output wavelength. These categories are related

V. L. Granatstein

1978-01-01

417

During the recovery phase of a magnetic storm, fluxes of relativistic (>1 MeV) electrons in the inner magnetosphere (3<=L<=6) increase to beyond prestorm levels, reaching a peak ~4 days after the initiation of the storm. In order to account for the generation of these ``killer electrons'' a model is presented primarily on the basis of the stochastic acceleration of electrons

Danny Summers; Chun-yu Ma

2000-01-01

418

During the recovery phase of a magnetic storm, fluxes of relativistic ($>1$\\u000aMeV) electrons in the inner magnetosphere ($3\\\\le L \\\\le 6$) increase to beyond\\u000apre-storm levels, reaching a peak about 4 days after the initiation of the\\u000astorm. In order to account for the generation of these \\

Danny Summers; Chun-yu Ma

1999-01-01

419

Blast wave from buried charges

While much airblast data are available for height-of-burst (HOB) effects, systematic airblast data for depth-of-burst (DOB) effects are more limited. It is logical to ask whether the spherical 0.5-g Nitropenta charges that, proved to be successful for HOB tests at EMI are also suitable for experiments with buried charges in the laboratory scale; preliminary studies indicated in the alternative. Of special interest is the airblast environment generated by detonations just above or below the around surface. This paper presents a brief summary of the test results.

Reichenbach, H.; Behrens, K. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany); Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States)

1993-08-01

420

Nuclear blast program for mini-calculators. Engineering report

A program has been written for the HP-97 (HP-67) minicomputer to solve the blast wave from a nuclear detonation. The program first determines standard-altitude parameters for the altitude of interest. Using these parameters as input, the program then calculates pressures, temperatures, densities, velocities, and Mach Numbers in front and behind the shock. Three subroutines allows the user to input (for any altitude < or = 82,000 ft) a specific overpressure across the shock, a specific gust velocity behind the blast wave, or a specific dynamic pressure behind the blast wave. Corresponding parameters for each input are calculated.

Patrick, R.P.

1981-03-09

421

Relativistic Effects on Chemical Properties.

ERIC Educational Resources Information Center

Discusses how anomalous chemical properties may be explained by considering relativistic effects. Traces development of the relativistic wave equation (Dirac equation) starting with the Borh treatment of the hydrogen atom and discusses major consequences of the Dirac equation. Suggests that these topics receive greater attention in the…

McKelvey, Donald R.

1983-01-01

422

Experimental modeling of explosive blast-related traumatic brain injuries.

This study aims to characterize the interaction of explosive blast waves through simulated anatomical systems. We have developed physical models and a systematic approach for testing traumatic brain injury (TBI) mechanisms and occurrences. A simplified series of models consisting of spherical poly(methyl methacrylate) (PMMA) shells housing synthetic gelatins as brain simulants have been utilized. A series of experiments was conducted to compare the sensitivity of the system response to mechanical properties of the simulants under high strain-rate explosive blasts. Small explosive charges were directed at the models to produce a realistic blast wave in a scaled laboratory setting. Blast profiles were measured and analyzed to compare system response severity. High-speed shadowgraph imaging captured blast wave interaction with the head model while particle tracking captured internal response for displacement and strain correlation. The results suggest amplification of shock waves inside the head near material interfaces due to impedance mismatches. In addition, significant relative displacement was observed between the interacting materials suggesting large strain values of nearly 5%. Further quantitative results were obtained through shadowgraph imaging of the blasts confirming a separation of time scales between blast interaction and bulk movement. These results lead to a conclusion that primary blast effects may potentially contribute significantly to the occurrence of military associated TBI. PMID:20580931

Alley, Matthew D; Schimizze, Benjamin R; Son, Steven F

2011-01-01

423

Blast Loading Experiments of Surrogate Models for Tbi Scenarios

NASA Astrophysics Data System (ADS)

This study aims to characterize the interaction of explosive blast waves through simulated anatomical models. We have developed physica