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Sample records for outburst thermonuclear runaways

  1. Thermonuclear runaways in nova outbursts

    NASA Technical Reports Server (NTRS)

    Shankar, Anurag; Arnett, David; Fryxell, Bruce A.

    1992-01-01

    Results of exploratory, two-dimensional numerical calculations of a local thermonuclear runaway on the surface of a white dwarf are reported. It is found that the energy released by the runaway can induce a significant amount of vorticity near the burning region. Such mass motions account naturally for mixing of core matter into the envelope during the explosion. A new mechanism for the lateral spread of nuclear burning is also discussed.

  2. The Thermonuclear Runaway and the Classical Nova Outburst

    NASA Astrophysics Data System (ADS)

    Starrfield, S.; Iliadis, C.; Hix, W. R.

    2016-05-01

    Nova explosions occur on the white dwarf component of a cataclysmic variable binary stellar system that is accreting matter lost by its companion. When sufficient material has been accreted by the white dwarf, a thermonuclear runaway occurs and ejects material in what is observed as a classical nova explosion. We describe both the recent advances in our understanding of the progress of the outburst and outline some of the puzzles that are still outstanding. We report on the effects of improving both the nuclear reaction rate library and including a modern nuclear reaction network in our one-dimensional, fully implicit, hydrodynamic computer code. In addition, there has been progress in observational studies of supernovae Ia with implications about the progenitors, and we discuss that in this review.

  3. The Nova Outburst: Thermonuclear Runaways on Degenerated Dwarfs

    SciTech Connect

    Starrfield, S.; Truran, J.W.; Sparks, W.M.

    1999-07-08

    Observational and theoretical studies of the outbursts of classical novae have provided critical insights into a broad range of astrophysical phenomena. Thermonuclear runaways (TNRs) in accreted hydrogen-rich envelopes on the white dwarf (WD) components of close binary systems constitute not only the outburst mechanism for a classical nova explosion, but also the recurrent novae and a fraction of the symbiotic novae explosions. Studies of the general characteristics of these explosions, both in our own galaxy and in neighboring galaxies of varying metallicity, can teach us about binary stellar evolution, while studies of the evolution of nova binary systems can constrain models for the (as yet unidentified) progenitors of Type Ia supernovae. Further, the empirical relation between the peak luminosity of a nova and the rate of decline, which presents a challenge to theoretical models, allows novae to be utilized as standard candles for distance determinations out to the Virgo Cluster. E xtensive studies of novae with IUE and the resulting abundance determinations have revealed the existence of oxygen-neon white dwarfs in some systems. The high levels of enrichment of novae ejecta in elements ranging from carbon to sulfur confirm that there is significant dredge-up of matter from the core of the underlying white dwarf and enable novae to contribute to the chemical enrichment of the interstellar medium. Observations of the epoch of dust formation in the expanding shells of novae allow important constraints to be placed on the dust formation process and confirm that graphite, SiC, and SiO{sub 2} grains are formed by the outburst. It is possible that grains from novae were injected into the pre-solar nebula and can be identified with some of the pre-solar grains or ''stardust'' found in meteorites. Finally, g-ray observations during the first several years of their outburst, using the next generation of satellite observatories, could confirm

  4. A review of the thermonuclear runaway model of a nova outburst

    NASA Technical Reports Server (NTRS)

    Sparks, W. M.; Starrfield, S.; Truran, J. W.

    1977-01-01

    Kraft's (1963) model for a nova outburst caused by a thermonuclear runaway in the hydrogen-rich matter accreted onto the white dwarf in a binary system is reviewed. Hydrostatic and hydrodynamic studies of this phenomenon are summarized, analyses of shock ejection based on hydrodynamic computer codes are discussed, and one specific hydrodynamic code is outlined. Results obtained with this code are presented and evaluated for an initial model containing a white dwarf with a hydrogen-rich envelope of 0.0001 to 0.001 solar mass in hydrostatic and thermal equilibrium. It is shown that an implicit hydrodynamic computer code is required in order to study the thermonuclear-runaway phenomenon. The early evolution of three models with different intrinsic luminosities is illustrated, and enhancement of CNO nuclei at the bottom of the hydrogen-rich envelope is investigated. It is suggested that the concentration of C-13, N-15, and O-17 should be greatly enhanced in nova ejecta.

  5. Thermonuclear runaways in nova outbursts. 2: Effect of strong, instantaneous, local fluctuations

    NASA Technical Reports Server (NTRS)

    Shankar, Anurag; Arnett, David

    1994-01-01

    In an attempt to understand the manner in which nova outbursts are initiated on the surface of a white dwarf, we investigate the effects fluctuations have on the evolution of a thermonuclear runaway. Fluctuations in temperature density, or the composition of material in the burning shell may arise due to the chaotic flow field generated by convection when it occurs, or by the accretion process itself. With the aid of two-dimensional reactive flow calculations, we consider cases where a strong fluctutation in temperature arises during the early, quiescent accretion phase or during the later, more dynamic, explosion phase. In all cases we find that an instantaneous, local temperature fluctuation causes the affected material to become Rayleigh-Taylor unstable. The rapid rise and subsequent expansion of matter immediately cools the hot blob, which prevents the lateral propagation of burning. This suggests that local temperature fluctuations do not play a significant role in directly initiating the runaway, especially during the early stages. However, they may provide an efficient mechanism of mixing core material into the envelope (thereby pre-enriching the fuel for subsequent episodes of explosive hydrogen burning) and of mixing substantial amounts of the radioactive nucleus N-13 into the surface layers, making novae potential gamma-ray sources. This suggests that it is the global not the local, evolution of the core-envelope interface to high temperatures which dominates the development of the runaway. We also present a possible new scenario for the initiation of nova outbursts based on our results.

  6. A hydrodynamic study of a slow nova outburst. [computerized simulation of thermonuclear runaway in white dwarf envelope

    NASA Technical Reports Server (NTRS)

    Sparks, W. M.; Starrfield, S.; Truran, J. W.

    1978-01-01

    The paper reports use of a Lagrangian implicit hydrodynamics computer code incorporating a full nuclear-reaction network to follow a thermonuclear runaway in the hydrogen-rich envelope of a 1.25 solar-mass white dwarf. In this evolutionary sequence the envelope was assumed to be of normal (solar) composition and the resulting outburst closely resembles that of the slow nova HR Del. In contrast, previous CNO-enhanced models resemble fast nova outbursts. The slow-nova model ejects material by radiation pressure when the high luminosity of the rekindled hydrogen shell source exceeds the local Eddington luminosity of the outer layers. This is in contrast to the fast nova outburst where ejection is caused by the decay of the beta(+)-unstable nuclei. Nevertheless, radiation pressure probably plays a major role in ejecting material from the fast nova remnants. Therefore, the sequence from slow to fast novae can be interpreted as a sequence of white dwarfs with increasing amounts of enhanced CNO nuclei in their hydrogen envelopes, although other parameters such as the white-dwarf mass and accretion rate probably contribute to the observed variation between novae.

  7. Simulating Thermonuclear Runaway in Novae

    NASA Astrophysics Data System (ADS)

    Dursi, L. J.; Truran, J.; Zingale, M.; Calder, A. C.; Fryxell, B.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.; Tufo, H. M.; MacNeice, P.

    2000-12-01

    A nova is a thought to result from a partially degenerate thermonuclear runaway on the surface of a white dwarf. Material from the underlying white dwarf must be dredged up into the atmosphere in order to produce an explosion with the observed energies; the carbon and oxygen serve as catalysts for the hydrogen burning, allowing the much more temperature-sensitive CNO burning to occur. In order to understand this dredge-up problem, we are running two different types of simulations. The first are large-scale simulations with the FLASH code (Fryxell et al., 2000), using a one-dimensional set of initial conditions of a nova about to undergo runaway created by Ami Glasner. These initial conditions have been used in previous multidimensional simulations (Glasner et al. 1997; Kercek et al. 1998), but these simulations have given widely different results because of different mixing behaviors in the two codes. Our set of simulations will shed some light on this discrepancy; since our code has adaptive mesh refinement (MacNeice et al., 2000), we can afford to highly refine the region of the star where the mixing occurs, without the cost of highly refining the entire region. Because these large-scale computations are extremely compute-intensive, they are not appropriate for broad exploration of initial conditions. To do this, we use a One-Dimensional Turbulence (ODT) model which has been used in astrophysical models previously (Niemeyer & Kerstein, 1997). This allows us to use ODT simulations of the nova as experiments to guide us to interesting regimes to study further with multidimensional FLASH code simulations. This work was supported in part by the Department of Energy Grant No. B341495 to the Center for Astrophysical Thermonuclear Flashes at the University of Chicago under the ASCI Strategic Alliances Program and by NASA/Goddard Space Flight Center

  8. Thermonuclear runaways on neutron stars

    NASA Technical Reports Server (NTRS)

    Taam, R. E.; Picklum, R. E.

    1979-01-01

    Thermonuclear runaways which develop when neutron stars of 0.476 solar masses accrete hydrogen-rich material at 10 to the -10th and 2 x 10 to the -9th solar masses/year have been followed using a numerical model. It is found that a thermal instability occurs at densities in excess of 10 to the 5th g/cu cm and that the maximum accumulated mass required to initiate the runaway is 0.7 x 10 to the -12th and 2.1 x 10 to the -12th solar masses for the mass accretion rates of 10 to the -10th and 2 x 10 to the -9th solar masses/year, respectively. Heating the of the neutron star envelope by hydrogen burning leads to the ignition of helium. The nonequilibrium burning of helium by a combination of (alpha, p), (p, gamma), and (alpha, gamma) reactions involving O-14, O-15, and other heavy nuclei provides the energy for an X-ray burst. The gross properties of these models bear suggestive resemblance to those observed for some X-ray burst sources.

  9. Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

    NASA Technical Reports Server (NTRS)

    Starrfield, S. G.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1981-01-01

    A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to evolve thermonuclear runaways in the accreted hydrogen rich envelopes of 1.0 Msub solar neutron stars with radii of 10 km and 20 km. Simulations produce outbursts which last from about 750 seconds to about one week. Peak effective temeratures and luninosities were 26 million K and 80 thousand Lsub solar for the 10 km study and 5.3 millison and 600 Lsub solar for the 20 km study. Hydrodynamic expansion on the 10 km neutron star produced a precursor lasting about one ten thousandth seconds.

  10. Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1982-01-01

    A Lagrangian, fully implicit, one-dimensional hydrodynamic computer code is used to evolve thermonuclear runaways in the accreted hydrogen-rich envelopes of 1.0-solar-mass neutron stars with radii of 10 km and 20 km. The simulations produce outbursts lasting from approximately 750 seconds to approximately one week. The peak effective temperatures and luminosities are 2.6 x 10 to the 7th K and 8 x 10 to the 4th solar luminosities for the 10 km study and 5.3 x 10 to the 6th K and 600 solar luminosities for the 20 km study. It is found that hydrodynamic expansion on the 10 km neutron star produced a precursor lasting approximately 0.0001 second. The study assumes that the bursters and transient X-ray sources occur as a result of mass transfer from a secondary onto a neutron star in a fashion analogous to the nova phenomena. The peak temperatures and luminosities are found to be inversely proportional to the radius of the neutron stars and the calculations here, together with those in the literature, indicate that the actual radii of most neutron stars must be closer to 10 km than 20 km.

  11. Thermonuclear runaways investigated using drip line beta decays

    NASA Astrophysics Data System (ADS)

    Wrede, Christopher

    2016-09-01

    In close binary star systems, mass transfer onto the surface of a white dwarf or neutron star can lead to spectacular periodic emissions including classical novae and x-ray bursts. Accurate nuclear reaction rates are needed to model energy generation and nucleosynthesis in these thermonuclear runaways enabling meaningful comparisons to observations. An experimental program has been established at the National Superconducting Cyclotron Laboratory to constrain the most influential nuclear physics uncertainties using the beta decays of nuclides adjacent to the proton drip line. In particular, the beta decays of 20Mg, 26P, and 31Cl have been used to investigate the 15O(α,γ)19Ne, 25Al(p,γ)26Si, and 30P(p,γ)31S reaction rates, respectively. These studies relate to the shapes of x-ray burst light curves, the production of the radionuclide 26Al in the Milky Way, and the identification of presolar nova grains in meteoritic material.

  12. Hydrodynamic studies of the nova outburst

    SciTech Connect

    Starrfield, S.

    1980-01-01

    Hydrostatic studies have shown that a thermonuclear runaway will occur in the hydrogen-rich material accumulated on the surface of a degenerate star. Results of earlier studies are used to obtain models for calculations which show that the resulting thermonuclear runaway produces a nova outburst; the characteristics of this outburst depending on the carbon-oxygen abundance in the envelope. (GHT)

  13. Size-frequency distribution of gamma ray bursts from thermonuclear runaway on neutron stars accreting interstellar gas

    SciTech Connect

    Higdon, J.C.; Lingenfelter, R.E.

    1984-05-26

    We present some preliminary results of calculations we have made suggesting that runaway thermonuclear burning of interstellar gas accreted onto magnetic neutron stars can account for the observed size-frequency distribution of gamma ray bursts.

  14. Thermonuclear ignition and runaway in type Ia supernovae

    SciTech Connect

    Wheeler, J.C. )

    1990-12-01

    Recent theoretical models of type Ia SN explosions are examined analytically. Qualitatively, the process described involves mass transfer to a C/O white dwarf in a binary system, bringing it near the Chandrasekhar limit and initiating runaway carbon burning. Particular attention is given to (1) carbon ignition and the convective Urca process, which acts to delay runaway, (2) detonation and deflagration models of SN dynamics, and (3) the application of observational data (light curves and spectra) to place limits on dynamical models. It is shown that most deflagration-type models do not give good agreement with spectroscopic observations, while those that do fail to explain density profiles deduced from other observations. Further research on damped-detonation models is recommended. 32 refs.

  15. Thermonuclear ignition and runaway in type IA supernovae

    NASA Astrophysics Data System (ADS)

    Wheeler, J. Craig

    1990-12-01

    Recent theoretical models of type Ia SN explosions are examined analytically. Qualitatively, the process described involves mass transfer to a C/O white dwarf in a binary system, bringing it near the Chandrasekhar limit and initiating runaway carbon burning. Particular attention is given to (1) carbon ignition and the convective Urca process, which acts to delay runaway, (2) detonation and deflagration models of SN dynamics, and (3) the application of observational data (light curves and spectra) to place limits on dynamical models. It is shown that most deflagration-type models do not give good agreement with spectroscopic observations, while those that do fail to explain density profiles deduced from other observations. Further research on damped-detonation models is recommended.

  16. The historical record for Sirius - Evidence for a white-dwarf thermonuclear runaway?

    NASA Technical Reports Server (NTRS)

    Bruhweiler, Frederick C.; Kondo, Yoji; Sion, Edward M.

    1986-01-01

    Evidence was recently presented that in medieval times Sirius was a bright red star, rather than the present bluish-white star. Here, the results of attempts to detect possible planetary nebula ejecta toward Sirius using data obtained by the IUE are presented. Based on these results and in the light of recent advances in understanding white-dwarf evolution, it is proposed that Sirius B underwent a recent thermonuclear runaway event triggered by a diffusion-induced CN reaction.

  17. Radio outbursts in RS Canum Venaticorum stars - coronal heating and electron runaway

    SciTech Connect

    Mullan, D.J.

    1985-08-01

    Radio outbursts of RS CVn stars are sometimes thought of as analogs of flares in red dwarf stars. The possibility is examined that the outbursts are not due to flares, but rather to a highly efficient case of coronal heating: mechanical energy reaching the corona from the convection zone of an RS CVn star gives rise to induced electric fields which may be so large that electron runaway becomes possible. It is proposed that gyrosynchrotron emission from fast electrons which are produced by this process are the source of radio outbursts from RS CVn stars. 31 references.

  18. A burst from a thermonuclear runaway on an ONeMg white dwarf

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Politano, M.; Truran, J. W.; Sparks, W. M.

    1992-01-01

    Studies which examine the consequences of accretion, at rates of 10(exp -9) solar mass/yr and 10(exp -10) solar mass/yr, onto an ONeMg white dwarf with a mass of 1.35 solar masses are performed. In these studies, a Lagrangian, hydrodynamic, one-dimensional computer code was used. The code now includes a network with 89 nuclei up to Ca-40, elemental diffusion, new opacities, and new equation of state. The initial abundance distribution corresponded to a mixture that was enriched to either 25, 50, or 75 percent in products of carbon burning. The remaining material in each case is assumed to have a solar composition. The evolution of the thermonuclear runaway in the 1.35 solar mass white dwarf, with M = 10(exp -9) solar mass, produced peak temperatures in the shell source exceeding 300 million degrees. The sequence produced significant amounts of Na-22 from proton captures onto Ne-20 and significant amounts of Al-26 from proton captures on Mg-24. This sequence ejected 5.2 x 10(exp -6) solar mass moving with speeds from approximately 100 km/s to 2300 km/s. When the mass accretion rate was decreased to 10(exp -10) solar mass, the resulting thermonuclear runaway produced a shock that moved through the outer envelope of the white dwarf and raised the surface luminosity to L greater than 10(exp 7) solar luminosity and the effective temperature to values exceeding 10(exp 7) K. The interaction of the material expanding from off of the white dwarf with the accretion disk should produce a burst of gamma-rays.

  19. A burst from a thermonuclear runaway on an ONeMg white dwarf

    NASA Astrophysics Data System (ADS)

    Starrfield, S.; Politano, M.; Truran, J. W.; Sparks, W. M.

    1992-02-01

    Studies which examine the consequences of accretion, at rates of 10-9 solar mass/yr and 10-10 solar mass/yr, onto an ONeMg white dwarf with a mass of 1.35 solar masses are performed. In these studies, a Lagrangian, hydrodynamic, one-dimensional computer code was used. The code now includes a network with 89 nuclei up to Ca-40, elemental diffusion, new opacities, and new equation of state. The initial abundance distribution corresponded to a mixture that was enriched to either 25, 50, or 75 percent in products of carbon burning. The remaining material in each case is assumed to have a solar composition. The evolution of the thermonuclear runaway in the 1.35 solar mass white dwarf, with M = 10-9 solar mass, produced peak temperatures in the shell source exceeding 300 million degrees. The sequence produced significant amounts of Na-22 from proton captures onto Ne-20 and significant amounts of Al-26 from proton captures on Mg-24. This sequence ejected 5.2 x 10-6 solar mass moving with speeds from approximately 100 km/s to 2300 km/s. When the mass accretion rate was decreased to 10-10 solar mass, the resulting thermonuclear runaway produced a shock that moved through the outer envelope of the white dwarf and raised the surface luminosity to L greater than 107 solar luminosity and the effective temperature to values exceeding 107 K. The interaction of the material expanding from off of the white dwarf with the accretion disk should produce a burst of gamma-rays.

  20. Outbursts in Symbiotic Binaries

    NASA Technical Reports Server (NTRS)

    Sonneborn, George (Technical Monitor); Keyes, Charles

    2005-01-01

    A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the slow novae are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic recurrent novae, which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called classical symbiotics, many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multiwavelength observations of these events. In FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project

  1. Outbursts in Symbiotic Binaries: Z and Continued Observation

    NASA Technical Reports Server (NTRS)

    Sonneborn, George (Technical Monitor); Keyes, Charles

    2005-01-01

    A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the "slow novae" are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic "recurrent novae", which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called "classical symbiotics," many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multi- wavelength observations of these events. First of all in FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project. The present program is a continuation of that cycle 2 effort. Indeed, the observations acquired in this program are vital to the proper interpretation of the material acquired in cycle 2 as the new data cover the critical time period when the star continues to decline from outburst and actually returns to quiescence. The utilization of these data have allowed us to refine and complete description of our new model for classical symbiotic system

  2. Nova outbursts in the case of mild hibernation

    SciTech Connect

    Livio, M.; Shankar, A.; Truran, J.W.

    1988-02-01

    The necessary conditions for the production of strong thermonuclear runaways in the hibernation scenario are identified and explored. It is found that a reduction in the accretion rate by a factor of about 100, for a period longer than a few thousand years, is generally sufficient to ensure nova-type outbursts, even in the presence of rather high preoutburst accretion rates. Nova outbursts can be obtained under mild hibernation conditions on 1 solar mass white dwarfs as well as on very massive ones. A reduction in the accretion rate by a factor of 10 only is insufficient to produce a nova outburst, if the preoutburst accretion rate is as high as 10 to the -8th solar mass/yr. 28 references.

  3. Target of Opportunity Observations of TOADS: Finding the Dust in Super-Outburst Ejecta

    NASA Astrophysics Data System (ADS)

    Hoard, Donald; Ciardi, David; Howell, Steve

    2008-03-01

    Tremendous Outburst Amplitude Dwarf novae (TOADs) consist of a white dwarf primary star and an extremely low mass main sequence or brown dwarf-like secondary star. The latter fills its Roche lobe and transfers matter to the white dwarf through the inner Lagrange point into an accretion disk. TOADs undergo non-thermonuclear (i.e., disk instability) super-outbursts on timescales of decades. During the decline from super-outburst peak they display a characteristic dip in light curves at visible wavelengths, reminiscent of what is observed in slow classical (i.e., thermonuclear runaway) novae. In classical novae, the visible light dip is attributed to the formation of dust in the nova ejecta but, until now, the cause of the dip in TOAD light curves has remained unclear. In 2004, a previously unknown TOAD was discovered as it went into super-outburst, and our team was granted a Spitzer DDT program with which we have detected the likely formation of dust in the outburst ejecta. We now propose a Target of Opportunity program with Spitzer to observe an additional super-outbursting TOAD, in order to address the following questions: 1) Do all TOADs produce dust during their outbursts?; 2) What is the timescale for dust formation and dissipation?; 3) How much dust is produced during a super-outburst?; and 4) How does the dust production scale with the outburst amplitude? Spitzer is uniquely capable of detecting and characterizing the dust formed in the ejecta during super-outbursts and fundamentally changing the understanding of TOADs, their super-outbursts, and their contribution to the recycling of the interstellar medium.

  4. Thermonuclear model for. gamma. -ray bursts

    SciTech Connect

    Woosley, S.E.

    1981-08-26

    The evolution of magnetized neutron stars with field strengths of approx. 10/sup 12/ gauss that are accreting mass onto kilometer-sized polar regions at a rate of approx. /sup 13/ M/sub 0/yr/sup -1/ is examined. Based on the results of one-dimensional calculations, one finds that stable hydrogen burning, mediated by the hot CNO-cycle, will lead to a critical helium mass in the range 10/sup 20/ to 10/sup 22/ g km/sup -2/. Owing to the extreme degeneracy of the electron gas providing pressure support, helium burning occurs as a violent thermonuclear runaway which may propagate either as a convective deflagration (Type I burst) or as a detonation wave (Type II burst). Complete combustion of helium into /sup 56/Ni releases from 10/sup 38/ to 10/sup 40/ erg km/sup -2/ and pushes hot plasma with ..beta.. > 1 above the surface of the neutron star. Rapid expansion of the plasma channels a substantial fraction of the explosion energy into magnetic field stress. Spectral properties are expected to be complex with emission from both thermal and non-thermal processes. The hard ..gamma..-outburst of several seconds softens as the event proceeds and is followed by a period, typically of several minutes duration, of softer x-ray emission as the subsurface ashes of the thermonuclear explosion cool. In this model, most ..gamma..-ray bursts currently being observed are located at a distance of several hundred parsecs and should recur on a timescale of months to centuries with convective deflagrations (Type I bursts) being the more common variety. An explanation for Jacobson-like transients is also offered.

  5. Swift observations of the 2015 outburst of AG Peg - from slow nova to classical symbiotic outburst

    NASA Astrophysics Data System (ADS)

    Ramsay, Gavin; Sokoloski, J. L.; Luna, G. J. M.; Nuñez, N. E.

    2016-10-01

    Symbiotic stars often contain white dwarfs with quasi-steady shell burning on their surfaces. However, in most symbiotics, the origin of this burning is unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear runaway. In 2015 June, the symbiotic slow nova AG Peg was seen in only its second optical outburst since 1850. This recent outburst was of much shorter duration and lower amplitude than the earlier eruption, and it contained multiple peaks - like outbursts in classical symbiotic stars such as Z And. We report Swift X-ray and UV observations of AG Peg made between 2015 June and 2016 January. The X-ray flux was markedly variable on a time-scale of days, particularly during four days near optical maximum, when the X-rays became bright and soft. This strong X-ray variability continued for another month, after which the X-rays hardened as the optical flux declined. The UV flux was high throughout the outburst, consistent with quasi-steady shell burning on the white dwarf. Given that accretion discs around white dwarfs with shell burning do not generally produce detectable X-rays (due to Compton-cooling of the boundary layer), the X-rays probably originated via shocks in the ejecta. As the X-ray photoelectric absorption did not vary significantly, the X-ray variability may directly link to the properties of the shocked material. AG Peg's transition from a slow symbiotic nova (which drove the 1850 outburst) to a classical symbiotic star suggests that shell burning in at least some symbiotic stars is residual burning from prior novae.

  6. Restablished Accretion in Post-outburst Classical Novae Revealed by X-rays

    NASA Astrophysics Data System (ADS)

    Hernanz, Margarita; Ferri, Carlo; Sala, Glòria

    2009-05-01

    Classical novae are explosions on accreting white dwarfs (hereinafter WDs) in cataclysmic variables (hereinafter CVs) a hydrogen thermonuclear runaway on top of the WD is responsible for the outburst. X-rays provide a unique way to study the turn-off of H-burning, because super soft X-rays reveal the hot WD photosphere, but also to understand how accretion is established again in the binary system. Observations with XMM-Newton of some post-outburst novae have revealed such a process, but a coverage up to larger energies -as Simbol-X will provide- is fundamental to well understand the characteristics of the binary system and of the nova ejecta. We present a brief summary of our results up to now and prospects for the Simbol-X mission.

  7. Synthesis of C-rich dust in CO nova outbursts

    NASA Astrophysics Data System (ADS)

    José, Jordi; Halabi, Ghina M.; El Eid, Mounib F.

    2016-09-01

    Context. Classical novae are thermonuclear explosions that take place in the envelopes of accreting white dwarfs in stellar binary systems. The material transferred onto the white dwarf piles up under degenerate conditions, driving a thermonuclear runaway. In these outbursts, about 10-7-10-3 M⊙, enriched in CNO and sometimes other intermediate-mass elements (e.g., Ne, Na, Mg, or Al for ONe novae) are ejected into the interstellar medium. The large concentrations of metals spectroscopically inferred in the nova ejecta reveal that the solar-like material transferred from the secondary mixes with the outermost layers of the underlying white dwarf. Aims: Most theoretical models of nova outbursts reported to date yield, on average, outflows characterized by O > C, from which, in principle, only oxidized condensates (e.g., O-rich grains) would be expected. Methods: To specifically address whether CO novae can actually produce C-rich dust, six different hydrodynamic nova models have been evolved, from accretion to the expansion and ejection stages, with different choices for the composition of the substrate with which the solar-like accreted material mixes. Updated chemical profiles inside the H-exhausted core have been used, based on stellar evolution calculations for a progenitor of 8 M⊙ through H- and He-burning phases. Results: We show that these profiles lead to C-rich ejecta after the nova outburst. This extends the possible contribution of novae to the inventory of presolar grains identified in meteorites, particularly in a number of carbonaceous phases (i.e., nanodiamonds, silicon carbides, and graphites).

  8. Probing thermonuclear burning on accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Keek, L.

    2008-12-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating

  9. Merging white dwarfs and thermonuclear supernovae.

    PubMed

    van Kerkwijk, M H

    2013-06-13

    Thermonuclear supernovae result when interaction with a companion reignites nuclear fusion in a carbon-oxygen white dwarf, causing a thermonuclear runaway, a catastrophic gain in pressure and the disintegration of the whole white dwarf. It is usually thought that fusion is reignited in near-pycnonuclear conditions when the white dwarf approaches the Chandrasekhar mass. I briefly describe two long-standing problems faced by this scenario, and the suggestion that these supernovae instead result from mergers of carbon-oxygen white dwarfs, including those that produce sub-Chandrasekhar-mass remnants. I then turn to possible observational tests, in particular, those that test the absence or presence of electron captures during the burning.

  10. Thermonuclear model for high energy transients

    SciTech Connect

    Woosley, S.E.

    1982-01-01

    The thermonuclear model for x- and ..gamma..-ray bursts is discussed. Different regimes of nuclear burning are reviewed, each appropriate to a given range of (steady state) accretion rate. Accretion rates in the range 10/sup -14/ to 10/sup -8/ Msub solar y/sup -1/ all appear capable of producing x-ray transients of various durations and intervals. Modifications introduced by radiatively driven mass loss, the thermal inertia of the envelope, different burning mechanisms, and two-dimensional considerations are discussed as are difficulties encountered when the thermonuclear model is confronted with observations of rapidly recurrent bursts (less than or equal to 10 min), and super-Eddington luminosities and temperatures. Results from a numerical simulation of a combined hydrogen-helium runaway initiated at pycnonuclear density are presented for the first time. The thermonuclear model for ..gamma..-ray bursts is also reviewed and updated, particularly with regard to the breakdown of the steady state hypothesis employed in previous work. Solely on the basis of nuclear instability, ..gamma..-ray bursts of various types appear possible for a very broad variety of accretion rates (approx. 10/sup -17/ to approx. 10/sup -11/ Msub solar y/sup -1/) although other considerations may restrict this range. The thermonuclear model appears capable of yielding a great diversity of high energy transient phenomena for various accretion rates, magnetic field configurations, and neutron star envelope histories.

  11. Outburst activity of the symbiiotic binary AG Dra

    NASA Astrophysics Data System (ADS)

    Gális, R.; Hric, L.; Leedjärv, L.; Merc, J.

    2016-03-01

    The outburst activity of the symbiotic system AG Dra has been studied using extensive spectroscopic observational material. High luminosity and temperature of the hot component of AG Dra indicate that quasi-steady thermonuclear shell burning takes place on the surface of the white dwarf. The major (cool) outbursts at the beginning of active phases might occur due to enhanced thermonuclear burning triggered by disk instability. Smaller scale hot outbursts might be explained by the accretion disc instability model like in dwarf novae. We discovered significant similarities in photometric and spectroscopic behaviour of AG Dra and prototypical symbiotic star Z And.

  12. Thermonuclear processes and accretion onto neutron star envelopes - X-ray burst and transient sources

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1982-01-01

    A Lagrangian, fully implicit, one-dimensional hydrodynamic computer code is used to investigate the evolution of thermonuclear runaways in the thick accreted hydrogen-rich envelopes of 1.0-solar-mass neutron stars having radii of 10 km and 20 km. The simulations produce outbursts that range in time scale from about 2000 seconds to more than a day. For the 10-km study, the peak effective temperature is 3.3 x 10 to the 7th K, and the peak luminosity is 2 x 10 to the 5th solar luminosities. The 20-km neutron star produces a peak effective temperature and luminosity of 5.3 x 10 to the 6th K and 5.9 x 10 to the 2nd solar luminosities. Also investigated are the effects of changes in the rates of the O-14(alpha, proton) and O-15(alpha, gamma) reactions on the evolution. Hydrodynamic expansion on the 10-km neutron star produces a precursor lasting about 10 to the -6th sec. The evolution of a gas cloud impacting the surface of a 20-km, 1-solar-mass neutron star is studied in an attempt to simulate the magnetospheric gate model of the X-ray burst sources.

  13. Nucleosynthesis in Thermonuclear Supernovae

    SciTech Connect

    Claudia, Travaglio; Hix, William Raphael

    2013-01-01

    We review our understanding of the nucleosynthesis that occurs in thermonuclear supernovae and their contribution to Galactic Chemical evolution. We discuss the prospects to improve the modeling of the nucleosynthesis within simulations of these events.

  14. Runaway quarks

    SciTech Connect

    Gurarie, V.

    1995-08-01

    When heavy nuclei collide, a quark-gluon plasma is formed. The plasma is subject to a strong electric field due to the charge of the colliding nuclei. The electric field can influence the behavior of the quark-gluon plasma. In particular, we might observe an increased number of quarks moving in the direction of that field, as we do in the standard electron-ion plasma. In this paper we show that this phenomenon, called the runaway quarks, does not exist.

  15. Recombinative plasma in electron runaway discharge

    SciTech Connect

    Kuznetsov, Yu.K.; Galvao, R.M.O.; Usuriaga, O.C.; Krasheninnikov, S.I.; Soboleva, T.K.; Tsypin, V.S.; Fonseca, A.M.M.; Ruchko, L.F.; Sanada, E.K.

    2005-07-15

    Cold recombinative plasma is the basic feature of the new regime of runaway discharges recently discovered in the Tokamak Chauffage Alfven Bresilien tokamak [R. M. O. Galvao et al., Plasma Phys. Controlled Fusion 43, 1181 (2001)]. With low plasma temperature, the resistive plasma current and primary Dreicer process of runaway generation are strongly suppressed at the stationary phase of the discharge. In this case, the runaway avalanche, which has been recently recognized as a novel important mechanism for runaway electron generation in large tokamaks, such as International Thermonuclear Experimental Reactor, during disruptions, and for electric breakdown in matter, is the only mechanism responsible for toroidal current generation and can be easily observed. The measurement of plasma temperature by the usual methods is a difficult task in fully runaway discharges. In the present work, various indirect evidences for low-temperature recombinative plasma are presented. The direct observation of recombinative plasma is obtained as plasma detachment from the limiter. The model of cold recombinative plasma is also supported by measurements of plasma density and H{sub {alpha}} emission radial profiles, analysis of time variations of these parameters due to the relaxation instability, estimations of plasma resistivity from voltage spikes, and energy and particle balance calculations.

  16. Thermonuclear land of plenty

    NASA Astrophysics Data System (ADS)

    Gasior, P.

    2014-11-01

    Since the process of energy production in the stars has been identified as the thermonuclear fusion, this mechanism has been proclaimed as a future, extremely modern, reliable and safe for sustaining energetic needs of the humankind. However, the idea itself was rather straightforward and the first attempts to harness thermonuclear reactions have been taken yet in 40s of the twentieth century, it quickly appeared that physical and technical problems of domesticating exotic high temperature medium known as plasma are far from being trivial. Though technical developments as lasers, superconductors or advanced semiconductor electronics and computers gave significant contribution for the development of the thermonuclear fusion reactors, for a very long time their efficient performance was out of reach of technology. Years of the scientific progress brought the conclusions that for the development of the thermonuclear power plants an enormous interdisciplinary effort is needed in many fields of science covering not only plasma physics but also material research, superconductors, lasers, advanced diagnostic systems (e.g. spectroscopy, interferometry, scattering techniques, etc.) with huge amounts of data to be processed, cryogenics, measurement-control systems, automatics, robotics, nanotechnology, etc. Due to the sophistication of the problems with plasma control and plasma material interactions only such a combination of the research effort can give a positive output which can assure the energy needs of our civilization. In this paper the problems of thermonuclear technology are briefly outlined and it is shown why this domain can be a broad field for the experts dealing with electronics, optoelectronics, programming and numerical simulations, who at first glance can have nothing common with the plasma or nuclear physics.

  17. Red Runaways

    NASA Astrophysics Data System (ADS)

    Vickers, John; Smith, M. C.; Grebel, E.

    2014-01-01

    We present results of a kinematic analysis of high-metallicity late-type dwarfs in SDSS spectroscopic data. These dwarfs, most likely having been generated in the disks of the Milky Way, are fit to phase-space profiles using maximum likelihood methods. Outliers from these kinematic profiles (objects having abnormally high or incongruous velocities related to their neighbors) are then extracted based on stars' individual likelihoods according to these fits. Since these high metallicity dwarfs were probably born close to the midplane, we expect that they obtained outlying phase space properties through some sort of ejection process; as such we then examine these objects in the context of various ejection processes (dynamic binary encounters, supernovae kicks, black hole encounters). This is one of the first studies of runaway and hypervelocity stars in the F-M dwarf regime and is made possible by the advent of million item spectroscopy surveys and machine learning techniques.

  18. Anomalous Cooling of the Massive White Dwarf in U Geminorum Following a Narrow Dwarf Nova Outburst

    NASA Astrophysics Data System (ADS)

    Sion, Edward M.; Cheng, F. H.; Szkody, Paula; Sparks, Warren; Gänsicke, Boris; Huang, Min; Mattei, Janet

    1998-03-01

    We obtained Hubble Space Telescope Goddard High-Resolution Spectrograph medium-resolution (G160M grating), phase-resolved spectroscopic observations of the prototype dwarf nova U Geminorum during dwarf nova quiescence, 13 days and 61 days following the end of a narrow outburst. The spectral wavelength ranges were centered on three different line regions: N V (1238 Å, 1242 Å), Si III (1300 Å), and He II (1640 Å). All of the quiescent spectra at both epochs are dominated by absorption lines and show no emission features. The Si III and He II absorption-line velocities versus orbital phase trace the orbital motion of the white dwarf, but the N V absorption velocities appear to deviate from the white dwarf motion. We confirm our previously reported low white dwarf rotational velocity, V sin i = 100 km s-1. We obtain a white dwarf orbital velocity semiamplitude K1 = 107 km s-1. Using the γ-velocity of Wade, we obtain an Einstein redshift of 80.4 km s-1 and hence a carbon core white dwarf mass of ~1.1 M⊙. We report the first subsolar chemical abundances of C and Si for U Gem with C/H = 0.05 times solar, almost certainly a result of C depletion due to thermonuclear processing. This C depletion is discussed within the framework of a weak thermonuclear runaway, contamination of the secondary during the common envelope phase, and mixing of C-depleted white dwarf gas with C-depleted matter deposited during a dwarf nova event. Remarkably, the Teff of the white dwarf 13 days after outburst is only 32,000 K, anomalously cooler than previous early postoutburst measurements. Extensive cooling during an extraordinarily long (210 days) quiescence followed by accretion onto an out-of-equilibrium cooled degenerate could explain the lower Teff. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  19. Runaways: A Silent Crisis.

    ERIC Educational Resources Information Center

    Ellenwood, Audrey E.; And Others

    This paper discusses several factors that contribute to running away, characteristics of runaways, and approaches to dealing with runaway youth. The decision of a youth to run away is usually the climax of several smaller events that have built over time and contribute to the youth's feeling out-of-control at home, in school, and in society. Peers…

  20. Pathway parameter and thermonuclear functions

    NASA Astrophysics Data System (ADS)

    Mathai, A. M.; Haubold, H. J.

    2008-04-01

    In the theory of thermonuclear reaction rates, analytical evaluation of thermonuclear functions for non-resonant reactions, including cases with cut-off and depletion of the tail of the Maxwell-Boltzmann distribution function were considered in a series of papers by Mathai and Haubold [A.M. Mathai, H.J. Haubold, Modern Problems in Nuclear and Neutrino Astrophysics, Akademie-Verlag, Berlin, 1988]. In the present paper we study more general classes of thermonuclear functions by introducing a pathway parameter α, so that when α→1 the thermonuclear functions in the Maxwell-Boltzmannian case are recovered. We will also give interpretations for the pathway parameter α in the case of cut-off and in terms of moments. Non-extensive statistical mechanics, as developed by Tsallis [C. Tsallis, What should a statistical mechanics satisfy to reflect nature? Physica D 193 (2004) 3-34], provides the physical basis for the generalized thermonuclear functions considered in this paper.

  1. National Runaway Safeline

    MedlinePlus

    ... Asked Questions Leadership Financials Events Media Resource Center Work at NRS Visit the Blog Youth & Teens Do you need help? The National Runaway Safeline (NRS) is here to listen whether you are ...

  2. National Runaway Safeline

    MedlinePlus

    ... Asked Questions Leadership Financials Events Media Resource Center Work at NRS Visit the Blog Youth & Teens Do you need help? The National Runaway Safeline (NRS) is here to listen whether you are ...

  3. Thermonuclear supernova models, and observations of Type Ia supernovae

    SciTech Connect

    Bravo, E.; Garcia-Senz, D.; Badenes, C.

    2005-10-21

    In this paper, we review the present state of theoretical models of thermonuclear supernovae, and compare their predictions with the constraints derived from observations of Type Ia supernovae. The diversity of explosion mechanisms usually found in one-dimensional simulations is a direct consequence of the impossibility to resolve the flame structure under the assumption of spherical symmetry. Spherically symmetric models have been successful in explaining many of the observational features of Type Ia supernovae, but they rely on two kinds of empirical models: one that describes the behaviour of the flame on the scales unresolved by the code, and another that takes account of the evolution of the flame shape. In contrast, three-dimensional simulations are able to compute the flame shape in a self-consistent way, but they still need a model for the propagation of the flame in the scales unresolved by the code. Furthermore, in three dimensions the number of degrees of freedom of the initial configuration of the white dwarf at runaway is much larger than in one dimension. Recent simulations have shown that the sensitivity of the explosion output to the initial conditions can be extremely large. New paradigms of thermonuclear supernovae have emerged from this situation, as the Pulsating Reverse Detonation. The resolution of all these issues must rely on the predictions of observational properties of the models, and their comparison with current Type Ia supernova data, including X-ray spectra of Type Ia supernova remnants.

  4. Runaway electrons and ITER

    NASA Astrophysics Data System (ADS)

    Boozer, Allen

    2016-10-01

    ITER planning for avoiding runaway damage depends on magnetic surface breakup in fast relaxations. These arise in thermal quenches and in the spreading of impurities from massive gas injection or shattered pellets. Surface breakup would prevent a runaway to relativistic energies were it not for non-intercepting flux tubes, which contain magnetic field lines that do not intercept the walls. Such tubes persist near the magnetic axis and in the cores of islands but must dissipate before any confining surfaces re-form. Otherwise, a highly dangerous situation arises. Electrons that were trapped and accelerated in these flux tubes can fill a large volume of stochastic field lines and serve as a seed for the transfer of the full plasma current to runaways. If the outer confining surfaces are punctured, as by a drift into the wall, then the full runaway inventory will be lost in a short pulse along a narrow flux tube. Although not part of ITER planning, currents induced in the walls by the fast magnetic relaxation could be used to passively prevent outer surfaces re-forming. If magnetic surface breakup can be avoided during impurity injection, the plasma current could be terminated in tens of milliseconds by plasma cooling with no danger of runaway. Support by DoE Office of Fusion Energy Science Grant De-FG02-03ER54696.

  5. PU Vulpeculae - The outburst of a symbiotic nova

    NASA Astrophysics Data System (ADS)

    Vogel, M.; Nussbaumer, H.

    1992-06-01

    We report the full history of PU Vulpeculae from outburst to 1991 as seen in its ultraviolet emission. We show that PU Vul is a symbiotic nova, which went into outburst in 1977 after a nova-like thermonuclear event. The outbursting object went first into an F supergiant phase. The spectrum evolved between 1979 and 1989 from F-type into that of Ao. In 1990 PU Vul entered the nebular phase, showing a rich emission line spectrum in the UV and in the optical. Between 1979 and 1983-1985 the luminosity of the outbursting object increased by approximately a factor of 2 against 2600 solar luminosities in 1979. It subsequently decreased to reach in 1989 approximately the same value as in 1979. During 1980 the lightcurve went through a minimum and the spectral appearance changed. We interpret this as an eclipse of the outbursting star by the M giant companion. Based on IUE observations we discuss the early nebular phase of PU Vul, and we show that the UV is still dominated by the outbursting component, which in 1991 has reached a temperature of 40,000 K.

  6. Velocity Distributions of Runaway Stars Produced by Supernovae in the Galaxy

    NASA Astrophysics Data System (ADS)

    Yisikandeer, Abudusaimaitijiang; Zhu, Chunhua; Wang, Zhaojun; Lü, Guoliang

    2016-09-01

    Using a method of population synthesis, we investigate the runaway stars produced by disrupted binaries via asymmetric core collapse supernova explosions (CC-RASs) and thermonuclear supernova explosions (TN-RASs). We find the velocities of CC-RASs in the range of about 30-100 km s -1. The runaway stars observed in the galaxy are possibly CC-RASs. Due to differences in stellar chemical components and structures, TN-RASs are divided into hydrogen-rich TN-RASs and helium-rich TN-RASs. The velocities of the former are about 100-500 km s -1, while the velocities of the latter are mainly between 600 and 1100 km s -1. The hypervelocity stars observed in the galaxy may originate from thermonuclear supernova explosions. Our results possibly cover the US 708 which is a compact helium star and travels with a velocity of 1157 ±53 km s-1 in our galaxy.

  7. Runaways in History

    ERIC Educational Resources Information Center

    Lipschutz, Mark R.

    1977-01-01

    Although running away is a glorified part of American folk tradition, today's runaway runs afoul of a host of laws, including those which make the act itself illegal. This article examines the history of the social and legal status of youth and why they run away. (Author)

  8. Probing thermonuclear flame spreading on neutron stars using burst rise oscillations

    NASA Astrophysics Data System (ADS)

    Chakraborty, Manoneeta; Bhattacharyya, Sudip

    2016-07-01

    Intense X-ray bursts (type-I bursts), originated from runaway thermonuclear processes, are observed from the surfaces of many accreting neutron star Low Mass X-ray Binary (LMXB) systems and they provide an important tool to constrain the neutron star equation of state. Periodic intensity variations during these bursts, termed burst oscillations, are observed in about 10% of thermonuclear bursts. Oscillations during the rising phases of thermonuclear bursts are hypothesized to originate from an expanding hot-spot on the surface of the neutron star. We studied the evolution of oscillations during the rising phase of a large sample of thermonuclear bursts from 10 bursting neutron stars in order to probe the process of burning front propagation during an X-ray burst. Our results show observational evidences of expanding hot-spot with spin modulated flame speeds, possibly due to the effects of the Coriolis force present as a result of the high stellar spin (270-620 Hz). This implies that the flame propagation is latitude-dependent and we address the factors affecting the detection and non-detection of burst rise oscillations in the light of this Coriolis force modulated flame spreading scenario.

  9. ON THE COOLING TAILS OF THERMONUCLEAR X-RAY BURSTS: THE IGR J17480-2446 LINK

    SciTech Connect

    Linares, M.; Chakrabarty, D.; Van der Klis, M.

    2011-06-01

    The neutron star transient and 11 Hz X-ray pulsar IGR J17480-2446, recently discovered in the globular cluster Terzan 5, showed unprecedented bursting activity during its 2010 October-November outburst. We analyzed all X-ray bursts detected with the Rossi X-ray Timing Explorer and find strong evidence that they all have a thermonuclear origin, despite the fact that many do not show the canonical spectral softening along the decay imprinted on type I X-ray bursts by the cooling of the neutron star photosphere. We show that the persistent-to-burst power ratio is fully consistent with the accretion-to-thermonuclear efficiency ratio along the whole outburst, as is typical for type I X-ray bursts. The burst energy, peak luminosity, and daily-averaged spectral profiles all evolve smoothly throughout the outburst, in parallel with the persistent (non-burst) luminosity. We also find that the peak-burst to persistent luminosity ratio determines whether or not cooling is present in the bursts from IGR J17480-2446, and argue that the apparent lack of cooling is due to the 'non-cooling' bursts having both a lower peak temperature and a higher non-burst (persistent) emission. We conclude that the detection of cooling along the decay is a sufficient, but not a necessary condition to identify an X-ray burst as thermonuclear. Finally, we compare these findings with X-ray bursts from other rapidly accreting neutron stars.

  10. Runaway electrons and ITER

    NASA Astrophysics Data System (ADS)

    Boozer, Allen H.

    2017-05-01

    The potential for damage, the magnitude of the extrapolation, and the importance of the atypical—incidents that occur once in a thousand shots—make theory and simulation essential for ensuring that relativistic runaway electrons will not prevent ITER from achieving its mission. Most of the theoretical literature on electron runaway assumes magnetic surfaces exist. ITER planning for the avoidance of halo and runaway currents is focused on massive-gas or shattered-pellet injection of impurities. In simulations of experiments, such injections lead to a rapid large-scale magnetic-surface breakup. Surface breakup, which is a magnetic reconnection, can occur on a quasi-ideal Alfvénic time scale when the resistance is sufficiently small. Nevertheless, the removal of the bulk of the poloidal flux, as in halo-current mitigation, is on a resistive time scale. The acceleration of electrons to relativistic energies requires the confinement of some tubes of magnetic flux within the plasma and a resistive time scale. The interpretation of experiments on existing tokamaks and their extrapolation to ITER should carefully distinguish confined versus unconfined magnetic field lines and quasi-ideal versus resistive evolution. The separation of quasi-ideal from resistive evolution is extremely challenging numerically, but is greatly simplified by constraints of Maxwell’s equations, and in particular those associated with magnetic helicity. The physics of electron runaway along confined magnetic field lines is clarified by relations among the poloidal flux change required for an e-fold in the number of electrons, the energy distribution of the relativistic electrons, and the number of relativistic electron strikes that can be expected in a single disruption event.

  11. Cosmic Chandlery with thermonuclear supernovae

    DOE PAGES

    Calder, Alan C.; Krueger, Brendan K.; Jackson, A. P.; ...

    2017-05-30

    Thermonuclear (Type Ia) supernovae are bright stellar explosions, the light curves of which can be calibrated to allow for use as "standard candles" for measuring cosmological distances. Contemporary research investigates how the brightness of an event may be influenced by properties of the progenitor system that follow from properties of the host galaxy such as composition and age. The goals are to better understand systematic effects and to assess the intrinsic scatter in the brightness, thereby reducing uncertainties in cosmological studies. We present the results from ensembles of simulations in the single-degenerate paradigm addressing the influence of age and metallicitymore » on the brightness of an event and compare our results to observed variations of brightness that correlate with properties of the host galaxy. As a result, we also present results from "hybrid" progenitor models that incorporate recent advances in stellar evolution.« less

  12. Cosmic Chandlery with Thermonuclear Supernovae

    NASA Astrophysics Data System (ADS)

    Calder, A. C.; Krueger, B. K.; Jackson, A. P.; Willcox, D. E.; Miles, B. J.; Townsley, D. M.

    2017-05-01

    Thermonuclear (Type Ia) supernovae are bright stellar explosions, the light curves of which can be calibrated to allow for use as “standard candles” for measuring cosmological distances. Contemporary research investigates how the brightness of an event may be influenced by properties of the progenitor system that follow from properties of the host galaxy such as composition and age. The goals are to better understand systematic effects and to assess the intrinsic scatter in the brightness, thereby reducing uncertainties in cosmological studies. We present the results from ensembles of simulations in the single-degenerate paradigm addressing the influence of age and metallicity on the brightness of an event and compare our results to observed variations of brightness that correlate with properties of the host galaxy. We also present results from “hybrid” progenitor models that incorporate recent advances in stellar evolution.

  13. Tidally-Induced Thermonuclear Supernovae

    SciTech Connect

    Rosswog, S.; Ramirez-Ruiz, E.; Hix, William Raphael

    2009-01-01

    We discuss the results of 3D simulations of tidal disruptions of white dwarfs by moderate-mass black holes as they may exist in the cores of globular clusters or dwarf galaxies. Our simulations follow self-consistently the hydrodynamic and nuclear evolution from the initial parabolic orbit over the disruption to the build-up of an accretion disk around the black hole. For strong enough encounters (pericentre distances smaller than about 1/3 of the tidal radius) the tidal compression is reversed by a shock and finally results in a thermonuclear explosion. These explosions are not restricted to progenitor masses close to the Chandrasekhar limit, we find exploding examples throughout the whole white dwarf mass range. There is, however, a restriction on the masses of the involved black holes: black holes more massive than 2x105M{circle_dot} swallow a typical 0.6M{circle_dot} white dwarf before their tidal forces can overwhelm the star's selfgravity. Therefore, this mechanism is characteristic for black holes of moderate masses. The material that remains bound to the black hole settles into an accretion disk and produces an Xray flare close to the Eddington limit of L{sub Edd} {approx} 10{sup 41}erg/s (Mbh/1000M{circle_dot}), typically lasting for a few months. The combination of a peculiar thermonuclear supernova together with an X-ray flare thus whistle-blows the existence of such moderate-mass black holes. The next generation of wide field space-based instruments should be able to detect such events.

  14. Thermonuclear fusion in a strong laser field

    NASA Astrophysics Data System (ADS)

    Krainov, V. P.

    2014-08-01

    Thermonuclear fusion induced by the irradiation of solid deuterated cluster targets and foils with fields of strong femtosecond and picosecond laser pulses is discussed. The thermonuclear-fusion process D( d, n)3He in a collision of two deuterons at an energy of 50 to 100 keV in a deuterium cluster target irradiated with a strong laser pulse is discussed. A theory of thermonuclear fusion proceeding upon the irradiation of clusters formed by deuterium iodide (DI) molecules with the field of a superintense femtosecond laser pulse is developed. This theory is based on an above-barrier process in which the sequential multiple inner ionization of atomic ions within a cluster is accompanied by field-induced outer ionization. The yield of neutrons from thermonuclear fusion in a deuteron-deuteron collision after the completion of a laser pulse is calculated. The yield of neutrons is determined for the thermonuclear-fusion reaction proceeding in the interaction of an intense picosecond laser pulse with thin TiD2 foils. A multiple ionization of titanium atoms at the front edge of the laser pulse is considered. The heating of free electron occurs in induced inverse bremsstrahlung in the process of electron scattering on multiply charged titanium ions. The yield of alpha particles in the thermonuclear-fusion reaction involving protons and 11B nuclei that is induced in microdrops by a strong laser field is determined. Experimental data on laser-induced thermonuclear fusion are discussed.

  15. Study of Fifteen Runaway Patients.

    ERIC Educational Resources Information Center

    Benalcazar, Becquer

    1982-01-01

    Studied 15 adolescent runaways in an inpatient long-term treatment setting. Results showed that more runaways were male, and most were away only a short time. In many cases, behavior improvement resulted. Impulsive behavior and anxiety were related to the short time and distance of elopement. (Author/JAC)

  16. Runaway electron studies in TEXTOR

    NASA Astrophysics Data System (ADS)

    Wongrach, K.; Finken, K. H.; Abdullaev, S. S.; Willi, O.; Zeng, L.; Xu, Y.; the TEXTOR Team

    2015-05-01

    The evolution of runaway electrons in disruptive plasmas in TEXTOR is determined by observing the synchrotron radiation (hard component E > 25 MeV) and by measuring the runway electrons with an energy of a few MeV using a scintillator probe. Disruptions are initiated by a massive argon gas injection performed by a fast valve. The observed runaway beam of the high energy component (synchrotron radiation) fills about half of the diameter of the original plasma. The beam is smooth and shows no indication of filamentation. The initial conditions are in all cases very similar. The temporal development of the runaway electrons, however, is different: one observes cases with and without subsequent mode excitation and other cases in which the hard runaway component survives the apparent end of the runaway plateau. Several methods are applied to remove the runaway electrons including massive gas injection from two additional valves of different sizes as well as external and internal ergodization by inducing a tearing mode. The mitigation is only marginally successful and it is clearly found that the runaways in disruptions are substantially more robust than runaways created in stationary, low density discharges.

  17. EX Hydrae in outburst

    NASA Technical Reports Server (NTRS)

    Hellier, C.; Mason, K. O.; Smale, A. P.; Corbet, R. H. D.; O'Donoghue, D.

    1989-01-01

    Photometry and red spectroscopy of the intermediate polar EX Hya in its rare outburst state are presented. Photometry during the declining phase of the July-August 1986 outburst shows the 67-min (spin) modulation to be present with similar characteristics to that in quiescence. In contrast, photometry from near the peak of the 1987 May outburst shows little evidence of the 67-min modulation, while spectroscopy obtained nearly simultaneously is similarly lacking in such evidence, despite its presence in quiescent spectroscopic data. Near the beginning of the May 1987 outburst the H alpha emission line develops a broad, high velocity base component whose velocity is modulated with the orbital cycle. The velocity and phase of the broad base component suggest that it is produced near the magnetosphere of the white dwarf at a point along the projected trajectory of the gas stream from the companion. The feature disappears later in the outburst and is not present during quiescence. It is suggested that the outbursts in EX Hya are caused by an increase in the rate of mass transfer from the companion, and that part of this enhanced mass-transfer stream skims over the top of the accretion disk to strike the magnetosphere directly. The interaction of the stream with the magnetosphere gives rise to the broad-base component observed.

  18. Controlled thermonuclear fusion, high temperature plasma physics

    NASA Astrophysics Data System (ADS)

    1985-05-01

    The primary source of nuclear energy comes from the fission process of heavy nuclei. To utilize the energy released by a thermonuclear fusion process, methods of controlling the fusion reaction were studied. This is controlled thermonuclear fusion technology. The fuel used in a thermonuclear fusion process are isotopes of hydrogen: deuterium and tritium. They can be extracted from the almost unlimited seawater. Nuclear fusion also produces very little radioactive waste. Thermonuclear fusion is a promising energy source with an almost unlimited supply; it is economical, safe, and relatively clean. Ways to raise plasma temperature to a very high level and to maintain it to allow fusion reactions to take place are studied. The physical laws of high temperature plasma was studied to reach this goal which resulted in the development of high temperature plasma physics.

  19. Ignition of thermonuclear microexplosions with antimatter

    SciTech Connect

    Shmatov, M.L.

    1994-10-01

    The use of antimatter for the indirect ignition of staged thermonuclear microexplosions is proposed. The space propulsion system based on this method may become economically acceptable earlier than that which uses only the energy of annihilation. 19 refs.

  20. A detailed photometric and spectroscopic study of the 2011 outburst of the recurrent nova T Pyxidis from 0.8 to 250 days after discovery

    SciTech Connect

    Surina, F.; Bode, M. F.; Darnley, M. J.; Harman, D. J.; Hounsell, R. A.; Walter, F. M.

    2014-05-01

    We investigated the optical light curve of T Pyx during its 2011 outburst by compiling a database of Solar Mass Ejection Imager (SMEI) and AAVSO observations. The SMEI light curve, providing unprecedented detail covering t = 1.5-49 days post-discovery, was divided into four phases based on the idealized nova optical light curve: the initial rise (1.5-3.3 days), the pre-maximum halt (3.3-13.3 days), the final rise (14.7-27.9 days), and the early decline (27.9+ days). The SMEI light curve contains a strongly detected period of 1.44 ± 0.05 days during the pre-maximum halt phase. These oscillations resemble those found in recent thermonuclear runaway models arising from instabilities in the expanding envelope. No spectral variations that mirror the light curve periodicity were found, however. The marked dip at t ∼ 22-24 days just before the light curve maximum at t = 27.9 days may represent the same (shorter duration) phenomenon seen in other novae observed by SMEI and present in some model light curves. The spectra from the 2 m Liverpool Telescope and SMARTS 1.5 m telescope were obtained from t = 0.8-80.7 and 155.1-249.9 days, covering the major phases of development. The nova was observed very early in its rise where a distinct high-velocity ejection phase was evident with initially derived V {sub ej} ∼ 4000 km s{sup –1}. A marked drop occurred at t = 5.7 days, and then a gradual increase in derived V {sub ej} to stabilize at ∼1500 km s{sup –1} at the pre-maximum halt. Here, we propose two different stages of mass loss, a short-lived phase occurring immediately after outburst and lasting ∼6 days, followed by a more steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a classical nova and comparison with the photometric behavior reveals consistencies with the simple evolving pseudo-photosphere model of the nova outburst. Comparing optical spectra to X-ray and radio light curves, weak [Fe X] 6375

  1. A Detailed Photometric and Spectroscopic Study of the 2011 Outburst of the Recurrent Nova T Pyxidis from 0.8 to 250 Days after Discovery

    NASA Astrophysics Data System (ADS)

    Surina, F.; Hounsell, R. A.; Bode, M. F.; Darnley, M. J.; Harman, D. J.; Walter, F. M.

    2014-05-01

    We investigated the optical light curve of T Pyx during its 2011 outburst by compiling a database of Solar Mass Ejection Imager (SMEI) and AAVSO observations. The SMEI light curve, providing unprecedented detail covering t = 1.5-49 days post-discovery, was divided into four phases based on the idealized nova optical light curve: the initial rise (1.5-3.3 days), the pre-maximum halt (3.3-13.3 days), the final rise (14.7-27.9 days), and the early decline (27.9+ days). The SMEI light curve contains a strongly detected period of 1.44 ± 0.05 days during the pre-maximum halt phase. These oscillations resemble those found in recent thermonuclear runaway models arising from instabilities in the expanding envelope. No spectral variations that mirror the light curve periodicity were found, however. The marked dip at t ~ 22-24 days just before the light curve maximum at t = 27.9 days may represent the same (shorter duration) phenomenon seen in other novae observed by SMEI and present in some model light curves. The spectra from the 2 m Liverpool Telescope and SMARTS 1.5 m telescope were obtained from t = 0.8-80.7 and 155.1-249.9 days, covering the major phases of development. The nova was observed very early in its rise where a distinct high-velocity ejection phase was evident with initially derived V ej ~ 4000 km s-1. A marked drop occurred at t = 5.7 days, and then a gradual increase in derived V ej to stabilize at ~1500 km s-1 at the pre-maximum halt. Here, we propose two different stages of mass loss, a short-lived phase occurring immediately after outburst and lasting ~6 days, followed by a more steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a classical nova and comparison with the photometric behavior reveals consistencies with the simple evolving pseudo-photosphere model of the nova outburst. Comparing optical spectra to X-ray and radio light curves, weak [Fe X] 6375 Å emission was marginally detected before the

  2. Runaway cultural niche construction

    PubMed Central

    Rendell, Luke; Fogarty, Laurel; Laland, Kevin N.

    2011-01-01

    Cultural niche construction is a uniquely potent source of selection on human populations, and a major cause of recent human evolution. Previous theoretical analyses have not, however, explored the local effects of cultural niche construction. Here, we use spatially explicit coevolutionary models to investigate how cultural processes could drive selection on human genes by modifying local resources. We show that cultural learning, expressed in local niche construction, can trigger a process with dynamics that resemble runaway sexual selection. Under a broad range of conditions, cultural niche-constructing practices generate selection for gene-based traits and hitchhike to fixation through the build up of statistical associations between practice and trait. This process can occur even when the cultural practice is costly, or is subject to counteracting transmission biases, or the genetic trait is selected against. Under some conditions a secondary hitchhiking occurs, through which genetic variants that enhance the capability for cultural learning are also favoured by similar dynamics. We suggest that runaway cultural niche construction could have played an important role in human evolution, helping to explain why humans are simultaneously the species with the largest relative brain size, the most potent capacity for niche construction and the greatest reliance on culture. PMID:21320897

  3. Pre-outburst Chandra observations of the recurrent nova T Pyxidis

    NASA Astrophysics Data System (ADS)

    Balman, Ş.

    2014-12-01

    Aims: I study the spectral, temporal, and spatial characteristics of the quiescent X-ray emission (not in outburst) of the recurrent nova T Pyx. Methods: I performed the spectral analysis of the X-ray data obtained using the Chandra Observatory, Advanced CCD Imaging Spectrometer (ACIS-S3) detector. I fit the spectra with several models that describe plasma emission characteristics. In addition, I calculated the light curve of the data and performed power spectral analysis using Fourier transform. Finally, I did high-resolution imaging analysis of the data at the subpixel level and produced radial surface brightness profiles. Results: I present a total of 98.8 ks (~ 3 × 30 ks) observation of T Pyx obtained with the ACIS-S3 detector onboard the Chandra Observatory obtained during the quiescent phase, about 2-3 months before its outburst in April 2011. The total Chandra spectrum of the source T Pyx gives a maximum temperature kTmax> 37.0 keV (2σ lower limit) with (0.9-1.5) × 10-13 erg s-1 cm-2 and (1.3-2.2) × 1032 erg s-1 (at 3.5 kpc) in the 0.1-50 keV range using a multitemperature plasma emission model with a power-law distribution of temperatures (i.e., CEVMKL in XSPEC). I find a ratio of (Lx/Ldisk) ≃ (2-7) × 10-4 and the ratio is smaller if Ldisk is higher than 3 × 1035 erg s-1 indicating considerable inefficiency of emission in the boundary layer. There is no soft X-ray blackbody emission from T Pyx with a 2σ upper limit on the blackbody temperature and the flux/luminosity as kTBB< 25 eV and Lsoft< 2.0 × 1033 erg s-1 in the 0.1-10.0 keV band. All fits yield only interstellar NH during quiescence. I suggest that T Pyx has an optically thin boundary layer merged with an advection-dominated accretion flow and/or X-ray corona in the inner disk indicating ongoing quasi-spherical accretion at (very) high rates during quiescent phases. Such a boundary layer structure may be excessively heating the white dwarf, influencing the thermonuclear runaway leading to

  4. Inflation expels runaways

    DOE PAGES

    Bachlechner, Thomas C.

    2016-12-30

    We argue that moduli stabilization generically restricts the evolution following transitions between weakly coupled de Sitter vacua and can induce a strong selection bias towards inflationary cosmologies. The energy density of domain walls between vacua typically destabilizes Kähler moduli and triggers a runaway towards large volume. This decompactification phase can collapse the new de Sitter region unless a minimum amount of inflation occurs after the transition. A stable vacuum transition is guaranteed only if the inflationary expansion generates overlapping past light cones for all observable modes originating from the reheating surface, which leads to an approximately flat and isotropic universe.more » High scale inflation is vastly favored. Finally, our results point towards a framework for studying parameter fine-tuning and inflationary initial conditions in flux compactifications.« less

  5. Inflation expels runaways

    SciTech Connect

    Bachlechner, Thomas C.

    2016-12-30

    We argue that moduli stabilization generically restricts the evolution following transitions between weakly coupled de Sitter vacua and can induce a strong selection bias towards inflationary cosmologies. The energy density of domain walls between vacua typically destabilizes Kähler moduli and triggers a runaway towards large volume. This decompactification phase can collapse the new de Sitter region unless a minimum amount of inflation occurs after the transition. A stable vacuum transition is guaranteed only if the inflationary expansion generates overlapping past light cones for all observable modes originating from the reheating surface, which leads to an approximately flat and isotropic universe. High scale inflation is vastly favored. Finally, our results point towards a framework for studying parameter fine-tuning and inflationary initial conditions in flux compactifications.

  6. Inflation expels runaways

    NASA Astrophysics Data System (ADS)

    Bachlechner, Thomas C.

    2016-12-01

    We argue that moduli stabilization generically restricts the evolution following transitions between weakly coupled de Sitter vacua and can induce a strong selection bias towards inflationary cosmologies. The energy density of domain walls between vacua typically destabilizes Kähler moduli and triggers a runaway towards large volume. This decompactification phase can collapse the new de Sitter region unless a minimum amount of inflation occurs after the transition. A stable vacuum transition is guaranteed only if the inflationary expansion generates overlapping past light cones for all observable modes originating from the reheating surface, which leads to an approximately flat and isotropic universe. High scale inflation is vastly favored. Our results point towards a framework for studying parameter fine-tuning and inflationary initial conditions in flux compactifications.

  7. Pellet interaction with runaway electrons

    SciTech Connect

    James, A. N.; Hollmann, E. M.; Yu, J.H.; Austin, M. E.; Commaux, Nicolas JC; Evans, T.E.; Humphrey, D. A.; Jernigan, T. C.; Parks, P. B.; Putvinski, S.; Strait, E. J.; Tynan, G. R.; Wesley, J. C.

    2011-01-01

    We describe results from recent experiments studying interaction of solid polystyrene pellets with a runaway electron current channel generated after cryogenic argon pellet rapid shutdown of DIII-D. Fast camera imaging shows the pellet trajectory and continuum emission from the subsequent explosion, with geometric calibration providing detailed explosion analysis and runaway energy. Electron cyclotron emission also occurs, associated with knock-on electrons broken free from the pellet by RE which then accelerate and runaway, and also with a short lived hot plasma blown off the pellet surface. In addition, we compare heating and explosion times from observations and a model of pellet heating and breakdown by runaway interaction. (C) 2011 Elsevier B.V. All rights reserved

  8. Thermonuclear Burst Observations for Model Comparisons: A Reference Sample

    NASA Astrophysics Data System (ADS)

    Galloway, Duncan K.; Goodwin, Adelle J.; Keek, Laurens

    2017-04-01

    We present observations of thermonuclear (type-I) X-ray bursts, selected for comparison with numerical models. We provide examples of four distinct cases of ignition: He-ignition in mixed H/He fuel (case 1); He-ignition in pure He fuel, following exhaustion of accreted H by steady burning (case 2); ignition in (almost) pure He accumulated from an evolved donor in an ultracompact system; and a superburst, thought to arise from ignition of carbon fuel produced as a by-product of H/He bursts. For regular bursts, we measured the recurrence time and calculated averaged burst profiles from RXTE observations. We also estimated the recurrence time for pairs of bursts, including those observed during a transient outburst, modelled using a numerical ignition code. For each example we list the burst properties including recurrence time, fluence, peak flux, the persistent flux level (and inferred accretion rate), and the ratio of persistent flux to fluence. In the accompanying material, we provide a bolometric lightcurve for each burst, determined from time-resolved spectral analysis. Along with the inferred or adopted parameters for each burst system, including distance, surface gravity, and redshift, these data are suggested as suitable test cases for ignition models.

  9. MILLIHERTZ QUASI-PERIODIC OSCILLATIONS AND THERMONUCLEAR BURSTS FROM TERZAN 5: A SHOWCASE OF BURNING REGIMES

    SciTech Connect

    Linares, M.; Chakrabarty, D.; Altamirano, D.; Cumming, A.; Keek, L.

    2012-04-01

    We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480-2446, located in the globular cluster Terzan 5. The increase in burst rate that we found during its 2010 outburst, when persistent luminosity rose from 0.1 to 0.5 times the Eddington limit, is in qualitative agreement with thermonuclear burning theory yet contrary to all previous observations of thermonuclear bursts. Thermonuclear bursts gradually evolved into a mHz QPO when the accretion rate increased, and vice versa. The mHz QPOs from IGR J17480-2446 resemble those previously observed in other accreting NSs, yet they feature lower frequencies (by a factor {approx}3) and occur when the persistent luminosity is higher (by a factor 4-25). We find four distinct bursting regimes and a steep (close to inverse cubic) decrease of the burst recurrence time with increasing persistent luminosity. We compare these findings to nuclear burning models and find evidence for a transition between the pure helium and mixed hydrogen/helium ignition regimes when the persistent luminosity was about 0.3 times the Eddington limit. We also point out important discrepancies between the observed bursts and theory, which predicts brighter and less frequent bursts, and suggest that an additional source of heat in the NS envelope is required to reconcile the observed and expected burst properties. We discuss the impact of NS magnetic field and spin on the expected nuclear burning regimes, in the context of this particular pulsar.

  10. Spreading of thermonuclear flames on the neutron star in SAX J1808.4-3658: an observational tool

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip; Strohmayer, Tod E.

    2005-01-01

    We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX 51808.4-3658. We present evidence of a complex frequency modulation of oscillations during burst rise, and correlations among the time evolution of the oscillation frequency, amplitude, and the inferred burning region area. We discuss these findings in the context of a model, based on thermonuclear flame spreading on the neutron star surface, that can qualitatively explain these features. From our model, we infer that for the 2002 Oct. 15 thermonuclear burst, the ignition likely occurred in the mid-latitudes, the burning region took approx. 0.2 s to nearly encircle the equatorial region of the neutron star, and after that the lower amplitude oscillation originated from the remaining asymmetry of the burning front in the same hemisphere where the burst ignited. We emphasize that studies of the evolution of burst oscillation properties during burst rise can provide a powerful tool to understand thermonuclear flame spreading on neutron star surfaces under extreme physical conditions.

  11. A nova outburst powered by shocks

    NASA Astrophysics Data System (ADS)

    Li, Kwan-Lok; Metzger, Brian D.; Chomiuk, Laura; Vurm, Indrek; Strader, Jay; Finzell, Thomas; Beloborodov, Andrei M.; Nelson, Thomas; Shappee, Benjamin J.; Kochanek, Christopher S.; Prieto, José L.; Kafka, Stella; Holoien, Thomas W.-S.; Thompson, Todd A.; Luckas, Paul J.; Itoh, Hiroshi

    2017-10-01

    Classical novae are runaway thermonuclear burning events on the surfaces of accreting white dwarfs in close binary star systems, sometimes appearing as new naked-eye sources in the night sky1. The standard model of novae predicts that their optical luminosity derives from energy released near the hot white dwarf, which is reprocessed through the ejected material2-5. Recent studies using the Fermi Large Area Telescope have shown that many classical novae are accompanied by gigaelectronvolt γ-ray emission6,7. This emission likely originates from strong shocks, providing new insights into the properties of nova outflows and allowing them to be used as laboratories for the study of the unknown efficiency of particle acceleration in shocks. Here, we report γ-ray and optical observations of the Milky Way nova ASASSN-16ma, which is among the brightest novae ever detected in γ-rays. The γ-ray and optical light curves show a remarkable correlation, implying that the majority of the optical light comes from reprocessed emission from shocks rather than the white dwarf8. The ratio of γ-ray to optical flux in ASASSN-16ma directly constrains the acceleration efficiency of non-thermal particles to be around 0.005, favouring hadronic models for the γ-ray emission9. The need to accelerate particles up to energies exceeding 100 gigaelectronvolts provides compelling evidence for magnetic field amplification in the shocks.

  12. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Supid

    2007-01-01

    This viewgraph presentation describes neutron stars and thermonuclear x ray bursts. The contents include: 1) Neutron Stars: why do we care?; 2) Thermonuclear Bursts: why do we care?; 3) Neutron Stars: Mass, Radius and Spin: a. Continuum Spectroscopy of Bursts b. Spectral Lines from Bursts c. Timing Properties of Bursts; 4) Neutron Star Atmosphere: Thermonuclear Flame Spreading; and 5) Future Prospects and Conclusions.

  13. Probing an Ancient Thermonuclear Runaway on a White Dwarf in a Dwarf Nova

    NASA Astrophysics Data System (ADS)

    Sion, Edward

    1999-07-01

    We unexpectedly discovered evidence, based upon two GHRS G160M spectra, of greatly elevated abundances of odd-numbered nuclei Phosphorus and Aluminum as well as a Nitrogen to Carbon ratio of 10 in the photosphere of the white dwarf in the dwarf nova VW Hy ons and determine the first chem ical abundances of many odd-numbered proton capture species; {2} determine a accurate mass for the white dwarf and; {3} probe changes in the accretion belt and surface abundances as a function of time since a superoutburst. This study will hold important

  14. Plasma physics and controlled thermonuclear fusion

    SciTech Connect

    Krikorian, R. )

    1989-01-01

    This proceedings contains papers on plasma physics and controlled thermonuclear fusion. Included are the following topics: Plasma focus and Z-pinch, Review of mirror fusion research, Progress in studies of x-ray and ion-beam emission from plasma focus facilities.

  15. The polonium-210 problem in thermonuclear reactor

    SciTech Connect

    Shchipakhin, O.L.; Borisov, N.B.; Churkin, S.L.

    1993-12-31

    Polonium 210 forms in the lithium-lead eutectic blanket of a thermonuclear reactor. On the basis of obtained experimental data some estimates have been calculated on the ITER blanket accident consequences. The LOCA type accident represents the failure of eutectic circuit in the process of transfusion of liquid eutectic from blanket to the tritium reprocessing plant.

  16. Laser Fusion - A New Thermonuclear Concept

    ERIC Educational Resources Information Center

    Cooper, Ralph S.

    1975-01-01

    Describes thermonuclear processes induced by interaction of a laser beam with the surface of a fuel pellet. An expanding plasma is formed which results in compression of the element. Laser and reactor technology are discussed. Pictures and diagrams are included. (GH)

  17. Laser Fusion - A New Thermonuclear Concept

    ERIC Educational Resources Information Center

    Cooper, Ralph S.

    1975-01-01

    Describes thermonuclear processes induced by interaction of a laser beam with the surface of a fuel pellet. An expanding plasma is formed which results in compression of the element. Laser and reactor technology are discussed. Pictures and diagrams are included. (GH)

  18. Runaway electrons in plasma current sheets

    SciTech Connect

    Gurevich, A.V.; Sudan, R.N. )

    1994-01-31

    It is shown that a runaway electron population accelerates along the main magnetic field in a Sweet-Parker current sheet. After a characteristic distance the entire current is carried by runaways. The thickness of this runaway sheet is much smaller than the original Ohmic sheet. The influence of microinstabilities is discussed.

  19. Numerical analysis of thermonuclear detonation in dense plasma

    NASA Astrophysics Data System (ADS)

    Avronin, Y. N.; Bunatyan, A. A.; Gadzhiyev, A. D.; Mustafin, K. A.; Nurbakov, A. S.; Pisarev, V. N.; Feoktistov, L. P.; Frolov, V. D.; Shibarshov, L. I.

    1985-01-01

    The propagation of thermonuclear combustion from the region heated to thermonuclear temperatures by an external source to the remaining part of the target was investigated. The target was a tube of inert material (gold, lead, beryllium, etc.) filled with a deuterium-tritium mixture. It was determined analytically that thermonuclear combustion can propagate from a small portion of a nonspherical target to the remainder of the target and that a steady-state thermonuclear detonation wave can be formed. The role of various physical processes in thermonuclear detonation was investigated. Shock wave is the main mechanism underlying detonation propagation. The detonation rate and intensity of the thermonuclear reaction is influenced by the leakage of heat due to transvere heat conductivity. The critical diameter for thermonuclear detonation was determined approximately for a plasma filament encased in a housing with twice the density of the fuel.

  20. 30S(α , p) Thermonuclear Reaction Rate from Experimental Level Structure of 34Ar

    NASA Astrophysics Data System (ADS)

    Kahl, D.; Chen, A. A.; Kubono, S.; Yamaguchi, H.; Binh, D. N.; Chen, J.; Cherubini, S.; Duy, N. N.; Hashimoto, T.; Hayakawa, S.; Iwasa, N.; Jung, H. S.; Kato, S.; Kwon, Y. K.; Nishimura, S.; Ota, S.; Setoodehnia, K.; Teranishi, T.; Tokieda, H.; Yamada, T.; Yun, C. C.; Zhang, L. Y.

    Type I X-ray bursts are the most frequent thermonuclear explosions in the galaxy. Owing to their recurrence from known astronomical objects, burst morphology is extensively documented, and they are modeled very successfully as neutron-deficient, thermonuclear runaway on the surface of accreting neutron stars. While reaction networks include hundreds of isotopes and thousands of nuclear processes, only a small subset appear to play a pivotal role. One such reaction is the 30S(α , p) reaction, which is believed to be a crucial link in the explosive helium burning which is responsible for the large energy flux. However, very little experimental information is available concerning the cross section itself, nor the 34Ar compound nucleus at the relevant energies. We performed the first study of the entrance channel via 30S alpha resonant elastic scattering using a state-of-the-art, low-energy, 30S radioactive ion beam. The measurement was performed in inverse kinematics using a newly-developed active target. An R-matrix analysis of the excitation function reveals previously unknown resonances, including their quantum properties of spin, parity, width, and energy.

  1. THE 2008 OUTBURST OF EX Lup-SILICATE CRYSTALS IN MOTION

    SciTech Connect

    Juhasz, A.; Dullemond, C. P.; Van Boekel, R.; Bouwman, J.; Henning, Th.; Sicilia-Aguilar, A.; Abraham, P.; Moor, A.; Mosoni, L.; Regaly, Zs.; Sipos, N.; Acosta-Pulido, J. A.; Kospal, A.; Jones, A.; Szokoly, Gy.

    2012-01-10

    EX Lup is the prototype of the EXor class of eruptive young stars. These objects show optical outbursts which are thought to be related to runaway accretion onto the star. In a previous study we observed in situ crystal formation in the disk of EX Lup during its latest outburst in 2008, making the object an ideal laboratory to investigate circumstellar crystal formation and transport. This outburst was monitored by a campaign of ground-based and Spitzer Space Telescope observations. Here we modeled the spectral energy distribution (SED) of EX Lup in the outburst from optical to millimeter wavelengths with a two-dimensional radiative transfer code. Our results showed that the shape of the SED at optical wavelengths was more consistent with a single-temperature blackbody than a temperature distribution. We also found that this single-temperature component emitted 80%-100% of the total accretion luminosity. We concluded that a thermal instability, the most widely accepted model of EXor outbursts, was likely not the triggering mechanism of the 2008 outburst of EX Lup. Our mid-infrared Spitzer spectra revealed that the strength of all crystalline bands between 8 and 30 {mu}m increased right after the end of the outburst. Six months later, however, the crystallinity in the 10 {mu}m silicate feature complex decreased. Our modeling of the mid-infrared spectral evolution of EX Lup showed that, although vertical mixing should be stronger during the outburst than in the quiescent phase, fast radial transport of crystals (e.g., by stellar/disk wind) was required to reproduce the observed mid-infrared spectra.

  2. Personality Profile of Adolescent Runaways.

    ERIC Educational Resources Information Center

    Rohr, Michael E.

    An overview of the history of adolescent runaway behavior indicates that it has become a social and psychological problem of significant proportions. This study investigated the use of a personality measure that was hypothesized to be representative of a cluster of behaviors associated with running away. The study also sought to determine a…

  3. Remote Shutoff Stops Runaway Lawnmower

    ERIC Educational Resources Information Center

    Grambo, Alan A.

    2007-01-01

    In this article, the author describes how electronics students at Central Nine Career Center designed a kill switch circuit to stop a runaway lawnmower. This project is ideal for a career center since the electronics/robotics, small engines and horticulture classes can all work together on their respective parts of the modification, installation…

  4. Remote Shutoff Stops Runaway Lawnmower

    ERIC Educational Resources Information Center

    Grambo, Alan A.

    2007-01-01

    In this article, the author describes how electronics students at Central Nine Career Center designed a kill switch circuit to stop a runaway lawnmower. This project is ideal for a career center since the electronics/robotics, small engines and horticulture classes can all work together on their respective parts of the modification, installation…

  5. Runaway Youths: Families in Conflict.

    ERIC Educational Resources Information Center

    Beyer, Margaret; And Others

    The Hamden Mental Health Service staff collaborated with the police on a joint research project concerning runaway youth. The data suggest that adolescents who run away come from broken homes where disruption during preadolescence has been associated with parental separation and remarriage. These adolescents often exhibit symptoms of depression…

  6. Thermonuclear microdetonation macron accelerator for impact ignition

    NASA Astrophysics Data System (ADS)

    Winterberg, F.

    2008-03-01

    It is proposed to replace the expensive ~150 kJ petawatt laser as a means for the fast ignition of a highly compressed dense DT target by a small flyer plate propelled to high velocities by a thermonuclear microdetonation ignited at one end of a super-pinch. It appears that this can most efficiently be done with the previously proposed modification of the dense plasma focus device, adding a high voltage relativistic electron beam emitting diode inside the coaxial plasma focus discharge tube, igniting at the end of the plasma focus pinch column a thermonuclear detonation wave, propagating in the axial direction and accelerating at the end of the pinch a flyer plate to a velocity of 103 km s-1.

  7. Mechanism of instantaneous coal outbursts

    SciTech Connect

    Guan, P.; Wang, H.Y.; Zhang, Y.X.

    2009-10-15

    Thousands of mine workers die every year from mining accidents, and instantaneous coal outbursts in underground coal mines are one of the major killers. Various models for these outbursts have been proposed, but the precise mechanism is still unknown. We hypothesize that the mechanism of coal outbursts is similar to magma fragmentation during explosive volcanic eruptions; i.e., it is caused by high gas pressure inside coal but low ambient pressure on it, breaking coal into pieces and releasing the high-pressure gas in a shock wave. Hence, coal outbursts may be regarded as another type of gas-driven eruption, in addition to explosive volcanic, lake, and possible ocean eruptions. We verify the hypothesis by experiments using a shock-tube apparatus. Knowing the mechanism of coal outbursts is the first step in developing prediction and mitigation measures. The new concept of gas-driven solid eruption is also important to a better understanding of salt-gas outbursts, rock-gas outbursts, and mud volcano eruptions.

  8. Radio outbursts in extragalactic sources

    NASA Astrophysics Data System (ADS)

    Kinzel, Wayne Morris

    Three aspects of the flux density variability of extragalactic radio sources were examined: millimeter wavelength short timescale variability, the spectral evolution of outbursts, and whether the outbursts are periodically spaced. Observations of extragalactic radio sources were conducted using the Five College Radio Astronomy Observatory between January and June 1985 at 88.2 GHz and during June and July 1985 at 40.0 GHz. Many of the sources exhibited significant flux density variations during the observing span. In addition, the most rapid variations observed were comparable with those reported in previous works. Two sources, 0355+50 and OJ287, both exhibited outbursts whose rise and fall timescales were less than a month. An anomalous flux density dropout was observed in 3C446 and was interpreted as an occultation event. Data at five frequencies between 2.7 and 89.6 GHz from the Dent-Balonek monitoring program were used to investigate the spectral evolution of eight outbursts. Outburst profile fitting was used to deconvolve the individual outbursts from one another at each frequency. The fit profiles were used to generate multiple epoch spectra to investigate the evolution of the outbursts. A phase residual minimization method was used to examine four sources for periodic behavior.

  9. Passive runaway electron suppression in tokamak disruptions

    SciTech Connect

    Smith, H. M.; Helander, P.

    2013-07-15

    Runaway electrons created in disruptions pose a serious problem for tokamaks with large current. It would be desirable to have a runaway electron suppression method which is passive, i.e., a method that does not rely on an uncertain disruption prediction system. One option is to let the large electric field inherent in the disruption drive helical currents in the wall. This would create ergodic regions in the plasma and increase the runaway losses. Whether these regions appear at a suitable time and place to affect the formation of the runaway beam depends on disruption parameters, such as electron temperature and density. We find that it is difficult to ergodize the central plasma before a beam of runaway current has formed. However, the ergodic outer region will make the Ohmic current profile contract, which can lead to instabilities that yield large runaway electron losses.

  10. Ion Runaway in Lightning Discharges

    NASA Astrophysics Data System (ADS)

    Fülöp, T.; Landreman, M.

    2013-07-01

    Runaway ions can be produced in plasmas with large electric fields, where the accelerating electric force is augmented by the low mean ionic charge due to the imbalance between the number of electrons and ions. Here we derive an expression for the high-energy tail of the ion distribution function in lightning discharges and investigate the energy range that the ions can reach. We also estimate the corresponding energetic proton and neutron production due to fusion reactions.

  11. A Risk Profile Comparison of Runaway and Non-Runaway Youth.

    ERIC Educational Resources Information Center

    Yates, Gary L.; And Others

    1988-01-01

    Examination of data from 1985 visits by 110 runaway and 655 non-runaway youth to an outpatient medical clinic reveals that runaway youth are at greater risk for a wide variety of medical problems and of health-compromising behaviors including suicide, depression, prostitution, and drug use. (Author/BJV)

  12. Simulations of the runaway electron distributions

    SciTech Connect

    Wiley, J.C.; Choi, D.; Horton, W.

    1980-11-01

    The time evolution of the electron distribution function is followed from an initial Maxwellian to the quasi-steady-state runaway distribution as a function of E/E/sub D/ and Z using a new two-dimensional Fokker--Planck code. The electron distributions are used to determine the runaway production rate, the current density along with the fraction of Ohmic power directed to the runaways, and the perpendicular and parallel temperatures of the high energy distributions. A simple parameterization of the high energy distribution is given and used to investigate the high frequency runaway instability for the infinite uniform plasma.

  13. Simulations of the runaway electron distributions

    SciTech Connect

    Wiley, J. C.; Choi, D. I.; Horton, W.

    1980-03-01

    The time evolution of the electron distribution function is followed from an initial Maxwellian to the quasi-steady state runaway distribution as a function of E/E/sub D/ and Z using a new two-dimensional Fokker-Planck code. The electron distributions are used to determine the runaway production rate, the current density along with the fraction of Ohmic power directed to the runaways, and the perpendicular and parallel temperatures of the high energy distributions. A simple parameterization of the high energy distribution is given and used to investigate the high frequency runaway instability for the infinite uniform plasma.

  14. Radiation effects on the runaway electron avalanche

    NASA Astrophysics Data System (ADS)

    Liu, Chang

    2016-10-01

    Runaway electrons are a critical area of research into tokamak disruptions. A thermal quench on ITER can result in avalanche production of a large amount of runaway electrons and a transfer of the plasma current to be carried by runaway electrons. The potential damage caused by the highly energetic electron beam poses a significant challenge for ITER to achieve its mission. It is therefore extremely important to have a quantitative understanding of the avalanche process, including (1) the critical energy for an electron to run away to relativistic energy and (2) the avalanche growth rate dependence on electric field, which is related to the poloidal flux change required for an e-fold in current. It is found that the radiative energy loss of runaway electrons plays an important role in determining these two quantities. In this talk we discuss three kinds of radiation from runaway electrons, synchrotron radiation, Cerenkov radiation, and electron cyclotron emission (ECE) radiation. Synchrotron radiation, which mainly comes from the cyclotron motion of highly relativistic runaway electrons, dominates the energy loss of runaway electrons in the high-energy regime. The Cerenkov radiation from runaway electrons gives an additional correction to the Coulomb logarithm in the collision operator, which changes the avalanche growth rate. The ECE emission mainly comes from electrons in the energy range 1.2 < γ < 3 , and gives an important approach to diagnose the runaway electron distribution in momentum and pitch angle. To study the runaway electron dynamics in momentum space including all the radiation and scattering effects, we use a novel tool, the adjoint method to obtain both the runaway probability and the expected slowing-down time. The method is then combined with kinetic simulations to calculate the avalanche threshold and growth rate. This work is supported by US Department of Energy under Grant No. DE-AC02-09CH-11466.

  15. Taking the temperature of the superburster 4U 1608-522 after an outburst

    NASA Astrophysics Data System (ADS)

    Keek, Laurens

    2010-10-01

    Superbursts are rare thermonuclear flashes from accreting neutron stars that can only ignite in case of a sufficiently high temperature of the neutron star crust, which is heated during accretion. Most superbursts take place when the neutron star accretes continuously for over 10 years. In 2005, however, a superburst was observed from the transient 4U 1608-522, when accretion started only 55 days earlier. Crustal heating models predict a significantly lower temperature than the superburst models require. If the superburst models are correct in their prediction of a high temperature, crustal cooling is observable after an accretion outburst. We propose to observe 4U 1608-522 two times for 30 ks. triggered after an outburst, to measure the presence of cooling.

  16. Taking the temperature of the superburster 4U 1608-522 after an outburst

    NASA Astrophysics Data System (ADS)

    Keek, Laurens

    2011-09-01

    Superbursts are rare thermonuclear flashes from accreting neutron stars. One condition for ignition is a sufficiently high temperature of the neutron star crust, which is heated during accretion. Most superbursts take place when the neutron star was accreting continuously above 10% of the Eddington limit for more then 10 years. In 2005 a superburst was observed from the transient system 4U 1608-522, when accretion started 55 days earlier. Crustal heating models predict a significantly lower temperature than the superburst models require. If the superburst models are correct in their prediction of a high temperature, crustal cooling is observable after an accretion outburst. We propose to observe 4U 1608-522 two times for 30 ks triggered after an outburst, to measure the cooling rate.

  17. ACCRETION OUTBURSTS IN CIRCUMPLANETARY DISKS

    SciTech Connect

    Lubow, S. H.; Martin, R. G.

    2012-04-20

    We describe a model for the long-term evolution of a circumplanetary disk that is fed mass from a circumstellar disk and contains regions of low turbulence (dead zones). We show that such disks can be subject to accretion-driven outbursts, analogous to outbursts previously modeled in the context of circumstellar disks to explain FU Ori phenomena. Circumplanetary disks around a proto-Jupiter can undergo outbursts for infall accretion rates onto the disks in the range M-dot{sub infall} approx. 10{sup -9} to 10{sup -7} M{sub Sun} yr{sup -1}, typical of accretion rates in the T Tauri phase. During outbursts, the accretion rate and disk luminosity increases by several orders of magnitude. Most of the planet mass growth during planetary gas accretion may occur via disk outbursts involving gas that is considerably hotter than predicted by steady state models. For low infall accretion rates M-dot{sub infall} {approx}< 10{sup -10} M{sub sun} yr{sup -1} that occur in late stages of disk accretion, disk outbursts are unlikely to occur, even if dead zones are present. Such conditions are favorable for the formation of icy satellites.

  18. Oscillations During Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    High amplitude, nearly coherent X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries, a long sought goal of X-ray astronomy. Studies carried out over the past year have led to the discovery of burst oscillations in four new sources, bringing to ten the number with confirmed burst oscillations. I review the status of our knowledge of these oscillations and indicate how they can be used to probe the physics of neutron stars. For a few burst oscillation sources it has been proposed that the strongest and most ubiquitous frequency is actually the first overtone of the spin frequency and hence that two nearly antipodal hot spots are present on the neutron star. This inference has important implications for both the physics of thermonuclear burning as well as the mass - radius relation for neutron stars, so its confirmation is crucial. I discuss recent attempts to confirm this hypothesis for 4U 1636-53, the source for which a signal at the putative fundamental (290Hz) has, been claimed.

  19. Runaway Slave Advertisements: Teaching from Primary Documents

    ERIC Educational Resources Information Center

    Costa, Tom; Doyle, Brooke

    2004-01-01

    In this article, the authors discuss how children can learn from runaway slave advertisements. The advertisements for runaway slaves that masters placed in eighteenth- and nineteenth-century newspapers are among the documentary sources available to teachers for studying the lives of African-American slaves. Such advertisements often describe a…

  20. Runaways: A Review of the Literature.

    ERIC Educational Resources Information Center

    Taylor, Jennifer; Mosteller, Frederick

    More than half of runaway adolescents cite poor family communication and conflict as the primary reasons for running. Runaways (.5-1.5 million annually) generally arrive on the streets with few survival skills and little money. They are often subject to abuse of various sorts, and many eventually resort to criminal activity or use drugs in efforts…

  1. Runaway Slave Advertisements: Teaching from Primary Documents

    ERIC Educational Resources Information Center

    Costa, Tom; Doyle, Brooke

    2004-01-01

    In this article, the authors discuss how children can learn from runaway slave advertisements. The advertisements for runaway slaves that masters placed in eighteenth- and nineteenth-century newspapers are among the documentary sources available to teachers for studying the lives of African-American slaves. Such advertisements often describe a…

  2. Trapped-electron runaway effect

    NASA Astrophysics Data System (ADS)

    Nilsson, E.; Decker, J.; Fisch, N. J.; Peysson, Y.

    2015-08-01

    In a tokamak, trapped electrons subject to a strong electric field cannot run away immediately, because their parallel velocity does not increase over a bounce period. However, they do pinch toward the tokamak center. As they pinch toward the center, the trapping cone becomes more narrow, so eventually they can be detrapped and run away. When they run away, trapped electrons will have a very different signature from circulating electrons subject to the Dreicer mechanism. The characteristics of what are called trapped-electron runaways are identified and quantified, including their distinguishable perpendicular velocity spectrum and radial extent.

  3. Disk tides and accretion runaway

    NASA Technical Reports Server (NTRS)

    Ward, William R.; Hahn, Joseph M.

    1995-01-01

    It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

  4. Runaway Stars in Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Pannicke, Anna; Neuhaeuser, Ralph; Dinçel, Baha

    2016-07-01

    Half of all stars and in particular 70 % of the massive stars are a part of a multiple system. A possible development for the system after the core collapse supernova (SN) of the more massive component is as follows: The binary is disrupted by the SN. The formed neutron star is ejected by the SN kick whereas the companion star either remains within the system and is gravitationally bounded to the neutron star, or is ejected with a spatial velocity comparable to its former orbital velocity (up to 500 km/s). Such stars with a large peculiar space velocity are called runaway stars. We present our observational results of the supernova remnants (SNRs) G184.6-5.8, G74.0-8.5 and G119.5+10.2. The focus of this project lies on the detection of low mass runaway stars. We analyze the spectra of a number of candidates and discuss their possibility of being the former companions of the SN progenitor stars. The spectra were obtained with INT in Tenerife, Calar Alto Astronomical Observatory and the University Observatory Jena. Also we investigate the field stars in the neighborhood of the SNRs G74.0-8.5 and G119.5+10.2 and calculate more precise distances for these SNRs.

  5. Runaway Stars in Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Pannicke, A.; Dincel, B.; Neuhauser, R.

    2016-06-01

    Half of all stars and in particular 70 percent of the massive stars are part of a multiple system. A possible development for the system after the core collapse supernova (SN) of the more massive component is as follows: The binary is disrupted by the SN. The formed neutron star is ejected by the SN kick whereas the companion star either remains within the system and is gravitationally bounded to the neutron star, or is ejected with a spatial velocity comparable to its former orbital velocity (up to 500 km/s). Such stars with a large peculiar space velocity are called runaway stars. We present our observational results of the supernova remnants (SNRs) G184.6-5.8, G74.0-8.5 and G119.5+10.2. The focus of this project lies on the detection of low mass runaway stars. We analyze the spectra of a number of candidates and discuss their possibility of being the former companions of the SN progenitor stars. The spectra were obtained with INT in Tenerife, Calar Alto Astronomical Observatory and the University Observatory Jena. Also, we investigate the field stars in the neighborhood of the SNRs G74.0-8.5 and G119.5+10.2 and calculate more precise distances for these SNRs.

  6. Enigma of Runaway Stars Solved

    NASA Astrophysics Data System (ADS)

    1997-01-01

    Supernova Propels Companion Star through Interstellar Space The following success story is a classical illustration of scientific progress through concerted interplay of observation and theory. It concerns a 35-year old mystery which has now been solved by means of exciting observations of a strange double star. An added touch is the successive involvement of astronomers connected to the European Southern Observatory. For many years, astronomers have been puzzled by the fact that, among the thousands of very young, hot and heavy stars which have been observed in the Milky Way, there are some that move with exceptionally high velocities. In some cases, motions well above 100 km/sec, or ten times more than normal for such stars, have been measured. How is this possible? Which mechanism is responsible for the large amounts of energy needed to move such heavy bodies at such high speeds? Could it be that these stars are accelerated during the powerful explosion of a companion star as a supernova? Such a scenario was proposed in 1961 by Adriaan Blaauw [1], but until now, observational proof has been lacking. Now, however, strong supporting evidence for this mechanism has become available from observations obtained at the ESO La Silla observatory. The mysterious runaway stars OB-runaway stars [2] are heavy stars that travel through interstellar space with an anomalously high velocity. They have been known for several decades, but it has always been a problem to explain their high velocities. Although most OB-runaway stars are located at distances of several thousands of lightyears, their high velocity results in a measurable change in position on sky photos taken several years apart. The velocity component in the direction of the Earth can be measured very accurately from a spectrogram. From a combination of such observations, it is possible to measure the space velocity of OB-runaways. Bow shocks reveal runaway stars It has also been found that some OB-runaways display

  7. Runaway youths and correlating factors, study in Thailand.

    PubMed

    Techakasem, Pisarn; Kolkijkovin, Varuna

    2006-02-01

    To study differences between runaways and non-runaways in a mental health clinic and to study differences between runaways in a mental health clinic and legal / shelter system. Psychiatric records of runaways and non-runaways from Vajira Hospital were collected from June 1994 to October 2003. 21 cases in each group were studied in various factors. 21 runaway cases who were in child and adolescent shelters were interviewed by the researchers. Neglect, sexual abuse, rejection, poverty and truancy were more common in the runaway group. The runaway group had more conduct disorder and substance abuse. Physical abuse, authoritarian and being in custody were more common in runaways in shelters. Various factors correlate with running away. These factors lie beneath long before runaway has taken place and understanding and managing them help in preventing and prompt treatment.

  8. X-ray bursts and neutron-star thermonuclear flashes

    NASA Technical Reports Server (NTRS)

    Joss, P. C.

    1977-01-01

    A description is presented of a model concerning the production of X-ray bursts by thermonuclear flashes in the freshly accreted matter near the surface of an accreting neutron star. An investigation is conducted regarding the physical processes relevant to such thermonuclear flashes. It is concluded that thermonuclear flashes may account for some, but not all, of the observed X-ray burst sources. Attention is given to a neutron star undergoing accretion of mass from a binary stellar companion, aspects of energetics, nuclear reactions, and heat transport mechanisms.

  9. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star approaching EOS model of high density cold matter in the neutron star cores. +k Extensive observation and analysis of the data from the rising portions of the bursts - modeling of burst oscillations and thermonuclear flame spreading. +k Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  10. Understanding Neutron Stars using Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star = EOS model of high density cold matter in the neutron star cores. Extensive observation and analysis of the data from the rising portions of the bursts = modeling of burst oscillations and thermonuclear flame spreading. Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  11. X-ray bursts and neutron-star thermonuclear flashes

    NASA Technical Reports Server (NTRS)

    Joss, P. C.

    1977-01-01

    A description is presented of a model concerning the production of X-ray bursts by thermonuclear flashes in the freshly accreted matter near the surface of an accreting neutron star. An investigation is conducted regarding the physical processes relevant to such thermonuclear flashes. It is concluded that thermonuclear flashes may account for some, but not all, of the observed X-ray burst sources. Attention is given to a neutron star undergoing accretion of mass from a binary stellar companion, aspects of energetics, nuclear reactions, and heat transport mechanisms.

  12. Optical Outburst of AQL X-1

    NASA Astrophysics Data System (ADS)

    Jain, R.; Bailyn, C.; Garcia, M.; Rines, K.; Levine, A.; Espinoza, J.; Gonzalez, D.

    1999-05-01

    We report YALO consortium observations using the Yale 1-m telescope at CTIO and observations with the 48" telescope at the Whipple Observatory: Aql X-1 = V1333 Aql appears to be beginning a new outburst. This x-ray binary outbursts approximately once per year, and based on its recent outbursts was due to erupt.

  13. Comet 29P/SW1 outburst

    NASA Astrophysics Data System (ADS)

    Trigo-Rodriguez, Josep M.

    2008-10-01

    The present outburst experienced by this Centaur (#IAUC 8978) is the brightest detected since September 2004 [for more details see Trigo-Rodriguez et al. (2008) A&A485, pp. 599-606]. In the previously reported work the outburst frequency was established in 7.3 outbursts/year, typically reaching a +13 maximum magnitude or less.

  14. Adjoint method and runaway electron avalanche

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Brennan, Dylan P.; Boozer, Allen H.; Bhattacharjee, Amitava

    2017-02-01

    The adjoint method for the study of runaway electron dynamics in momentum space Liu et al (2016 Phys. Plasmas 23 010702) is rederived using the Green’s function method, for both the runaway probability function (RPF) and the expected loss time (ELT). The RPF and ELT obtained using the adjoint method are presented, both with and without the synchrotron radiation reaction force. The adjoint method is then applied to study the runaway electron avalanche. Both the critical electric field and the growth rate for the avalanche are calculated using this fast and novel approach.

  15. Adjoint method and runaway electron avalanche

    SciTech Connect

    Liu, Chang; Brennan, Dylan P.; Boozer, Allen H.; Bhattacharjee, Amitava

    2016-12-16

    The adjoint method for the study of runaway electron dynamics in momentum space Liu et al (2016 Phys. Plasmas 23 010702) is rederived using the Green's function method, for both the runaway probability function (RPF) and the expected loss time (ELT). The RPF and ELT obtained using the adjoint method are presented, both with and without the synchrotron radiation reaction force. In conclusion, the adjoint method is then applied to study the runaway electron avalanche. Both the critical electric field and the growth rate for the avalanche are calculated using this fast and novel approach.

  16. THE PROPERTIES OF DYNAMICALLY EJECTED RUNAWAY AND HYPER-RUNAWAY STARS

    SciTech Connect

    Perets, Hagai B.; Subr, Ladislav

    2012-06-01

    Runaway stars are stars observed to have large peculiar velocities. Two mechanisms are thought to contribute to the ejection of runaway stars, both of which involve binarity (or higher multiplicity). In the binary supernova scenario, a runaway star receives its velocity when its binary massive companion explodes as a supernova (SN). In the alternative dynamical ejection scenario, runaway stars are formed through gravitational interactions between stars and binaries in dense, compact clusters or cluster cores. Here we study the ejection scenario. We make use of extensive N-body simulations of massive clusters, as well as analytic arguments, in order to characterize the expected ejection velocity distribution of runaway stars. We find that the ejection velocity distribution of the fastest runaways (v {approx}> 80 km s{sup -1}) depends on the binary distribution in the cluster, consistent with our analytic toy model, whereas the distribution of lower velocity runaways appears independent of the binaries' properties. For a realistic log constant distribution of binary separations, we find the velocity distribution to follow a simple power law: {Gamma}(v){proportional_to}v{sup -8/3} for the high-velocity runaways and v{sup -3/2} for the low-velocity ones. We calculate the total expected ejection rates of runaway stars from our simulated massive clusters and explore their mass function and their binarity. The mass function of runaway stars is biased toward high masses and strongly depends on their velocity. The binarity of runaways is a decreasing function of their ejection velocity, with no binaries expected to be ejected with v > 150 km s{sup -1}. We also find that hyper-runaways with velocities of hundreds of km s{sup -1} can be dynamically ejected from stellar clusters, but only at very low rates, which cannot account for a significant fraction of the observed population of hyper-velocity stars in the Galactic halo.

  17. Energy source for comet outbursts

    NASA Technical Reports Server (NTRS)

    Patashnick, H.; Schuerman, D. W.; Rupprecht, G.

    1974-01-01

    Development of a mechanism explaining the internal source of energy of comet outbursts. A mechanism is proposed which automatically provides a source of particulate matter which creates a huge surface area which contains a substantial percentage of amorphous ice, so that the phase transition of the amorphous ice to a cubic structure provides a release of energy which may be responsible for the outbursts observed in many comets. In addition, the volume into which the transition can propagate is estimated for a spherical comet with a radius of 5 km.

  18. On the inward drift of runaway electrons during the plateau phase of runaway current

    DOE PAGES

    Hu, Di; Qin, Hong

    2016-03-29

    The well observed inward drift of current carrying runaway electrons during runaway plateau phase after disruption is studied by considering the phase space dynamic of runaways in a large aspect ratio toroidal system. We consider the case where the toroidal field is unperturbed and the toroidal symmetry of the system is preserved. The balance between the change in canonical angular momentum and the input of mechanical angular momentum in such a system requires runaways to drift horizontally in configuration space for any given change in momentum space. The dynamic of this drift can be obtained by integrating the modified Euler-Lagrangemore » equation over one bounce time. It is then found that runaway electrons will always drift inward as long as they are decelerating. This drift motion is essentially non-linear, since the current is carried by runaways themselves, and any runaway drift relative to the magnetic axis will cause further displacement of the axis itself. A simplified analytical model is constructed to describe such inward drift both in the ideal wall case and no wall case, and the runaway current center displacement as a function of parallel momentum variation is obtained. The time scale of such displacement is estimated by considering effective radiation drag, which shows reasonable agreement with the observed displacement time scale. Furthermore, this indicates that the phase space dynamic studied here plays a major role in the horizontal displacement of runaway electrons during plateau phase. (C) 2016 AIP Publishing LLC.« less

  19. On the inward drift of runaway electrons during the plateau phase of runaway current

    SciTech Connect

    Hu, Di; Qin, Hong

    2016-03-29

    The well observed inward drift of current carrying runaway electrons during runaway plateau phase after disruption is studied by considering the phase space dynamic of runaways in a large aspect ratio toroidal system. We consider the case where the toroidal field is unperturbed and the toroidal symmetry of the system is preserved. The balance between the change in canonical angular momentum and the input of mechanical angular momentum in such a system requires runaways to drift horizontally in configuration space for any given change in momentum space. The dynamic of this drift can be obtained by integrating the modified Euler-Lagrange equation over one bounce time. It is then found that runaway electrons will always drift inward as long as they are decelerating. This drift motion is essentially non-linear, since the current is carried by runaways themselves, and any runaway drift relative to the magnetic axis will cause further displacement of the axis itself. A simplified analytical model is constructed to describe such inward drift both in the ideal wall case and no wall case, and the runaway current center displacement as a function of parallel momentum variation is obtained. The time scale of such displacement is estimated by considering effective radiation drag, which shows reasonable agreement with the observed displacement time scale. Furthermore, this indicates that the phase space dynamic studied here plays a major role in the horizontal displacement of runaway electrons during plateau phase. (C) 2016 AIP Publishing LLC.

  20. On the inward drift of runaway electrons during the plateau phase of runaway current

    NASA Astrophysics Data System (ADS)

    Hu, Di; Qin, Hong

    2016-03-01

    The well observed inward drift of current carrying runaway electrons during runaway plateau phase after disruption is studied by considering the phase space dynamic of runaways in a large aspect ratio toroidal system. We consider the case where the toroidal field is unperturbed and the toroidal symmetry of the system is preserved. The balance between the change in canonical angular momentum and the input of mechanical angular momentum in such a system requires runaways to drift horizontally in configuration space for any given change in momentum space. The dynamic of this drift can be obtained by integrating the modified Euler-Lagrange equation over one bounce time. It is then found that runaway electrons will always drift inward as long as they are decelerating. This drift motion is essentially non-linear, since the current is carried by runaways themselves, and any runaway drift relative to the magnetic axis will cause further displacement of the axis itself. A simplified analytical model is constructed to describe such inward drift both in the ideal wall case and no wall case, and the runaway current center displacement as a function of parallel momentum variation is obtained. The time scale of such displacement is estimated by considering effective radiation drag, which shows reasonable agreement with the observed displacement time scale. This indicates that the phase space dynamic studied here plays a major role in the horizontal displacement of runaway electrons during plateau phase.

  1. On the inward drift of runaway electrons during the plateau phase of runaway current

    SciTech Connect

    Hu, Di; Qin, Hong

    2016-03-15

    The well observed inward drift of current carrying runaway electrons during runaway plateau phase after disruption is studied by considering the phase space dynamic of runaways in a large aspect ratio toroidal system. We consider the case where the toroidal field is unperturbed and the toroidal symmetry of the system is preserved. The balance between the change in canonical angular momentum and the input of mechanical angular momentum in such a system requires runaways to drift horizontally in configuration space for any given change in momentum space. The dynamic of this drift can be obtained by integrating the modified Euler-Lagrange equation over one bounce time. It is then found that runaway electrons will always drift inward as long as they are decelerating. This drift motion is essentially non-linear, since the current is carried by runaways themselves, and any runaway drift relative to the magnetic axis will cause further displacement of the axis itself. A simplified analytical model is constructed to describe such inward drift both in the ideal wall case and no wall case, and the runaway current center displacement as a function of parallel momentum variation is obtained. The time scale of such displacement is estimated by considering effective radiation drag, which shows reasonable agreement with the observed displacement time scale. This indicates that the phase space dynamic studied here plays a major role in the horizontal displacement of runaway electrons during plateau phase.

  2. Runaway tails in magnetized plasmas

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Vlahos, L.; Rowland, H. L.; Papadopoulos, K.

    1985-01-01

    The evolution of a runaway tail driven by a dc electric field in a magnetized plasma is analyzed. Depending on the strength of the electric field and the ratio of plasma to gyrofrequency, there are three different regimes in the evolution of the tail. The tail can be (1) stable with electrons accelerated to large parallel velocities, (2) unstable to Cerenkov resonance because of the depletion of the bulk and the formation of a positive slope, (3) unstable to the anomalous Doppler resonance instability driven by the large velocity anisotropy in the tail. Once an instability is triggered (Cerenkov or anomalous Doppler resonance) the tail relaxes into an isotropic distribution. The role of a convection type loss term is also discussed.

  3. Runaway electrons in TEXT-U

    SciTech Connect

    Freeman, M.R.

    1994-08-01

    Runaway electrons have long been studied in tokamak plasmas. The previous results regarding runaway electrons and the detection of hard x-rays are reviewed. The hard x-ray energy on TEXT-U is measured and the scaling of energy with electron density, n{sub e}, is noted. This scaling suggests a runaway source term that scales roughly as n{sub e}/{sup 1}. The results indicate that runaways are created throughout the discharges. An upper bound for X{sub e} due to magnetic fluctuations was found to be .0343 m{sup 2}/s. This is an order of magnitude too low to explain the thermal transport in TEXT, implying that electrostatic fluctuations are important in thermal transport in TEXT.

  4. Runaway electron generation in a cooling plasma

    SciTech Connect

    Smith, H.; Helander, P.; Eriksson, L.-G.; Fueloep, T.

    2005-12-15

    The usual calculation of Dreicer [Phys. Rev. 115, 238 (1959); 117, 329 (1960)] generation of runaway electrons assumes that the plasma is in a steady state. In a tokamak disruption this is not necessarily true since the plasma cools down quickly and the collision time for electrons at the runaway threshold energy can be comparable to the cooling time. The electron distribution function then acquires a high-energy tail which can easily be converted to a burst of runaways by the rising electric field. This process is investigated and simple criteria for its importance are derived. If no rapid losses of fast electrons occur, this can be a more important source of runaway electrons than ordinary Dreicer generation in tokamak disruptions.

  5. New outburst of NGC 2617

    NASA Astrophysics Data System (ADS)

    Oknyansky, V. L.; Huseynov, N. A.; Lipunov, .; Gorbovskoy, E. S.; Kuznetsov, A. S.; Balanutza, P. V.; Tatarnikov, A. M.; Metlov, V. G.; Shatsky, N. I.; Nadzhip, A. E.; Burlak, M. A.; Malanchev, K. L.; Gaskell, C. M.

    2016-05-01

    Optical and IR photometry show that the activity of NGC 2617 is continuing and that it is undergoing another outburst. We obtained further JK photometry with the 2.5-m telescope of the SAI Caucasus Mountain Observatory on May 11 (see ATel #9015 for details).

  6. ON THE EFFECT OF EXPLOSIVE THERMONUCLEAR BURNING ON THE ACCRETED ENVELOPES OF WHITE DWARFS IN CATACLYSMIC VARIABLES

    SciTech Connect

    Sion, Edward M.; Sparks, Warren E-mail: warrensparks@comcast.net

    2014-11-20

    The detection of heavy elements at suprasolar abundances in the atmospheres of some accreting white dwarfs in cataclysmic variables (CVs), coupled with the high temperatures needed to produce these elements, requires explosive thermonuclear burning. The central temperatures of any formerly more massive secondary stars in CVs undergoing hydrostatic CNO burning are far too low to produce these elements. Evidence is presented that at least some CVs contain donor secondaries that have been contaminated by white dwarf remnant burning during the common envelope phase and are transferring this material back to the white dwarf. This scenario does not exclude the channel in which formerly more massive donor stars underwent CNO processing in systems with thermal timescale mass transfer. Implications for the progenitors of CVs are discussed and a new scenario for the white dwarf's accretion-nova-outburst is given.

  7. Parameters of a runaway electron avalanche

    NASA Astrophysics Data System (ADS)

    Oreshkin, E. V.; Barengolts, S. A.; Oreshkin, V. I.; Mesyats, G. A.

    2017-10-01

    The features of runaway electron avalanches developing in air at different pressures are investigated using a three-dimensional numerical simulation. The simulation results indicate that an avalanche of this type can be characterized, besides the time and length of its exponential growth, by the propagation velocity and by the average kinetic energy of the runaway electrons. It is shown that these parameters obey the similarity laws applied to gas discharges.

  8. Post-disruptive runaway electron beams in the COMPASS tokamak

    NASA Astrophysics Data System (ADS)

    Vlainic, Milos; Mlynar, J.; Cavalier, J.; Weinzettl, V.; Paprok, R.; Imrisek, M.; Ficker, O.; Varavin, M.; Vondracek, P.; Noterdaeme, J.-M.; Noterdaeme

    2015-10-01

    > For ITER-relevant runaway electron studies, such as suppression, mitigation, termination and/or control of a runaway beam, it is important to obtain the runaway electrons after the disruption. In this paper we report on the first discharges achieved with a post-disruptive runaway electron beam, termed a `runaway plateau', in the COMPASS tokamak. The runaway plateau is produced by a massive gas injection of argon. Almost all of the disruptions with runaway electron plateaus occurred during the plasma current ramp-up phase. The Ar injection discharges with and without a runaway plateau were compared for various parameters. Parametrisation of the discharges shows that the COMPASS disruptions fulfil the range of parameters important for runaway plateau occurrence. These parameters include electron density, electric field, disruption speed, effective safety factor, and the maximum current quench electric field. In addition to these typical parameters, the plasma current value just before the massive gas injection proved to be surprisingly important.

  9. MULTI-INSTRUMENT X-RAY OBSERVATIONS OF THERMONUCLEAR BURSTS WITH SHORT RECURRENCE TIMES

    SciTech Connect

    Keek, L.; Heger, A.; Galloway, D. K.; In't Zand, J. J. M.

    2010-07-20

    Type I X-ray bursts from low-mass X-ray binaries result from a thermonuclear runaway in the material accreted onto the neutron star. Although typical recurrence times are a few hours, consistent with theoretical ignition model predictions, there are also observations of bursts occurring as promptly as 10 minutes or less after the previous event. We present a comprehensive assessment of this phenomenon using a catalog of 3387 bursts observed with the BeppoSAX/WFCs and RXTE/PCA X-ray instruments. This catalog contains 136 bursts with recurrence times of less than 1 hr, that come in multiples of up to four events, from 15 sources. Short recurrence times are not observed from the so-called ultra-compact binaries, indicating that hydrogen-burning processes play a crucial role. As far as the neutron star spin frequency is known, these sources all spin fast at over 500 Hz; the rotationally induced mixing may explain burst recurrence times of the order of 10 minutes. Short recurrence time bursts generally occur at all mass accretion rates where normal bursts are observed, but for individual sources the short recurrence times may be restricted to a smaller interval of accretion rate. The fraction of such bursts is roughly 30%. We also report the shortest known recurrence time of 3.8 minutes.

  10. Design considerations for ITER (International Thermonuclear Experimental Reactor) plasma facing components

    SciTech Connect

    McGrath, R.T.; Koski, J.A.; Watson, R.D.; Causey, R.A.; Croessmann, C.D.; Dempsey, J.F.; Hosking, M.; Neimer, K.A.; Russo, A.J.; Salmonson, J.C.; Stephens, J.; Smith, M.F.; Watkins, J.G.; Whitley, J.B.

    1989-07-01

    The International Thermonuclear Experimental Reactor (ITER) is a joint design and R D project involving the USA, the Soviet Union, Japan and the European Community. These international partners are working together on the design of a fusion tokamak reactor that will operate in the D-T ignition regime. This report compiles the contributions to ITER made by Sandia National Laboratories in the area of design and R D for plasma facing components, such as the first wall and divertor. The following topics are discussed: divertor fabrication issues, divertor thermal-hydraulic analysis, separatrix sweeping effects, divertor tile 2-D stress analysis, electromechanical disruption effects, runaway electron and intense energy deposition analyses, lifetime analysis and tritium retention in plasma facing materials. Material properties for pyrolytic graphite and beryllium are presented. Use of pyrolytic graphite as the plasma facing material allows for operation with thicker graphite armor at the design heat flux level of 10 MW/m/sup 2/. The design of a divertor coated with plasma sprayed beryllium is presented as an attractive alternative to pyrolytic graphite armor tiles. Finally, the Sandia research and development plan for ITER is discussed. 82 figs.

  11. Diffusion with varying drag; the runaway problem

    SciTech Connect

    Rollins, D.K.

    1986-01-01

    The motion of electrons in an ionized plasma of electrons and ions in an external electric field is studied. A probability distribution function describes the electron motion and is a solution of a Fokker-Planck equation. In zero field, the solution approaches an equilibrium Maxwellian. For arbitrarily small field, electrons overcome the diffusive effects and are freely accelerated by the field. This is the electron-runaway phenomenon. The electric field is treated as a small perturbation. Various diffusion coefficients are considered for the one dimensional problem, and the runaway current is determined as a function of the field strength. Diffusion coefficients, non-zero on a finite interval are examined. Some non-trivial cases of these can be solved exactly in terms of known special functions. The more realistic case where the diffusion coeffient decays with velocity are then considered. To determine the runaway current, the equivalent Schroedinger eigenvalue problem is analyzed. The smallest eigenvalue is shown to be equal to the runaway current. Using asymptotic matching, a solution can be constructed which is then used to evaluate the runaway current. The runaway current is exponentially small as a function of field strength. This method is used to extract results from the three dimensional problem.

  12. Thermonuclear Reaction Rate Parameterization for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Sharp, Jacob; Kozub, Raymond L.; Smith, Michael S.; Scott, Jason; Lingerfelt, Eric

    2004-10-01

    The knowledge of thermonuclear reaction rates is vital to simulate novae, supernovae, X-ray bursts, and other astrophysical events. To facilitate dissemination of this knowledge, a set of tools has been created for managing reaction rates, located at www.nucastrodata.org. One tool is a rate parameterizer, which provides a parameterization for nuclear reaction rate vs. temperature values in the most widely used functional form. Currently, the parameterizer uses the Levenberg-Marquardt method (LMM), which requires an initial estimate of the best-fit parameters. The initial estimate is currently provided randomly from a preselected pool. To improve the quality of fits, a new, active method of selecting parameters has been developed. The parameters of each set in the pool are altered for a few iterations to replicate the input data as closely as possible. Then, the set which most nearly matches the input data (based on chi squared) is used in the LMM as the initial estimate for the final fitting procedure. A description of the new, active algorithm and its performance will be presented. Supported by the U. S. Department of Energy.

  13. Bayesian Estimation of Thermonuclear Reaction Rates

    NASA Astrophysics Data System (ADS)

    Iliadis, C.; Anderson, K. S.; Coc, A.; Timmes, F. X.; Starrfield, S.

    2016-11-01

    The problem of estimating non-resonant astrophysical S-factors and thermonuclear reaction rates, based on measured nuclear cross sections, is of major interest for nuclear energy generation, neutrino physics, and element synthesis. Many different methods have been applied to this problem in the past, almost all of them based on traditional statistics. Bayesian methods, on the other hand, are now in widespread use in the physical sciences. In astronomy, for example, Bayesian statistics is applied to the observation of extrasolar planets, gravitational waves, and Type Ia supernovae. However, nuclear physics, in particular, has been slow to adopt Bayesian methods. We present astrophysical S-factors and reaction rates based on Bayesian statistics. We develop a framework that incorporates robust parameter estimation, systematic effects, and non-Gaussian uncertainties in a consistent manner. The method is applied to the reactions d(p,γ)3He, 3He(3He,2p)4He, and 3He(α,γ)7Be, important for deuterium burning, solar neutrinos, and Big Bang nucleosynthesis.

  14. Outbursts of EX Hydrae revisited

    NASA Astrophysics Data System (ADS)

    Mhlahlo, N.; Buckley, D. A. H.; Dhillon, V. S.; Potter, S. B.; Warner, B.; Woudt, P. A.

    2007-09-01

    We present optical spectroscopy of EX Hya during its 1991 outburst. This outburst is characterized by strong irradiation of the front face of the secondary star by the white dwarf, an overflowing stream which is seen strongly in HeII λ4686 and by a dip in the light curves, which extends from 0.1 to 0.6 in the binary and spin phases. Strong irradiation of the accretion curtain and that of the inner regions of the disc led to strong emission of HeII λ4686 and to the suppression of the Hγ and Hβ emission. Disc overflow was observed in quiescence in earlier studies, where the overflow stream material was modulated at high velocities close to 1000 km s-1. In outburst, the overflowing material is modulated at even higher velocities (~1500 km s-1). These are streaming velocities down the field lines close to the white dwarf. Evidence for material collecting near the outer edge of the disc and corotating with the accretion curtain was observed. In decline, this material and the accretion curtain obscured almost all the emission near binary phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse minimum. This has provided additional evidence for an extended accretion curtain, and for the corotation of material with the accretion curtain at the outer edge of the disc. From these observations we suggest that a mechanism similar to that of Spruit and Taam, where outbursts result due to the storage and release of matter outside the magnetosphere, triggers the outbursts of EX Hya. This is followed by the irradiation of the secondary star due to accretion induced radiation.

  15. What is the fate of runaway positrons in tokamaks?

    DOE PAGES

    Liu, Jian; Qin, Hong; Fisch, Nathaniel J.; ...

    2014-06-19

    In this study, massive runaway positrons are generated by runaway electrons in tokamaks. The fate of these positrons encodes valuable information about the runaway dynamics. The phase space dynamics of a runaway position is investigated using a Lagrangian that incorporates the tokamak geometry, loop voltage, radiation and collisional effects. It is found numerically that runaway positrons will drift out of the plasma to annihilate on the first wall, with an in-plasma annihilation possibility less than 0.1%. The dynamics of runaway positrons provides signatures that can be observed as diagnostic tools.

  16. Modeling the classical nova outburst. I - Exploring the physics of a new mechanism

    NASA Technical Reports Server (NTRS)

    Kutter, G. Siegfried; Sparks, Warren M.

    1989-01-01

    Model calculations were performed to describe a mechanism that produces classical nova outbursts on white dwarfs of 1 solar mass or less and for accretion rates of 4 x 10 to the -10th solar mass/yr or greater, i.e., the parameters corresponding to observed data of nova systems. Calculations point to four factors that can induce nuclear runaways of sufficient strength to eject about 0.0001 solar mass at speeds of several hundred to a few thousand km per second, as is observed in classical novae. These are (1) the effects of storage of angular momentum in the star's envelope during the accretion phase; (2) the reduction of centrifugal forces in the star's outer layers during the early nuclear runaway phase, through the inward transport of angular momentum; (3) the inward movement of the zone of peak nuclear burning through the convectively induced shear instability during the runaway phase; and (4) the mixing of original CO stellar matter and H-rich matter, also through the convectively induced shear instability.

  17. Runaway electron studies in the ATF torsatron

    SciTech Connect

    England, A.C.; Bell, G.L.; Fowler, R.H.; Glowienka, J.C.; Harris, J.H.; Lee, D.K.; Murakami, M.; Neilson, G.H.; Rasmussen, D.A.; Rome, J.A.; Saltmarsh, M.J.; Wilgen, J.B. )

    1991-07-01

    Runaway electron formation and confinement occur readily in pulsed torsatrons and heliotrons because of the high loop voltages during initiation and termination of the helical and vertical fields ( field ramping'') and the inherently good containment of the electrons on the flux surfaces in the vacuum fields. This has been confirmed for the Advanced Toroidal Facility (AFT) (Fusion Technol. {bold 10}, 179 (1986)) and other stellarators by orbit calculations. Since runaway electrons can cause an unacceptable level of hard x rays near the machine, a runaway electron suppression system was incorporated in ATF. The main component of the system is a movable paddle, which is normally left in the center of the plasma chamber during the field ramps. This device, in conjunction with programmed vertical field ramping, which reduces the volume of good flux surfaces, has proved to be very effective in reducing the runaway electron population. Measurements of hard x rays from ATF have shown that the runaway electrons are produced primarily during the field ramping but that there is usually also a small steady-state runaway electron component during the flat-top'' portion of the fields. The paddle is the main source of the hard x radiation (thick-target bremsstrahlung). There is evidence that some of the runaway electrons may be confined to islands. The maximum x-ray energy found by pulse height analysis is {similar to}12--15 MeV. The mean energy appears to be a few million electron volts. There is a noticeable forward peaking of the bremsstrahlung from the paddle. The limiters do not appear to be major sources of x rays.

  18. Symmetrically converging plane thermonuclear burn waves

    NASA Astrophysics Data System (ADS)

    Charakhch'yan, A. A.; Khishchenko, K. V.

    2013-10-01

    Five variants of a one-dimensional problem on synchronous bilateral action of two identical drivers on opposite surfaces of a plane layer of DT fuel with the normal or five times greater initial density, where the solution includes two thermonuclear burn waves propagating to meet one another at the symmetry plane, are simulated. A laser pulse with total absorption of energy at the critical density (in two variants) and a proton bunch that provides for a nearly isochoric heating (in three variants) are considered as drivers. A wide-range equation of state for the fuel, electron and ion heat conduction, self-radiation of plasma and plasma heating by α-particles are taken into account. In spite of different ways of ignition, various models of α-particle heat, whether the burn wave remains slow or transforms into the detonation wave, and regardless of way of such a transformation, the final value of the burn-up factor depends essentially on the only parameter Hρ0, where H is the half-thickness of the layer and ρ0 is the initial fuel density. This factor is about 0.35 at Hρ0 ≈ 1 g cm-2 and about 0.7 at Hρ0 ≈ 5 g cm-2. The expansion stage of the flow (after reflecting the burn or detonation wave from the symmetry plane) gives the main contribution in forming the final values of the burn-up factor and the gain at Hρ0 ≈ 1 g cm-2 and increases them approximately two times at Hρ0 ≈ 5 g cm-2. In the case of the proton driver, the final value of the gain is about 200 at Hρ0 ≈ 1 g cm-2 and about 2000 at Hρ0 ≈ 5 g cm-2. In the case of the laser driver, the above values are four times less in conformity with the difference between the driver energies.

  19. Polarized fuel for controlled thermonuclear fusion

    NASA Astrophysics Data System (ADS)

    Bartalucci, Sergio

    2017-07-01

    The use of polarized nuclei as a fuel for thermonuclear fusion reactors was suggested more than 30 years ago, providing evidence for a significant increase of the total cross section. In particular, an enhancement factor close to 1.5 is expected in the energy range below 100 keV for the dominant nuclear fusion reactions 2H + 3H → 4He + n + 17.58 MeV and 2H + 3He → 4He + p + 18.34 MeV. Furthermore, the use of polarized fuel allows one to control the ejectile trajectories, via an enhancement in the forward-backward cross section asymmetry due to polarization. This allows some control on the energy transfer from the plasma to the reactor wall or helps concentrate the neutron flux to defined wall areas. Nevertheless, this idea was received with skepticism by the relevant scientific community, due to some uncertainty in the physics of the process, the low efficiency in the production of polarized beams for injection into plasma and the apparent difficulty of preserving the ion polarization for a time long compared with nuclear burning time. But more recently, as a consequence of significant progress in the field of atomic beam sources and polarized targets, the interest in this matter has been refreshed for both inertially and magnetically confined plasmas. The possibility of implementing nuclear polarization in present and future fusion reactors is discussed in this paper. In particular, the interaction between polarized ions and magnetic fields, both static and RF, which are typically used in a Tokamak for plasma heating via ion cyclotron resonance (ICRH), is considered. Also, experimental issues for practically performing a feasibility test on a real fusion reactors are illustrated.

  20. Runaway electron generation and control

    NASA Astrophysics Data System (ADS)

    Esposito, B.; Boncagni, L.; Buratti, P.; Carnevale, D.; Causa, F.; Gospodarczyk Martin-Solis, M., Jr.; Popovic, Z.; Agostini, M.; Apruzzese, G.; Bin, W.; Cianfarani, C.; De Angelis, R.; Granucci, G.; Grosso, A.; Maddaluno, G.; Marocco, D.; Piergotti, V.; Pensa, A.; Podda, S.; Pucella, G.; Ramogida, G.; Rocchi, G.; Riva, M.; Sibio, A.; Sozzi, C.; Tilia, B.; Tudisco, O.; Valisa, M.; FTU Team

    2017-01-01

    We present an overview of FTU experiments on runaway electron (RE) generation and control carried out through a comprehensive set of real-time (RT) diagnostics/control systems and newly installed RE diagnostics. An RE imaging spectrometer system detects visible and infrared synchrotron radiation. A Cherenkov probe measures RE escaping the plasma. A gamma camera provides hard x-ray radial profiles from RE bremsstrahlung interactions in the plasma. Experiments on the onset and suppression of RE show that the threshold electric field for RE generation is larger than that expected according to a purely collisional theory, but consistent with an increase due to synchrotron radiation losses. This might imply a lower density to be targeted with massive gas injection for RE suppression in ITER. Experiments on active control of disruption-generated RE have been performed through feedback on poloidal coils by implementing an RT boundary-reconstruction algorithm evaluated on magnetic moments. The results indicate that the slow plasma current ramp-down and the simultaneous reduction of the reference plasma external radius are beneficial in dissipating the RE beam energy and population, leading to reduced RE interactions with plasma facing components. RE active control is therefore suggested as a possible alternative or complementary technique to massive gas injection.

  1. Food insecurity among homeless and runaway adolescents

    PubMed Central

    Whitbeck, Les B; Chen, Xiaojin; Johnson, Kurt D

    2008-01-01

    Objective The purpose of this study was to investigate the prevalence of food insecurity and factors related to it among homeless and runaway adolescents. Design Computer-assisted personal interviews were conducted with homeless and runaway adolescents directly on the streets and in shelters. Setting Interviews were conducted in eight Midwest cities: Des Moines, Cedar Rapids, Iowa City, Kansas City, Lincoln, Omaha, St. Louis and Wichita. Subjects The subjects were 428 (187 males; 241 females) homeless and runaway adolescents aged 16−19 years. Average age of the adolescents was 17.4 (standard deviation 1.05) years. Results About one-third of the adolescents had experienced food insecurity in the past 30 days. Factors associated with food insecurity were age of adolescent, a history of caretaker neglect and abuse, having ever spent time directly on the street, a small post-runaway social network, and engaging in deviant and non-deviant street food-acquisition strategies. Conclusions Based on these findings, our conservative estimate is that nationally more than 165 000 homeless and runaway adolescents experienced food insecurity in the past 30 days. These adolescents are largely hidden from public notice and they are usually missed in studies that address national hunger. PMID:16480533

  2. Acceleration of runaway electrons in solar flares

    SciTech Connect

    Moghaddam-taaheri, E.; Goertz, C.K. )

    1990-03-01

    The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2. 23 refs.

  3. Acceleration of runaway electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Goertz, C. K.

    1990-01-01

    The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

  4. Hypervelocity runaways from the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Boubert, D.; Erkal, D.; Evans, N. W.; Izzard, R. G.

    2017-08-01

    We explore the possibility that the observed population of Galactic hypervelocity stars (HVSs) originate as runaway stars from the Large Magellanic Cloud (LMC). Pairing a binary evolution code with an N-body simulation of the interaction of the LMC with the Milky Way, we predict the spatial distribution and kinematics of an LMC runaway population. We find that runaway stars from the LMC can contribute Galactic HVSs at a rate of 3 × 10-6 yr-1. This is composed of stars at different points of stellar evolution, ranging from the main sequence to those at the tip of the asymptotic giant branch. We find that the known B-type HVSs have kinematics that are consistent with an LMC origin. There is an additional population of hypervelocity white dwarfs whose progenitors were massive runaway stars. Runaways that are even more massive will themselves go supernova, producing a remnant whose velocity will be modulated by a supernova kick. This latter scenario has some exotic consequences, such as pulsars and supernovae far from star-forming regions, and a small rate of microlensing from compact sources around the halo of the LMC.

  5. Wave enhancement of electron runaway rate in a collisional plasma

    SciTech Connect

    An, Z.; Liu, C.; Lee, Y.; Boyd, D.

    1982-06-01

    The effects of plasma waves on the electron runaway production rate is studied. For a wave packet with a one-dimensional spectrum directed along the electric field and with a phase velocity range containing the critical velocity v/sub c/ for runaway, the runaway production rate is found to be enhanced by many orders of magnitude. For an isotropic wave spectrum, however, the runaway production rate is reduced because of the wave-enhanced pitch angle scattering.

  6. Measuring Cooling Curves Following Magnetar Outbursts

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2012-09-01

    Magnetars have been observed to increase their flux output by several orders of magnitude in outbursts. Following outbursts they cool on timescales of months to years. We propose to observe two magnetars, Swift J1822.3-1606 and 1E 1547.0-5408, using Chandra as they approach their quiescent state following their recent outbursts in 2011 and 2009, respectively. We will apply a newly developed crustal cooling model to these cooling curves to constrain the properties of the magnetars, such as the crust thickness and heat capacity, and of their outbursts, such as the location of energy deposition.

  7. Predictors of Social Network Composition among Homeless and Runaway Adolescents

    ERIC Educational Resources Information Center

    Johnson, K.D.; Whitbeck, L.B.; Hoyt, D.R.

    2005-01-01

    Recent research on the social support networks of homeless and runaway youth suggest the social networks of runaway youth are made up largely of transient deviant peer relationships. This paper examined social network characteristics of 428 homeless and runaway adolescents from small-to moderate-sized cities in four Midwestern states. We…

  8. Thermonuclear supernova light curves: Progenitors and cosmology

    NASA Astrophysics Data System (ADS)

    Rodney, Steven A.

    Thermonuclear Supernovae (TN SNe) are an extremely important tool in modern astronomy. In their role as cosmological distance probes, they have revealed the accelerated expansion of the universe and have begun to constrain the nature of the dark energy that may be driving that expansion. The next decade will see a succession of wide-field surveys producing thousands of TNSN detections each year. Traditional methods of SN analysis, rooted in time-intensive spectroscopic follow-up, will become completely impractical. To realize the potential of this coming tide of massive data sets, we will need to extract cosmographic parameters (redshift and luminosity distance) from SN photometry without any spectroscopic support. In this dissertation, I present the Supernova Ontology with Fuzzy Templates (SOFT) method, an innovative new approach to the analysis of SN light curves. SOFT uses the framework of fuzzy set theory to perform direct comparisons of SN candidates against template light curves, simultaneously producing both classifications and cosmological parameter estimates. The SOFT method allows us to shed new light on two rich archival data sets. I revisit the IfA Deep Survey and HST GOODS to extract new and improved measurements of the TNSN rate from z=0.2 out to z=1.6. Our new analysis shows a steady increase in the TNSN rate out to z˜1, and adds support for a decrease in the rate at z=1.5. Comparing these rate measurements to theoretical models, I conclude that the progenitor scenario most favored by the collective observational data is a single degenerate model, regulated by a strong wind from the accreting white dwarf. Using a compilation of SN light curves from five recent surveys, I demonstrate that SOFT is able to derive useful constraints on cosmological models from a data set with no spectroscopic information at all. Looking ahead to the near future, I find that photometric analysis of data sets containing 2,000 SNe will be able to improve our constraints on

  9. Do spherical tokamaks have a thermonuclear future?

    NASA Astrophysics Data System (ADS)

    Mirnov, S. V.

    2012-12-01

    the potential possibility of their use in thermonuclear research.

  10. Velocity-space structure of runaway electrons

    SciTech Connect

    Fuchs, V.; Cairns, R.A.; Lashmore-Davies, C.N.; Shoucri, M.M.

    1986-09-01

    The region of velocity space is determined in which electron runaway occurs because of a dc electric field. Phase-space analysis of the relaxation equations describing test electrons, corroborated by two-dimensional (2-D) numerical integration of the Fokker--Planck equation, reveals that the Dreicer condition for runaway v-italic/sup 2//sub parallel/> or =(2+Z-italic/sub i-italic/)E-italic/sub c-italic//E-italic is only sufficient. A weaker condition v-italic/sup 2//sub parallel/> or =(2+Z-italic/sub i-italic/)/sup 1//sup ///sup 2/E-italic/sub c-italic//E-italic is established, and it is shown, in general, that runaway in velocity space only occurs for those electrons that are outside one of the separatrices of the relaxation equations. The scaling with v-italic/sub parallel/ of the parallel distribution function and of the perpendicular temperature is also derived.

  11. The origin of OB runaway stars.

    PubMed

    Fujii, Michiko S; Portegies Zwart, Simon

    2011-12-09

    About 20% of all massive stars in the Milky Way have unusually high velocities, the origin of which has puzzled astronomers for half a century. We argue that these velocities originate from strong gravitational interactions between single stars and binaries in the centers of star clusters. The ejecting binary forms naturally during the collapse of a young (≤1 million years old) star cluster. This model replicates the key characteristics of OB runaways in our galaxy, and it explains the presence of runaway stars of ≥100 solar masses (M(⊙)) around young star clusters, such as R136 and Westerlund 2. The high proportion and the distributions in mass and velocity of runaways in the Milky Way are reproduced if the majority of massive stars are born in dense and relatively low-mass (5000 to 10,000 M(⊙)) clusters.

  12. The Origin of OB Runaway Stars

    NASA Astrophysics Data System (ADS)

    Fujii, Michiko S.; Portegies Zwart, Simon

    2011-12-01

    About 20% of all massive stars in the Milky Way have unusually high velocities, the origin of which has puzzled astronomers for half a century. We argue that these velocities originate from strong gravitational interactions between single stars and binaries in the centers of star clusters. The ejecting binary forms naturally during the collapse of a young (≲1 milion years old) star cluster. This model replicates the key characteristics of OB runaways in our galaxy, and it explains the presence of runaway stars of ≳100 solar masses (M⊙) around young star clusters, such as R136 and Westerlund 2. The high proportion and the distributions in mass and velocity of runaways in the Milky Way are reproduced if the majority of massive stars are born in dense and relatively low-mass (5000 to 10,000 M⊙) clusters.

  13. Localization of thermonuclear burning in accreting millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Boutloukos, Stratos; Miller, Cole

    Nuclear-powered oscillations during Type-I X-ray bursts have so far revealed the spin of about twenty accreting millisecond pulsars in low-mass X-ray binaries. Constraining strong gravity through the emission from the hot spots on the neutron star surface requires understanding of the properties of such burst oscillations. We use adaptive mesh refinement hydrodynamical numerical computations to model the ignition and spreading of thermonuclear flames. Our preliminary simulations suggest that confinement of fuel is important for the localization of thermonuclear burning, like that required for the observed burst oscillations. This is consistent with spectral analyses of RXTE observations that we also present here. The software used in this work was in part developed by the DOE-supported ASCI/Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago. This work was supported by NSF Grant AST0708424.

  14. Runaway electrons and magnetic island confinement

    DOE PAGES

    Boozer, Allen H.

    2016-08-19

    The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativisticmore » energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. Furthermore, the physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.« less

  15. Runaway electrons and magnetic island confinement

    NASA Astrophysics Data System (ADS)

    Boozer, Allen H.

    2016-08-01

    The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativistic energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. The physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.

  16. Runaway electrons and magnetic island confinement

    SciTech Connect

    Boozer, Allen H.

    2016-08-19

    The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativistic energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. Furthermore, the physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.

  17. Runaway electrons and magnetic island confinement

    SciTech Connect

    Boozer, Allen H.

    2016-08-19

    The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativistic energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. Furthermore, the physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.

  18. Runaway electrons and magnetic island confinement

    SciTech Connect

    Boozer, Allen H.

    2016-08-15

    The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativistic energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. The physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.

  19. Formation and termination of runaway beams in ITER disruptions

    NASA Astrophysics Data System (ADS)

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2017-06-01

    A self-consistent analysis of the relevant physics regarding the formation and termination of runaway beams during mitigated disruptions by Ar and Ne injection is presented for selected ITER scenarios with the aim of improving our understanding of the physics underlying the runaway heat loads onto the plasma facing components (PFCs) and identifying open issues for developing and accessing disruption mitigation schemes for ITER. This is carried out by means of simplified models, but still retaining sufficient details of the key physical processes, including: (a) the expected dominant runaway generation mechanisms (avalanche and primary runaway seeds: Dreicer and hot tail runaway generation, tritium decay and Compton scattering of γ rays emitted by the activated wall), (b) effects associated with the plasma and runaway current density profile shape, and (c) corrections to the runaway dynamics to account for the collisions of the runaways with the partially stripped impurity ions, which are found to have strong effects leading to low runaway current generation and low energy conversion during current termination for mitigated disruptions by noble gas injection (particularly for Ne injection) for the shortest current quench times compatible with acceptable forces on the ITER vessel and in-vessel components ({τ\\text{res}}∼ 22~\\text{ms} ). For the case of long current quench times ({τ\\text{res}}∼ 66~\\text{ms} ), runaway beams up to  ∼10 MA can be generated during the disruption current quench and, if the termination of the runaway current is slow enough, the generation of runaways by the avalanche mechanism can play an important role, increasing substantially the energy deposited by the runaways onto the PFCs up to a few hundreds of MJs. Mixed impurity (Ar or Ne) plus deuterium injection proves to be effective in controlling the formation of the runaway current during the current quench, even for the longest current quench times, as well as in decreasing

  20. Thermonuclear supernovae: simulations of the deflagration stage and their implications.

    PubMed

    Gamezo, Vadim N; Khokhlov, Alexei M; Oran, Elaine S; Chtchelkanova, Almadena Y; Rosenberg, Robert O

    2003-01-03

    Large-scale, three-dimensional numerical simulations of the deflagration stage of a thermonuclear supernova explosion show the formation and evolution of a highly convoluted turbulent flame in the gravitational field of an expanding carbon-oxygen white dwarf. The flame dynamics are dominated by the gravity-induced Rayleigh-Taylor instability that controls the burning rate. The thermonuclear deflagration releases enough energy to produce a healthy explosion. The turbulent flame, however, leaves large amounts of unburned and partially burned material near the star center, whereas observations that imply these materials are present only in outer layers. This disagreement could be resolved if the deflagration triggers a detonation.

  1. Transport of runaway and thermal electrons due to magnetic microturbulence

    SciTech Connect

    Mynick, H.E.; Strachan, J.D.

    1981-04-01

    The ratio of the runaway electron confinement to thermal electron energy confinement is derived for tokamaks where both processes are determined by free streaming along stochastic magnetic field lines. The runaway electron confinement is enhanced at high runaway electron energies due to phase averaging over the magnetic perturbations when the runaway electron drift surfaces are displaced from the magnetic surfaces. Comparison with experimental data from LT-3, Ormak, PLT, ST, and TM-3 indicates that magnetic stochasticity may explain the relative transport rates of runaways and thermal electron energy.

  2. The influence of plasma motion on disruption generated runaway electrons

    SciTech Connect

    Russo, A.J.

    1991-01-01

    One of the possible consequences of disruptions is the generation of runaway electrons which can impact plasma facing components and cause damage due to high local energy deposition. This problem becomes more serious as the machine size and plasma current increases. Since large size and high currents are characteristics of proposed future machines, control of runaway generation is an important design consideration. A lumped circuit model for disruption runaway electron generation indicates that control circuitry on strongly influence runaway behavior. A comparison of disruption data from several shots on JET and D3-D with model results, demonstrate the effects of plasma motion on runaway number density and energy. 6 refs., 12 figs.

  3. Outbursts and cavities in comets

    NASA Astrophysics Data System (ADS)

    Ipatov, Sergei

    Based on analysis of the images made during the first 13 minutes after the collision of the impact module of the Deep Impact (DI) spacecraft with Comet 9P/Tempel 1, Ipatov & A'Hearn [1] studied time variations of ejection of material after this impact. They showed that, besides the normal ejection, at time t_{e} after the DI collision between 8 s and 60 s there was a considerable additional ejection (a triggered outburst) of small (micron size) particles. It increased the mean velocities of observed small ejected particles (compared with the normal ejection). The outburst could be caused by excavation of a large cavity with dust and gas under pressure. The largest cavity excavated after the collision could be relatively deep because a considerable excess ejection lasted during about 50 s. Schultz et al. [2] concluded that the diameter d_{tc} of the DI transient crater was about 200 m. Some authors support smaller values of d_{tc}. The depth of the DI crater at t_{e}=8 s was estimated in [3] to be about 6 m for d_{tc}=200 m and 4 m for d_{tc}=100 m. The distance between the pre-impact surface of Comet 9P/Tempel 1 and the upper border of the largest excavated cavity equal to about 4-6 m, and sizes of particles inside the cavities of a few microns are in good agreement with the results obtained by Kossacki & Szutowicz [4]. In their models of the explosion of Comet 17P/Holmes, the initial sublimation front of the CO ice was located at a depth of 4 m, 10 m, or 20 m, and calculations were finished when the CO pressure exceeded the threshold value 10 kPa. It was shown that the pressure of CO vapor can rise to this value only when the nucleus is composed of very fine grains, a few microns in radius. The porous structure of comets provides enough space for sublimation. The projection of the velocity of the leading edge of the DI cloud (onto the plane perpendicular to the line of sight) was about 100-200 m/s and is typical for outburst particles ejected from comets

  4. RUNAWAY STARS, HYPERVELOCITY STARS, AND RADIAL VELOCITY SURVEYS

    SciTech Connect

    Bromley, Benjamin C.; Kenyon, Scott J.; Brown, Warren R.; Geller, Margaret J. E-mail: skenyon@cfa.harvard.ed E-mail: mgeller@cfa.harvard.ed

    2009-12-01

    Runaway stars ejected from the Galactic disk populate the halo of the Milky Way. To predict the spatial and kinematic properties of runaways, we inject stars into a Galactic potential, compute their trajectories through the Galaxy, and derive simulated catalogs for comparison with observations. Runaways have a flattened spatial distribution, with higher velocity stars at Galactic latitudes less than 30{sup 0}. Due to their shorter stellar lifetimes, massive runaway stars are more concentrated toward the disk than low mass runaways. Bound (unbound) runaways that reach the halo probably originate from distances of 6-12 kpc (10-15 kpc) from the Galactic center, close to the estimated origin of the unbound runaway star HD 271791. Because runaways are brighter and have smaller velocities than hypervelocity stars (HVSs), radial velocity surveys are unlikely to confuse runaway stars with HVSs. We estimate that at most one runaway star contaminates the current sample. We place an upper limit of 2% on the fraction of A-type main-sequence stars ejected as runaways.

  5. Observations of classical novae in outburst

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Stryker, L. L.; Sonneborn, G.; Sparks, Warren M.; Ferland, Gary; Wagner, R. M.; Williams, R. E.; Gehrz, Robert D.; Ney, Edward P.; Kenyon, Scott

    1988-01-01

    The IUE obtained ultraviolet data on novae in outburst. The characteristics of every one of the outbursts are different. Optical and infrared data on many of the same novae were also obtained. Three members of the carbon-oxygen class of novae are presented.

  6. On the avalanche generation of runaway electrons during tokamak disruptions

    NASA Astrophysics Data System (ADS)

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2015-08-01

    A simple zero dimensional model for a tokamak disruption is developed to evaluate the avalanche multiplication of a runaway primary seed during the current quench phase of a fast disruptive event. Analytical expressions for the plateau runaway current, the energy of the runaway beam, and the runaway energy distribution function are obtained allowing the identification of the parameters dominating the formation of the runaway current during disruptions. The effect of the electromagnetic coupling to the vessel and the penetration of the external magnetic energy during the disruption current quench as well as of the collisional dissipation of the runaway current at high densities are investigated. Current profile shape effects during the formation of the runaway beam are also addressed by means of an upgraded one-dimensional model.

  7. Hot tail runaway electron generation in tokamak disruptions

    SciTech Connect

    Smith, H. M.; Verwichte, E.

    2008-07-15

    Hot tail runaway electron generation is caused by incomplete thermalization of the electron velocity distribution during rapid plasma cooling. It is an important runaway electron mechanism in tokamak disruptions if the thermal quench phase is sufficiently fast. Analytical estimates of the density of produced runaway electrons are derived for cases of exponential-like temperature decay with a cooling rate lower than the collision frequency. Numerical simulations, aided by the analytical results, are used to compare the strength of the hot tail runaway generation with the Dreicer mechanism for different disruption parameters (cooling rate, post-thermal quench temperature, and electron density) assuming that no losses of runaway electrons occur. It is seen that the hot tail runaway production is going to be the dominant of these two primary runaway mechanisms in ITER [R. Aymar et al., Plasma Phys. Controlled Fusion 44, 519 (2002)].

  8. Synchrotron radiation from a runaway electron distribution in tokamaks

    SciTech Connect

    Stahl, A.; Fülöp, T.; Landreman, M.; Papp, G.; Hollmann, E.

    2013-09-15

    The synchrotron radiation emitted by runaway electrons in a fusion plasma provides information regarding the particle momenta and pitch-angles of the runaway electron population through the strong dependence of the synchrotron spectrum on these parameters. Information about the runaway density and its spatial distribution, as well as the time evolution of the above quantities, can also be deduced. In this paper, we present the synchrotron radiation spectra for typical avalanching runaway electron distributions. Spectra obtained for a distribution of electrons are compared with the emission of mono-energetic electrons with a prescribed pitch-angle. We also examine the effects of magnetic field curvature and analyse the sensitivity of the resulting spectrum to perturbations to the runaway distribution. The implications for the deduced runaway electron parameters are discussed. We compare our calculations to experimental data from DIII-D and estimate the maximum observed runaway energy.

  9. On the avalanche generation of runaway electrons during tokamak disruptions

    SciTech Connect

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2015-08-15

    A simple zero dimensional model for a tokamak disruption is developed to evaluate the avalanche multiplication of a runaway primary seed during the current quench phase of a fast disruptive event. Analytical expressions for the plateau runaway current, the energy of the runaway beam, and the runaway energy distribution function are obtained allowing the identification of the parameters dominating the formation of the runaway current during disruptions. The effect of the electromagnetic coupling to the vessel and the penetration of the external magnetic energy during the disruption current quench as well as of the collisional dissipation of the runaway current at high densities are investigated. Current profile shape effects during the formation of the runaway beam are also addressed by means of an upgraded one-dimensional model.

  10. Characterizing the 2016 Perseid Meteor Shower Outburst

    NASA Technical Reports Server (NTRS)

    Blaauw, R. C.; Moser, D. E.; Molau, S.; Schult, C.; Stober, G.

    2017-01-01

    The Perseid meteor shower has been observed for millennia and is known for its visually spectacular meteors and occasional outbursts. Normal activity displays Zenithal Hourly Rates (ZHRs) of approximately100. The Perseids were expected to outburst in 2016, primarily due to particles released during the 1862 and 1479 revolutions of parent Comet Swift-Tuttle. NASA's Meteoroid Environment Office predicted the timing, strength and duration of the outburst for spacecraft risk using the MSFC Meteoroid Stream Model [1]. A double peak was predicted, with an outburst displaying a ZHR of 210 +/- 50 at 00:30 UTC Aug 12 (139.5deg Solar Longitude), and a traditional peak 12 hours later with rates still heightened from the outburst [2]. Video, visual, and radar observations taken worldwide by various entities were used to characterize the shower and compare to predictions.

  11. Characterizing the 2016 Perseid Meteor Shower Outburst

    NASA Technical Reports Server (NTRS)

    Blaauw, R. C.; Moser, D. E.; Ehlert, S. R.; Kingery, A. M.; Molau, S.; Schult, C.; Stober, G.

    2017-01-01

    The Perseid meteor shower has been observed for millennia and known for its visually spectacular meteors and occasional outbursts. The Perseids were expected to outburst in 2016, primarily due to particles released during the 1862 and 1479 revolutions of Comet Swift-Tuttle. NASA's Meteoroid Environment Office predicted the timing, strength and duration of the outburst for spacecraft risk using the MSFC Meteoroid Stream Model. A double peak was predicted, with an outburst displaying a ZHR of 210 +/- 50 at 00:30 UTC Aug 12, and a traditional peak approximately 12 hours later with rates still heightened from the outburst. Video, visual, and radar observations taken worldwide by various entities were used to characterize the shower and compare to predictions.

  12. Runaway breakdown and electrical discharges in thunderstorms

    NASA Astrophysics Data System (ADS)

    Milikh, Gennady; Roussel-Dupré, Robert

    2010-12-01

    This review considers the precise role played by runaway breakdown (RB) in the initiation and development of lightning discharges. RB remains a fundamental research topic under intense investigation. The question of how lightning is initiated and subsequently evolves in the thunderstorm environment rests in part on a fundamental understanding of RB and cosmic rays and the potential coupling to thermal runaway (as a seed to RB) and conventional breakdown (as a source of thermal runaways). In this paper, we describe the basic mechanism of RB and the conditions required to initiate an observable avalanche. Feedback processes that fundamentally enhance RB are discussed, as are both conventional breakdown and thermal runaway. Observations that provide clear evidence for the presence of energetic particles in thunderstorms/lightning include γ-ray and X-ray flux intensifications over thunderstorms, γ-ray and X-ray bursts in conjunction with stepped leaders, terrestrial γ-ray flashes, and neutron production by lightning. Intense radio impulses termed narrow bipolar pulses (or NBPs) provide indirect evidence for RB particularly when measured in association with cosmic ray showers. Our present understanding of these phenomena and their enduring enigmatic character are touched upon briefly.

  13. WISE Catches a Runaway Star in Flames

    NASA Image and Video Library

    2010-11-24

    NASA Wide-field Infrared Survey captured this view of a runaway star racing away from its original home. Surrounded by a glowing cloud of gas and dust, the star AE Aurigae appears on fire. Appropriately, the cloud is called the Flaming Star nebula.

  14. Leakage of runaway electrons from tokamaks

    SciTech Connect

    Wong, K.L.

    1982-02-01

    Runaway electron orbits are calculated in a tokamak magnetic field. It is shown that these electrons tend to drift towards a larger major radius with a velocity v Vector/sub R/ = qcE/B/sub 0/ R. This effect may be relevant to some recent experimental observations in tokamaks.

  15. Dynamics of runaway electrons in magnetized plasmas

    SciTech Connect

    Moghaddam-Taaheri, E.

    1986-01-01

    The evolution of a runaway electron tail driven by a subcritical dc electric field in a magnetized plasma is studied numerically using a quasi-linear numerical code (2-D in v- and k-space) based on the Ritz-Galerkin method and finite elements. Three different regimes in the evolution of the runaway tail depending on the strength of the dc electric field and the ratio of plasma to gyrofrequency, were found. The tail can be (a) stable and the electrons are accelerated to large parallel velocities, (b) unstable to the Cerenkov resonance due to the formation of a positive slope on the runaway tail, (c) unstable to the anomalous Doppler resonance instability driven by the large velocity anisotropy in the tail. Once an instability is triggered (Cerenkov or anomalous Doppler resonance) the tail relaxes into an isotropic distribution resulting in less acceleration. The synchrotron emission of the runaway electrons shows large enhancement in the radiation level at the high-frequency end of the spectrum during the pitch-angle scattering of the fast particles. The results are relevant to recent experimental data from the Princeton Large Torus (PLT) during current-drive experiments and to the microwave bursts observed during solar flares.

  16. Synchrotron emission from runaway electron distributions

    SciTech Connect

    Winske, D.; Peter, T.; Boyd, D.A.

    1983-12-01

    Synchrotron emission from a relativistic anti-loss-cone (runaway) distribution is investigated numerically and compared with various analytical approximations. The results are applied to recent measurements of enhanced emission during current-drive experiments on the Princeton Large Torus (PLT) as well as to impulsive solar microwave bursts.

  17. Simulation of runaway electrons in tokamak

    NASA Astrophysics Data System (ADS)

    Guo, Zehua; Tang, Xianzhu; McDevitt, Chris

    2015-11-01

    Runaway electrons with relativisitc energy (>Mev) are generated in tokamaks when the acceleration by parallel electric field exceeds the drag due to Coulomb collisions with the bulk plasma. Carrying about 70% of the ITER thermal current (15MA), they can possibly cause severe damage to tokamak facing components. Here we report the development of a solver for computing the evolution of runaway electron distribution in tokamak geometries. Essential effects from Coulomb collisions, radiation losses, toroidal effects and the radial transport are included on the same footings. Numerical techniques (implicit-explicit time-stepping, KT/NT central schemes) to overcome the difficulties arising from the wide spread of time scales in runaway electron dynamics and the hyperbolic nature of the relativistic Fokker-Planck equation will be discussed. We will use the solver to study two important physics: 1) the presence of stable point in the phase space and its relation to the electric field threshold; 2) the radial transport of runaways in tokamak geometry and its effects on the distribution function. Work supported by DOE via LANL-LDRD.

  18. Picosecond runaway electron beams in air

    SciTech Connect

    Mesyats, G. A.; Yalandin, M. I.; Reutova, A. G.; Sharypov, K. A.; Shpak, V. G.; Shunailov, S. A.

    2012-01-15

    Experimental data on the generation of picosecond runaway electron beams in an air gap with an inhomogeneous electric field at a cathode voltage of up to 500 kV are presented. The methods and equipment developed for these experiments made it possible to measure the beam characteristics with a time resolution of better than 10{sup -11} s, determine the voltage range and the beam formation time in the breakdown delay stage, and demonstrate the influence of the state of the cathode surface on the stability of runaway electron generation. It is demonstrated that the critical electron runaway field in air agrees with the classical concepts and that the accelerated beam can be compressed to {approx}20 ps. It is unlikely that, under these conditions, the beam duration is limited due to the transition of field emission from the cathode to a microexplosion of inhomogeneities. The maximum energy acquired by runaway electrons in the course of acceleration does not exceed the value corresponding to the electrode voltage.

  19. A Runaway Red Supergiant in M31

    NASA Astrophysics Data System (ADS)

    Evans, Kate Anne; Massey, Philip

    2016-01-01

    A significant percentage of OB stars are runaways, so we should expect a similar percentage of their evolved descendants to also be runaways. However, recognizing such stars presents its own set of challenges, as these older, more evolved stars will have drifted further from their birthplace, and thus their velocities might not be obviously peculiar. Several Galactic red supergiants (RSGs) have been described as likely runaways, based upon the existence of bow shocks, including Betelgeuse. Here we announce the discovery of a runaway RSG in M31, based upon a 300 km s-1 discrepancy with M31's kinematics. The star is found about 21‧ (4.6 kpc) from the plane of the disk, but this separation is consistent with its velocity and likely age (˜10 Myr). The star, J004330.06+405258.4, is an M2 I, with MV=-5.7, log L/L⊙=4.76, an effective temperature of 3700 K, and an inferred mass of 12-15 M⊙. The star may be a high-mass analog of the hypervelocity stars, given that its peculiar space velocity is probably 400-450 km s-1, comparable to the escape speed from M31's disk. K. A. E.'s work was supported by the NSF's Research Experience for Undergraduates program through AST-1461200, and P. M.'s was partially supported by the NSF through AST-1008020 and through Lowell Observatory.

  20. Runaway Children and Social Network Interaction.

    ERIC Educational Resources Information Center

    Libertoff, Kenneth

    A review of the history and literature about the runaway child in America reveals that young people from poor families have always viewed running away as a reasonable way of leaving a poverty stricken home. For many adolescents, running away has been a response to an unhealthy family or work situation, and at times it has been a problem-solving…

  1. Runaway electron beam in atmospheric pressure discharges

    NASA Astrophysics Data System (ADS)

    Oreshkin, E. V.; Barengolts, S. A.; Chaikovsky, S. A.; Oreshkin, V. I.

    2015-11-01

    A numerical simulation was performed to study the formation of a runaway electron (RAE) beam from an individual emission zone in atmospheric pressure air discharges with a highly overvolted interelectrode gap. It is shown that the formation of a RAE beam in discharges at high overvoltages is much contributed by avalanche processes.

  2. A Runaway Red Supergiant in M31

    NASA Astrophysics Data System (ADS)

    Evans, Kate Anne; Massey, Philip

    2015-11-01

    A significant percentage of OB stars are runaways, so we can expect a similar percentage of their evolved descendants to also be runaways. However, recognizing such stars presents its own set of challenges, as these older, more evolved stars will have drifted farther from their birthplace, and thus their velocities might not be obviously peculiar. Several Galactic red supergiants (RSGs) have been described as likely runaways based on the existence of bow shocks, including Betelgeuse. Here we announce the discovery of a runaway RSG in M31 based on a 300 km s-1 discrepancy with M31's kinematics. The star is found about 21‧ (4.6 kpc) from the plane of the disk, but this separation is consistent with its velocity and likely age (˜10 Myr). The star, J004330.06+405258.4, is an M2 I, with MV = -5.7, {log}L/{L}⊙ = 4.76, an effective temperature of 3700 K, and an inferred mass of 12-15M⊙. The star may be a high-mass analog of the hypervelocity stars, given that its peculiar space velocity is probably 400-450 km s-1, comparable to the escape speed from M31's disk. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.

  3. The prevalence of disabilities and maltreatment among runaway children.

    PubMed

    Sullivan, P M; Knutson, J F

    2000-10-01

    This research was conducted to determine the prevalence of disabilities among abused and nonabused runaways within a hospital population (Study 1) and community school population (Study 2) and to identify any associations between disability, maltreatment, family stress factors, academic achievement, school attendance, domestic violence and runaway status. Descriptive information was collected for maltreated and nonmaltreated runaways from hospital (N = 39,352; 255 runaways) and school (N = 40,211; 562 runaways) populations including: disability status, type of maltreatment, family stress factors, record of domestic violence in the family, academic achievement and attendance. The prevalence rate of disabilities among the maltreated runaways was 83.1% and 47% among the nonmaltreated runaways in the hospital sample and 34% and 17%, respectively, in the school sample. Children and youth with disabilities were at increased risk to become runaways in both populations. The presence of maltreatment significantly increased the association between running away and disability status. Children with behavior disorders, mental retardation, and some type of communication disorder were significantly more likely to run away than children with other disabilities. Among the maltreated runaways with and without disabilities, physical abuse and sexual abuse were significantly associated with running away. Records of domestic violence were more prevalent in the families of runaways with behavior disorders and no diagnosed disability. Lower academic achievement, poor school attendance, and more family stress factors were associated with maltreatment, disability and runaway status. Children and youth with disabilities are unidentified and unrecognized among runaways. Professionals working with runaways and their families need to be cognizant of the special needs of the population, particularly with respect to behavior disorders, communication disabilities, and mental retardation and

  4. Thermonuclear Fusion: An Energy Source for the Future

    ERIC Educational Resources Information Center

    Drummond, William E.

    1973-01-01

    Discusses current research in thermonuclear fusion with particular emphasis on the problem of confining hot plasma. Recent experiments indicate that magnetic bottles called tokamaks may achieve the necessary confinement times, and this break-through has given renewed optimism to the feasibility of commercial fusion power by the turn of the…

  5. Thermonuclear Fusion: An Energy Source for the Future

    ERIC Educational Resources Information Center

    Drummond, William E.

    1973-01-01

    Discusses current research in thermonuclear fusion with particular emphasis on the problem of confining hot plasma. Recent experiments indicate that magnetic bottles called tokamaks may achieve the necessary confinement times, and this break-through has given renewed optimism to the feasibility of commercial fusion power by the turn of the…

  6. Eclipse Mapping Experiments in Dwarf Novae Outbursts

    NASA Astrophysics Data System (ADS)

    Borges, B. W.; Baptista, R.

    2006-06-01

    In this work, we report the eclipse mapping analysis of CCD photometric data of two short period dwarf novae - V4140 Sgr (Borges & Baptista 2005) and HT Cas (Borges, Baptista & Catalán, in preparation) - during observed outburst events. The analysis of the observations of V4140 Sgr, done between 1991 and 2001, reveals that the object was in the decline from an outburst in 1992 and again in outburst in 2001. A distance of d = 170+/-30 pc is obtained from a method similar to that used to constrain the distance to open clusters. From this distance, disc radial brightness temperature distributions are determined, and the disc temperatures remain below the critical effective temperature T_{crit} at all disc radii during the outburst. The distributions in quiescence and in outburst are significantly different from those of other dwarf novae of similar orbital period. These results cannot be explained within the framework of the disc instability model and the small amplitude outbursts of V4140 Sgr can be due bursts of enhanced mass transfer rate from the secondary star. Our HT Cas data consist of V and R CCD photometric observations done in 2005 November with the 0.95-m James Gregory Telescope (JGT) and cover a outburst cycle. We used the entropy associated to the eclipse maps to obtain the semi-opening disc angle α evolution throught the outburst. The obtained angles are systematically lower than those obtained by Ioannou et al. (1999) and we can conclude that the outburst radial profiles must be flatter than the the T ∝ r^{-3/4} law of steady state dics, against the expectations of the disc instability model. Our intensity radial distributions presents the same ``outside-in'' outburst behavior as obtained by the referred author.

  7. Perpendicular dynamics of runaway electrons in tokamak plasmas

    SciTech Connect

    Fernandez-Gomez, I.; Martin-Solis, J. R.; Sanchez, R.

    2012-10-15

    In this paper, it will be shown that the runaway phenomenon in tokamak plasmas cannot be reduced to a one-dimensional problem, based on the competence between electric field acceleration and collisional friction losses in the parallel direction. A Langevin approach, including collisional diffusion in velocity space, will be used to analyze the two-dimensional runaway electron dynamics. An investigation of the runaway probability in velocity space will yield a criterion for runaway, which will be shown to be consistent with the results provided by the more simple test particle description of the runaway dynamics [Fuchs et al., Phys. Fluids 29, 2931 (1986)]. Electron perpendicular collisional scattering will be found to play an important role, relaxing the conditions for runaway. Moreover, electron pitch angle scattering perpendicularly broadens the runaway distribution function, increasing the electron population in the runaway plateau region in comparison with what it should be expected from electron acceleration in the parallel direction only. The perpendicular broadening of the runaway distribution function, its dependence on the plasma parameters, and the resulting enhancement of the runaway production rate will be discussed.

  8. Runaway electrons in a Tokamak: A free-electron maser

    SciTech Connect

    Kurzan, B.; Steuer, K.; Suttrop, W.

    1997-01-01

    In Ohmic divertor plasma discharges of the ASDEX Upgrade tokamak a small population of runaway electrons is purposely generated at the beginning of the discharge. About 1.5 s after the runaways` generation fluctuating emission in the microwave region with a very narrow bandwidth is observed. The radiation can be explained by relativistic runaway electrons forming a free-electron maser in the tokamak: The dynamics of the runaways is simulated by taking into account the acceleration in the electric field, collisions with the plasma particles, synchrotron radiation losses and the resonances between the gyromotion and harmonics of the magnetic ripple field. According to this the runaways reach a final energy determined by the ripple resonance mechanism and are monoenergetic enough to form a cyclotron autoresonance maser. The guiding of the radiation along the bent path of the runaways is accomplished by nearly resonant runaways around the amplifying runaways. The emission frequency depends on the final energy of the runaways and the observed bandwidth via the maser`s gain on their particle density. Analyzing the emitted fluctuating emission is thus a potentially new diagnostic for runaways. {copyright} {ital 1997 American Institute of Physics.}

  9. FU Orionis Outbursts and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Bell, Robbins; Young, Rich (Technical Monitor)

    1998-01-01

    Protostellar systems are variable on many timescales. The FU Orionis outburst is one of the most drastic forms of variability known to occur in low mass stellar systems. During a typical outburst lasting several decades, system luminosities may be a hundred times what is normal of the quiescent state. FU Orionis outburst events are believed to have significant impacts on the thermal structure of the protosolar nebula. Their existence has been utilized to explain features in the meteoritic record from thermally induced homogenization to chondrule formation. Recent numerical models have shown the viability of the hypothesis that the radiation observed during outburst is emitted by a luminous circumstellar disk transporting mass at a thousand times the quiescent rate. We will begin by describing what is known about the FU Orionis outburst phenomenon from recent observations and theory. We will discuss evidence that suggests that outburst radiation is emitted by a circumstellar disk rather than by the star and will briefly describe the thermal instability as a mechanism for outburst. Additional information is contained in the original extended abstract.

  10. FU Orionis Outbursts and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Bell, Robbins; Young, Rich (Technical Monitor)

    1998-01-01

    Protostellar systems are variable on many timescales. The FU Orionis outburst is one of the most drastic forms of variability known to occur in low mass stellar systems. During a typical outburst lasting several decades, system luminosities may be a hundred times what is normal of the quiescent state. FU Orionis outburst events are believed to have significant impacts on the thermal structure of the protosolar nebula. Their existence has been utilized to explain features in the meteoritic record from thermally induced homogenization to chondrule formation. Recent numerical models have shown the viability of the hypothesis that the radiation observed during outburst is emitted by a luminous circumstellar disk transporting mass at a thousand times the quiescent rate. We will begin by describing what is known about the FU Orionis outburst phenomenon from recent observations and theory. We will discuss evidence that suggests that outburst radiation is emitted by a circumstellar disk rather than by the star and will briefly describe the thermal instability as a mechanism for outburst. Additional information is contained in the original extended abstract.

  11. Are Comet Outbursts the Result of Avalanches?

    NASA Astrophysics Data System (ADS)

    Steckloff, Jordan; Melosh, H. Jay

    2016-10-01

    Recently, Rosetta became the first spacecraft to make high-resolution observations of a comet outburst (a rapid, ephemeral increase in dust production) emerging from the surface of a comet nucleus. These outbursts occurred near perihelion, lasted only a few minutes, and produced a highly collimated outburst plume without any corresponding increase in H2O or CO2 gas production (See abstract by Rinaldi et al.). These observations cannot be explained by proposed driving outburst mechanisms (such as crystallization of amorphous ice, cryovolcanic gas exsolution, or explosive outgasing of subsurface chambers), all of which are driven by gas, and would therefore lead to an increase in the gas production.We propose instead that the observed outbursts on Comet 67P/Churyumov-Gerasimenko (hereafter 67P) are the result of cometary avalanches. The surface of 67P contains many cliffs and scarps, with dusty surface layers blanketing the shallower slopes above and below these steep surfaces. The Rosetta spacecraft returned clear evidence of mass wasting, which form icy talus fields that are the source of much of 67P's cometary activity. Additionally, Rosetta observed morphological changes over time in the shallower, dusty surface layers above these steep slopes, which suggest that avalanches periodically release dusty materials onto these active talus fields.Here we present the results of a numerical simulation of dusty material avalanching into an active area (active talus field). These simulations show that such avalanches will generate a transient, highly collimated outburst plume that closely matches the observed morphology of the outbursts emanating from the surface of 67P. This mechanism predicts that cometary outbursting should not be directly associated with any increase in gas production, consistent with observations. Additionally, we show that regions of the nucleus that have sourced outburst plumes contain steep surfaces (above the angle of repose), which is required

  12. Does Turbulence in the Iron Convection Zone Cause the Massive Outbursts of Eta Carinae?

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1999-01-01

    Taken at face value, the observed properties of the central object in Eta-Car suggest a very massive, hot main-sequence star, only slightly evolved. If this is so, the star's extraordinarily high steady rate of mass loss must dynamically perturb its outer envelope down to the iron convection zone, where the kinetic energy associated with turbulent convection can be directly fed into mass ejection. Runaway mass loss, triggered by either internal (pulsational, rotational) or external (tidal) forcing, would produce a secular oscillation of the outer envelope. In either case, the oscillation is potentially able to account for the observed approximately 5 yr cycles of visual outbursts in Eta-Car, including the giant eruption of 1843.

  13. Outburst of 2325+43 DX Andromedae

    NASA Astrophysics Data System (ADS)

    Mattei, Janet A.

    1995-06-01

    DX Andromedae is reported in outburst by Jack Nordby and Tonny Vanmunster. Current magnitude is approx. 12.3. Tonny Vanmunster also reports that EP Peg has gone into outburst. Current magntude is approx. 13.8. A new variable is reported as 1250-60 Var CRU by the Observatorio Astronomico del Colegio Cristo Rey in Argentina. Position RA=12h 56m 25.64s DEC=-60° 57' 56.6". BZ UMa is undergoing a short outburst with current magnitudes reported as approx. 13. Also, observations of VW HYD and SS CYG continue to be solicited.

  14. A Study of Alcohol Abuse Among Runaway Youth and Their Families. Survey of Alcohol Related Problems Among Runaway Youth Seen in Runaway Centers.

    ERIC Educational Resources Information Center

    Treanor, William; van Houten, Therese

    The objectives of this project are two-fold: (1) to provide runaway counselors--both professional and paraprofessional--with training in the knowledge and skills needed to effectively deal with runaways and families affected by alcohol abuse, and to evaluate the impact of this training, and (2) to document the incidence and degree of alcohol abuse…

  15. Adjoint Fokker-Planck equation and runaway electron dynamics

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Brennan, Dylan P.; Bhattacharjee, Amitava; Boozer, Allen H.

    2016-01-01

    The adjoint Fokker-Planck equation method is applied to study the runaway probability function and the expected slowing-down time for highly relativistic runaway electrons, including the loss of energy due to synchrotron radiation. In direct correspondence to Monte Carlo simulation methods, the runaway probability function has a smooth transition across the runaway separatrix, which can be attributed to effect of the pitch angle scattering term in the kinetic equation. However, for the same numerical accuracy, the adjoint method is more efficient than the Monte Carlo method. The expected slowing-down time gives a novel method to estimate the runaway current decay time in experiments. A new result from this work is that the decay rate of high energy electrons is very slow when E is close to the critical electric field. This effect contributes further to a hysteresis previously found in the runaway electron population.

  16. Numerical simulations of runaway electron generation in pressurized gases

    SciTech Connect

    Levko, D.; Yatom, S.; Vekselman, V.; Gleizer, J. Z.; Gurovich, V. Tz.; Krasik, Ya. E.

    2012-01-01

    The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.

  17. Experimental study on runaway characteristics of pump system

    NASA Astrophysics Data System (ADS)

    Yang, F.; Liu, C.; Tang, F. P.; Zhou, J. R.

    2013-12-01

    Experiments on runaway characteristics were conducted for two sets of tubular pump systems and two sets of vertical axial pump systems. The measurement results show that at different blade angles the unit runaway speeds are different and increase with the increase of the blade angle. For the same pump system at the same blade angle the unit runaway speeds decrease with decrease of reverse-water-head of the system. The different outflow passages of pumps also caused variation of the unit runaway speeds. Through the calculation of resistance torque the variable factors of runaway speed with same blade angle are analyzed under different operation conditions of reverse-water-head. It is evident that the unit runaway speed obtained from model pump system is applicable and safe for conversion to prototype pump system.

  18. Adjoint Fokker-Planck equation and runaway electron dynamics

    SciTech Connect

    Liu, Chang; Brennan, Dylan P.; Bhattacharjee, Amitava; Boozer, Allen H.

    2016-01-15

    The adjoint Fokker-Planck equation method is applied to study the runaway probability function and the expected slowing-down time for highly relativistic runaway electrons, including the loss of energy due to synchrotron radiation. In direct correspondence to Monte Carlo simulation methods, the runaway probability function has a smooth transition across the runaway separatrix, which can be attributed to effect of the pitch angle scattering term in the kinetic equation. However, for the same numerical accuracy, the adjoint method is more efficient than the Monte Carlo method. The expected slowing-down time gives a novel method to estimate the runaway current decay time in experiments. A new result from this work is that the decay rate of high energy electrons is very slow when E is close to the critical electric field. This effect contributes further to a hysteresis previously found in the runaway electron population.

  19. Studies of runaway electron transport in TEXT

    SciTech Connect

    Wang, Pei-Wen.

    1991-12-01

    The transport of runaway electrons is studied by a plasma position shift experiment and by imposing an externally applied perturbing magnetic field on the edge. The perturbing magnetic field can produce either magnetic islands or, with overlapping islands, a stochastic field. Hard X-ray signals are then measured and compared with analytic and numerical model results. Diffusion coefficients in the edge, {approximately}10{sup 4} cm{sup 2}/sec, and inside the plasma, {approximately}10{sup 2} {minus} 10{sup 3} cm{sup 2}/sec, are estimated. The averaged drift effects are small and the intrinsic magnetic fluctuations are estimated to be < (b{sub r}/B{sub 0}){sup 2} > {approximately}1-{sup {minus}10} at the edge and decreasing inward. Runaway electrons are a good diagnostic of the magnetic fluctuations. It is considered that the magnetic fluctuations have a negligible effect on electron thermal diffusion in the edge plasma.

  20. Numerical calculation of ion runaway distributions

    SciTech Connect

    Embréus, O.; Stahl, A.; Hirvijoki, E.; Fülöp, T.; Newton, S.

    2015-05-15

    Ions accelerated by electric fields (so-called runaway ions) in plasmas may explain observations in solar flares and fusion experiments; however, limitations of previous analytic work have prevented definite conclusions. In this work, we describe a numerical solver of the 2D non-relativistic linearized Fokker-Planck equation for ions. It solves the initial value problem in velocity space with a spectral-Eulerian discretization scheme, allowing arbitrary plasma composition and time-varying electric fields and background plasma parameters. The numerical ion distribution function is then used to consider the conditions for runaway ion acceleration in solar flares and tokamak plasmas. Typical time scales and electric fields required for ion acceleration are determined for various plasma compositions, ion species, and temperatures, and the potential for excitation of toroidal Alfvén eigenmodes during tokamak disruptions is considered.

  1. Runaway electrons as a diagnostic of magnetic fluctuations (abstract)

    SciTech Connect

    Bengtson, R.D. ); Wang, P.W. ); Freeman, M.; Wootton, A.J. ); Catto, P.J.; Myra, J.R. )

    1992-10-01

    The transport of runaway electrons in a hot plasma can be comparatively easily measured by perturbation experiments. The runaway electron diffusion coefficient is determined by intrinsic magnetic fluctuations rather than electrostatic fluctuations because of the high energies involved. The results presented here demonstrate the efficacy of using runaway transport techniques for determining intrinsic magnetic fluctuations. This work was supported in part by U. S. Department of Energy under grant DE-FG05-88ER-53267 and the Texas Advanced Research Program.

  2. Collisionless pitch-angle scattering of runaway electrons

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Wang, Yulei; Qin, Hong

    2016-06-01

    It is discovered that the tokamak field geometry generates a toroidicity induced broadening of the pitch-angle distribution of runaway electrons. This collisionless pitch-angle scattering is much stronger than the collisional scattering and invalidates the gyro-center model for runaway electrons. As a result, the energy limit of runaway electrons is found to be larger than the prediction of the gyro-center model and to depend heavily on the background magnetic field.

  3. Quasisteady turbulence driven by runaway electrons

    SciTech Connect

    Muschietti, L.; Appert, K.; Vaclavik, J.

    1982-07-01

    The evolution of the turbulence driven by runaway electrons has been followed by means of a computer code based on the quasilinear equations. The evolution is not characterized by periodic relaxations as claimed in previous works but ends in a quasisteady turbulent, yet very persistent state, accessible from different initial conditions. This discrepancy is clarified as being due to the excessive stiffness of the moment equations used to demonstrate the relaxations. Moreover, a theory is developed to interpret the quasisteady state found.

  4. Dynamics of the Pin Pallet Runaway Escapement

    DTIC Science & Technology

    1978-06-01

    pin pallet simulation to a spring- driven timing mechanism. 3. Modification of the present model to accommcdate the simulation of a plate pallet ...NUMULER( Technical Report ARLCD-TFR-77062 4. TITLE (and Sublttle) 5. TYPE OF REPORT & PERIOD COVERED DYNAMICS OF THE PIN PALLET RUNAWAY ESCAPEMENT 6...instantaneous positions of the pallet pin and the escape-wheel form the basis of the controls in the computer program. DO I FJAN 1473AVr1t’I o INOV 6IS

  5. Protoplanetary Formation and the FU Orionis Outburst

    NASA Technical Reports Server (NTRS)

    Bodenheimer, P. H.

    1996-01-01

    The following three publications which reference the above grant from the NASA Origins of Solar Systems program are attached and form the final technical report for this project. The research involved comparisons of the spectral energy distributions of FU Orionis objects with theoretical models and associated studies of the structure of the outbursting accretion disks, as well as related studies on the effects of magnetic fields in disks, which will lead in the future to models of FU Orionis outbursts which include the effects of magnetic fields. The project was renewed under a new grant NAGW-4456, entitled 'Effects of FU Orionis Outbursts on Protoplanetary Disks'. Work now being prepared for publication deals more specifically with the issue of the effects of the outbursts on protoplanetary formation. Models of the spectral energy distribution of FU Orionis stars. A simple model of a buoyant magnetic dynamo in accretion disks and a numerical study of magnetic buoyancy in an accretion disk have been submitted.

  6. ScienceCast 31: Draconid Meteor Outburst

    NASA Image and Video Library

    2011-10-05

    Forecasters say Earth is heading for a stream of dust from Comet 21P/Giacobini-Zinner. A close encounter with the comet's fragile debris could spark a meteor outburst over parts of our planet on October 8th.

  7. Sonoluminescence, shock waves, and micro-thermonuclear fusion

    SciTech Connect

    Moss, W.C.; Clarke, D.B.; White, J.W.; Young, D.A.

    1995-08-01

    We have performed numerical hydrodynamic simulations of the growth and collapse of a sonoluminescing bubble in a liquid. Our calculations show that spherically converging shock waves are generated during the collapse of the bubble. The combination of the shock waves and a realistic equation of state for the gas in the bubble provides an explanation for the measured picosecond optical pulse widths and indicates that the temperatures near the center of the bubble may exceed 3O eV. This leads naturally to speculation about obtaining micro-thermonuclear fusion in a bubble filled with deuterium (D{sub 2}) gas. Consequently, we performed numerical simulations of the collapse of a D{sub 2} bubble in D{sub 2}0. A pressure spike added to the periodic driving amplitude creates temperatures that may be sufficient to generate a very small, but measurable number of thermonuclear D-D fusion reactions in the bubble.

  8. Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs

    SciTech Connect

    Rosswog, S.; Ramirez-Ruiz, E.; Hix, William Raphael

    2008-01-01

    Suggestive evidence has accumulated that intermediate mass black holes (IMBHs) exist in some globular clusters. Some stars will inevitably wander sufficiently close to the hole to suffer a tidal disruption. IMBHs can disrupt not only solar-type stars but also compact white dwarf stars. We investigate the fate of white dwarfs that approach the hole close enough to be disrupted and compressed to such an extent that explosive nuclear burning is triggered. Based on a precise modeling of the gas dynamics together with the nuclear reactions, it is argued that thermonuclear ignition is a natural outcome for white dwarfs of all masses passing well within the tidal radius. A good fraction of the star is accreted, yielding high luminosities that persist for up to a year. A peculiar, underluminous thermonuclear explosion accompanied by a soft X-ray transient signal would, if detected, be a compelling testimony for the presence of an IMBH.

  9. Thermonuclear Burning as a Probe of Neutron Star

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2008-01-01

    Thermonuclear fusion is a fundamental process taking place in the matter transferred onto neutron stars in accreting binary systems. The heat deposited by nuclear reactions becomes readily visible in the X-ray band when the burning is either unstable or marginally stable, and results in the rich phenomenology of X-ray bursts, superbursts, and mHz quasiperiodic oscillations. Fast X-ray timing observations with NASA's Rossi X-ray Timing Explorer (RXTE) over the past decade have revealed a wealth of new phenomena associated with thermonuclear burning on neutron stars, including the discovery of nuclear powered pulsations during X-ray bursts and superbursts. I will briefly review our current observational and theoretical understanding of these new phenomena, with an emphasis on recent findings, and discuss what they are telling us about the structure of neutron stars.

  10. Parameters of the focusing optics in a laser thermonuclear reactor

    SciTech Connect

    Basov, N.G.; Belousov, N.I.; Vergunova, G.A.; Grishunin, P.A.; Danilov, A.E.; Lebo, I.G.; Rozanov, V.B.; Sklizkov, G.V.; Subbotin, V.I.; Fedotov, S.I.

    1985-03-01

    The energy balance of a laser thermonuclear reactor is considered and it is shown that the energy of the reaction products absorbed by the focusing optics of the reactor considerably exceeds the energy absorbed from the laser pulse. The x-ray spectrum of the target emission is calculated and used to find the minimum distances from the center of the chamber to the optical system. Variants of the gas shield are analyzed. The laser radiation brightness required to ignite the reaction is used to obtain a relationship between the minimum focal length and the optical strength of the material employed for the optics. It is shown that thermonuclear neutrons incident on the focusing system generate considerable thermal stresses and deformations.

  11. Thermonuclear Burning as a Probe of Neutron Star

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2008-01-01

    Thermonuclear fusion is a fundamental process taking place in the matter transferred onto neutron stars in accreting binary systems. The heat deposited by nuclear reactions becomes readily visible in the X-ray band when the burning is either unstable or marginally stable, and results in the rich phenomenology of X-ray bursts, superbursts, and mHz quasiperiodic oscillations. Fast X-ray timing observations with NASA's Rossi X-ray Timing Explorer (RXTE) over the past decade have revealed a wealth of new phenomena associated with thermonuclear burning on neutron stars, including the discovery of nuclear powered pulsations during X-ray bursts and superbursts. I will briefly review our current observational and theoretical understanding of these new phenomena, with an emphasis on recent findings, and discuss what they are telling us about the structure of neutron stars.

  12. Shock ignition of thermonuclear fuel with high areal density.

    PubMed

    Betti, R; Zhou, C D; Anderson, K S; Perkins, L J; Theobald, W; Solodov, A A

    2007-04-13

    A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.

  13. Strong plasma screening in thermonuclear reactions: Electron drop model

    NASA Astrophysics Data System (ADS)

    Kravchuk, P. A.; Yakovlev, D. G.

    2014-01-01

    We analyze enhancement of thermonuclear fusion reactions due to strong plasma screening in dense matter using a simple electron drop model. In the model we assume fusion in a potential that is screened by an effective electron cloud around colliding nuclei (extended Salpeter ion-sphere model). We calculate the mean-field screened Coulomb potentials for atomic nuclei with equal and nonequal charges, appropriate astrophysical S factors, and enhancement factors of reaction rates. As a byproduct, we study the analytic behavior of the screening potential at small separations between the reactants. In this model, astrophysical S factors depend not only on nuclear physics but on plasma screening as well. The enhancement factors are in good agreement with calculations by other methods. This allows us to formulate a combined, pure analytic model of strong plasma screening in thermonuclear reactions. The results can be useful for simulating nuclear burning in white dwarfs and neutron stars.

  14. Enhancement of thermonuclear reaction rates in extremely dense stellar plasmas

    NASA Astrophysics Data System (ADS)

    Itoh, Naoki; Kuwashima, Fumiyoshi; Munakata, Hiroharu

    1990-10-01

    The enhancement factor of the thermonuclear reaction rates is calculated for the extremely dense stellar plasmas in the liquid phase where the condition 3Gamma/tau less than or equal to 1.6 is not necessarily imposed. Here the parameter 3Gamma/tau corresponds to the ratio of the classical turning point radius at the Gamow peak and the mean interionic distance in the case of the pure Coulomb potential. Direct double integration is carried out to obtain the thermonuclear reaction rates. The result is presented in the form of an analytic fitting formula to facilitate applications. The present fitting formula is valid for 3Gamma/tau = 0-5.4. The present calculation is intended to serve as the best available one for the case that ions are in the semiquantum regime.

  15. Runaway stars in the Gum Nebula

    NASA Technical Reports Server (NTRS)

    Got, J. R., III; Ostriker, J. P.

    1971-01-01

    It is proposed that the two pulsars PSR 0833-45 (the Vela pulsar) and MP 0835 are runaways from a common binary system originally located in the B association around gamma Velorum. Arguments are presented for a simple model of the Gum nebula in which two distinct ionized regions are present. The first consists of the Stromgren spheres of gamma Velorum and zeta Puppis, while the second is a larger, more filamentary region ionized by the supernova explosion associated with PSR 0833-45. Using this model and the available dispersion measures, the distances to the two pulsars were estimated and found to be compatible with a runaway origin. The position angle of the rotation axis of PSR 0833-45 is also compatible with this origin. The masses of the parent stars of the two pulsars can be deduced from the runaway star dynamics and an assumed age for MP 0835. It is concluded that the masses were in excess of 10 solar masses. The dynamically-determined parent star masses are in agreement with the values expected for evolved members of the B association around gamma Velorum.

  16. Numerical analysis on pump turbine runaway points

    NASA Astrophysics Data System (ADS)

    Guo, L.; Liu, J. T.; Wang, L. Q.; Jiao, L.; Li, Z. F.

    2012-11-01

    To research the character of pump turbine runaway points with different guide vane opening, a hydraulic model was established based on a pumped storage power station. The RNG k-ε model and SMPLEC algorithms was used to simulate the internal flow fields. The result of the simulation was compared with the test data and good correspondence was got between experimental data and CFD result. Based on this model, internal flow analysis was carried out. The result show that when the pump turbine ran at the runway speed, lots of vortexes appeared in the flow passage of the runner. These vortexes could always be observed even if the guide vane opening changes. That is an important way of energy loss in the runaway condition. Pressure on two sides of the runner blades were almost the same. So the runner power is very low. High speed induced large centrifugal force and the small guide vane opening gave the water velocity a large tangential component, then an obvious water ring could be observed between the runner blades and guide vanes in small guide vane opening condition. That ring disappeared when the opening bigger than 20°. These conclusions can provide a theory basis for the analysis and simulation of the pump turbine runaway points.

  17. Global crustal dynamics of Magnetars in relation to their bright X-ray outbursts

    NASA Astrophysics Data System (ADS)

    Yang, Huan; Thompson, Christopher; Ortiz, Nestor

    2017-01-01

    We consider the yielding response of a neutron star crust to smooth, unbalanced Maxwell stresses imposed at the core-crust boundary, and the coupling of the dynamic crust to the external magnetic field. Stress buildup and yielding in a magnetar crust is a global phenomenon: an elastic distortion radiating from one plastically deforming zone is shown to dramatically increase the creep rate in distant zones. Runaway creep to dynamical rates is shown to be possible, being enhanced by in situ heating and suppressed by thermal conduction and shearing of an embedded magnetic field. A global and time-dependent model of elastic, plastic, magnetic, and thermal evolution is developed. Fault-like structures develop naturally, and a range of outburst timescales is observed. Transient events with time profiles similar to giant magnetar flares (millisecond rise, about 0.1 s duration, and decaying power-law tails) result from runaway creep that starts in localized sub-km-sized patches and spreads across the crust. We also discuss the key role of crust's plastic and elastic motion in Magnetar short bursts and after-flare quasi-periodic oscillations.

  18. Runaway electrons as a diagnostic of magnetic fluctuations (invited)

    SciTech Connect

    Bengtson, R.D.; Freeman, M.R.; Wootton, A.J. ); Wang, P.W. ); Myra, J.R.; Catto, P.J. )

    1992-10-01

    The transport of runaway electrons in a hot plasma can be comparatively easily measured by perturbation experiments which provide a runaway electron diffusivity {ital D}. The diffusion can be interpreted in terms of a magnetic fluctuation level, from which an electron thermal diffusivity can be deduced. We find the runaway electron diffusion coefficient is determined by intrinsic magnetic fluctuations rather than electrostatic fluctuations because of the high energies involved. The results presented here demonstrate the efficacy of using runaway transport techniques for determining intrinsic magnetic fluctuations.

  19. Generation of runaway electrons during the thermal quench in tokamaks

    NASA Astrophysics Data System (ADS)

    Aleynikov, Pavel; Breizman, Boris N.

    2017-04-01

    This work provides a systematic description of electron kinetics during impurity dominated thermal quenches. A Fokker–Planck equation for the hot electrons and a power balance equation for the bulk plasma are solved self-consistently, with impurity radiation as the dominant energy loss mechanism. We find that runaway production is facilitated by heavy injection of impurities up to prompt conversion of the total current into a sub-MeV runaway current. We also find that runaway formation is less efficient in plasmas with high pre-quench temperatures and predict significant radial variation of the runaway seed in such plasmas.

  20. Observations of classical novae in outburst

    SciTech Connect

    Starrfield, S.; Stryker, L.L.; Sonneborn, G.; Sparks, W.M.; Ferland, G.; Wagner, R.M.; Williams, R.E.; Gehrz, R.D.; Ney, E.P.; Kenyon, S.

    1988-01-01

    Over the past 10 years the IUE Satellite has obtained ultraviolet data on a number of novae in outbursts and the characteristics of every one of the outbursts have been different. In addition, our group has also obtained optical and infrared data on many of the same novae. In this paper we present the data on three members of the carbon-oxygen class of novae. 6 refs., 5 figs.

  1. BF Cyg during its Current Outburst

    NASA Astrophysics Data System (ADS)

    Siviero, A.; Tamajo, E.; Lutz, J.; Wallerstein, G.; ANS Collaboration

    We are intensively monitoring the current outburst on BF Cyg, both spectroscopically (high and low resolution modes) and photometrically (so far 450 BVR CI C measurements have been collected). The outburst is photometrically reminiscent of the major event BF Cyg experienced in 1890 when it rose by 4 mag in the blue. In this contribution we present the data and describe the plans to investigate this object.

  2. Method of achieving the controlled release of thermonuclear energy

    DOEpatents

    Brueckner, Keith A.

    1986-01-01

    A method of achieving the controlled release of thermonuclear energy by illuminating a minute, solid density, hollow shell of a mixture of material such as deuterium and tritium with a high intensity, uniformly converging laser wave to effect an extremely rapid build-up of energy in inwardly traveling shock waves to implode the shell creating thermonuclear conditions causing a reaction of deuterons and tritons and a resultant high energy thermonuclear burn. Utilizing the resulting energy as a thermal source and to breed tritium or plutonium. The invention also contemplates a laser source wherein the flux level is increased with time to reduce the initial shock heating of fuel and provide maximum compression after implosion; and, in addition, computations and an equation are provided to enable the selection of a design having a high degree of stability and a dependable fusion performance by establishing a proper relationship between the laser energy input and the size and character of the selected material for the fusion capsule.

  3. Outburst activity of the symbiotic binary AG Dra

    NASA Astrophysics Data System (ADS)

    Gális, R.; Merc, J.; Leedjärv, L.

    2017-04-01

    AG Dra regularly undergoes quiescent and active stages which consist of a series of individual outbursts repeating at about a one-year interval. After seven years of flat quiescence following the 2006-08 major outbursts, in the late spring of 2015, AG Dra begun rising again in brightness toward what appeared to be a new minor outburst. The recent outburst activity of AG Dra was definitely confirmed by a more prominent outburst in April 2016. The photometric and spectroscopic observations suggest that these outbursts are of the hot type. Such behaviour is quite unusual, because the major outbursts in the beginning of active stages are usually cool. Can we expect the major cool or minor hot outburst during the spring of 2017? AG Dra demonstrates the importance of long-term monitoring of symbiotic stars in order to disentangle the nature and mechanisms of their active stages and outbursts.

  4. Fu Ori outbursts and the planet-disc mass exchange

    NASA Astrophysics Data System (ADS)

    Nayakshin, Sergei; Lodato, Giuseppe

    2012-10-01

    It has been recently proposed that giant protoplanets migrating inwards through the disc more rapidly than they contract could be tidally disrupted when they fill their Roche lobes ˜0.1 au away from their parent protostars. Here we consider the process of mass and angular momentum exchange between the tidally disrupted planet and the surrounding disc in detail. We find that the planet's adiabatic mass-radius relation and its ability to open a deep gap in the disc determine whether the disruption proceeds as a sudden runaway or a balanced quasi-static process. In the latter case, the planet feeds the inner disc through its Lagrangian L1 point like a secondary star in a stellar binary system. As the planet loses mass, it gains specific angular momentum and normally migrates in the outward direction until the gap closes. Numerical experiments show that planet disruption outbursts are preceded by long 'quiescent' periods during which the disc inward of the planet is empty. The hole in the disc is created when the planet opens a deep gap, letting the inner disc to drain on to the star while keeping the outer one stalled behind the planet. We find that the mass-losing planet embedded in a realistic protoplanetary disc spawns an extremely rich set of variability patterns. In a subset of parameter space, there is a limit cycle behaviour caused by non-linear interaction between the planet mass-loss and the disc hydrogen ionization instability. We suggest that tidal disruptions of young massive planets near their stars may be responsible for the observed variability of young accreting protostars such as FU Ori, EXor and T Tauri stars in general.

  5. Possibilities of applications of fiber Bragg gratings for thermonuclear fusion technology

    NASA Astrophysics Data System (ADS)

    Gasior, P.

    2016-09-01

    The research on harnessing thermonuclear fusion is considered to be important for reaching global energetic safety as the future thermonuclear fusion reactors offer an inexhaustible and CO2 emission free source of electric power. The development of thermonuclear fusion reactors is a great interdisciplinary effort which needs participation of scientists dealing with many fields of physics and engineering. Due to the experimental character of the works (the best example is the effort for the development of ITER - International Thermonuclear Experimental Reactor) its crucial part is in the design and application of diagnostics operating in harsh thermonuclear environments. Fiber optics and especially fiber Bragg gratings are components which can operate feasibly in both irradiation and electromagnetic interference conditions. This paper is to give a prospect of application of fiber Bragg grating sensors in devices aimed on the research in the thermonuclear fusion field.

  6. A backward Monte Carlo method for efficient computation of runaway probabilities in runaway electron simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Guannan; Del-Castillo-Negrete, Diego

    2016-10-01

    Kinetic descriptions of RE are usually based on the bounced-averaged Fokker-Planck model that determines the PDFs of RE in the 2 dimensional momentum space. Despite of the simplification involved, the Fokker-Planck equation can rarely be solved analytically and direct numerical approaches (e.g., continuum and particle-based Monte Carlo (MC)) can be time consuming specially in the computation of asymptotic-type observable including the runaway probability, the slowing-down and runaway mean times, and the energy limit probability. Here we present a novel backward MC approach to these problems based on backward stochastic differential equations (BSDEs). The BSDE model can simultaneously describe the PDF of RE and the runaway probabilities by means of the well-known Feynman-Kac theory. The key ingredient of the backward MC algorithm is to place all the particles in a runaway state and simulate them backward from the terminal time to the initial time. As such, our approach can provide much faster convergence than the brute-force MC methods, which can significantly reduce the number of particles required to achieve a prescribed accuracy. Moreover, our algorithm can be parallelized as easy as the direct MC code, which paves the way for conducting large-scale RE simulation. This work is supported by DOE FES and ASCR under the Contract Numbers ERKJ320 and ERAT377.

  7. Disruption runaway modeling, ripple effects and energy limits

    SciTech Connect

    Russo, A.J.

    1990-07-18

    Several models of runaway electron generation during a disruption are described and applied to the problem of determining the radiation loss and energy limit of runaway electrons. In particular the prediction of orbits and energy limits for proposed ITER design are discussed. It was found that resonance between the electron gyrofrequency and the fundamental ripple frequency can lead to large synchrotron radiation losses and create an upper bound on runaway energy. Interactions with the second harmonic of the ripple field are very sensitive to ripple amplitude and may lead to a further reduction in runaway energy. In ITER this effect can limit the runaway energy to values of 270 MeV. A lump circuit model of the plasma can be used to determine the coupled interactions of the runaway currents with the plasma and control circuit currents. Depending on what is assumed about the perpendicular energy of the runaway electrons. Maximum values of runaway energy predicted for ITER are in the range of 35 to 120 MeV. 4 refs., 15 figs.

  8. Theoretical analysis of a runaway electron suppression device

    SciTech Connect

    Niemer, K.A.; Gilligan, J.G. . Dept. of Nuclear Engineering); Croessmann, C.D. ); England, A.C. )

    1990-01-01

    A new runaway electron suppression paddle was designed with the PTA code package to reduce the runaway electron population in the Advanced Toroidal Facility (ATF), Oak Ridge National Laboratory. The PTA code package is a unique application of PATRAN, the Integrated TIGER Series, and ABAQUS for modeling high energy electron impact on magnetic fusion components and materials. By its nature, ATF is susceptible to runaway electron formation and confinement resulting in the production of a high level of hard x-rays near the machine. Four previous stainless steel paddles proved effective in reducing the runaway electron population; however, electrons above 15 MeV have still been observed. Melting and bending were observed in each of the previous paddles, reducing their effectiveness. Scoping experiments are under way to further characterize the runaway electrons in ATF. Data from these experiments will provide insight into runaway electron damage mechanisms. Proposals for the insertion of a new paddle in ATF are being considered. These analyses add to the knowledge of runaway electron damage and will aid in the design of future components to withstand runaway electron discharges in all magnetic fusion devices, including tokamaks. 8 refs., 3 figs., 1 tab.

  9. Kinetic modelling of runaway electrons in dynamic scenarios

    NASA Astrophysics Data System (ADS)

    Stahl, A.; Embréus, O.; Papp, G.; Landreman, M.; Fülöp, T.

    2016-11-01

    Improved understanding of runaway-electron formation and decay processes are of prime interest for the safe operation of large tokamaks, and the dynamics of the runaway electrons during dynamical scenarios such as disruptions are of particular concern. In this paper, we present kinetic modelling of scenarios with time-dependent plasma parameters; in particular, we investigate hot-tail runaway generation during a rapid drop in plasma temperature. With the goal of studying runaway-electron generation with a self-consistent electric-field evolution, we also discuss the implementation of a collision operator that conserves momentum and energy and demonstrate its properties. An operator for avalanche runaway-electron generation, which takes the energy dependence of the scattering cross section and the runaway distribution into account, is investigated. We show that the simplified avalanche model of Rosenbluth and Putvinskii (1997 Nucl. Fusion 37 1355) can give inaccurate results for the avalanche growth rate (either lower or higher) for many parameters, especially when the average runaway energy is modest, such as during the initial phase of the avalanche multiplication. The developments presented pave the way for improved modelling of runaway-electron dynamics during disruptions or other dynamic events.

  10. Predictors of Trauma-Related Symptoms among Runaway Adolescents

    ERIC Educational Resources Information Center

    McCarthy, Michael D.; Thompson, Sanna J.

    2010-01-01

    Little is known about trauma-related symptoms among runaway adolescents. Precocious departure from familial homes often exposes youth to traumatic victimization. This study examined the extent to which runaway adolescents present trauma symptomotology and assessed factors that predict trauma symptoms. Participants (N = 350) were 12-18 years of age…

  11. Runaway greenhouse atmospheres: Applications to Earth and Venus

    NASA Technical Reports Server (NTRS)

    Kasting, James F.

    1991-01-01

    Runaway greenhouse atmospheres are discussed from a theoretical standpoint and with respect to various practical situation in which they might occur. The following subject areas are covered: (1) runaway greenhouse atmospheres; (2) moist greenhouse atmospheres; (3) loss of water from Venus; (4) steam atmosphere during accretion; and (5) the continuously habitable zone.

  12. Becoming a Runaway: From the Accounts of Youthful Runners.

    ERIC Educational Resources Information Center

    Ek, Carl A.; Steelman, Lala Carr

    1988-01-01

    Interviews with runaways reveals the following stages of a runaway episode: (1) problematic relationships at home, characterized by violence, power struggles, sibling favoritism, and a lack of love; (2) the fight, which includes a transgression and a parental threat; and (3) running away, where the youth must manage fear and handle logistical…

  13. Longitudinal Outcomes for Youth Receiving Runaway/Homeless Shelter Services

    ERIC Educational Resources Information Center

    Pollio, David E.; Thompson, Sanna J.; Tobias, Lisa; Reid, Donna; Spitznagel, Edward

    2006-01-01

    This research examined outcomes and use of specific types of services 6 weeks, 3 and 6 months post-discharge for a large sample of runaway/homeless youth using crisis shelter services. Data were collected for 371 runaway/homeless youth using emergency shelter and crisis services at eleven agencies across a four-state midwestern region. Outcomes…

  14. Predictors of Trauma-Related Symptoms among Runaway Adolescents

    ERIC Educational Resources Information Center

    McCarthy, Michael D.; Thompson, Sanna J.

    2010-01-01

    Little is known about trauma-related symptoms among runaway adolescents. Precocious departure from familial homes often exposes youth to traumatic victimization. This study examined the extent to which runaway adolescents present trauma symptomotology and assessed factors that predict trauma symptoms. Participants (N = 350) were 12-18 years of age…

  15. Runaway electrons in a tokamak: A free-electron maser

    SciTech Connect

    Kurzan, B.; Steuer, K.

    1997-04-01

    In ohmic divertor plasma discharges of the ASDEX upgrade tokamak containing a small population of runaway electrons, fluctuating emission in the microwave region with a very narrow bandwidth is observed. The radiation can be explained by relativistic runaway electrons, which are captured in a ripple resonance of the tokamak and are thus made monoenergetic enough that they can undergo the collective instability of a free-electron maser. From the frequency of the maser, the energy of the runaway electrons, and from the linewidth and energy per radiation pulse, the particle density of the runaway electrons is determined locally. Observing this maser radiation is thus a different diagnostic for runaway electrons in tokamaks. {copyright} {ital 1997} {ital The American Physical Society}

  16. Runaway electron dynamics in tokamak plasmas with high impurity content

    NASA Astrophysics Data System (ADS)

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2015-09-01

    The dynamics of high energy runaway electrons is analyzed for plasmas with high impurity content. It is shown that modified collision terms are required in order to account for the collisions of the relativistic runaway electrons with partially stripped impurity ions, including the effect of the collisions with free and bound electrons, as well as the scattering by the full nuclear and the electron-shielded ion charge. The effect of the impurities on the avalanche runaway growth rate is discussed. The results are applied, for illustration, to the interpretation of the runaway electron behavior during disruptions, where large amounts of impurities are expected, particularly during disruption mitigation by massive gas injection. The consequences for the electron synchrotron radiation losses and the resulting runaway electron dynamics are also analyzed.

  17. Runaway electron dynamics in tokamak plasmas with high impurity content

    SciTech Connect

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2015-09-15

    The dynamics of high energy runaway electrons is analyzed for plasmas with high impurity content. It is shown that modified collision terms are required in order to account for the collisions of the relativistic runaway electrons with partially stripped impurity ions, including the effect of the collisions with free and bound electrons, as well as the scattering by the full nuclear and the electron-shielded ion charge. The effect of the impurities on the avalanche runaway growth rate is discussed. The results are applied, for illustration, to the interpretation of the runaway electron behavior during disruptions, where large amounts of impurities are expected, particularly during disruption mitigation by massive gas injection. The consequences for the electron synchrotron radiation losses and the resulting runaway electron dynamics are also analyzed.

  18. An Impact Triggered Runaway Greenhouse on Mars

    NASA Technical Reports Server (NTRS)

    Segura, T. L.; McKay, C. P.; Toon, O. B.

    2004-01-01

    When a planet is in radiative equilibrium, the incoming solar flux balances the outgoing longwave flux. If something were to perturb the system slightly, say the incoming solar flux increased, the planet would respond by radiating at a higher surface temperature. Since any radiation that comes in must go out, if the incoming is increased, the outgoing must also increase, and this increase manifests itself as a warmer equilibrium temperature. The increase in solar flux would correspond to an increase in temperature, which would increase the amount of water vapor in the atmosphere due to increased evaporation. Since water vapor is a greenhouse gas, it would absorb more radiation in the atmosphere leading to a yet warmer equilibrium temperature. The planet would reach radiative equilibrium at this new temperature. There exists a point, however, past which this positive feedback leads to a "runaway" situation. In this case, the planet does not simply evaporate a little more water and eventually come to a slightly higher equilibrium temperature. Instead, the planet keeps evaporating more and more water until all of the planet's available liquid and solid water is in the atmosphere. The reason for this is generally understood. If the planet's temperature increases, evaporation of water increases, and the absorption of radiation increases. This increases the temperature and the feedback continues until all water is in the atmosphere. The resulting equilibrium temperature is very high, much higher than the equilibrium temperature of a point with slightly lower solar flux. One can picture that as solar flux increases, planetary temperature also increases until the runaway point where temperature suddenly "jumps" to a higher value, in response to all the available water now residing in the atmosphere. This new equilibrium is called a "runaway greenhouse" and it has been theorized that this is what happened to the planet Venus, where the surface temperature is more than 700 K

  19. Thermonuclear milestones: (2) Beginnings of the Soviet H-bomb program

    SciTech Connect

    Goncharov, G.A.

    1996-11-01

    Early Soviet theoretical work on thermonuclear ignition was adied by espionage, but many important ideas were conceived and developed independently {copyright} {ital 1996 American Institute of Physics.}

  20. Nucleosynthesis and the nova outburst

    SciTech Connect

    Starrfield, S.; Truran, J.W.; Wiescher, M.; Sparks, W.M.

    1995-12-31

    A nova outburst is the consequence of the accretion of hydrogen rich material onto a white dwarf and it can be considered as the largest hydrogen bomb in the Universe. The fuel is supplied by a secondary star in a close binary system while the strong degeneracy of the massive white dwarf acts to contain the gas during the early stages of the explosion. The containment allows the temperature in the nuclear burning region to exceed 10{sup 8}K under all circumstances. As a result a major fraction of CNO nuclei in the envelope are transformed into {beta}{sup +}-unstable nuclei. We discuss the effects of these nuclei on the evolution. Recent observational studies have shown that there are two compositional classes of novae; one which occurs on carbon-oxygen white dwarfs, and a second class that occurs on oxygen-neon-magnesium white dwarfs. In this review we will concentrate on the latter explosions since they produce the most interesting nucleosynthesis. We report both on the results of new observational determinations of nova abundances and, in addition, new hydrodynamic calculations that examine the consequences of the accretion process on 1.0M{sub {circle_dot}}, 1.25M{sub {circle_dot}}, and 1.35M{sub {circle_dot}} white dwarfs. Our results show that novae can produce {sup 22}Na, {sup 26}Al, and other intermediate mass nuclei in interesting amounts. We will present the results of new calculations, done with updated nuclear reaction rates and opacities, which exhibit quantitative differences with respect to published work.

  1. Nucleosynthesis and the nova outburst

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Truran, J.W.; Wiescher, M.; Sparks, W.M.

    1995-01-01

    A nova outburst is the consequence of the accretion of hydrogen rich material onto a white dwarf and it can be considered as the largest hydrogen bomb in the Universe. The fuel is supplied by a secondary star in a close binary system while the strong degeneracy of the massive white dwarf acts to contain the gas during the early stages of the explosion. The containment allows the temperature in the nuclear burning region to exceed 10(sup 8)K under all circumstances. As a result a major fraction of CNO nuclei in the envelope are transformed into (beta)(sup +)-unstable nuclei. We discuss the effects of these nuclei on the evolution. Recent observational studies have shown that there are two compositional classes of novae; one which occurs on carbon-oxygen white dwarfs, and a second class that occurs on oxygen-neon-magnesium white dwarfs. In this review we will concentrate on the latter explosions since they produce the most interesting nucleosynthesis. We report both on the results of new observational determinations of nova abundances and, in addition, new hydrodynamic calculations that examine the consequences of the accretion process on 1.0M(sub (circle dot)), 1.25M(sub (circle dot)), and 1.35M(sub (circle dot)) white dwarfs. Our results show that novae can produce (sup 22)Na, (sup 26)Al, and other intermediate mass nuclei in interesting amounts. We will present the results of new calculations, done with updated nuclear reaction rates and opacities, which exhibit quantitative differences with respect to published work.

  2. Nucleosynthesis and the nova outburst

    NASA Technical Reports Server (NTRS)

    Starrfield, S.; Truran, J.W.; Wiescher, M.; Sparks, W.M.

    1995-01-01

    A nova outburst is the consequence of the accretion of hydrogen rich material onto a white dwarf and it can be considered as the largest hydrogen bomb in the Universe. The fuel is supplied by a secondary star in a close binary system while the strong degeneracy of the massive white dwarf acts to contain the gas during the early stages of the explosion. The containment allows the temperature in the nuclear burning region to exceed 10(sup 8)K under all circumstances. As a result a major fraction of CNO nuclei in the envelope are transformed into (beta)(sup +)-unstable nuclei. We discuss the effects of these nuclei on the evolution. Recent observational studies have shown that there are two compositional classes of novae; one which occurs on carbon-oxygen white dwarfs, and a second class that occurs on oxygen-neon-magnesium white dwarfs. In this review we will concentrate on the latter explosions since they produce the most interesting nucleosynthesis. We report both on the results of new observational determinations of nova abundances and, in addition, new hydrodynamic calculations that examine the consequences of the accretion process on 1.0M(sub (circle dot)), 1.25M(sub (circle dot)), and 1.35M(sub (circle dot)) white dwarfs. Our results show that novae can produce (sup 22)Na, (sup 26)Al, and other intermediate mass nuclei in interesting amounts. We will present the results of new calculations, done with updated nuclear reaction rates and opacities, which exhibit quantitative differences with respect to published work.

  3. Alfvénic instabilities driven by runaways in fusion plasmas

    SciTech Connect

    Fülöp, T.; Newton, S.

    2014-08-15

    Runaway particles can be produced in plasmas with large electric fields. Here, we address the possibility that such runaway ions and electrons excite Alfvénic instabilities. The magnetic perturbation induced by these modes can enhance the loss of runaways. This may have important implications for the runaway electron beam formation in tokamak disruptions.

  4. Kinetic modelling of runaway electron avalanches in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Nilsson, E.; Decker, J.; Peysson, Y.; Granetz, R. S.; Saint-Laurent, F.; Vlainic, M.

    2015-09-01

    Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128-202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker-Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355-62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally, the

  5. Dwarf nova outbursts in intermediate polars

    NASA Astrophysics Data System (ADS)

    Hameury, J.-M.; Lasota, J.-P.

    2017-06-01

    Context. The disc instability model (DIM) has been very successful in explaining the dwarf nova outbursts observed in cataclysmic variables. When, as in intermediate polars, the accreting white dwarf is magnetised, the disc is truncated at the magnetospheric radius, but for mass-transfer rates corresponding to the thermal-viscous instability such systems should still exhibit dwarf-nova outbursts. Yet, the majority of intermediate polars, in which the magnetic field is not large enough to completely disrupt the accretion disc, seem to be stable, and the rare observed outbursts, in particular in systems with long orbital periods, are much shorter than normal dwarf-nova outbursts. Aims: We investigate the predictions of the disc instability model for intermediate polars in order to determine which of the observed properties of these systems can be explained by the DIM. Methods: We use our numerical code for the time evolution of accretion discs, modified to include the effects of the magnetic field, with constant or variable mass transfer from the secondary star. Results: We show that intermediate polars have mass transfer low enough and magnetic fields large enough to keep the accretion disc stable on the cold equilibrium branch. We show that the infrequent and short outbursts observed in long-period systems, such as, for example, TV Col, cannot be attributed to the thermal-viscous instability of the accretion disc, but instead have to be triggered by an enhanced mass-transfer from the secondary, or, more likely, by some instability coupling the white dwarf magnetic field with that generated by the magnetorotational instability operating in the accretion disc. Longer outbursts (a few days) could result from the disc instability.

  6. Thermal runaway in semiconductor laser windows.

    PubMed

    Johnson, R L; O'Keefe, J D

    1972-12-01

    A small perturbation model is used to obtain analytical expressions for the critical or runaway power density for laser windows constructed of semiconductor materials. These equations are used to compute the critical power density for several realistic window installations taking account of the finite value of realizable convection cooling coefficients. Computations were prepared for silicon transmitting 4 .0-micro. radiation and for germanium at 10.6 micro. In this way it is shown that power densities are principally limited by the effectiveness of cooling from the face of the window, that is, the surface perpendicular to the laser beam. Since convection cooling coefficients are small the transmission of high power densities through semiconductor windows is therefore contingent upon finding more effective means to cool the window from the face. Finally, a simplified calculation was made in an attempt to account for nonuniformity of the incident laser beam. a given window, but not severely. The results show the onuniformity reduces the runaway power for a given window, but not severely.

  7. Transit probabilities around hypervelocity and runaway stars

    NASA Astrophysics Data System (ADS)

    Fragione, G.; Ginsburg, I.

    2017-04-01

    In the blooming field of exoplanetary science, NASA's Kepler Space Telescope has revolutionized our understanding of exoplanets. Kepler's very precise and long-duration photometry is ideal for detecting planetary transits around Sun-like stars. The forthcoming Transiting Exoplanet Survey Satellite (TESS) is expected to continue Kepler's legacy. Along with transits, the Doppler technique remains an invaluable tool for discovering planets. The next generation of spectrographs, such as G-CLEF, promise precision radial velocity measurements. In this paper, we explore the possibility of detecting planets around hypervelocity and runaway stars, which should host a very compact system as consequence of their turbulent origin. We find that the probability of a multiplanetary transit is 10-3 ≲ P ≲ 10-1. We therefore need to observe ∼10-1000 high-velocity stars to spot a transit. However, even if transits are rare around runaway and hypervelocity stars, the chances of detecting such planets using radial velocity surveys is high. We predict that the European Gaia satellite, along with TESS and the new-generation spectrographs G-CLEF and ESPRESSO, will spot planetary systems orbiting high-velocity stars.

  8. Measurements of the runaway electron energy during disruptions in the tokamak TEXTOR

    SciTech Connect

    Forster, M.; Finken, K. H.; Willi, O.; Lehnen, M.; Xu, Y.; Collaboration: TEXTOR Team

    2012-05-15

    Calorimetric measurements of the total runaway electron energy are carried out using a reciprocating probe during induced TEXTOR disruptions. A comparison with the energy inferred from runaway energy spectra, which are measured with a scintillator probe, is used as an independent check of the results. A typical runaway current of 100 kA at TEXTOR contains 30 to 35 kJ of runaway energy. The dependencies of the runaway energy on the runaway current, the radial probe position, the toroidal magnetic field and the predisruptive plasma current are studied. The conversion efficiency of the magnetic plasma energy into runaway energy is calculated to be up to 26%.

  9. Review of the classical nova outburst

    SciTech Connect

    Starrfield, S.; Sparks, W.M.

    1986-06-01

    Observational studies have not only identified a new class of novae but theoretical simulations of this class have been found to be in excellent agreement with the observations. This new class consists of outbursts occurring on ONeMg white dwarfs in close binar systems in contrast to the other outbursts which are occurring on CO white dwarfs. We also review the effects of the ..beta../sup +/-unstable nuclei and show how their presence has a major effect on the evolution. 77 refs.

  10. Possible Ursid Outburst on December 22, 2000

    NASA Technical Reports Server (NTRS)

    Jenniskens, Peter; Lyytinen, Esko; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The Ursid shower has broad Filament-type outbursts around the perihelion passage of parent 8P/Tuttle, but also isolated narrow outbursts at aphelion. We calculated Tuttle's dust trail encounters in the same way as for the Leonid showers. We discovered that it takes 6 centuries to change the orbit enough to bring the meteoroids to Earth's orbit. During that time, the meteoroids and comet separate in mean anomaly by 6 years, thus explaining the unusual aphelion occurrences. We predict enhanced activity on December 22, 2000, at around 7:29 LT.

  11. Runaway studies in the ATF (Advanced Toroidal Facility) torsatron

    SciTech Connect

    England, A.C.; DeVan, W.R.; Eberle, C.C.; Fowler, R.H.; Gabbard, W.A.; Glowienka, J.C.; Harris, J.H.; Haste, G.R.; Kindsfather, R.R.; Morris, R.N.

    1989-01-01

    Pulsed torsatrons and heliotrons are susceptible to runaway electron formation and confinement resulting from the inherent good containment in the vacuum fields and the high loop voltages during the initiation and termination of the helical and vertical fields (''field ramping''). Because runaway electrons can cause an unacceptable level of hard X rays near the machine, a runaway suppression system was designed and included in the initial operation of the Advanced Toroidal Facility (ATF). The main component of the system is a rotating paddle that is normally left in the vacuum chamber during the field ramps. This device proved to be very effective in reducing the runaway population. Measurements of hard X rays from ATF have shown that the runaways are produced primarily during the field ramping but that usually a small steady-state runaway component is also present during the ''flat-top'' portion of the fields. The paddle is the main source of the hard X rays (thick-target bremsstrahlung), although other objects in the vacuum chamber also serve as targets for the runaways at various times. The maximum X-ray energy found by pulse height analysis is /approximately/12--15 MeV; the mean energy appears to be a few mega-electron-volts. A noticeable forward peaking of the bremsstrahlung from the paddle is evident. The limiters do not appear to be major sources of bremsstrahlung. 17 refs., 14 figs.

  12. Thermonuclear Supernova Explosions From Hybrid White Dwarf Progenitors

    NASA Astrophysics Data System (ADS)

    Willcox, Donald E.; Townsley, Dean; Calder, Alan; Denissenkov, Pavel; Herwig, Falk

    2016-01-01

    Motivated by recent results in stellar evolution in which convective boundary mixing in SAGB stars can give rise to hybrid white dwarf (WD) stars with a C-O core inside an O-Ne shell, we simulate thermonuclear (Type Ia) supernovae from these hybrid progenitors. We use the FLASH code to perform multidimensional simulations in the deflagration to detonation transition (DDT) explosion paradigm from progenitor models produced with the MESA stellar evolution code that include the thermal energetics of the Urca process. We performed a suite of DDT simulations over a range of ignition conditions and compare to previous results from a suite of C-O white dwarfs. Despite significant variability within each suite, distinguishing trends are apparent in their Ni-56 yields and the kinetic properties of their ejecta. We comment on the feasibility of these hybrid WD explosions as the source of some classes of observed subluminous events. This research was supported in part by the U.S. Department of Energy under grant DE-FG02-87ER40317 and by resources at the Institute for Advanced Computational Science at Stony Brook University. The software used in this work was in part developed by the DOE-supported ASC/Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago.

  13. The classification of magnetohydrodynamic regimes of thermonuclear combustion

    SciTech Connect

    Remming, Ian S.; Khokhlov, Alexei M.

    2014-10-10

    Physical properties of magnetohydrodynamic (MHD) reaction fronts are studied as functions of the thermodynamic conditions, and the strength and orientation of the magnetic field in the unburned matter through which the fronts propagate. We determine the conditions for the existence of the various types of MHD reaction fronts and the character of the changes in physical quantities across these reaction fronts. The analysis is carried out in general for a perfect gas equation of state and a constant energy release, and then extended to thermonuclear reaction fronts in degenerate carbon-oxygen mixtures and degenerate helium in conditions typical of Type Ia supernova explosions. We find that as unburned matter enters perpendicular to a reaction front, the release of energy through burning generates shear velocity in the reacting gas that, depending on the type of reaction front, strengthens or weakens the magnetic field. In addition, we find that the steady-state propagation of a reaction front is impossible for certain ranges of magnetic field direction. Our results provide insight into the phenomena of MHD thermonuclear combustion that is relevant to the interpretation of future simulations of SN Ia explosions that have magnetic fields systematically incorporated.

  14. Role of Bremsstrahlung Radiation in Limiting the Energy of Runaway Electrons in Tokamaks

    SciTech Connect

    Bakhtiari, M.; Takechi, M.; Tamai, H.; Miura, Y.; Kusama, Y.; Kamada, Y.; Kramer, G.J.

    2005-06-03

    Bremsstrahlung radiation of runaway electrons is found to be an energy limit for runaway electrons in tokamaks. The minimum and maximum energy of runaway electron beams is shown to be limited by collisions and bremsstrahlung radiation, respectively. It is also found that a massive injection of a high-Z gas such as xenon can terminate a disruption-generated runaway current before the runaway electrons hit the walls.

  15. Evaluation of potential runaway generation in large-tokamak disruptions

    SciTech Connect

    Fleischmann, H.H.; Zweben, S.J. . Plasma Physics Lab. Cornell Univ., Ithaca, NY . School of Applied and Engineering Physics)

    1993-06-01

    A detailed evaluation of various potential mechanisms for the generation of strong runaway beams during disruptions of largetokamak devices, including TFTR, JET, DIIID and ITER, is performed based on typical operating parameters of these devices and the presently accepted disruption model. The main results include: (1) In the existing devices, the evaporative preicer'' process by itself can lead to sizable runaway beams in disruptions of high-current-medium-to-low-ne discharges. In ITER, such runaways are expected mainly for discharges with ne values sizably smaller than the projected typical ones. (2) Runaway generation also may occur during post-thermal-quench period through the untrapping of trapped hot-thermal electrons remaining from the pre-thermal-quench plasma; this process may be directly important in particular in disruptions of high-T[sub e] discharges with details depending on the time required for reclosure of the magnetic surfaces. Both processes (1) and (2) will occur and be completed mostly during the initial few 100 [mu]sec after the thermal quench. (3) Subsequently, close collisions of runaways with cold plasma electrons generally will lead to an exponential growth ( avalanching'') of runaway populations generated by processes (1) and/or (2) and/or others; this process will be effective in particular during the current quench phase and will continue until the resulting runaway beam will carry essentially all of the remaining discharge current. In presently existing devices, possible avalanche factors of up to 10[sup 2]--10[sup 5] may be expected; in ITER, avalanche factors of up to 10[sup 10]--10[sup 15] -- if not properly suppressed -- are expected to lead to strong runaway beams in most disruptions, except those at particularly high densities. At the same time, avalanching will shift the main part of their energy spectrum down to relatively low energies around 10--20 MeV, and may sizably change the spatial distribution of the runaways.

  16. Evaluation of potential runaway generation in large-tokamak disruptions

    SciTech Connect

    Fleischmann, H.H.; Zweben, S.J. |

    1993-06-01

    A detailed evaluation of various potential mechanisms for the generation of strong runaway beams during disruptions of largetokamak devices, including TFTR, JET, DIIID and ITER, is performed based on typical operating parameters of these devices and the presently accepted disruption model. The main results include: (1) In the existing devices, the evaporative ``preicer`` process by itself can lead to sizable runaway beams in disruptions of high-current-medium-to-low-ne discharges. In ITER, such runaways are expected mainly for discharges with ne values sizably smaller than the projected typical ones. (2) Runaway generation also may occur during post-thermal-quench period through the untrapping of trapped hot-thermal electrons remaining from the pre-thermal-quench plasma; this process may be directly important in particular in disruptions of high-T{sub e} discharges with details depending on the time required for reclosure of the magnetic surfaces. Both processes (1) and (2) will occur and be completed mostly during the initial few 100 {mu}sec after the thermal quench. (3) Subsequently, close collisions of runaways with cold plasma electrons generally will lead to an exponential growth (``avalanching``) of runaway populations generated by processes (1) and/or (2) and/or others; this process will be effective in particular during the current quench phase and will continue until the resulting runaway beam will carry essentially all of the remaining discharge current. In presently existing devices, possible avalanche factors of up to 10{sup 2}--10{sup 5} may be expected; in ITER, avalanche factors of up to 10{sup 10}--10{sup 15} -- if not properly suppressed -- are expected to lead to strong runaway beams in most disruptions, except those at particularly high densities. At the same time, avalanching will shift the main part of their energy spectrum down to relatively low energies around 10--20 MeV, and may sizably change the spatial distribution of the runaways.

  17. INSTRUMENTS AND METHODS OF INVESTIGATION Nanostructures in controlled thermonuclear fusion devices

    NASA Astrophysics Data System (ADS)

    Krauz, V. I.; Martynenko, Yurii V.; Svechnikov, N. Yu; Smirnov, Valentin P.; Stankevich, V. G.; Khimchenko, L. N.

    2011-01-01

    It is shown that the presence of nano-sized and nano-structured erosion products not only affects the operation of thermonuclear devices but also, to a large extent, determines the safety and economy of future thermonuclear reactors. The formation mechanisms and the characteristics and properties of deposited films and nano-sized dust that form in tokamaks are reviewed.

  18. Runaway electrons in a fully and partially ionized nonideal plasma

    SciTech Connect

    Ramazanov, T.S.; Turekhanova, K.M.

    2005-10-01

    This paper reports on a study of electron runaway for a nonideal plasma in an external electric field. Based on pseudopotential models of nonideal fully and partially ionized plasmas, the friction force was derived as a function of electron velocities. Dependences of the electron free path on plasma density and nonideality parameters were obtained. The impact of the relative number of runaway electrons on their velocity and temperature was considered for classical and semiclassical models of a nonideal plasma. It has been shown that for the defined intervals of the coupled plasma parameter, the difference between the relative numbers of runaway electron values is essential for various plasma models.

  19. Runaway Geneeration In Disruptions Of Plasmas In TFTR

    SciTech Connect

    Fredrickson, E. D.; Bell, M. G.; Taylor, G.; Medley, S. S.

    2014-03-31

    Many disruptions in the Tokamak Fusion Test Reactor (TFTR) [D. Meade and the TFTR Group, in Proceedings of the International Conference on Plasma Physics and Controlled Nuclear Fusion, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, pp. 9-24] produced populations of runaway electrons which carried a significant fraction of the original plasma current. In this paper, we describe experiments where, following a disruption of a low-beta, reversed shear plasma, currents of up to 1 MA carried mainly by runaway electrons were controlled and then ramped down to near zero using the ohmic transformer. In the longer lasting runaway plasmas, Parail-Pogutse instabilities were observed.

  20. Runaway of energetic test ions in a toroidal plasma

    SciTech Connect

    Eilerman, S. Anderson, J. K.; Sarff, J. S.; Forest, C. B.; Reusch, J. A.; Nornberg, M. D.; Kim, J.

    2015-02-15

    Ion runaway in the presence of a large-scale, reconnection-driven electric field has been conclusively measured in the Madison Symmetric Torus reversed-field pinch (RFP). Measurements of the acceleration of a beam of fast ions agree well with test particle and Fokker-Planck modeling of the runaway process. However, the runaway mechanism does not explain all measured ion heating in the RFP, particularly previous measurements of strong perpendicular heating. It is likely that multiple energization mechanisms occur simultaneously and with differing significance for magnetically coupled thermal ions and magnetically decoupled tail and beam ions.

  1. A Failed outburst of H1743-322

    NASA Astrophysics Data System (ADS)

    Capitanio, F.; Belloni, T.; Del Santo, M.; Ubertini, P.

    2010-07-01

    H1743-322 is a bright BHC observed by HEAO-1 in 1977. The source underwent again in outburst in 2003 after about 25 years. After the 2003 outburst (the brightest one) the source exhibited other 5 outbursts. We report a brief summary of the results found during a campaign of X-ray observations performed with RXTE during the two 2008 outbursts. In particular the October 2008 outburst showed a singular behaviour that has been rarely observed in transient X-ray binaries.

  2. RUNAWAY MASSIVE STARS FROM R136: VFTS 682 IS VERY LIKELY A 'SLOW RUNAWAY'

    SciTech Connect

    Banerjee, Sambaran; Kroupa, Pavel; Oh, Seungkyung E-mail: pavel@astro.uni-bonn.de

    2012-02-10

    We conduct a theoretical study on the ejection of runaway massive stars from R136-the central massive, starburst cluster in the 30 Doradus complex of the Large Magellanic Cloud. Specifically, we investigate the possibility of the very massive star (VMS) VFTS 682 being a runaway member of R136. Recent observations of the above VMS, by virtue of its isolated location and its moderate peculiar motion, have raised the fundamental question of whether isolated massive star formation is indeed possible. We perform the first realistic N-body computations of fully mass-segregated R136-type star clusters in which all the massive stars are in primordial binary systems. These calculations confirm that the dynamical ejection of a VMS from an R136-like cluster, with kinematic properties similar to those of VFTS 682, is common. Hence, the conjecture of isolated massive star formation is unnecessary to account for this VMS. Our results are also quite consistent with the ejection of 30 Dor 016, another suspected runaway VMS from R136. We further note that during the clusters' evolution, mergers of massive binaries produce a few single stars per cluster with masses significantly exceeding the canonical upper limit of 150 M{sub Sun }. The observations of such single super-canonical stars in R136, therefore, do not imply an initial mass function with an upper limit greatly exceeding the accepted canonical 150 M{sub Sun} limit, as has been suggested recently, and they are consistent with the canonical upper limit.

  3. Project Runaway: Calibrating the Spectroscopic Distance Scale Using Runaway O and Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Hartkopf, William I.; Mason, B. D.

    2009-05-01

    Well-determined O star masses are notoriously difficult to obtain, due to such factors as broad spectral lines, larger and less-reliable average distances, high multiplicity rates, crowded fields, and surrounding nebulosity. Some of these difficulties are reduced for the subset of O stars known as runaways, however. They have escaped some of the nebulosity and crowding, and the event leading to their ejection virtually guarantees that these objects are either single stars or extremely hard spectroscopic binaries. The goal of this project is to increase the sample of known runaway stars, using updated proper motions from the soon-to-be-released UCAC3 catalog, as well as published radial velocities and data from recent duplicity surveys of massive stars using AO and speckle interferometry. Input files include the Galactic O Star Catalog of Maiz-Apellaniz et al. (2004 ApJSS 151, 103) as well as the Seventh Catalogue of Galactic Wolf-Rayet Stars and its more recent Annex (van der Hucht 2001 NewAR 45, 135; 2006 A&A 458, 453). The new runaway star sample will form the basis for a list of SIM targets aimed at improving the distances of Galactic O and WR stars, calibrating the spectroscopic distance scale and leading to more accurate mass estimates for these massive stars.

  4. Numerical modelling of the classical nova outburst

    SciTech Connect

    Kutter, G.S.; Sparks, W.M.

    1987-01-01

    We describe a mechanism that promises to explain how nova outbursts take place on white dwarf of 1 Msub solar or less and for accretion rates of 4 x 10/sup -10/ Msub solar yr/sup -1/ or greater. 7 refs.

  5. Runaway electron generation as possible trigger for enhancement of magnetohydrodynamic plasma activity and fast changes in runaway beam behavior

    NASA Astrophysics Data System (ADS)

    Pankratov, I. M.; Zhou, R. J.; Hu, L. Q.

    2015-07-01

    Peculiar phenomena were observed during experiments with runaway electrons: rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the electron cyclotron emission (ECE) signal (cyclotron radiation of suprathermal electrons). These phenomena were initially observed in TEXTOR (Tokamak Experiment for Technology Oriented Research), where these events only occurred in the current decay phase or in discharges with thin stable runaway beams at a q = 1 drift surface. These rapid changes in the synchrotron spot were interpreted by the TEXTOR team as a fast pitch angle scattering event. Recently, similar rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the non-thermal ECE signal were observed in the EAST (Experimental Advanced Superconducting Tokamak) runaway discharge. Runaway electrons were located around the q = 2 rational magnetic surface (ring-like runaway electron beam). During the EAST runaway discharge, stepwise ECE signal increases coincided with enhanced magnetohydrodynamic (MHD) activity. This behavior was peculiar to this shot. In this paper, we show that these non-thermal ECE step-like jumps were related to the abrupt growth of suprathermal electrons induced by bursting electric fields at reconnection events during this MHD plasma activity. Enhancement of the secondary runaway electron generation also occurred simultaneously. Local changes in the current-density gradient appeared because of local enhancement of the runaway electron generation process. These current-density gradient changes are considered to be a possible trigger for enhancement of the MHD plasma activity and the rapid changes in runaway beam behavior.

  6. Runaway electron generation as possible trigger for enhancement of magnetohydrodynamic plasma activity and fast changes in runaway beam behavior

    SciTech Connect

    Pankratov, I. M. E-mail: rjzhou@ipp.ac.cn; Zhou, R. J. E-mail: rjzhou@ipp.ac.cn; Hu, L. Q.

    2015-07-15

    Peculiar phenomena were observed during experiments with runaway electrons: rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the electron cyclotron emission (ECE) signal (cyclotron radiation of suprathermal electrons). These phenomena were initially observed in TEXTOR (Tokamak Experiment for Technology Oriented Research), where these events only occurred in the current decay phase or in discharges with thin stable runaway beams at a q = 1 drift surface. These rapid changes in the synchrotron spot were interpreted by the TEXTOR team as a fast pitch angle scattering event. Recently, similar rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the non-thermal ECE signal were observed in the EAST (Experimental Advanced Superconducting Tokamak) runaway discharge. Runaway electrons were located around the q = 2 rational magnetic surface (ring-like runaway electron beam). During the EAST runaway discharge, stepwise ECE signal increases coincided with enhanced magnetohydrodynamic (MHD) activity. This behavior was peculiar to this shot. In this paper, we show that these non-thermal ECE step-like jumps were related to the abrupt growth of suprathermal electrons induced by bursting electric fields at reconnection events during this MHD plasma activity. Enhancement of the secondary runaway electron generation also occurred simultaneously. Local changes in the current-density gradient appeared because of local enhancement of the runaway electron generation process. These current-density gradient changes are considered to be a possible trigger for enhancement of the MHD plasma activity and the rapid changes in runaway beam behavior.

  7. Outbursts Large and Small from EXO 2030+375

    NASA Technical Reports Server (NTRS)

    Wilson, Colleen A.; Arranz, Ascension Camero; Finger, Mark H.

    2008-01-01

    The Be/X-ray pulsar EXO 2030+375 has now been observed for more than 22 years. In this time, it underwent two giant outbursts, in 1985 and 2006, and numerous normal outbursts at its 46-day orbital period. Our observations include daily monitoring of EXO 2030+375 with RXTE from 2006 June through 2007 May and several snapshots of normal outbursts before and after the giant outburst. During this giant outburst, we discovered evidence for a cyclotron feature at about 11 keV. This feature was confidently detected for about 90 days during the brighter portion of the outburst. Daily observations after the giant outburst detected pulsations throughout EXO 2030+375's orbit and included five normal outbursts shifted later in orbital phase relative to those before the giant outburst. Here we will present results from our detailed RXTE observations of the giant outburst and the normal outbursts that surrounded it and examine how they fit into the long-term picture we have of EXO 2030+375 and Be/X-ray binaries.

  8. Experimental modelling of outburst flood - bed interactions

    NASA Astrophysics Data System (ADS)

    Carrivick, J. L.; Xie, Z.; Sleigh, A.; Hubbard, M.

    2009-04-01

    Outburst floods are a sudden release and advancing wave of water and sediment, with a peak discharge that is often several orders of magnitude greater than perennial flows. Common outburst floods from natural sources include those from glacial and moraine-impounded lakes, freshwater dyke and levee bursts, volcanic debris dams, landslides, avalanches, coastal bay-bars, and those from tree or vegetation dams. Outburst flood hazards are regularly incorporated into risk assessments for urban, coastal and mountainous areas, for example. Outburst flood hazards are primarily due to direct impacts, caused by a frontal surge wave, from debris within a flow body, and from the mass and consistency of the flows. A number of secondary impacts also pose hazards, including widespread deposition of sediment and blocked tributary streams. It is rapid landscape change, which is achieved the mobilization and redistribution of sediment that causes one of the greatest hazards due to outburst floods. The aim of this project is therefore to parameterise hydrodynamic - sedimentary interactions in experimental outburst floods. Specifically, this project applies laboratory flume modelling, which offers a hitherto untapped opportunity for examining complex interactions between water and sediment within outburst floods. The experimental set-up is of a tradition lock-gate design with a straight 4 m long tank. Hydraulics are scaled at 1:20 froude scale and the following controls on frontal wave flow-bed interactions and hence on rapid landscape change are being investigated: 1. Pre-existing mobile sediment effects, fixed bed roughness effects, sediment concentration effects, mobile bed effects. An emphasis is being maintained on examining the downstream temporal and spatial change in physical character of the water / sediment frontal wave. Facilities are state-of-the-art with a fully-automated laser bed-profiler to measure bed elevation after a run, Seatek arrays to measure transient flow

  9. Runaway electron transport via tokamak microturbulence

    SciTech Connect

    Hauff, T.; Jenko, F.

    2009-10-15

    The mechanisms found for the magnetic transport of fast ions in the work of Hauff et al. [Phys. Rev. Lett. 102, 075004 (2009)] are extended to the diffusion of runaway electrons. Due to their smaller mass and larger energy, they behave strongly relativistically, for which reason the scaling laws defined previously have to be modified. It is found that due to these changes, the regime of constant magnetic transport does not exist anymore, but diffusivity scales with E{sup -1} for magnetic transport, or even with E{sup -2} in the case that finite gyroradius effects become important. It is shown that the modified analytical approaches are able to explain the surprisingly small values found in experiments, although it cannot be excluded that possibly other reduction mechanisms are present at the same time.

  10. Relativistic Langevin equation for runaway electrons

    NASA Astrophysics Data System (ADS)

    Mier, J. A.; Martin-Solis, J. R.; Sanchez, R.

    2016-10-01

    The Langevin approach to the kinetics of a collisional plasma is developed for relativistic electrons such as runaway electrons in tokamak plasmas. In this work, we consider Coulomb collisions between very fast, relativistic electrons and a relatively cool, thermal background plasma. The model is developed using the stochastic equivalence of the Fokker-Planck and Langevin equations. The resulting Langevin model equation for relativistic electrons is an stochastic differential equation, amenable to numerical simulations by means of Monte-Carlo type codes. Results of the simulations will be presented and compared with the non-relativistic Langevin equation for RE electrons used in the past. Supported by MINECO (Spain), Projects ENE2012-31753, ENE2015-66444-R.

  11. Naturalness from runaways in direct mediation

    SciTech Connect

    Schaefer-Nameki, Sakura; Tamarit, Carlos; Torroba, Gonzalo

    2011-02-01

    Postulating that the nonminimal supersymmetric standard model singlet is a meson of a microscopic confining theory opens up new model-building possibilities. Based on this, we construct calculable models of direct mediation that solve the {mu}/B{sub {mu}} problem and simultaneously lead to realistic phenomenology. The singlet that couples to the Higgs fields develops a runaway produced by soft interactions and then stabilized by a small superpotential perturbation. The mechanism is first realized in an O'Raifeartaigh model of direct gauge mediation with metastable supersymmetry breaking. Focusing then on the microscopic theory, we argue that super QCD with massless and massive flavors in the free magnetic phase gives rise to this dynamics in the infrared. A deformation of the super QCD superpotential leads to large spontaneous R-symmetry breaking, gaugino masses naturally at the scale of the Higgs mass parameters, and the absence of CP violating phases.

  12. Naturalness from Runaways in Direct Mediation

    SciTech Connect

    Schafer-Nameki, Sakura; Tamarit, Carlos; Torroba, Gonzalo; /SLAC

    2011-02-07

    Postulating that the NMSSM singlet is a meson of a microscopic confining theory opens up new model-building possibilities. Based on this, we construct calculable models of direct mediation that solve the {mu}/B{mu} problem and simultaneously lead to realistic phenomenology. The singlet that couples to the Higgs fields develops a runaway produced by soft interactions, then stabilized by a small superpotential perturbation. The mechanism is first realized in an O'Raifeartaigh model of direct gauge mediation with metastable supersymmetry breaking. Focusing then on the microscopic theory, we argue that super QCD with massless and massive flavors in the free magnetic phase gives rise to this dynamics in the infrared. A deformation of the SQCD superpotential leads to large spontaneous R-symmetry breaking, gaugino masses naturally at the scale of the Higgs mass parameters, and absence of CP violating phases.

  13. Naturalness from runaways in direct mediation

    NASA Astrophysics Data System (ADS)

    Schäfer-Nameki, Sakura; Tamarit, Carlos; Torroba, Gonzalo

    2011-02-01

    Postulating that the nonminimal supersymmetric standard model singlet is a meson of a microscopic confining theory opens up new model-building possibilities. Based on this, we construct calculable models of direct mediation that solve the μ/Bμ problem and simultaneously lead to realistic phenomenology. The singlet that couples to the Higgs fields develops a runaway produced by soft interactions and then stabilized by a small superpotential perturbation. The mechanism is first realized in an O’Raifeartaigh model of direct gauge mediation with metastable supersymmetry breaking. Focusing then on the microscopic theory, we argue that super QCD with massless and massive flavors in the free magnetic phase gives rise to this dynamics in the infrared. A deformation of the super QCD superpotential leads to large spontaneous R-symmetry breaking, gaugino masses naturally at the scale of the Higgs mass parameters, and the absence of CP violating phases.

  14. Recurrent Nova U Scorpii in outburst

    NASA Astrophysics Data System (ADS)

    Templeton, Matthew R.; Schaefer, Bradley E.

    2010-01-01

    The outburst is announced of the recurrent nova U Sco at magnitude V=8.05 on 2010 January 28.4385 UT, according to observations by Barbara G. Harris, New Smyrna Beach, FL, USA. The outburst was confirmed by Shawn Dvorak, Clermont, FL, USA, who estimated it at V~8.8 at Jan 28.4743. Prior to outburst, U Scorpii was measured at V=18.2 on Jan 27.4501 (Harris), and estimated at m(vis) <16.5 on January 27.6271 (Mike Linnolt, Hoolehua, HI, USA). Observations in the AAVSO International Database show that the last outburst of U Sco occurred on 1999 February 25, when the star reached visual magnitude 7.5. U Sco is an extremely fast nova, and will reach maximum and decline by one magnitude within one day. Visual, CCD, and PEP observations are urgently requested, including unfiltered CCD time series. Please obtain S/N of at least 50 for all instrumental photometry. Observers are asked to use filters when performing single-measure photometry, but unfiltered time series is also requested beginning immediately and continuing for the next month. The AAVSO has been participating in a campaign on U Sco by request of Dr. Bradley Schaefer (LSU; see AAVSO Alert Notice 367). This nova outburst will be observed by several ground- and space-based observatories world-wide, and your observations are urgently requested to provide the overall, long-term optical light curve of U Sco. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details.

  15. Relativistic outflow from two thermonuclear shell flashes on neutron stars

    NASA Astrophysics Data System (ADS)

    in't Zand, J. J. M.; Keek, L.; Cavecchi, Y.

    2014-08-01

    We study the exceptionally short (32-43 ms) precursors of two intermediate-duration thermonuclear X-ray bursts observed with the Rossi X-ray Timing Explorer from the neutron stars in 4U 0614+09 and 2S 0918-549. They exhibit photon fluxes that surpass those at the Eddington limit later in the burst by factors of 2.6 to 3.1. We are able to explain both the short duration and the super-Eddington flux by mildly relativistic outflow velocities of 0.1c to 0.3c subsequent to the thermonuclear shell flashes on the neutron stars. These are the highest velocities ever measured from any thermonuclear flash. The precursor rise times are also exceptionally short: about 1 ms. This is inconsistent with predictions for nuclear flames spreading laterally as deflagrations and suggests detonations instead. This is the first time that a detonation is suggested for such a shallow ignition column depth (yign ≈ 1010 g cm-2). The detonation would possibly require a faster nuclear reaction chain, such as bypassing the α-capture on 12C with the much faster 12C(p,γ)13N(α,p)16O process previously proposed. We confirm the possibility of a detonation, albeit only in the radial direction, through the simulation of the nuclear burning with a large nuclear network and at the appropriate ignition depth, although it remains to be seen whether the Zel'dovich criterion is met. A detonation would also provide the fast flame spreading over the surface of the neutron star to allow for the short rise times. This needs to be supported by future two-dimensional calculations of flame spreading at the relevant column depth. As an alternative to the detonation scenario, we speculate on the possibility that the whole neutron star surface burns almost instantly in the auto-ignition regime. This is motivated by the presence of 150 ms precursors with 30 ms rise times in some superexpansion bursts from 4U 1820-30 at low ignition column depths of ~108 g cm-2.

  16. Mitigating Thermal Runaway Risk in Lithium Ion Batteries

    NASA Technical Reports Server (NTRS)

    Darcy, Eric; Jeevarajan, Judy; Russell, Samuel

    2014-01-01

    The JSC/NESC team has successfully demonstrated Thermal Runaway (TR) risk reduction in a lithium ion battery for human space flight by developing and implementing verifiable design features which interrupt energy transfer between adjacent electrochemical cells. Conventional lithium ion (li-Ion) batteries can fail catastrophically as a result of a single cell going into thermal runaway. Thermal runaway results when an internal component fails to separate electrode materials leading to localized heating and complete combustion of the lithium ion cell. Previously, the greatest control to minimize the probability of cell failure was individual cell screening. Combining thermal runaway propagation mitigation design features with a comprehensive screening program reduces both the probability, and the severity, of a single cell failure.

  17. Lifetime of Runaway Electrons at Phase-space Attractor

    NASA Astrophysics Data System (ADS)

    Fontanilla, Adrian; Breizman, Boris

    2016-10-01

    The kinetic theory for relativistic runaway electrons is extended to find a structure of the distribution function that is peaked around a phase-space attractor. Runaway electron dynamics are examined when the electric field is close to the threshold value required to sustain pre-existing runaways. The near vicinity of predicted stable and unstable points in momentum-space characterize a competition between accumulation and depletion which ultimately determines a finite lifetime for the accumulated runaways, albeit one that can be exponentially long and amenable to avalanche onset. The developed theory is then generalized to the case of stronger driving fields. Worked supported by the U.S. DOE Contract No. DEFG02-04ER54742.

  18. Radio-frequency wave enhanced runaway production rate

    SciTech Connect

    Chan, V.S.; McClain, F.W.

    1983-06-01

    Enhancement of runaway electron production (over that of an Ohmic discharge) can be achieved by the addition of radio-frequency waves. This effect is studied analytically and numerically using a two-dimensional Fokker--Planck quasilinear equation.

  19. Reaction of runaway electron distributions to radiative processes

    NASA Astrophysics Data System (ADS)

    Stahl, Adam; Embréus, Ola; Hirvijoki, Eero; Pusztai, István; Decker, Joan; Newton, Sarah L.; Fülöp, Tünde

    2015-11-01

    The emission of electromagnetic radiation by a charged particle in accelerated motion is associated with a reduction in its energy, accounted for by the inclusion of a radiation reaction force in the kinetic equation. For runaway electrons in plasmas, the dominant radiative processes are the emission of bremsstrahlung and synchrotron radiation. In this contribution, we investigate the impact of the associated radiation reaction forces on the runaway electron distribution, using both analytical and numerical studies, and discuss the corresponding change to the runaway electron growth rate, which can be substantial. We also report on the formation of non-monotonic features in the runaway electron tail as a consequence of the more complicated momentum-space dynamics in the presence of radiation reaction.

  20. Effective critical electric field for runaway-electron generation.

    PubMed

    Stahl, A; Hirvijoki, E; Decker, J; Embréus, O; Fülöp, T

    2015-03-20

    In this Letter we investigate factors that influence the effective critical electric field for runaway-electron generation in plasmas. We present numerical solutions of the kinetic equation and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway-electron formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature and (2) synchrotron radiation losses. We also address the effective critical field in the context of a transition from runaway growth to decay. We find agreement with recent experiments, but show that the observation of an elevated effective critical field can mainly be attributed to changes in the momentum-space distribution of runaways, and only to a lesser extent to a de facto change in the critical field.

  1. Dual and multiple diagnosis among substance using runaway youth.

    PubMed

    Slesnick, Natasha; Prestopnik, Jillian

    2005-01-01

    Although research on runaway and homeless youth is increasing, relatively little is known about the diagnostic profile of runaway adolescents. The current study examined patterns of psychiatric dual and multiple diagnosis among a sample (N=226) of treatment-engaged substance-abusing youth (ages 13 to 17) who were residing at a runaway shelter. As part of a larger treatment outcome study, the youths' psychiatric status was assessed using the DSM-IV based computerized diagnostic interview schedule for children [CDISC; (1)]. The majority of the youth in our sample met criteria for dual or multiple diagnosis (60%) with many having more than one substance-use diagnosis (56%). The severity of mental-health and substance-use problems in this sample of substance-abusing runaways suggests the need for continued development of comprehensive services. The range and intensity of diagnoses seen indicates a need for greater focus on treatment development and strategies to address their multiple areas of risk.

  2. Phase-space dynamics of runaway electrons in magnetic fields

    NASA Astrophysics Data System (ADS)

    Guo, Zehua; McDevitt, Christopher J.; Tang, Xian-Zhu

    2017-04-01

    Dynamics of runaway electrons in magnetic fields are governed by the competition of three dominant physics: parallel electric field acceleration, Coulomb collision, and synchrotron radiation. Examination of the energy and pitch-angle flows reveals that the presence of local vortex structure and global circulation is crucial to the saturation of primary runaway electrons. Models for the vortex structure, which has an O-point to X-point connection, and the bump of runaway electron distribution in energy space have been developed and compared against the simulation data. Identification of these velocity-space structures opens a new venue to re-examine the conventional understanding of runaway electron dynamics in magnetic fields.

  3. Empirical Quantification of the Runaway Greenhouse Limit on Earth

    NASA Astrophysics Data System (ADS)

    Goldblatt, C.; Dewey, M. C.

    2015-12-01

    There have been many modeling studies of the runaway greenhouse effect and the conditions required to produce one on an Earth-like planet, however these models have not been verified with empirical evidence. It has been suggested that the Earth's tropics may be near a state of localized runaway greenhouse, meaning the surface temperature and atmospheric composition in those areas could cause runaway greenhouse, were it not for the tempering effects of meridional heat transport and circulation (Pierrehumbert, 1995). Using the assumption that some areas of the Earth's tropics may be under these conditions, this study uses measurements of the atmospheric properties, surface properties, and radiation budgets of these areas to quantify a radiation limit for runaway greenhouse on Earth, by analyzing the dependence of outgoing longwave radiation (OLR) at the top of the atmosphere on surface temperature and total column water vapour. An upper limit on OLR for clear-sky conditions was found between 289.8 W/m2 and 292.2 W/m2, which occurred at surface temperatures near 300K. For surface temperatures above this threshold, total column water vapour increased, but OLR initially decreased and then remained relatively constant, between 273.6 W/m2 and 279.7 W/m2. These limits are in good agreement with recent modeling results (Goldblatt et al., 2013), supporting the idea that some of the Earth's tropics may be in localized runaway greenhouse, and that radiation limits for runaway greenhouse on Earth can be empirically derived. This research was done as part of Maura Dewey's undergraduate honours thesis at the University of Victoria. Refs: Robert T. Pierrehumbert. Thermostats, radiator fins, and the local runaway greenhouse. Journal of Atmospheric Sciences, 52(10):1784-1806, 1995. Colin Goldblatt, Tyler D. Robinson, Kevin J. Zahnle, and David Crisp. Low simulated radiation limit for runaway greenhouse climates. Nature Geoscience, 6:661-667, 2013.

  4. Destabilization of the electron Bernstein modes by runaway electrons

    SciTech Connect

    Hitchcock, D.A.; Mahajan, S.M.

    1982-01-01

    It is shown that the electromagnetic finite k/sub parallel/ electron Bernstein mode can be destabilized by the runaway electron distribution which results from the quasilinear action of the magnetized plasma oscillation. This mechanism is shown to yield growth rates of the order of 10/sup 8/ sec/sup -1/ and is suggested as a mechanism for the enchanced cyclotron harmonic emission in the presence of runaway electrons.

  5. Fan instability and limitation of the runaway-electron current

    SciTech Connect

    Mal'kov, M.A.; Sagdeev, R.Z.; Shapiro, V.D.

    1983-05-01

    The effect of the fan instability of the runaway-electron tail on the dynamics of the acceleration of these electrons by the electric field is analyzed. A system of equations describing the conversion of the electron energy from longitudinal to transverse and also describing the anomalous electron thermal conductivity is derived and solved. These effects result from the fan instability. The anomalous electrical conductivity of a plasma is calculated from the runaway-electron current.

  6. ITER (International Thermonuclear Experimental Reactor) reactor building design study

    SciTech Connect

    Thomson, S.L.; Blevins, J.D.; Delisle, M.W.; Canadian Fusion Fuels Technology Project, Mississauga, ON )

    1989-01-01

    The International Thermonuclear Experimental Reactor (ITER) is at the midpoint of a two-year conceptual design. The ITER reactor building is a reinforced concrete structure that houses the tokamak and associated equipment and systems and forms a barrier between the tokamak and the external environment. It provides radiation shielding and controls the release of radioactive materials to the environment during both routine operations and accidents. The building protects the tokamak from external events, such as earthquakes or aircraft strikes. The reactor building requirements have been developed from the component designs and the preliminary safety analysis. The equipment requirements, tritium confinement, and biological shielding have been studied. The building design in progress requires continuous iteraction with the component and system designs and with the safety analysis. 8 figs.

  7. Multiplexing thermography for International Thermonuclear Experimental Reactor divertor targets

    SciTech Connect

    Itami, K.; Sugie, T.; Vayakis, G.; Walker, C.

    2004-10-01

    The concept of multiplexing thermography is applied to the design of the divertor thermography system for International Thermonuclear Experimental Reactor (ITER). The combination of the front mirror with multiellipticity and a Czerney-Turner spectrometer with a 0.2 mm pitched multichannel detector enables a spatial resolution of 3 mm and a time resolution of 20 {mu}s above a target temperature of 300 deg. C to be achieved. This should be sufficient to measure ELM heat fluxes to the targets in ITER. To satisfy the measurement requirement, it is very important to keep an accurate alignment around the optical axis against movement of the vessel during the plasma discharges. Several key engineering problems, such as the survivability of components against mirror coating by redeposited divertor material, remain to be solved. Potential solutions have been identified.

  8. Joining of carbon-carbon composites for thermonuclear fusion applications

    SciTech Connect

    Salvo, M.; Lemoine, P.; Ferraris, M.; Montorsi, M.; Merola, M.

    1997-01-01

    Carbon-fiber-reinforced carbon (CfC) composites have been joined by using different joining agents: metals (silicon, aluminum, and titanium), an intermetallic compound (magnesium silicide, Mg{sub 2}Si), and glasses (borosilicates and zinc borates). These joining agents have been chosen by considering their possible use in a thermonuclear fusion reactor, as suggested by their low-activation properties, reasonably high working temperature, industrial feasibility, and potential scale-up of the joined carbon-carbon structures using pressureless-processing techniques. Each joined structure (CfC composite-joining material-CfC composite) has been first morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. Then, single-lap shear tests have been performed on the most-promising joined structures, i.e., silicon- and aluminum-joined CfC-composite samples, which have shown an average shear strength of 22 and 10 MPa, respectively.

  9. Laser induced sonofusion: A new road toward thermonuclear reactions

    NASA Astrophysics Data System (ADS)

    Sadighi-Bonabi, Rasoul; Gheshlaghi, Maryam

    2016-03-01

    The Possibility of the laser assisted sonofusion is studied via single bubble sonoluminescence (SBSL) in Deuterated acetone (C3D6O) using quasi-adiabatic and hydro-chemical simulations at the ambient temperatures of 0 and -28.5 °C. The interior temperature of the produced bubbles in Deuterated acetone is 1.6 × 106 K in hydro-chemical model and it is reached up to 1.9 × 106 K in the laser induced SBSL bubbles. Under these circumstances, temperature up to 107 K can be produced in the center of the bubble in which the thermonuclear D-D fusion reactions are promising under the controlled conditions.

  10. Acoustically driven spherical implosions and the possibility of thermonuclear reactions

    NASA Astrophysics Data System (ADS)

    Gaitan, D. Felipe; Tessien, Ross

    2003-04-01

    Acoustically driven, gas-filled cavities in liquids have been known to collapse violently, generating short flashes of light of ~100-ps duration. More recently, the possibility of generating fusion reactions using acoustics (acoustic inertial confinement fusion) has been considered. Results of computer simulations using the HYADES hydrocode (Cascade Applied Sciences, Inc) plus the SESAME equations of state for free collapsing and acoustically driven cavities in molten metals will be presented as well as experimental data at high ambient pressures in different liquids. Back-of-the-envelope calculations in terms of the acoustical and thermodynamic parameters necessary to achieve thermonuclear reactions will be presented in an effort to evaluate the feasibility of acoustic ICF as an energy source.

  11. On some features of plane waves of thermonuclear burn

    NASA Astrophysics Data System (ADS)

    Khishchenko, K. V.; Charakhch'yan, A. A.

    2015-01-01

    The behavior of a slow burn wave propagating over a precompressed thermonuclear fuel heated by several shock waves generated by a laser pulse is studied. It is shown that such a burn wave can rapidly increase the fuel density ahead of the wave front and transform to a pair of detonation waves moving in the opposite directions. Hydrodynamic equations with a linear velocity profile are solved. It is found that the proton beam intensity necessary for ignition increases with the initial fuel density in accordance with the known formula generalizing results of two-dimensional simulations. A possibility of using results of one-dimensional simulations for determining the energy of ignition of a cylindrical target is discussed.

  12. Current drive at plasma densities required for thermonuclear reactors.

    PubMed

    Cesario, R; Amicucci, L; Cardinali, A; Castaldo, C; Marinucci, M; Panaccione, L; Santini, F; Tudisco, O; Apicella, M L; Calabrò, G; Cianfarani, C; Frigione, D; Galli, A; Mazzitelli, G; Mazzotta, C; Pericoli, V; Schettini, G; Tuccillo, A A

    2010-08-10

    Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

  13. Transport simulation of ITER (International Thermonuclear Engineering Reactor) startup

    SciTech Connect

    Attenberger, S.E.; Houlberg, W.A.

    1989-01-01

    The present International Thermonuclear Engineering Reactor (ITER) reference configurations are the Technology Phase,'' in which the plasma current is maintained noninductively at a subignition density, and the Physics Phase,'' which is ignited but requires inductive maintenance of the current. The WHIST 1.5-D transport code is used to evaluate the volt-second requirements of both configurations. A slow current ramp (60-80's) is required for fixed-radius startup in ITER to avoid hollow current density profiles. To reach the operating point requires about 203 V{center dot}s for the Technology Phase (18 MA) and about 270 V{center dot}s for the Physics Phase (22 MA). The resistive losses can be reduced with expanding-radius startup. 5 refs., 4 figs.

  14. Multidimensional Simulations of Thermonuclear Supernovae from the First Stars

    NASA Astrophysics Data System (ADS)

    Chen, K. J.; Heger, A.; Almgren, A.

    2012-07-01

    Theoretical models suggest that the first stars in the universe could have been very massive, with typical masses ≥ 100 M⊙ . Many of them might have died as energetic thermonuclear explosions known as pair-instability supernovae (PSNe). We present multidimensional numerical simulations of PSNe with the new radiation-hydrodynamics code CASTRO. Our models capture all explosive burning and follow the explosion until the shock breaks out from the stellar surface. We find that fluid instabilities driven by oxygen and helium burning arise at the upper and lower boundaries of the oxygen shell ˜ 20 - 100 sec after the explosion begins. Later, when the shock reaches the hydrogen envelope a strong reverse shock forms that rapidly develops additional Rayleigh-Taylor instabilities. In red supergiant progenitors, the amplitudes of these instabilities are sufficient to mix the supernova's ejecta and alter its observational signature. Our results provide useful predictions for the detection of PSNe by forthcoming telescopes.

  15. Laser induced sonofusion: A new road toward thermonuclear reactions

    SciTech Connect

    Sadighi-Bonabi, Rasoul; Gheshlaghi, Maryam

    2016-03-15

    The Possibility of the laser assisted sonofusion is studied via single bubble sonoluminescence (SBSL) in Deuterated acetone (C{sub 3}D{sub 6}O) using quasi-adiabatic and hydro-chemical simulations at the ambient temperatures of 0 and −28.5 °C. The interior temperature of the produced bubbles in Deuterated acetone is 1.6 × 10{sup 6} K in hydro-chemical model and it is reached up to 1.9 × 10{sup 6} K in the laser induced SBSL bubbles. Under these circumstances, temperature up to 10{sup 7} K can be produced in the center of the bubble in which the thermonuclear D-D fusion reactions are promising under the controlled conditions.

  16. Influence of thermonuclear effects on the collapse of supermassive stars

    NASA Astrophysics Data System (ADS)

    Montero, Pedro J.; Janka, H.-T.; Müller, E.; Müller, B.

    2011-09-01

    We present results of general relativistic simulations of collapsing supermassive stars using the two-dimensional general relativistic numerical code Nada, which solves the Einstein equations written in the BSSN formalism and the general relativistic hydrodynamic equations with high resolution shock capturing schemes. These numerical simulations use a tabulated equation of state which includes effects of radiation and gas pressure, and those associated with the electron-positron pairs. We also take into account the effect of thermonuclear energy released by hydrogen and helium burning. We find that objects with mass ≈ 5 × 105M and initial metallicity greater than ZCNO ≈ 0.004 do explode if non-rotating, while the threshold metallicity for an explosion is reduced to ZCNO ≈ 0.002 for objects uniformly rotating.

  17. Close Binary Progenitors and Ejected Companions of Thermonuclear Supernovae

    NASA Astrophysics Data System (ADS)

    Geier, S.; Kupfer, T.; Heber, U.; Nemeth, P.; Ziegerer, E.; Irrgang, A.; Schindewolf, M.; Marsh, T. R.; Gänsicke, B. T.; Barlow, B. N.; Bloemen, S.

    2017-03-01

    Hot subdwarf stars (sdO/Bs) are evolved core helium-burning stars with very thin hydrogen envelopes, which can be formed by common envelope ejection. Close sdB binaries with massive white dwarf (WD) companions are potential progenitors of thermonuclear supernovae type Ia (SN Ia). We discovered such a progenitor candidate as well as a candidate for a surviving companion star, which escapes from the Galaxy. More candidates for both types of objects have been found by cross-matching known sdB stars with proper motion and light curve catalogues. We found 72 sdO/B candidates with high Galactic restframe velocities, 12 of them might be unbound to our Galaxy. Furthermore, we discovered the second-most compact sdB+WD binary known. However, due to the low mass of the WD companion, it is unlikely to be a SN Ia progenitor.

  18. Analytical Model for the Thermonuclear Instability in IGNITOR

    NASA Astrophysics Data System (ADS)

    Cardinali, A.; Sonnino, G.; Coppi, B.

    2013-10-01

    The non-linear energy balance equation for thermal equilibrium and stability, is analytically and numerically investigated in order to study the thermonuclear instability in the IGNITOR experiment facility. The expressions for the ion and the electron thermal coefficients, introduced in the thermal energy balance equation, are obtained by solving the nonlinear transport equations relevant to several collisional transport regimes (in particular the banana regime). The differential equation for the temperature profile at equilibrium is solved and the resulting profile is compared with the results obtained by a full transport code. The growth of the perturbation in the temperature is analyzed by integrating the equation in time. A scenario is considered where IGNITOR is led to operate in a slightly sub-critical regime by adding a small fraction of 3He to the nominal 50-50 Deuterium-Tritium mixture and heating the plasma by ICRH power. Sponsored in part by the US DOE.

  19. The Dynamic Mutation Characteristics of Thermonuclear Reaction in Tokamak

    PubMed Central

    Li, Jing; Quan, Tingting; Zhang, Wei; Deng, Wei

    2014-01-01

    The stability and bifurcations of multiple limit cycles for the physical model of thermonuclear reaction in Tokamak are investigated in this paper. The one-dimensional Ginzburg-Landau type perturbed diffusion equations for the density of the plasma and the radial electric field near the plasma edge in Tokamak are established. First, the equations are transformed to the average equations with the method of multiple scales and the average equations turn to be a Z2-symmetric perturbed polynomial Hamiltonian system of degree 5. Then, with the bifurcations theory and method of detection function, the qualitative behavior of the unperturbed system and the number of the limit cycles of the perturbed system for certain groups of parameter are analyzed. At last, the stability of the limit cycles is studied and the physical meaning of Tokamak equations under these parameter groups is given. PMID:24892099

  20. The dynamic mutation characteristics of thermonuclear reaction in Tokamak.

    PubMed

    Li, Jing; Quan, Tingting; Zhang, Wei; Deng, Wei

    2014-01-01

    The stability and bifurcations of multiple limit cycles for the physical model of thermonuclear reaction in Tokamak are investigated in this paper. The one-dimensional Ginzburg-Landau type perturbed diffusion equations for the density of the plasma and the radial electric field near the plasma edge in Tokamak are established. First, the equations are transformed to the average equations with the method of multiple scales and the average equations turn to be a Z 2-symmetric perturbed polynomial Hamiltonian system of degree 5. Then, with the bifurcations theory and method of detection function, the qualitative behavior of the unperturbed system and the number of the limit cycles of the perturbed system for certain groups of parameter are analyzed. At last, the stability of the limit cycles is studied and the physical meaning of Tokamak equations under these parameter groups is given.

  1. On mixing at the core-envelope interface during classical nova outbursts

    NASA Astrophysics Data System (ADS)

    Casanova, J.; José, J.; García-Berro, E.; Calder, A.; Shore, S. N.

    2010-04-01

    Classical novae are powered by thermonuclear runaways that occur on the white dwarf component of close binary systems. During these violent stellar events, whose energy release is only exceeded by gamma-ray bursts and supernova explosions, about 10-4-10-5 M⊙ of material is ejected into the interstellar medium. Because of the high peak temperatures attained during the explosion, Tpeak ~ (1-4) × 108 K, the ejecta are enriched in nuclear-processed material relative to solar abundances, containing significant amounts of 13C, 15N, and 17O and traces of other isotopes. The origin of these metal enhancements observed in the ejecta is not well-known and has puzzled theoreticians for about 40 years. In this paper, we present new 2-D simulations of mixing at the core-envelope interface. We show that Kelvin-Helmholtz instabilities can naturally lead to self-enrichment of the solar-like accreted envelopes with material from the outermost layers of the underlying white dwarf core, at levels that agree with observations.

  2. Enhancement of runaway production by resonant magnetic perturbation on J-TEXT

    NASA Astrophysics Data System (ADS)

    Chen, Z. Y.; Huang, D. W.; Izzo, V. A.; Tong, R. H.; Jiang, Z. H.; Hu, Q. M.; Wei, Y. N.; Yan, W.; Rao, B.; Wang, S. Y.; Ma, T. K.; Li, S. C.; Yang, Z. J.; Ding, D. H.; Wang, Z. J.; Zhang, M.; Zhuang, G.; Pan, Y.; J-TEXT Team

    2016-07-01

    The suppression of runaways following disruptions is key for the safe operation of ITER. The massive gas injection (MGI) has been developed to mitigate heat loads, electromagnetic forces and runaway electrons (REs) during disruptions. However, MGI may not completely prevent the generation of REs during disruptions on ITER. Resonant magnetic perturbation (RMP) has been applied to suppress runaway generation during disruptions on several machines. It was found that strong RMP results in the enhancement of runaway production instead of runaway suppression on J-TEXT. The runaway current was about 50% pre-disruption plasma current in argon induced reference disruptions. With moderate RMP, the runway current decreased to below 30% pre-disruption plasma current. The runaway current plateaus reach 80% of the pre-disruptive current when strong RMP was applied. Strong RMP may induce large size magnetic islands that could confine more runaway seed during disruptions. This has important implications for runaway suppression on large machines.

  3. Demonstration of thermonuclear conditions in Magnetized Liner Inertial Fusion experiments

    NASA Astrophysics Data System (ADS)

    Gomez, Matthew

    2014-10-01

    The Magnetized Liner Inertial Fusion concept utilizes a magnetic field and laser heating to relax the implosion requirements to achieve inertial confinement fusion. The first experiments to test the concept were recently conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z coils. Despite the relatively slow implosion velocity (70 km/s) in these experiments, electron and ion temperatures at stagnation were approximately 3 keV, and thermonuclear DD neutron yields up to 2e12 have been produced. X-ray emission from the fuel at stagnation had a width ranging from 60-120 microns over a roughly 6 mm height and lasted approximately 2 ns. X-ray spectra from these experiments are consistent with a stagnation density of the hot fuel equal to 0.4 g/cm3 . In these experiments 1-5e10 secondary DT neutrons were produced. Given that the areal density of the plasma was approximately 2 mg/cm2, this indicates the stagnation plasma was significantly magnetized. This is consistent with the anisotropy observed in the DT neutron time of flight spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and DD yields greater than 1e10. An additional control experiment where the fuel contained a sufficient dopant fraction to radiate away the laser energy deposited in the fuel also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.

  4. The Internal Structure and Propagation of Magnetohydrodynamical Thermonuclear Flames

    NASA Astrophysics Data System (ADS)

    Remming, Ian S.; Khokhlov, Alexei M.

    2016-11-01

    We present general equations for non-ideal, reactive flow magnetohydrodynamics (RFMHD) in the form best suited for describing thermonuclear combustion in high-density degenerate matter of SNe Ia. The relative importance of various non-ideal effects is analyzed as a function of characteristic spatial and temporal scales of the problem. From the general RFMHD equations, we derive the one-dimensional ordinary differential equations describing the steady-state propagation of a planar thermonuclear flame front in a magnetic field. The physics of the flame is first studied qualitatively using a simple case of one-step Arrhenius kinetics, a perfect gas equation of state (EOS), and constant thermal conductivity coefficients. After that, the equations are solved, the internal flame front structure is calculated, and the flame velocity, S l , and flame thickness, δ l , are found for carbon-oxygen degenerate material of supernovae using a realistic EOS, transport properties, and detailed nuclear kinetics. The magnetic field changes the flame behavior significantly, both qualitatively and quantitatively, as compared to the non-magnetic case of classical combustion. (1) The magnetic field influences the evolutionarity of a flame front and makes it impossible for a flame to propagate steadily in a wide range of magnetic field strengths and orientations relative to the front. (2) When the flame moves steadily, it can propagate in several distinct modes, the most important being the slow C S and super-Alfvénic C sup modes. (3) The speed of the flame can be diminished or enhanced by up to several factors relative to the non-magnetic laminar flame speed.

  5. Demonstration of thermonuclear conditions in magnetized liner inertial fusion experiments

    DOE PAGES

    Gomez, Matthew R.; Slutz, Stephen A.; Sefkow, Adam B.; ...

    2015-04-29

    In this study, the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as highmore » as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6–8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2–0.4 g/cm3. In these experiments, up to 5 ×1010 secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1–2 mg/cm2, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and primary deuterium-deuterium yields greater than 1010. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.« less

  6. Demonstration of thermonuclear conditions in magnetized liner inertial fusion experimentsa)

    NASA Astrophysics Data System (ADS)

    Gomez, M. R.; Slutz, S. A.; Sefkow, A. B.; Hahn, K. D.; Hansen, S. B.; Knapp, P. F.; Schmit, P. F.; Ruiz, C. L.; Sinars, D. B.; Harding, E. C.; Jennings, C. A.; Awe, T. J.; Geissel, M.; Rovang, D. C.; Smith, I. C.; Chandler, G. A.; Cooper, G. W.; Cuneo, M. E.; Harvey-Thompson, A. J.; Herrmann, M. C.; Hess, M. H.; Lamppa, D. C.; Martin, M. R.; McBride, R. D.; Peterson, K. J.; Porter, J. L.; Rochau, G. A.; Savage, M. E.; Schroen, D. G.; Stygar, W. A.; Vesey, R. A.

    2015-05-01

    The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as high as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6-8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2-0.4 g/cm3. In these experiments, up to 5 × 1010 secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1-2 mg/cm2, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and primary deuterium-deuterium yields greater than 1010. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.

  7. Runaway electrons beams in ITER disruptions. Final report

    SciTech Connect

    Fleischmann, H.H.

    1993-12-31

    In agreement with the initial projections, the potential generation of runaway beams in disruptions of ITER discharges was performed. This analysis was based on the best-available present projections of plasma parameters existing in large-tokamak disruptions. Using these parameters, the potential contributions from various basic mechanisms for the generation of runway electrons were estimated. The envisioned mechanisms included (i) the well-known Dreicer process (assuming an evaporation of the runways from the thermal distribution), (ii) the seeding of runaway beams resulting from the potential presence of trapped high-temperature electrons from the original discharge still remaining in the disruption plasma at time of reclosure of the magnetic surfaces, and (iii) the generation of runaway beams through avalanche exponentiation of low-level seed runaways resulting via close collisions of existing runaways with cold plasma electrons. Finally, the prospective behavior of the any generated runaway beams -- in particular during their decay -- as well as their potential avoidance and/or damage controlled extraction through the use of magnetic perturbation fields also was considered in some detail.

  8. Computational and experimental modeling of runaway electron damage

    SciTech Connect

    Niemer, K.A.; Gilligan, J.G. . Dept. of Nuclear Engineering); Croessmann, C.D. ); Bolt, H.H. . NET Design Team)

    1990-06-01

    Cracking, craters, spotty damage (discoloration), and missing chunks of material have been observed on limiters and along the midplane of tokamak inner walls. This damage is assumed to be due to runaway electron discharges. These runaway electrons have been predicted to range in energy from a few MeV to several hundred MeV. The energy density from the runaway electron discharges ranges from 10 to 500 MJ/m{sup 2} over pulse lengths of 5 to 50 msec. The PTA code package is a unique application of PATRAN, the Integrated TIGER Series, and ABAQUS for modeling high energy electron impact on tokamak first wall and limiter materials. The PTA code package provides a three-dimensional, time dependent, computational code package which predicts energy deposition, temperature rise, and damage on relevant fusion materials from runaway electrons. In this benchmark study, three experiments were modeled to validate the PTA code package. The first and third experiment simulated runaway electrons scattering through a plasma facing surface (graphite) into an internal structure (copper), and the second experiment tested the thermal and structural response from high energy electron impact on different fusion relevant materials. The PTA calculations compared favorably with the experimental results. In particular, the PTA models identified gap conductance, thermal contact, x-ray generation in materials, and the placement of high stopping power materials as key factors in the design of plasma facing components that are resistant to runaway electron damage. 13 refs., 40 figs., 3 tabs.

  9. Phase-space Dynamics of Runaway Electrons In Tokamaks

    SciTech Connect

    Xiaoyin Guan, Hong Qin, and Nathaniel J. Fisch

    2010-08-31

    The phase-space dynamics of runaway electrons is studied, including the influence of loop voltage, radiation damping, and collisions. A theoretical model and a numerical algorithm for the runaway dynamics in phase space are developed. Instead of standard integrators, such as the Runge-Kutta method, a variational symplectic integrator is applied to simulate the long-term dynamics of a runaway electron. The variational symplectic integrator is able to globally bound the numerical error for arbitrary number of time-steps, and thus accurately track the runaway trajectory in phase space. Simulation results show that the circulating orbits of runaway electrons drift outward toward the wall, which is consistent with experimental observations. The physics of the outward drift is analyzed. It is found that the outward drift is caused by the imbalance between the increase of mechanical angular momentum and the input of toroidal angular momentum due to the parallel acceleration. An analytical expression of the outward drift velocity is derived. The knowledge of trajectory of runaway electrons in configuration space sheds light on how the electrons hit the first wall, and thus provides clues for possible remedies.

  10. Phase-space dynamics of runaway electrons in tokamaks

    SciTech Connect

    Guan Xiaoyin; Qin Hong; Fisch, Nathaniel J.

    2010-09-15

    The phase-space dynamics of runaway electrons is studied, including the influence of loop voltage, radiation damping, and collisions. A theoretical model and a numerical algorithm for the runaway dynamics in phase space are developed. Instead of standard integrators, such as the Runge-Kutta method, a variational symplectic integrator is applied to simulate the long-term dynamics of a runaway electron. The variational symplectic integrator is able to globally bound the numerical error for arbitrary number of time-steps, and thus accurately track the runaway trajectory in phase space. Simulation results show that the circulating orbits of runaway electrons drift outward toward the wall, which is consistent with experimental observations. The physics of the outward drift is analyzed. It is found that the outward drift is caused by the imbalance between the increase of mechanical angular momentum and the input of toroidal angular momentum due to the parallel acceleration. An analytical expression of the outward drift velocity is derived. The knowledge of trajectory of runaway electrons in configuration space sheds light on how the electrons hit the first wall, and thus provides clues for possible remedies.

  11. Measurement of the runaway electrons in the HT-7 tokamak

    SciTech Connect

    Chen, Z.Y.; Wan, B.N.; Lin, S.Y.; Shi, Y.J.; Hu, L.Q.; Gong, X.Z.; Lin, H.; Asif, M.

    2006-01-15

    A thermographic camera and four hard x-ray detectors have been developed to measure the runaway electrons in the HT-7 tokamak. The synchrotron radiation originated from the runaway electrons was measured by an infrared (IR) camera working in the wavelength ranges of 7.5-13 {mu}m. With a tangential viewing into the plasma in the direction of the electron approach on the equatorial plane, the synchrotron radiation from the runaway electrons was measured in a full poloidal cross section. Three NaI scintillators are used to monitor the hard x-ray radiation (HXR) in the energy ranges of 0.5-7 MeV, and a CdTe detector is used to monitor the low-energy HXR in the energy ranges of 0.3-1.2 MeV. The combination of infrared camera and hard x-ray detectors provides a powerful tool to investigate the runaway electron dynamics in HT-7. Runaways in the core and edge regions are monitored simultaneously. The parameters of runaway beam in the core are deduced from the IR pictures. The interaction of runway electrons with toroidal magnetic field ripple is monitored from the HXR emission.

  12. Binary frequency and origin of the OB runaway stars

    SciTech Connect

    Gies, D.R.; Bolton, C.T.

    1986-06-01

    A radial velocity survey of the bright northern OB runaway stars has been undertaken to determine the frequency of binary stars in this high-velocity group. A total of 634 high-dispersion spectrograms of 36 proposed runaway stars were obtained over a two year period. Approximately half of the stars are velocity-variable; these include seven spectroscopic binaries, one possible beta-Cephei variable, and 10 stars with emission lines in their spectra. The latter group contains seven of the eight Be stars observed and three luminous O stars, and it is argued that their variability is caused by nonradial pulsation. Fifteen of the program stars have a peculiar radial velocity greater than 30 km/s; five others are probable runaways on the basis of distance from the galactic plane and proper motion. Only two of the confirmed and probable runaways, HD 3950 and HD 198846 (Y Cyg), are binaries, and both are double-lines systems. New orbital elements are presented for HD 3950 and the five new binary systems found among the low-velocity stars. The statisical methods used to assess velocity variability and periodic signals are described in detail. The higher fractional abundance of runaways among more massive stars, their binary frequency, and the properties of the runaway binaries suggest that they obtained their high velocities through single-binary, binary-binary, or n-body close encounters during the early dynamical evolution of associations. 208 references.

  13. Global Crustal Dynamics of Magnetars in Relation to Their Bright X-Ray Outbursts

    NASA Astrophysics Data System (ADS)

    Thompson, Christopher; Yang, Huan; Ortiz, Néstor

    2017-05-01

    This paper considers the yielding response of a neutron star crust to smooth, unbalanced Maxwell stresses imposed at the core-crust boundary, and the coupling of the dynamic crust to the external magnetic field. Stress buildup and yielding in a magnetar crust are global phenomena: an elastic distortion radiating from one plastically deforming zone is shown to dramatically increase the creep rate in distant zones. Runaway creep to dynamical rates is shown to be possible, being enhanced by in situ heating and suppressed by thermal conduction and shearing of an embedded magnetic field. A global and time-dependent model of elastic, plastic, magnetic, and thermal evolution is developed. Fault-like structures develop naturally, and a range of outburst timescales is observed. Transient events with time profiles similar to giant magnetar flares (millisecond rise, ˜0.1 s duration, and decaying power-law tails) result from runaway creep that starts in localized sub-kilometer-sized patches and spreads across the crust. A one-dimensional model of stress relaxation in the vertically stratified crust shows that a modest increase in applied stress allows embedded magnetic shear to escape the star over ˜3-10 ms, dissipating greater energy if the exterior field is already sheared. Several such zones coupled to each other naturally yield a burst of duration ˜0.1 s, as is observed over a wide range of burst energies. The collective interaction of many plastic zones forces an overstability of global elastic modes of the crust, consistent with quasi-periodic oscillation (QPO) activity extending over ˜100 s. Giant flares probably involve sudden meltdown in localized zones, with high-frequency (≫100 Hz) QPOs corresponding to standing Alfvén waves within these zones.

  14. Search for thermonuclear neutrons in a mega-ampere plasma focus

    NASA Astrophysics Data System (ADS)

    Klir, D.; Kubes, P.; Paduch, M.; Pisarczyk, T.; Chodukowski, T.; Scholz, M.; Kalinowska, Z.; Bienkowska, B.; Karpinski, L.; Kortanek, J.; Kravarik, J.; Rezac, K.; Ivanova-Stanik, I.; Tomaszewski, K.; Zielinska, E.

    2012-01-01

    Plasma focus experiments were carried out at a modified PF-1000 where the cathode disc was added in front of the anode. Experimental results indicated a fraction of thermonuclear neutrons on the mega-ampere current level. In order to prove the thermonuclear mechanism, the time of neutron production and the neutron energy spectrum were measured by time-of-flight (TOF) diagnostics. Neutron TOF signals showed that the neutron production was a multiphase process and more than one mechanism occurred simultaneously. The occurrence of the thermonuclear mechanism was most evident during the plasma stagnation at low deuterium pressures. At low filling pressures, the narrow width of the neutron energy spectra demonstrated an ion temperature of about 1 keV. The possibility of thermonuclear neutrons was studied also after the stagnation, during the main neutron emission. In this case, the thermonuclear mechanism could be verified by calculating the number of deuterons that participate in the fusion process. For the bulk of thermonuclear plasmas, a significant fraction of plasma should participate in fusion. Finally, the basic consideration of the thermonuclear mechanism in Z-pinches showed the reasonableness of the MagLIF concept.

  15. The 2015 outburst of the accretion-powered pulsar IGR J00291+5934: INTEGRAL and Swift observations

    NASA Astrophysics Data System (ADS)

    De Falco, V.; Kuiper, L.; Bozzo, E.; Galloway, D. K.; Poutanen, J.; Ferrigno, C.; Stella, L.; Falanga, M.

    2017-03-01

    The pulsar IGR J00291+5934 is the fastest-known accretion-powered X-ray pulsar, discovered during a transient outburst in 2004. In this paper, we report on INTEGRAL and Swift observations during the 2015 outburst, which lasts for 25 d. The source has not been observed in outburst since 2008, suggesting that the long-term accretion rate has decreased by a factor of two since discovery. The averaged broad-band (0.1-250 keV) persistent spectrum in 2015 is well described by a thermal Comptonization model with a column density of NH ≈ 4 × 1021 cm-2, a plasma temperature of kTe ≈ 50 keV, and a Thomson optical depth of τT ≈ 1. Pulsations at the known spin period of the source are detected in the INTEGRAL data up to the 150 keV energy band. We also report on the discovery of the first thermonuclear burst observed from IGR J00291+5934, which lasts around 7 min and occurs at a persistent emission level corresponding to roughly 1.6% of the Eddington accretion rate. The properties of the burst suggest it is powered primarily by helium ignited at a depth of yign ≈ 1.5 × 109 g cm-2 following the exhaustion by steady burning of the accreted hydrogen. The Swift/BAT data from the first 20 s of the burst provide indications of a photospheric radius expansion phase. Assuming this is the case, we infer a source distance of d = 4.2 ± 0.5 kpc.

  16. A family study of patients with temper outbursts.

    PubMed

    Mattes, J A; Fink, M

    1987-01-01

    To evaluate the heritability of a personality trait, "having temper outbursts," and of associated diagnoses, we obtained histories of first degree relatives on two groups: (1) patients with temper outbursts (N = 33), and (2) diverse psychiatric patients without temper outbursts (N = 12). Family interviews were conducted blind to patient (temper or not) status, using a modified version of the Family History RDC. Though Ns are relatively small, and results therefore require confirmation, the data indicate familial transmission of temper problems; an average of 18.2% of Group 1 relatives had temper problems, compared to 4.3% for Group 2. The trait of having temper outbursts was more strongly transmitted than were specific diagnoses (e.g. Intermittent Explosive Disorder, Antisocial Personality Disorder or Residual Attention Deficit Disorder) associated with temper outbursts. Patients with neurological conditions apparently related to their temper outbursts were less likely to have positive family histories.

  17. Outbursts in Two New Cool Pulsating DA White Dwarfs

    NASA Astrophysics Data System (ADS)

    Bell, Keaton J.; Hermes, J. J.; Montgomery, M. H.; Gentile Fusillo, N. P.; Raddi, R.; Gänsicke, B. T.; Winget, D. E.; Dennihy, E.; Gianninas, A.; Tremblay, P.-E.; Chote, P.; Winget, K. I.

    2016-10-01

    The unprecedented extent of coverage provided by Kepler observations recently revealed outbursts in two hydrogen-atmosphere pulsating white dwarfs (DAVs) that cause hours-long increases in the overall mean flux of up to 14%. We have identified two new outbursting pulsating white dwarfs in K2, bringing the total number of known outbursting white dwarfs to four. EPIC 211629697, with {T}{eff} = 10,780 ± 140 K and {log} g = 7.94 ± 0.08, shows outbursts recurring on average every 5.0 days, increasing the overall flux by up to 15%. EPIC 229227292, with {T}{eff} = 11,190 ± 170 K and {log} g = 8.02 ± 0.05, has outbursts that recur roughly every 2.4 days with amplitudes up to 9%. We establish that only the coolest pulsating white dwarfs within a small temperature range near the cool, red edge of the DAV instability strip exhibit these outbursts.

  18. Pulsations and outbursts of luminous blue variables

    SciTech Connect

    Cox, A.N.; Guzik, J.A.; Soukup, M.S.; Despain, K.M.

    1997-06-01

    We propose an outburst mechanism for the most luminous stars in our and other galaxies. These million solar luminosity stars, with masses (after earlier mass loss) of between 20 and maybe 70 solar masses, are pulsationally unstable for both radial and low-degree nonradial modes. Some of these modes are ``strange,`` meaning mostly that the pulsations are concentrated near the stellar surface and have very rapid growth rates in linear theory. The pulsation driving is by both the high iron line opacity (near 150,000 K) and the helium opacity (near 30,000 K) kappa effects. Periods range from 5 to 40 days. Depending on the composition, pulsations periodically produce luminosities above the Eddington limit for deep layers. The radiative luminosity creates an outward push that readily eases the very low gamma envelope to very large outburst radii. A key point is that a super-Eddington luminosity cannot be taken up by the sluggish convection rapidly enough to prevent an outward acceleration of much of the envelope. As the helium abundance in the envelope stellar material increases by ordinary wind mass loss and the luminous blue variable outbursts, the opacity in the deep pulsation driving layers decreases. This makes the current Eddington luminosity even higher so that pulsations can then no longer give radiative luminosities exceeding the limit. For the lower mass and luminosity luminous blue variables there is considerably less iron line opacity driving, and pulsations are almost all caused by the helium ionization kappa effect.

  19. Comet outbursts and the meteor showers

    NASA Astrophysics Data System (ADS)

    Guliyev, A. S.; Kokhirova, G. I.; Poladova, U. D.

    2014-07-01

    The features of 116 comets that have shown an outbursts in their brightness, are considered in the paper. The hypothesis on that the outburst in activity of comets are caused by their passing through meteoroid streams is studied. For this purpose the orbital elements of such comets relative to the planes of motion of 68 meteor showers from Cook's catalogue are analyzed. It was found that four of the nearest and distant nodes of comet orbits relative to the planes of motion of nine meteor showers exceeds the average statistical background with confidence probability from 0.90 to 0.95, and more than 0.95, respectively. The October Draconids, Aurigids, kappa-Serpentids, delta-Draconids, sigma-Hydrids}, Coma Berenicids, Leonids, Leo Minorids, and Perseids showers are the most effective. The results of calculation show that often, the comets outbursts may be caused by collisions of comets with meteoroids under the passing through the meteoroid streams that are producing listed meteor showers as well as solar activity.

  20. VARIABLE ACCRETION OUTBURSTS IN PROTOSTELLAR EVOLUTION

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles E-mail: lhartm@umich.edu E-mail: gammie@illinois.edu

    2013-02-20

    We extend the one-dimensional, two-zone models of long-term protostellar disk evolution with infall of Zhu et al. to consider the potential effects of a finite viscosity in regions where the ionization is too low for the magnetorotational instability (MRI) to operate (the {sup d}ead zone{sup )}. We find that the presence of a small but finite dead zone viscosity, as suggested by simulations of stratified disks with MRI-active outer layers, can trigger inside-out bursts of accretion, starting at or near the inner edge of the disk, instead of the previously found outside-in bursts with zero dead zone viscosity, which originate at a few AU in radius. These inside-out bursts of accretion bear a qualitative resemblance to the outburst behavior of one FU Ori object, V1515 Cyg, in contrast to the outside-in burst models, which more closely resemble the accretion events in FU Ori and V1057 Cyg. Our results suggest that the type and frequency of outbursts are potentially a probe of transport efficiency in the dead zone. Simulations must treat the inner disk regions, R {approx}< 0.5 AU, to show the detailed time evolution of accretion outbursts in general and to observe the inside-out bursts in particular.

  1. Chandra Discovers Eruption and Pulsation in Nova Outburst

    NASA Astrophysics Data System (ADS)

    2001-09-01

    NASA's Chandra X-ray Observatory has discovered a giant outburst of X-rays and unusual cyclical pulsing from a white dwarf star that is closely orbiting another star -- the first time either of these phenomena has been seen in X-rays. The observations are helping scientists better understand the thermonuclear explosions that occur in certain binary star systems. The observations of Nova Aquilae were reported today at the "Two Years of Science with Chandra" symposium by an international team led by Sumner Starrfield of Arizona State University. "We found two important results in our Chandra observations. The first was an underlying pulsation every 40 minutes in the X-ray brightness, which we believe comes from the cyclical expansion and contraction of the outer layers of the white dwarf," said Starrfield. "The other result was an enormous flare of X-rays that lasted for 15 minutes. Nothing like this has been seen before from a nova, and we don't know how to explain it." Novas occur on a white dwarf (a star which used up all its nuclear fuel and shrank to roughly the size of the Earth) that is orbiting a normal size star. Strong gravity tides drag hydrogen gas off the normal star and onto the white dwarf, where it can take more than 100,000 years for enough hydrogen to accumulate to ignite nuclear fusion reactions. Gradually, these reactions intensify until a cosmic-sized hydrogen bomb blast results. The outer layers of the white dwarf are then blown away, producing a nova outburst that can be observed for a period of months to years as the material expands into space. "Chandra has allowed us to see deep into the gases ejected by this giant explosion and extract unparalleled information on the evolution of the white dwarf whose surface is exploding," said Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics. The brightening of Nova Aquilae was first detected by optical astronomers in December 1999. "Although this star is at a distance of more than 6

  2. Verification of runaway migration in a massive disk

    SciTech Connect

    Li, Shengtai

    2009-01-01

    Runaway migration of a proto-planet was first proposed and observed by Masset and Papaloizou (2003). The semi-major axis of the proto-planet varies by 50% over just a few tens of orbits when runaway migration happens. More recent work by D'Angelo et al. (2005) solved the same problem with locally refined grid and found that the migration rate is sharply reduced and no runaway occurs when the grid cells surrounding the planet are refined enough. To verify these two seemly contradictory results, we independently perform high-resolution simulations, solving the same problem as Masset and Papaloizou (2003), with and without self-gravity. We find that the migration rate is highly dependent on the softening used in the gravitational force between thd disk and planet. When a small softening is used in a 2D massive disk, the mass of the circumplanetary disk (CPD) increases with time with enough resolution in the CPD region. It acts as the mass is continually accreted to the CPD, which cannot be settled down until after thousands of orbits. If the planet is held on a fixed orbit long enough, the mass of CPD will become so large that the condition for the runaway migration derived in Masset (2008) will not be satisfied, and hence the runaway migration will not be triggered. However, when a large softening is used, the mass of the CPD will begin to decrease after the initial increase stage. Our numerical results with and without disk-gravity confirm that the runaway migration indeed exists when the mass deficit is larger than the total mass of the planet and CPD. Our simulations results also show that the torque from the co-orbital region, in particular the planet's Hill sphere, is the main contributor to the runaway migration, and the CPD which is lagged behind by the planet becomes so asymmetric that it accelerates the migration.

  3. Defining Pre-Outburst and Post-Outburst Characteristics of Eruptive Young Stars

    NASA Astrophysics Data System (ADS)

    Stringfellow, Guy

    2005-10-01

    EXORs are extreme T Tauri stars that experience major UV-optical eruptions (3-5 mag) that last about a year. These recurring outbursts driven by high accretion rates assist in dispersal of the circumstellar disk and the large X-ray-UV flux injected into the local environment modifies the physical and chemical history, influencing planet formation and time scales. Little X-ray data exists on these stars during either quiescent or outburst phases, so basic details such as how much X-ray flux is produced during eruption is unknown. We will characterize the X-ray properties of 7 EXORs in their quiescent phase. TOO time is requested to obtain high-quality spectra if an eruption occurs during AO5. Contrasting quiescent and outburst properties provides crucial insight into the physics.

  4. Defining Pre-Outburst and Post-Outburst Characteristics of Eruptive Young Stars

    NASA Astrophysics Data System (ADS)

    Stringfellow, Guy

    2006-10-01

    EXORs are extreme T Tauri stars that experience major UV-optical eruptions (3-5 mag) that last about a year. These recurring outbursts driven by high accretion rates assist in dispersal of the circumstellar disk and the large X-ray-UV flux injected into the local environment modifies the physical and chemical history, influencing planet formation and time scales. Little X-ray data exists on these stars during either quiescent or outburst phases, so basic details such as how much X-ray flux is produced during eruption is unknown. We will characterize the X-ray properties of 6 EXORs in their quiescent phase. If an eruption of any known EXOR occurs during AO6, a high-quality spectrum will be obtained. Contrasting quiescent and outburst properties provides crucial insight into the physics.

  5. Outburst-related period changes of recurrent nova CI aquilae

    SciTech Connect

    Wilson, R. E.; Honeycutt, R. K. E-mail: rewilson@ufl.edu

    2014-11-01

    Pre-outburst and post-outburst light curves and post-outburst eclipse timings are analyzed to measure any period (P) change related to nova CI Aql's outburst of early 2000 and a mean post-outburst dP/dt, which then lead to estimates of the accreting component's rate of mass (M) change and its overall outburst-related change of mass over roughly a decade of observations. We apply a recently developed procedure for unified analysis of three timing-related data types (light curves, radial velocities, and eclipse timings), although with only light curves and timings in this case. Fits to the data are reasonably good without need for a disk in the light-curve model, although the disk certainly exists and has an important role in our post-outburst mass flow computations. Initial experiments showed that, although there seems to be an accretion hot spot, it has essentially no effect on derived outburst-related ΔP or on post-outburst dP/dt. Use of atomic time (HJED) in place of HJD also has essentially nil effect on ΔP and dP/dt. We find ΔP consistently negative in various types of solutions, although at best only marginally significant statistically in any one experiment. Pre-outburst HJD {sub 0} and P results are given, as are post-outburst HJD {sub 0}, P, and dP/dt, with light curves and eclipse times as joint input, and also with only eclipse time input. Post-outburst dP/dt is negative at about 2.4σ. Explicit formulae for mass transfer rates and epoch-to-epoch mass change are developed and applied. A known offset in the magnitude zero point for 1991-1994 is corrected.

  6. Cryogenic thermonuclear fuel implosions on the National Ignition Facilitya)

    NASA Astrophysics Data System (ADS)

    Glenzer, S. H.; Callahan, D. A.; MacKinnon, A. J.; Kline, J. L.; Grim, G.; Alger, E. T.; Berger, R. L.; Bernstein, L. A.; Betti, R.; Bleuel, D. L.; Boehly, T. R.; Bradley, D. K.; Burkhart, S. C.; Burr, R.; Caggiano, J. A.; Castro, C.; Casey, D. T.; Choate, C.; Clark, D. S.; Celliers, P.; Cerjan, C. J.; Collins, G. W.; Dewald, E. L.; DiNicola, P.; DiNicola, J. M.; Divol, L.; Dixit, S.; Döppner, T.; Dylla-Spears, R.; Dzenitis, E.; Eckart, M.; Erbert, G.; Farley, D.; Fair, J.; Fittinghoff, D.; Frank, M.; Frenje, L. J. A.; Friedrich, S.; Casey, D. T.; Gatu Johnson, M.; Gibson, C.; Giraldez, E.; Glebov, V.; Glenn, S.; Guler, N.; Haan, S. W.; Haid, B. J.; Hammel, B. A.; Hamza, A. V.; Haynam, C. A.; Heestand, G. M.; Hermann, M.; Hermann, H. W.; Hicks, D. G.; Hinkel, D. E.; Holder, J. P.; Holunda, D. M.; Horner, J. B.; Hsing, W. W.; Huang, H.; Izumi, N.; Jackson, M.; Jones, O. S.; Kalantar, D. H.; Kauffman, R.; Kilkenny, J. D.; Kirkwood, R. K.; Klingmann, J.; Kohut, T.; Knauer, J. P.; Koch, J. A.; Kozioziemki, B.; Kyrala, G. A.; Kritcher, A. L.; Kroll, J.; La Fortune, K.; Lagin, L.; Landen, O. L.; Larson, D. W.; LaTray, D.; Leeper, R. J.; Le Pape, S.; Lindl, J. D.; Lowe-Webb, R.; Ma, T.; McNaney, J.; MacPhee, A. G.; Malsbury, T. N.; Mapoles, E.; Marshall, C. D.; Meezan, N. B.; Merrill, F.; Michel, P.; Moody, J. D.; Moore, A. S.; Moran, M.; Moreno, K. A.; Munro, D. H.; Nathan, B. R.; Nikroo, A.; Olson, R. E.; Orth, C. D.; Pak, A. E.; Patel, P. K.; Parham, T.; Petrasso, R.; Ralph, J. E.; Rinderknecht, H.; Regan, S. P.; Robey, H. F.; Ross, J. S.; Rosen, M. D.; Sacks, R.; Salmonson, J. D.; Saunders, R.; Sater, J.; Sangster, C.; Schneider, M. B.; Séguin, F. H.; Shaw, M. J.; Spears, B. K.; Springer, P. T.; Stoeffl, W.; Suter, L. J.; Thomas, C. A.; Tommasini, R.; Town, R. P. J.; Walters, C.; Weaver, S.; Weber, S. V.; Wegner, P. J.; Whitman, P. K.; Widmann, K.; Widmayer, C. C.; Wilde, C. H.; Wilson, D. C.; Van Wonterghem, B.; MacGowan, B. J.; Atherton, L. J.; Edwards, M. J.; Moses, E. I.

    2012-05-01

    The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 MJ produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 μm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 ± 3) μm, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 ± 0.09) g cm-2 result in fuel densities approaching 600 g cm-3. The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 ± 0.1) keV that is measured with neutron time of flight spectra. The hot-spot plasma produces a total fusion neutron yield of 1015 that is measured with the magnetic recoil spectrometer and nuclear activation diagnostics that indicate a 14.1 MeV yield of (7.5±0.1)×1014 which is 70% to 75% of the total fusion yield due to the high areal density. Gamma ray measurements provide the duration of nuclear activity of (170 ± 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date

  7. A MASSIVE RUNAWAY STAR FROM 30 DORADUS

    SciTech Connect

    Evans, C. J.; Walborn, N. R.; Massa, D.; Lennon, D. J.; Crowther, P. A.; Henault-Brunet, V.; Taylor, W. D.; Howarth, I. D.; Sana, H.; Van Loon, J. Th.

    2010-06-01

    We present the first ultraviolet (UV) and multi-epoch optical spectroscopy of 30 Dor 016, a massive O2-type star on the periphery of 30 Doradus in the Large Magellanic Cloud. The UV data were obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope as part of the Servicing Mission Observatory Verification program after Servicing Mission 4, and reveal no. 016 to have one of the fastest stellar winds known. From analysis of the C IV {lambda}{lambda}1548-51 doublet we find a terminal velocity, v {sub {infinity}} = 3450 {+-} 50 km s{sup -1}. Optical spectroscopy is from the VLT-FLAMES Tarantula Survey, from which we rule out a massive companion (with 2 days < P < 1 yr) to a confidence of 98%. The radial velocity of no. 016 is offset from the systemic value by -85 km s{sup -1}, suggesting that the star has traveled the 120 pc from the core of 30 Doradus as a runaway, ejected via dynamical interactions.

  8. Probing Runaway Electrons with Nanoparticle Plasma Jet

    NASA Astrophysics Data System (ADS)

    Bogatu, I. N.; Thompson, J. R.; Galkin, S. A.; Kim, J. S.

    2014-10-01

    The injection of C60/C nanoparticle plasma jet (NPPJ) into tokamak plasma during a major disruption has the potential to probe the runaway electrons (REs) during different phases of their dynamics and diagnose them through spectroscopy of C ions visible/UV lines. A C60/C NPPJ of ~75 mg, high-density (>1023 m-3), hyper-velocity (>4 km/s), and uniquely fast response-to-delivery time (~1 ms) has been demonstrated on a test bed. It can rapidly and deeply deliver enough mass to increase electron density to ~2.4 × 1021 m-3, ~60 times larger than typical DIII-D pre-disruption value. We will present the results of our investigations on: 1) C60 fragmentation and gradual release of C atoms along C60 NPPJ penetration path through the RE carrying residual cold plasma, 2) estimation of photon emissivity coefficient for the lines of the C ions, and 3) simulation of C60/C PJ penetration to the RE beam location in equivalent conditions to the characteristic ~1 T B-field of DIII-D. The capabilities of this injection technique provide a unique possibility in understanding and controlling the RE beam, which is a critical problem for ITER. Work supported by US DOE DE-SC0011864 Grant.

  9. Glacier lake outburst floods - modelling process chains

    NASA Astrophysics Data System (ADS)

    Schaub, Yvonne; Huggel, Christian; Haeberli, Wilfried

    2013-04-01

    New lakes are forming in high-mountain areas all over the world due to glacier recession. Often they will be located below steep, destabilized flanks and are therefore exposed to impacts from rock-/ice-avalanches. Several events worldwide are known, where an outburst flood has been triggered by such an impact. In regions such as in the European Alps or in the Cordillera Blanca in Peru, where valley bottoms are densely populated, these far-travelling, high-magnitude events can result in major disasters. For appropriate integral risk management it is crucial to gain knowledge on how the processes (rock-/ice-avalanches - impact waves in lake - impact on dam - outburst flood) interact and how the hazard potential related to corresponding process chains can be assessed. Research in natural hazards so far has mainly concentrated on describing, understanding, modeling or assessing single hazardous processes. Some of the above mentioned individual processes are quite well understood in their physical behavior and some of the process interfaces have also been investigated in detail. Multi-hazard assessments of the entire process chain, however, have only recently become subjects of investigations. Our study aims at closing this gap and providing suggestions on how to assess the hazard potential of the entire process chain in order to generate hazard maps and support risk assessments. We analyzed different types of models (empirical, analytical, physically based) for each process regarding their suitability for application in hazard assessments of the entire process chain based on literature. Results show that for rock-/ice-avalanches, dam breach and outburst floods, only numerical, physically based models are able to provide the required information, whereas the impact wave can be estimated by means of physically based or empirical assessments. We demonstrate how the findings could be applied with the help of a case study of a recent glacier lake outburst event at Laguna

  10. Demonstration of thermonuclear conditions in magnetized liner inertial fusion experiments

    SciTech Connect

    Gomez, M. R.; Slutz, S. A.; Sefkow, A. B.; Hahn, K. D.; Hansen, S. B.; Knapp, P. F.; Schmit, P. F.; Ruiz, C. L.; Sinars, D. B.; Harding, E. C.; Jennings, C. A.; Awe, T. J.; Geissel, M.; Rovang, D. C.; Smith, I. C.; Chandler, G. A.; Cooper, G. W.; Cuneo, M. E.; Harvey-Thompson, A. J.; Hess, M. H.; and others

    2015-05-15

    The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as high as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 10{sup 12} have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6–8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2–0.4 g/cm{sup 3}. In these experiments, up to 5 × 10{sup 10} secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1–2 mg/cm{sup 2}, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and primary deuterium-deuterium yields greater than 10{sup 10}. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.

  11. Demonstration of thermonuclear conditions in magnetized liner inertial fusion experiments

    SciTech Connect

    Gomez, Matthew R.; Slutz, Stephen A.; Sefkow, Adam B.; Hahn, Kelly D.; Hansen, Stephanie B.; Knapp, Patrick F.; Schmit, Paul F.; Ruiz, Carlos L.; Sinars, Daniel Brian; Harding, Eric C.; Jennings, Christopher A.; Awe, Thomas James; Geissel, Matthias; Rovang, Dean C.; Smith, Ian C.; Chandler, Gordon A.; Cooper, Gary Wayne; Cuneo, Michael Edward; Harvey-Thompson, Adam James; Herrmann, Mark C.; Mark Harry Hess; Lamppa, Derek C.; Martin, Matthew R.; McBride, Ryan D.; Peterson, Kyle J.; Porter, John L.; Rochau, Gregory A.; Savage, Mark E.; Schroen, Diana G.; Stygar, William A.; Vesey, Roger Alan

    2015-04-29

    In this study, the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as high as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6–8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2–0.4 g/cm3. In these experiments, up to 5 ×1010 secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1–2 mg/cm2, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and primary deuterium-deuterium yields greater than 1010. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.

  12. AG Pegasi - now a classical symbiotic star in outburst?

    NASA Astrophysics Data System (ADS)

    Tomov, T. V.; Stoyanov, K. A.; Zamanov, R. K.

    2016-11-01

    Optical spectroscopy study of the recent AG Pegasi (AG Peg) outburst observed during the second half of 2015 is presented. Considerable variations of the intensity and the shape of the spectral features as well as the changes of the hot component parameters, caused by the outburst, are discussed and certain similarities between the outburst of AG Peg and the outburst of a classical symbiotic stars are shown. It seems that after the end of the symbiotic nova phase, AG Peg became a member of the classical symbiotic stars group.

  13. Thermal Runaway Severity Reduction Assessment and Implementation: On Li-Ion Batteries

    NASA Technical Reports Server (NTRS)

    Darcy, Eric

    2015-01-01

    Preventing cell-cell thermal runaway propagation and flames/sparks from exiting battery enclosure is possible with proper thermal & electrical design and cell thermal runaway ejecta/effluent management and can be had with minimal mass/volume penalty.

  14. The behavior of runaway current in massive gas injection fast shutdown plasmas in J-TEXT

    NASA Astrophysics Data System (ADS)

    Chen, Z. Y.; Huang, D. W.; Luo, Y. H.; Tang, Y.; Dong, Y. B.; Zeng, L.; Tong, R. H.; Wang, S. Y.; Wei, Y. N.; Wang, X. H.; Jian, X.; Li, J. C.; Zhang, X. Q.; Rao, B.; Yan, W.; Ma, T. K.; Hu, Q. M.; Yang, Z. J.; Gao, L.; Ding, Y. H.; Wang, Z. J.; Zhang, M.; Zhuang, G.; Pan, Y.; Jiang, Z. H.; J-TEXT Team

    2016-11-01

    Runaway currents following disruptions have an important effect on the first wall in current tokamaks and will be more severe in next generation tokamaks. The behavior of runaway currents in massive gas injection (MGI) induced disruptions have been investigated in the J-TEXT tokamak. The cold front induced by the gas jet penetrates helically along field lines, preferentially toward the high field side and stops at a location near the q  =  2 surface before the disruption. When the cold front reaches the q  =  2 surface it initiates magnetohydrodynamic activities and results in disruption. It is found that the MGI of He or Ne results in runaway free shutdown in a large range of gas injections. Mixture injection of He and Ar (90% He and 10%Ar) consistently results in runaway free shutdown. A moderate amount of Ar injection could produce significant runaway current. The maximum runaway energy in the runaway plateau is estimated using a simplified model which neglects the drag forces and other energy loss mechanisms. The maximum runaway energy increases with decreasing runaway current. Imaging of the runaway beam using a soft x-ray array during the runaway current plateau indicates that the runaway beam is located in the center of the plasma. Resonant magnetic perturbation (RMP) is applied to reduce the runaway current successfully during the disruption phase in a small scale tokamak, J-TEXT. When the runaway current builds up, the application of RMP cannot decouple the runaway beam due to the lower sensitivity of the energetic runaway electrons to the magnetic perturbation.

  15. Thermonuclear inverse magnetic pumping power cycle for stellarator reactors

    SciTech Connect

    Ho, D.D.M.; Kulsrud, R.M.

    1985-09-01

    A novel power cycle for direct conversion of alpha-particle energy into electricity is proposed for an ignited plasma in a stellarator reactor. The plasma column is alternately compressed and expanded in minor radius by periodic variation of the toroidal magnetic field strength. As a result of the way a stellarator is expected to work, the plasma pressure during expansion is greater than the corresponding pressure during compression. Therefore, negative work is done on the plasma during a complete cycle. This work manifests itself as a back-voltage in the toroidal field coils, and direct electrical energy is obtained from this voltage. For a typical reactor, the average power obtained from this cycle (with a minor radius compression factor on the order of 50%) can be as much as 50% of the electrical power obtained from the thermonuclear neutrons without compressing the plasma. Thus, if it is feasible to vary the toroidal field strength, the power cycle provides an alternative scheme of energy conversion for a deuterium-tritium fueled reactor. The cycle may become an important method of energy conversion for advanced neutron-lean fueled reactors. By operating two or more reactors in tandem, the cycle can be made self-sustaining.

  16. Current drive for stability of thermonuclear plasma reactor

    NASA Astrophysics Data System (ADS)

    Amicucci, L.; Cardinali, A.; Castaldo, C.; Cesario, R.; Galli, A.; Panaccione, L.; Paoletti, F.; Schettini, G.; Spigler, R.; Tuccillo, A.

    2016-01-01

    To produce in a thermonuclear fusion reactor based on the tokamak concept a sufficiently high fusion gain together stability necessary for operations represent a major challenge, which depends on the capability of driving non-inductive current in the hydrogen plasma. This request should be satisfied by radio-frequency (RF) power suitable for producing the lower hybrid current drive (LHCD) effect, recently demonstrated successfully occurring also at reactor-graded high plasma densities. An LHCD-based tool should be in principle capable of tailoring the plasma current density in the outer radial half of plasma column, where other methods are much less effective, in order to ensure operations in the presence of unpredictably changes of the plasma pressure profiles. In the presence of too high electron temperatures even at the periphery of the plasma column, as envisaged in DEMO reactor, the penetration of the coupled RF power into the plasma core was believed for long time problematic and, only recently, numerical modelling results based on standard plasma wave theory, have shown that this problem should be solved by using suitable parameter of the antenna power spectrum. We show here further information on the new understanding of the RF power deposition profile dependence on antenna parameters, which supports the conclusion that current can be actively driven over a broad layer of the outer radial half of plasma column, thus enabling current profile control necessary for the stability of a reactor.

  17. Evidence of Spreading Layer Emission in a Thermonuclear Superburst

    NASA Astrophysics Data System (ADS)

    Koljonen, K. I. I.; Kajava, J. J. E.; Kuulkers, E.

    2016-10-01

    When a neutron star (NS) accretes matter from a companion star in a low-mass X-ray binary, the accreted gas settles onto the stellar surface through a boundary/spreading layer. On rare occasions the accumulated gas undergoes a powerful thermonuclear superburst powered by carbon burning deep below the NS atmosphere. In this paper, we apply the non-negative matrix factorization spectral decomposition technique to show that the spectral variations during a superburst from 4U 1636-536 can be explained by two distinct components: (1) the superburst emission characterized by a variable temperature blackbody radiation component and (2) a quasi-Planckian component with a constant, ˜2.5 keV, temperature varying by a factor of ˜15 in flux. The spectrum of the quasi-Planckian component is identical in shape and characteristics to the frequency-resolved spectra observed in the accretion/persistent spectrum of NS low-mass X-ray binaries and agrees well with the predictions of the spreading layer model by Inogamov & Sunyaev. Our results provide yet more observational evidence that superbursts—and possibly also normal X-ray bursts—induce changes in the disc-star boundary.

  18. Poloidal flux linkage requirements for the International Thermonuclear Experimental Reactor

    SciTech Connect

    Jardin, S.C.; Kessel, C.; Pomphrey, N.

    1994-01-01

    We have applied two computational models to calculate the poloidal flux linkage requirements for the current ramp-up and for the flattop phase of the proposed International Thermonuclear Experimental Reactor (ITER). For the current ramp-up phase, we have used the TSC code to simulate the entire current ramp-up period as described in the TAC-3 Physics Report. We have extended the time of the simulation to cover the full current penetration time, that is, until the loop voltage is a constant throughout the plasma. Sensitivity studies have been performed with respect to current ramp-up time, impurity concentration, and to the time of onset of auxiliary heating. We have also used a steady state plasma equilibrium code that has the constant loop voltage constraint built in to survey the dependence of the steady state loop-voltage on the density and temperature profiles. This calculation takes into account the plasma bootstrap current contribution, including non-circular and collisional corrections. The results can be displayed as contours of the loop-voltage on a POPCON like diagram.

  19. Thermonuclear dynamo inside ultracentrifuge with supersonic plasma flow stabilization

    NASA Astrophysics Data System (ADS)

    Winterberg, F.

    2016-01-01

    Einstein's general theory of relativity implies the existence of virtual negative masses in the rotational reference frame of an ultracentrifuge with the negative mass density of the same order of magnitude as the positive mass density of a neutron star. In an ultracentrifuge, the repulsive gravitational field of this negative mass can simulate the attractive positive mass of a mini-neutron star, and for this reason can radially confine a dense thermonuclear plasma placed inside the centrifuge, very much as the positive mass of a star confines its plasma by its own attractive gravitational field. If the centrifuge is placed in an externally magnetic field to act as the seed field of a magnetohydrodynamic generator, the configuration resembles a magnetar driven by the release of energy through nuclear fusion, accelerating the plasma to supersonic velocities, with the magnetic field produced by the thermomagnetic Nernst effect insulating the hot plasma from the cold wall of the centrifuge. Because of the supersonic flow and the high plasma density the configuration is stable.

  20. Thermonuclear dynamo inside ultracentrifuge with supersonic plasma flow stabilization

    SciTech Connect

    Winterberg, F.

    2016-01-15

    Einstein's general theory of relativity implies the existence of virtual negative masses in the rotational reference frame of an ultracentrifuge with the negative mass density of the same order of magnitude as the positive mass density of a neutron star. In an ultracentrifuge, the repulsive gravitational field of this negative mass can simulate the attractive positive mass of a mini-neutron star, and for this reason can radially confine a dense thermonuclear plasma placed inside the centrifuge, very much as the positive mass of a star confines its plasma by its own attractive gravitational field. If the centrifuge is placed in an externally magnetic field to act as the seed field of a magnetohydrodynamic generator, the configuration resembles a magnetar driven by the release of energy through nuclear fusion, accelerating the plasma to supersonic velocities, with the magnetic field produced by the thermomagnetic Nernst effect insulating the hot plasma from the cold wall of the centrifuge. Because of the supersonic flow and the high plasma density the configuration is stable.

  1. Divertor impurity monitor for the International Thermonuclear Experimental Reactor

    NASA Astrophysics Data System (ADS)

    Sugie, T.; Ogawa, H.; Nishitani, T.; Kasai, S.; Katsunuma, J.; Maruo, M.; Ebisawa, K.; Ando, T.; Kita, Y.

    1999-01-01

    The divertor impurity monitoring system of the International Thermonuclear Experimental Reactor has been designed. The main functions of this system are to identify impurity species and to measure the two-dimensional distributions of the particle influxes in the divertor plasmas. The wavelength range is 200-1000 nm. The viewing fans are realized by molybdenum mirrors located in the divertor cassette. With additional viewing fans seeing through the gap between the divertor cassettes, the region approximately from the divertor leg to the x point will be observed. The light from the divertor region passes through the quartz windows on the divertor port plug and the cryostat, and goes through the dog-leg optics in the biological shield. Three different type of spectrometers: (i) survey spectrometers for impurity species monitoring, (ii) filter spectrometers for the particle influx measurement with the spatial resolution of 10 mm and the time resolution of 1 ms, and (iii) high dispersion spectrometers for high resolution wavelength measurements are designed. These spectrometers are installed just behind the biological shield (for λ<450 nm) to prevent the transmission loss in fiber and in the diagnostic room (for λ⩾450 nm) from the point of view of accessibility and flexibility. The optics have been optimized by a ray trace analysis. As a result, 10-15 mm spatial resolution will be achieved in all regions of the divertor.

  2. Wideband Heterodyne QWIP Receiver Development for Thermonuclear Fusion Measurements

    SciTech Connect

    Bennett, C.A.; Buchanan, M.; Hutchinson, D.P.; Liu, H.C.; Richards, R.K.; Simpson, M.L.

    1998-11-01

    Oak Ridge National Laboratory (ORNL) has been developing heterodyne receivers for plasma diagnostic applications for over 20 years. One area of this work has been the development of a diagnostic system for the measurement of the energy of alpha particles created in a thermonuclear fusion reactor. These particles originate with an energy of 3.5 MeV and cool to the thermal energy of the plasma (around 15 keV) after several seconds. To measure the velocity distribution of these alpha particles, a Thomson scattering diagnostic is under development based on a high power CO{sub 2} laser at 10 microns with a heterodyne receiver. The Doppler shift generated by Thomson scattering of the alpha particles requires a wideband heterodyne receiver (greater than 10 GHz). Because Mercury-Cadimum-Telluride (MCT) detectors are limited to a bandwidth of approximately 2 GHz, a Quantum Well Infrared Photodetector (QWIP) detector was obtained from the National Research Council of Canada (NRC) and evaluated for its heterodyne performance using the heterodyne testing facility developed at ORNL.

  3. Detection of burning ashes from thermonuclear X-ray bursts

    NASA Astrophysics Data System (ADS)

    Kajava, J. J. E.; Nättilä, J.; Poutanen, J.; Cumming, A.; Suleimanov, V.; Kuulkers, E.

    2017-01-01

    When neutron stars (NS) accrete gas from low-mass binary companions, explosive nuclear burning reactions in the NS envelope fuse hydrogen and helium into heavier elements. The resulting thermonuclear (type-I) X-ray bursts produce energy spectra that are fit well with black bodies, but a significant number of burst observations show deviations from Planck spectra. Here we present our analysis of RXTE/PCA observations of X-ray bursts from the NS low-mass X-ray binary HETE J1900.1-2455. We have discovered that the non-Planckian spectra are caused by photoionization edges. The anticorrelation between the strength of the edges and the colour temperature suggests that the edges are produced by the nuclear burning ashes that have been transported upwards by convection and become exposed at the photosphere. The atmosphere model fits show that occasionally the photosphere can consist entirely of metals, and that the peculiar changes in blackbody temperature and radius can be attributed to the emergence and disappearance of metals in the photosphere. As the metals are detected already in the Eddington-limited phase, it is possible that a radiatively driven wind ejects some of the burning ashes into the interstellar space.

  4. Nucleosynthesis in type Ia supernovae driven by asymmetric thermonuclear ignition

    NASA Astrophysics Data System (ADS)

    Maeda, Keiichi

    2012-11-01

    Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf. They can be used as mature cosmological standardized candles, leading to the discovery of the accelerating expansion of the Universe. However, the explosion mechanism has not yet been fully clarified. In this paper, we first present nucleosynthetic features of a leading explosion scenario, namely a delayed-detonation scenario. Based on this, we propose a new and strong observational constraint on the explosion mechanism through emission lines from neutron-rich Fe-peaks. Especially, we show that an asymmetry in the explosion is likely a generic feature. We further argue that the diversity arising from various viewing angles can be an origin of observational diversities of SNe Ia seen in their spectral features (suspected possible biases in cosmology) and colors (related to the extinction estimate in cosmology). Using these new insights could open up a possibility of using SNe Ia as more precise distance indicators than currently employed.

  5. Focused Study of Thermonuclear Bursts on Neutron Stars

    NASA Astrophysics Data System (ADS)

    Chenevez, Jérôme

    2009-05-01

    X-ray bursters form a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion bursts likely eject nuclear burning ashes into the interstellar medium, and may make possible the detection of photoionization edges. Indeed, theoretical models predict that absorption edges from 58Fe at 9.2 keV, 60Zn and 62Zn at 12.2 keV should be detectable by the future missions Simbol-X and NuSTAR. A positive detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X-ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of the focusing X-ray telescopes may therefore make possible to differentiate between the potential interpretations of the X-ray bursts spectral features.

  6. Nucleosynthesis in type Ia supernovae driven by asymmetric thermonuclear ignition

    SciTech Connect

    Maeda, Keiichi

    2012-11-12

    Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf. They can be used as mature cosmological standardized candles, leading to the discovery of the accelerating expansion of the Universe. However, the explosion mechanism has not yet been fully clarified. In this paper, we first present nucleosynthetic features of a leading explosion scenario, namely a delayed-detonation scenario. Based on this, we propose a new and strong observational constraint on the explosion mechanism through emission lines from neutron-rich Fe-peaks. Especially, we show that an asymmetry in the explosion is likely a generic feature. We further argue that the diversity arising from various viewing angles can be an origin of observational diversities of SNe Ia seen in their spectral features (suspected possible biases in cosmology) and colors (related to the extinction estimate in cosmology). Using these new insights could open up a possibility of using SNe Ia as more precise distance indicators than currently employed.

  7. High energy components and collective modes in thermonuclear plasmas

    SciTech Connect

    Coppi, B.; Cowley, S.; Detragiache, P.; Kulsrud, R.; Pegoraro, F.

    1986-02-01

    The theory of a class of collective modes of a thermonuclear magnetically confined plasma, with frequencies in the range of the ion cyclotron frequency and of its harmonics, is presented. These modes can be excited by their resonant cyclotron interaction with a plasma component of relatively high energy particles characterized by a strongly anisotropic distribution in velocity space. Normal modes that are spatially localized by the inhomogeneity of the plasma density are found. This ensures that the energy gained by their resonant interaction is not convected away. The mode spatial localization can be significantly altered by the magnetic field inhomogeneity for a given class of plasma density profiles. Special attention is devoted to the case of a spin polarized plasma, where the charged products of fusion reactions are anisotropically distributed. We show that for the mode of polarization that enhances nuclear reaction rates the tritium will be rapidly depolarized to toroidal configurations with relatively mild gradients of the confining magnetic field. 18 refs., 9 figs.

  8. Thermonuclear processes on accreting neutron stars - A systematic study

    NASA Technical Reports Server (NTRS)

    Ayasli, S.; Joss, P. C.

    1982-01-01

    A series of model calculations for the evolution of the surface layers of an accreting neutron star is carried out. The neutron star mass, radius, core temperature, and surface magnetic field strength are systematically varied, as are the accretion rate onto the neutron star surface and the metallicity of the accreting matter, in order to determine the effects of these parameters on the properties of thermonuclear flashes in the surface layers and the emitted X-ray bursts that result from such flashes. The core temperatures required for thermal equilibrium are found to be approximately a factor of 2 lower than estimated in earlier work. Owing to the effects of the gravitational redshift, the emitted X-ray bursts have lower peak luminosities and longer durations than those calculated in the Newtonian approximation. The entrainment of hydrogen into helium flashes can cause the flashes to exhibit a rather wide range of observable effects and can decrease by a factor of more than 2 the ratio of persistent accretion-driven luminosity to time-averaged burst luminosity emitted by the neutron star.

  9. Optimized heavy ion beam probing for International Thermonuclear Experimental Reactor

    NASA Astrophysics Data System (ADS)

    Melnikov, A. V.; Eliseev, L. G.

    1999-01-01

    The international workgroup developed the conceptual design of a heavy ion beam probe (HIBP) diagnostics for International Thermonuclear Experimental Reactor (ITER), which is intended for measurements of the plasma potential profile in a gradient area. Now we optimized it by the accurate analysis of the probing trajectories and variation of positions of the injection and detection points. Optimization allows us to reduce the energy of Tl+ beam from 5.6 to 3.4 MeV for standard ITER regime. The detector line starting at the plasma edge towards the center can get an outer part of the horizontal radial potential profile by variation of the energy. The observed radial interval is slightly increased up to 0.76<ρ<1 with respect to initial version 0.8<ρ<1, that allows to cover the region of the density gradient more reliably. Almost double reduction of the beam energy is a critical point. Thus we can significantly decrease the sizes of the accelerator and energy analyzer, the cost of the equipment, and impact of the diagnostics to the machine. Therefore the optimized HIBP design can be realized in ITER.

  10. Study of runaway electrons with Hard X-ray spectrometry of tokamak plasmas

    SciTech Connect

    Shevelev, A.; Chugunov, I.; Khilkevitch, E.; Gin, D.; Doinikov, D.; Naidenov, V.; Kiptily, V.; Collaboration: EFDA-JET Contributors

    2014-08-21

    Hard-X-ray spectrometry is a tool widely used for diagnostic of runaway electrons in existing tokamaks. In future machines, ITER and DEMO, HXR spectrometry will be useful providing information on runaway electron energy, runaway beam current and its profile during disruption.

  11. Generation of runaway electron beams in high-pressure nitrogen

    NASA Astrophysics Data System (ADS)

    Tarasenko, V. F.; Burachenko, A. G.; Baksht, E. Kh

    2017-07-01

    In this paper the results of experimental studies of the amplitude-temporal characteristics of a runaway electron beam, as well as breakdown voltage in nitrogen are presented. The voltage pulses with the amplitude in incident wave ≈120 kV and the rise time of ≈0.3 ns was used. The supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. The amplitude-time characteristics of the voltage and SAEB current were studied with subnanosecond time resolution. The maximum pressure at which a SAEB is detectable by collector was ∼1 MPa. This pressure increases with decreasing the voltage rise time. The waveforms of the discharge and runaway electron beam currents was synchronized with the voltage pulses. The mechanism of the runaway electron generation in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

  12. Ecologically based family therapy outcome with substance abusing runaway adolescents.

    PubMed

    Slesnick, Natasha; Prestopnik, Jillian L

    2005-04-01

    Runaway youth report a broader range and higher severity of substance-related, mental health and family problems relative to non-runaway youth. Most studies to date have collected self-report data on the family and social history; virtually no research has examined treatment effectiveness with this population. This study is a treatment development project in which 124 runaway youth were randomly assigned to (1) ecologically based family therapy (EBFT) or (2) service as usual (SAU) through a shelter. Youth completed an intake, posttreatment, 6 and 12 months follow-up assessment. Youth assigned to EBFT reported greater reductions in overall substance abuse compared to youth assigned to SAU while other problem areas improved in both conditions. Findings suggest that EBFT is an efficacious intervention for this relatively severe population of youth.

  13. A search for X-rays from runaway stars

    NASA Technical Reports Server (NTRS)

    Kumar, C. K.; Kallman, T. R.; Thomas, R. J.

    1983-01-01

    Enhanced X-ray emission from an early-type runaway star would be direct evidence for the presence of a collapsed companion, and thus for its origin as the result of a supernova explosion in a massive binary. To test this idea, measurements of X-ray fluxes in the 0.5-3 keV energy range from nine O and B type runaway stars were made with the Einstein Observatory. In each case, the X-ray luminosity observed does not exceed that expected from a normal OB star. Therefore we conclude that, if the runaway stars have collapsed companions, the separations of the components must be much greater than those in normal OB binaries.

  14. Effects of Spatial Gradients on Electron Runaway Acceleration

    NASA Technical Reports Server (NTRS)

    MacNeice, Peter; Ljepojevic, N. N.

    1996-01-01

    The runaway process is known to accelerate electrons in many laboratory plasmas and has been suggested as an acceleration mechanism in some astrophysical plasmas, including solar flares. Current calculations of the electron velocity distributions resulting from the runaway process are greatly restricted because they impose spatial homogeneity on the distribution. We have computed runaway distributions which include consistent development of spatial gradients in the energetic tail. Our solution for the electron velocity distribution is presented as a function of distance along a finite length acceleration region, and is compared with the equivalent distribution for the infinitely long homogenous system (i.e., no spatial gradients), as considered in the existing literature. All these results are for the weak field regime. We also discuss the severe restrictiveness of this weak field assumption.

  15. Phase-space dynamics of runaway electrons in magnetic fields

    DOE PAGES

    Guo, Zehua; McDevitt, Christopher Joseph; Tang, Xian-Zhu

    2017-02-16

    Dynamics of runaway electrons in magnetic fields are governed by the competition of three dominant physics: parallel electric field acceleration, Coulomb collision, and synchrotron radiation. Examination of the energy and pitch-angle flows reveals that the presence of local vortex structure and global circulation is crucial to the saturation of primary runaway electrons. Models for the vortex structure, which has an O-point to X-point connection, and the bump of runaway electron distribution in energy space have been developed and compared against the simulation data. Lastly, identification of these velocity-space structures opens a new venue to re-examine the conventional understanding of runawaymore » electron dynamics in magnetic fields.« less

  16. Symbiotic variable V4018 Sgr in outburst

    NASA Astrophysics Data System (ADS)

    Elizabeth O. Waagen

    2012-09-01

    The symbiotic variable V4018 Sgr is undergoing an outburst, according to observations reported to the AAVSO and confirmed by spectroscopy by Ulisse Munari et al. Prompted by an observation and comment from John Bortle (Stormville, NY) (16 June 2012, visual magnitude 12.2) about a possible outburst, Steven O'Connor (St. George's, Bermuda) obtained an observation (10 August 2012, 11.44V) that confirmed V4018 Sgr was bright. His subsequent BVRI observations in September and visual observations by Bortle and Andrew Pearce (Nedlands, Western Australia) show the system brightening and at V magnitude 11.07 as of 2012 Sep. 17.091 UT. Ulisse Munari (INAF Astr. Obs. Padua, Italy) and colleagues Paolo Valisa and Sergio Dallaporta (ANS Collaboration), after being informed by the AAVSO of the bright state of V4018 Sgr, carried out spectroscopy. Munari writes: "A low resolution, absolutely fluxed 4000-8650 Ang spectrum of V4018 Sgr was obtained on Sept 13.90 UT with the 0.6m telescope ! of the Schiaparelli Observatory in Varese (Italy). It shows the spectrum of the M giant overwhelmed by a blue continuum up to 6000 Ang, and all high ionization emission lines typical of quiescence are gone, leaving only hydrogen Balmer and weak HeI lines in emission. The spectrum looks like a template one for a symbiotic star in outburst. CCD photometry was obtained on Sept 13.79 UT and provides V=11.027 ± 0.002, B-V=+0.621 ± 0.003. The B-V color is appreciably bluer and the V magnitude much brighter than typical in quiescence (on average V=13.3, B-V=+1.09; Henden and Munari 2008, Baltic Astronomy 17, 293), and support the idea V4018 Sgr is undergoing an outburst." According to Munari, the last bright outburst of V4018 Sgr was underway in June 1990. Observations in the AAVSO International Database from Albert Jones (Nelson, New Zealand) beginning in May 1992 show the variable at visual magnitude 11.0, with fluctuations between 10.5 and 11.9 through October 1995. Numerous ! other observers

  17. Magnetic field modification to the relativistic runaway electron avalanche length

    NASA Astrophysics Data System (ADS)

    Cramer, E. S.; Dwyer, J. R.; Rassoul, H. K.

    2016-11-01

    This paper explores the impact of the geomagnetic field on the relativistic runaway electron avalanche length, λe-. Coleman and Dwyer (2006) developed an analytical fit to Monte Carlo simulations using the Runaway Electron Avalanche Model. In this work, we repeat this process but with the addition of the geomagnetic field in the range of [100,900]/n μT, where n is the ratio of the density of air at altitude to the sea level density. As the ambient electric field approaches the runaway threshold field (Eth≈284 kV/m sea level equivalent), it is shown that the magnetic field has an impact on the orientation of the resulting electron beam. The runaway electrons initially follow the vertically oriented electric field but then are deflected in the v × B direction, and as such, the electrons experience more dynamic friction due to the increase in path length. This will be shown to result in a difference in the avalanche length from the case where B = 0. It will also be shown that the average energy of the runaway electrons will decrease while the required electric field to produce runaway electrons increases. This study is also important in understanding the physics of terrestrial gamma ray flashes (TGFs). Not only will this work impact relativistic feedback rates determined from simulations, it may also be useful in studying spectroscopy of TGFs observed from balloon and aircraft measurements. These models may also be used in determining beaming properties of TGFs originating in the tropical regions seen from orbiting spacecraft.

  18. Numerical characterization of bump formation in the runaway electron tail

    NASA Astrophysics Data System (ADS)

    Decker, J.; Hirvijoki, E.; Embreus, O.; Peysson, Y.; Stahl, A.; Pusztai, I.; Fülöp, T.

    2016-02-01

    Runaway electrons are generated in a magnetized plasma when the parallel electric field exceeds a critical value. For such electrons with energies typically reaching tens of MeV, the Abraham-Lorentz-Dirac (ALD) radiation force, in reaction to the synchrotron emission, is significant and can be the dominant process limiting electron acceleration. The effect of the ALD force on runaway electron dynamics in a homogeneous plasma is investigated using the relativistic finite-difference Fokker-Planck codes LUKE (Decker and Peysson 2004 Report EUR-CEA-FC-1736, Euratom-CEA), and CODE (Landreman et al 2014 Comput. Phys. Commun. 185 847). The time evolution of the distribution function is analyzed as a function of the relevant parameters: parallel electric field, background magnetic field, and effective charge. Under the action of the ALD force, we find that runaway electrons are subject to an energy limit, and that the electron distribution evolves towards a steady-state. In addition, a bump is formed in the tail of the electron distribution function if the electric field is sufficiently strong. The mechanisms leading to the bump formation and energy limit involve both the parallel and perpendicular momentum dynamics; they are described in detail. An estimate for the bump location in momentum space is derived. We observe that the energy of runaway electrons in the bump increases with the electric field amplitude, while the population increases with the bulk electron temperature. The presence of the bump divides the electron distribution into a runaway beam and a bulk population. This mechanism may give rise to beam-plasma types of instabilities that could, in turn, pump energy from runaway electrons and alter their confinement.

  19. Diffusion with varying drag: The runaway problem. II

    SciTech Connect

    Rollins, D.; Corngold, N.

    1987-02-01

    Diffusion driven by a constant field, and opposed by a velocity-dependent diffusion coefficient that decreases to zero at large velocity, leads to the phenomenon of ''runaway.'' It is studied here in the case of a one-dimensional velocity space, when the Fokker--Planck equation is equivalent to an interesting Schroedinger equation. The runaway current is extracted from the smallest eigenvalue, after the equation has been solved by the method of matched asymptotic expansions. There is discussion of connections between our approach, the conventional approach, and the classical two-dimensional results.

  20. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics.

    PubMed

    Cheon, MunSeong; Kim, Junghee

    2015-08-01

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  1. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics

    NASA Astrophysics Data System (ADS)

    Cheon, MunSeong; Kim, Junghee

    2015-08-01

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  2. An in situ runaway electron diagnostic for DIII-D.

    PubMed

    Wurden, G A; Oertel, J A; Evans, T E

    2014-11-01

    We are designing a new diagnostic based on laser inverse Compton scattering to study the dynamics of runaway electron formation during killer-pellet triggered disruptions in DIII-D, and their subsequent loss. We can improve the expected S/N ratio by using a high-intensity short-pulse laser combined with gated x-ray imagers. With 80 ps sampling, time-of-flight spatial resolution within the laser chord can be obtained. We will measure the time-resolved spatial profile and energy distribution of the runaway electrons while they are in the core of the tokamak plasma.

  3. Runaway domain wall and space-time varying α

    SciTech Connect

    Chiba, Takeshi; Yamaguchi, Masahide E-mail: gucci@phys.titech.ac.jp

    2011-03-01

    Recently spatial as well as temporal variations of the fine structure constant α have been reported. We show that a ''runaway domain wall{sup ,} which arises for the scalar field potential without minima, can account for such variations simultaneously. The time variation is induced by a runaway potential and the spatial variation is induced by the formation of a domain wall. The model is consistent with the current cosmological data and can be tested by the future experiments to test the equivalence principle.

  4. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics

    SciTech Connect

    Cheon, MunSeong Kim, Junghee

    2015-08-15

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  5. Accretion among preplanetary bodies: The many faces of runaway growth

    NASA Astrophysics Data System (ADS)

    Ormel, C. W.; Dullemond, C. P.; Spaans, M.

    2010-11-01

    When preplanetary bodies reach proportions of ˜1 km or larger in size, their accretion rate is enhanced due to gravitational focusing (GF). We have developed a new numerical model to calculate the collisional evolution of the gravitationally-enhanced growth stage. The numerical model is novel as it attempts to preserve the individual particle nature of the bodies (like N-body codes); yet it is statistical in nature since it must incorporate the very large number of planetesimals. We validate our approach against existing N-body and statistical codes. Using the numerical model, we explore the characteristics of the runaway growth and the oligarchic growth accretion phases starting from an initial population of single planetesimal radius R0. In models where the initial random velocity dispersion (as derived from their eccentricity) starts out below the escape speed of the planetesimal bodies, the system experiences runaway growth. We associate the initial runaway growth phase with increasing GF-factors for the largest body. We find that during the runaway growth phase the size distribution remains continuous but evolves into a power-law at the high-mass end, consistent with previous studies. Furthermore, we find that the largest body accretes from all mass bins; a simple two-component approximation is inapplicable during this stage. However, with growth the runaway body stirs up the random motions of the planetesimal population from which it is accreting. Ultimately, this feedback stops the fast growth and the system passes into oligarchy, where competitor bodies from neighboring zones catch up in terms of mass. We identify the peak of GF with the transition between the runaway growth and oligarchy accretion stages. Compared to previous estimates, we find that the system leaves the runaway growth phase at a somewhat larger radius, especially at the outer disk. Furthermore, we assess the relevance of small, single-size fragments on the growth process. In classical

  6. An in situ runaway electron diagnostic for DIII-D

    SciTech Connect

    Wurden, G. A. Oertel, J. A.; Evans, T. E.

    2014-11-15

    We are designing a new diagnostic based on laser inverse Compton scattering to study the dynamics of runaway electron formation during killer-pellet triggered disruptions in DIII-D, and their subsequent loss. We can improve the expected S/N ratio by using a high-intensity short-pulse laser combined with gated x-ray imagers. With 80 ps sampling, time-of-flight spatial resolution within the laser chord can be obtained. We will measure the time-resolved spatial profile and energy distribution of the runaway electrons while they are in the core of the tokamak plasma.

  7. PS1-1000305 an AGN outburst?

    NASA Astrophysics Data System (ADS)

    Drake, A. J.; Mahabal, A. A.; Djorgovski, S. G.; Graham, M. J.; Williams, R.; Prieto, J.; Catelan, M.; Christensen, E.; Beshore, E. C.; Larson, S. M.

    2010-07-01

    Kankare et al. (2010, ATel#2716) recently reported the discovery of an AGN outburst (PS1-1000305) detected in PS1 taken data on May 19.3 UT. The redshift of the AGN is given by Kankare et al. as z=0.77 with the host galaxy SDSS J152844.16+425722.5. We have extracted the five year archival CSS/CRTS lightcurve at the location of PS1-1000305.

  8. The spectral evolution of dwarf nova outbursts

    NASA Technical Reports Server (NTRS)

    Cannizzo, John K.; Kenyon, Scott J.

    1987-01-01

    The disk instability model for dwarf nova eruptions is investigated by computing the spectral development of the accretion disk through a complete limit cycle. Observed stellar spectra are used to model the radiation emitted by optically thick annuli within the disc. The general findings agree with those of Smak (1984) and Pringle et al. (1986). It is suggested that the 'dwarf nova oscillations' might be a source of information concerning the evolution of the inner disk and that detailed observations of this phenomenon can be used to test various outburst mechanisms.

  9. MCNeil's Nebula in Orion: The Outburst History

    NASA Astrophysics Data System (ADS)

    Briceño, C.; Vivas, A. K.; Hernández, J.; Calvet, N.; Hartmann, L.; Megeath, T.; Berlind, P.; Calkins, M.; Hoyer, S.

    2004-05-01

    We present a sequence of I-band images obtained at the Venezuela 1 m Schmidt telescope during the outburst of the nebula recently discovered by J. W. McNeil in the Orion L1630 molecular cloud. We derive photometry spanning the preoutburst state and the brightening itself, which is a unique record including 14 epochs and spanning a timescale of ~5 years. We constrain the beginning of the outburst at some time between 2003 October 28 and November 15. The light curve of the object at the vertex of the nebula, the likely exciting source of the outburst, reveals that it has brightened ~5 mag in about 4 months. The timescale for the nebula to develop is consistent with the light-travel time, indicating that we are observing light from the central source scattered by the ambient cloud into the line of sight. We also show recent FLWO optical spectroscopy of the exciting source and of the nearby HH 22. The spectrum of the source is highly reddened; in contrast, the spectrum of HH 22 shows a shock spectrum superposed on a continuum, most likely the result of reflected light from the exciting source reaching the HH object through a much less reddened path. The blue portion of this spectrum is consistent with an early B spectral type, similar to the early outburst spectrum of the FU Orionis variable star V1057 Cygni; we estimate a luminosity of L~219 Lsolar. The eruptive behavior of McNeil's Nebula, its spectroscopic characteristics and luminosity, suggest that we may be witnessing an FU Ori event on its way to maximum. By further monitoring this object, we will be able decide whether or not it qualifies as a member of this rare class of objects. Based on observations obtained at the Llano del Hato National Astronomical Observatory of Venezuela, operated by CIDA for the Ministerio de Ciencia y Tecnología, and at the Fred Lawrence Whipple Observatory (FLWO) of the Smithsonian Institution.

  10. Classification and spectral evolution of outbursts of Aql X-1

    NASA Astrophysics Data System (ADS)

    Güngör, Can; Güver, Tolga; Ekşi, K. Yavuz

    2014-04-01

    We present a broad classification of all outbursts detected with the All-Sky Monitor on the Rossi X-Ray Timing Explorer (RXTE) and the Monitor of All Sky X-Ray Image (MAXI) of Aql X-1. We identify three types of outbursts: long high, medium low and short low, based on the duration and maximum flux. We analyse the trends in the `phase space' of flux derivative versus flux to demonstrate the differences in the three identified outburst types. We present a spectral analysis of the observations of Aql X-1 performed by the Proportional Counter Array on board RXTE during the 2000 and 2011 outbursts of the long high class and the 2010 outburst of the medium low class. We model the source spectrum with a hybrid thermal/non-thermal hot plasma emission model (EQPAIR in XSPEC) together with a Gaussian component to model the Fe Kα emission line. We construct time histories of the source flux, the optical depth of the corona (τ), the seed photon temperature (kTbb) and the hard state compactness (lh) for these three outbursts. We show that the physical parameters of either classes reach the same values throughout the outbursts, the only difference being the maximum flux. We discuss our results in the terms of modes of interaction of the star with the disc and the size of the disc kept hot by irradiation. We conclude that irradiation is the dominant physical process leading to the different classes of outbursts.

  11. A New Outburst of the Yellow Hypergiant Star ρ Cas

    NASA Astrophysics Data System (ADS)

    Aret, A.; Kraus, M.; Kolka, I.; Maravelias, G.

    2017-02-01

    Spectroscopic monitoring of the yellow hypergiant ρ Cas revealed a new outburst in 2013, which is obvious from the development of TiO bands in the spectra. Also many atmospheric lines characteristic of a later spectral type appear. This spectroscopic outburst is in agreement with the photometric light curve, which displays a drop by about 0.6 mag during the same period.

  12. The Impact of FU Orionis Outbursts and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Bell, Robbins; Young, Richard E. (Technical Monitor)

    1998-01-01

    Protostellar systems are variable on many timescales. One of the most dramatic forms of variability known to occur in low mass stellar systems is the FU Orionis outburst (Herbig 1977). Throughout a typical outburst lasting several decades, system luminosities may be a hundred times what is typical of the quiesent state. FU Orionis outburst events are thought to have significant impact on the thermal structure of the protosolar nebula; their existence has been used to explain features in the meteoritic record from thermally induced homogenization to the formation of chondrules. Until recently, the magnitude of the likely effect from such outbursts has been largely speculative due to the lack of a detailed understanding of the outburst mechanism. Recent numerical models (Bell\\& Lin 1994) have demonstrated the viability of the observational hypothesis (Hartmann\\& Kenyon 1985) that the radiation observed during outburst is emitted by a luminous circumstellar disk transporting mass at a thousand times the quiesent rate. Light curves and color and line width evolution observed in FU Orionis systems are naturally explained by time dependent outbursting model disks (Bell et al. 1995). The radial temperature structure and shape of the disk during outburst derived from these models may be used to calculate the outburst's expected impact on primitive material at various radii throughout the disk. In this review, we will begin by discussing what is known about the FU Orionis outburst phenomenon from recent observations and theory including statistically deduced outburst timescales and observed peak temperatures. Unless covered by another author, we will discuss the evidence which suggests that outburst radiation is emitted by a circumstellar disk rather than by the star and will briefly review the thermal instability as a mechanism for outburst. We will then report on recent work which investigates the likely heating of solar nebula material due to FU Orionis outbursts

  13. The Impact of FU Orionis Outbursts and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Bell, Robbins; Young, Richard E. (Technical Monitor)

    1998-01-01

    Protostellar systems are variable on many timescales. One of the most dramatic forms of variability known to occur in low mass stellar systems is the FU Orionis outburst (Herbig 1977). Throughout a typical outburst lasting several decades, system luminosities may be a hundred times what is typical of the quiesent state. FU Orionis outburst events are thought to have significant impact on the thermal structure of the protosolar nebula; their existence has been used to explain features in the meteoritic record from thermally induced homogenization to the formation of chondrules. Until recently, the magnitude of the likely effect from such outbursts has been largely speculative due to the lack of a detailed understanding of the outburst mechanism. Recent numerical models (Bell\\& Lin 1994) have demonstrated the viability of the observational hypothesis (Hartmann\\& Kenyon 1985) that the radiation observed during outburst is emitted by a luminous circumstellar disk transporting mass at a thousand times the quiesent rate. Light curves and color and line width evolution observed in FU Orionis systems are naturally explained by time dependent outbursting model disks (Bell et al. 1995). The radial temperature structure and shape of the disk during outburst derived from these models may be used to calculate the outburst's expected impact on primitive material at various radii throughout the disk. In this review, we will begin by discussing what is known about the FU Orionis outburst phenomenon from recent observations and theory including statistically deduced outburst timescales and observed peak temperatures. Unless covered by another author, we will discuss the evidence which suggests that outburst radiation is emitted by a circumstellar disk rather than by the star and will briefly review the thermal instability as a mechanism for outburst. We will then report on recent work which investigates the likely heating of solar nebula material due to FU Orionis outbursts

  14. Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion

    NASA Astrophysics Data System (ADS)

    Nigmatulin, Robert I.; Akhatov, Iskander Sh.; Topolnikov, Andrey S.; Bolotnova, Raisa Kh.; Vakhitova, Nailya K.; Lahey, Richard T.; Taleyarkhan, Rusi P.

    2005-10-01

    This paper provides the theoretical basis for energetic vapor bubble implosions induced by a standing acoustic wave. Its primary goal is to describe, explain, and demonstrate the plausibility of the experimental observations by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] of thermonuclear fusion for imploding cavitation bubbles in chilled deuterated acetone. A detailed description and analysis of these data, including a resolution of the criticisms that have been raised, together with some preliminary HYDRO code simulations, has been given by Nigmatulin et al. [Vestnik ANRB (Ufa, Russia) 4, 3 (2002); J. Power Energy 218-A, 345 (2004)] and Lahey et al. [Adv. Heat Transfer (to be published)]. In this paper a hydrodynamic shock (i.e., HYDRO) code model of the spherically symmetric motion for a vapor bubble in an acoustically forced liquid is presented. This model describes cavitation bubble cluster growth during the expansion period, followed by a violent implosion during the compression period of the acoustic cycle. There are two stages of the bubble dynamics process. The first, low Mach number stage, comprises almost all the time of the acoustic cycle. During this stage, the radial velocities are much less than the sound speeds in the vapor and liquid, the vapor pressure is very close to uniform, and the liquid is practically incompressible. This process is characterized by the inertia of the liquid, heat conduction, and the evaporation or condensation of the vapor. The second, very short, high Mach number stage is when the radial velocities are the same order, or higher, than the sound speeds in the vapor and liquid. In this stage high temperatures, pressures, and densities of the vapor and liquid take place. The model presented herein has realistic equations of state for the compressible liquid and vapor phases, and accounts for nonequilibrium evaporation/condensation kinetics at the liquid/vapor interface. There are interacting

  15. Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion

    SciTech Connect

    Nigmatulin, Robert I.; Akhatov, Iskander Sh.; Topolnikov, Andrey S.; Bolotnova, Raisa Kh.; Vakhitova, Nailya K.; Lahey, Richard T. Jr.; Taleyarkhan, Rusi P.

    2005-10-01

    This paper provides the theoretical basis for energetic vapor bubble implosions induced by a standing acoustic wave. Its primary goal is to describe, explain, and demonstrate the plausibility of the experimental observations by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] of thermonuclear fusion for imploding cavitation bubbles in chilled deuterated acetone. A detailed description and analysis of these data, including a resolution of the criticisms that have been raised, together with some preliminary HYDRO code simulations, has been given by Nigmatulin et al. [Vestnik ANRB (Ufa, Russia) 4, 3 (2002); J. Power Energy 218-A, 345 (2004)] and Lahey et al. [Adv. Heat Transfer (to be published)]. In this paper a hydrodynamic shock (i.e., HYDRO) code model of the spherically symmetric motion for a vapor bubble in an acoustically forced liquid is presented. This model describes cavitation bubble cluster growth during the expansion period, followed by a violent implosion during the compression period of the acoustic cycle. There are two stages of the bubble dynamics process. The first, low Mach number stage, comprises almost all the time of the acoustic cycle. During this stage, the radial velocities are much less than the sound speeds in the vapor and liquid, the vapor pressure is very close to uniform, and the liquid is practically incompressible. This process is characterized by the inertia of the liquid, heat conduction, and the evaporation or condensation of the vapor. The second, very short, high Mach number stage is when the radial velocities are the same order, or higher, than the sound speeds in the vapor and liquid. In this stage high temperatures, pressures, and densities of the vapor and liquid take place. The model presented herein has realistic equations of state for the compressible liquid and vapor phases, and accounts for nonequilibrium evaporation/condensation kinetics at the liquid/vapor interface. There are interacting

  16. Soft x-ray emission from classical novae in outburst

    SciTech Connect

    Starrfield, S. Arizona State Univ., Tempe, AZ . Dept. of Physics and Astronomy); Truran, J.W. . Dept. of Astronomy); Sparks, W.M. ); Krautter, J. ); MacDonald, J. . Dept. of Physics and Ast

    1989-01-01

    Theoretical modeling of novae in outburst predicts that they should be active emitters of radiation at soft x-ray wavelengths twice during their outburst. The first time occurs very early in the outburst when only a very sensitive all sky survey will be able to detect them. This period lasts only a few hours for the very fastest novae. They again become bright in x-rays late in the outburst when the remnant object becomes very hot and is still luminous. Both simulations and observations show that novae can remain very hot for months to years. It is important to observe them at these late times because a measurement both of the flux and temperature can provide information about the mass of the white dwarf, the turn-off time scale, and the energy budget of the outburst. 8 refs., 2 figs.

  17. The 1987 outburst of the BL Lacertid AO 0235 + 164

    NASA Astrophysics Data System (ADS)

    Webb, J. R.; Smith, A. G.

    1989-08-01

    The violently variable BL Lacertid AO 0235 + 164 displayed a 3.24 magnitude outburst in early 1987. This outburst was observed intensively from Rosemary Hill Observatory in three colors. Long term monitoring observations made at Rosemary Hill are examined in an effort to find any recurring timescales associated with this outburst and previous large amplitude outbursts. The energetics of the 1987 outburst are analyzed in terms of the Shields and Wheeler model of a magnetized accretion disk. The timescales identified in the power spectrum (2.8 and 1.6 yr) are input into the model as the storage timescales. Since the emitted energy calculated from the optical burst cannot be stored in a magnetized disk at an allowable radius, it is concluded that either the storage timescales are longer than those identified in the power spectrum, or relativistic beaming effects must be considered, with a Doppler factor of 1.3 to 1.6.

  18. On the origin of the HLX-1 outbursts

    NASA Astrophysics Data System (ADS)

    Sun, Mouyuan; Gu, Wei-Min; Yan, Zhen; Wu, Qingwen; Liu, Tong

    2016-11-01

    HLX-1, currently the best intermediate-mass black hole candidate, has undergone seven violent outbursts, each with a peak X-ray luminosity of Lpeak,X ˜ 1042 erg s-1. Interestingly, the properties of the HLX-1 outbursts evolve with time. In this work, we aim to constrain the physical parameters of the central engine of the HLX-1 outbursts in the framework of the black hole accretion. We find that the physical properties of the HLX-1 outbursts are consistent with being driven by the radiation pressure instability. This scenario can explain the evolution of the recurrent time-scales of the HLX-1 outbursts as a function of the durations.

  19. SUPER-EDDINGTON FLUXES DURING THERMONUCLEAR X-RAY BURSTS

    SciTech Connect

    Boutloukos, Stratos; Miller, M. Coleman; Lamb, Frederick K.

    2010-09-01

    It has been known for nearly three decades that the energy spectra of thermonuclear X-ray bursts are often well fit by Planck functions with temperatures so high that they imply a super-Eddington radiative flux at the emitting surface, even during portions of bursts when there is no evidence of photospheric radius expansion. This apparent inconsistency is usually set aside by assuming that the flux is actually sub-Eddington and that the fitted temperature is so high because the spectrum has been distorted by the energy-dependent opacity of the atmosphere. Here we show that the spectra predicted by currently available conventional atmosphere models appear incompatible with the highest precision measurements of burst spectra made using the Rossi X-ray Timing Explorer, such as during the 4U 1820-30 superburst and a long burst from GX 17+2. In contrast, these measurements are well fit by Bose-Einstein spectra with high temperatures and modest chemical potentials. Such spectra are very similar to Planck spectra. They imply surface radiative fluxes more than a factor of 3 larger than the Eddington flux. We find that segments of many other bursts from many sources are well fit by similar Bose-Einstein spectra, suggesting that the radiative flux at the emitting surface also exceeds the Eddington flux during these segments. We suggest that burst spectra can closely approximate Bose-Einstein spectra and have fluxes that exceed the Eddington flux because they are formed by Comptonization in an extended, low-density radiating gas supported by the outward radiation force and confined by a tangled magnetic field.

  20. Spontaneous Formation of Detonations by Turbulent Flames in Thermonuclear Supernovae

    NASA Astrophysics Data System (ADS)

    Poludnenko, Alexei Y.; Oran, E. S.

    2012-01-01

    Presently, the scenario best capable of explaining the observational properties of "normal" type Ia supernovae (SNIa), which are of primary importance for cosmology, is the delayed-detonation model. This model postulates that a subsonic thermonuclear deflagration, which originates close to the center of a Chandrasekhar-mass white dwarf (WD) in a single-degenerate binary system, transitions to a supersonic detonation (deflagration-to-detonation transition, or DDT) during the later stages of the explosion. Modern large-scale multidimensional simulations of SNIa cannot capture the DDT process and, thus, are forced to make two crucial assumptions, namely (a) that DDT does occur at some point, and (b) when and where it occurs. Significant progress has been made over the years in elucidating the nature of DDT in terrestrial confined systems with walls, obstacles, or pre-existing shocks. It remains unclear, however, whether and how a detonation can form in an unpressurized, unconfined system such as the interior of a WD. Here we show, through first-principles numerical simulations, that sufficiently fast, but subsonic, turbulent flames in such unconfined environments are inherently susceptible to DDT. The associated mechanism is based on the unsteady evolution of turbulent flames faster than the Chapman-Jouguet deflagrations and is qualitatively different from the traditionally suggested gradient (spontaneous reaction wave) model. It also does not require the formation of distributed flames. The proposed mechanism predicts the DDT density in SNIa to be 107 g/cm3, in agreement with the values previously found to give the best match with observations. This DDT mechanism opens the possibility for eliminating the transition density as a free parameter and, thus, for developing fully self-consistent global multidimensional SNIa models. This work was supported in part by the Naval Research Laboratory, the Air Force Office of Scientific Research, and by the Department of Defense

  1. 45 CFR 1351.10 - What is the purpose of the Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 45 Public Welfare 4 2010-10-01 2010-10-01 false What is the purpose of the Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.10 What is the purpose of the Runaway and Homeless...

  2. 45 CFR 1351.18 - What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... which Runaway and Homeless Youth Program grant applications to fund? 1351.18 Section 1351.18 Public... SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.18 What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant applications...

  3. 45 CFR 1351.17 - How is application made for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 4 2012-10-01 2012-10-01 false How is application made for a Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.17 How is application made for a Runaway and...

  4. 45 CFR 1351.18 - What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... which Runaway and Homeless Youth Program grant applications to fund? 1351.18 Section 1351.18 Public... SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.18 What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant applications...

  5. 45 CFR 1351.18 - What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... which Runaway and Homeless Youth Program grant applications to fund? 1351.18 Section 1351.18 Public... SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.18 What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant applications...

  6. 45 CFR 1351.18 - What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... which Runaway and Homeless Youth Program grant applications to fund? 1351.18 Section 1351.18 Public... SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.18 What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant applications...

  7. 45 CFR 1351.17 - How is application made for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 45 Public Welfare 4 2014-10-01 2014-10-01 false How is application made for a Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.17 How is application made for a Runaway and...

  8. 45 CFR 1351.17 - How is application made for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 45 Public Welfare 4 2010-10-01 2010-10-01 false How is application made for a Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.17 How is application made for a Runaway and...

  9. 45 CFR 1351.18 - What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... which Runaway and Homeless Youth Program grant applications to fund? 1351.18 Section 1351.18 Public... SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.18 What criteria has HHS established for deciding which Runaway and Homeless Youth Program grant applications...

  10. 45 CFR 1351.10 - What is the purpose of the Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 4 2012-10-01 2012-10-01 false What is the purpose of the Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.10 What is the purpose of the Runaway and Homeless...

  11. 45 CFR 1351.17 - How is application made for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 45 Public Welfare 4 2013-10-01 2013-10-01 false How is application made for a Runaway and Homeless... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.17 How is application made for a Runaway and...

  12. Temporal and spectral evolution of runaway electron bursts in TEXTOR disruptions

    SciTech Connect

    Forster, M.; Finken, K. H.; Kudyakov, T.; Willi, O.; Lehnen, M.; Xu, Y.; Zeng, L.; Collaboration: TEXTOR Team

    2012-09-15

    Novel observations of the burst-like runaway electron losses in tokamak disruptions are reported. The runaway bursts are temporally resolved and first-time measurements of the corresponding runaway energy spectra are presented. A characteristic shape and burst to burst changes of the spectra are found. The runaway energy content of the disruptions and the conversion of the predisruptive magnetic energy are estimated. The radial decay of the runaways can be approximated by an exponential distribution. Deriving from the measurements, resistive tearing modes or kink modes are suggested to trigger the formation of the bursts.

  13. Study of the generation and suppression of runaway currents in provoked disruptions in J-TEXT

    NASA Astrophysics Data System (ADS)

    Chen, Z. Y.; Chen, Z. P.; Zhang, Y.; Jin, W.; Fang, D.; Ba, W. G.; Wang, Z. J.; Zhang, M.; Yang, Z. J.; Ding, Y. H.; Zhuang, G.; J-TEXT Team

    2012-05-01

    Runaway currents following disruptions have an important effect on the first wall for the next generation tokamak. The behaviors of runaway currents following intentional provoked disruptions have been investigated in the J-TEXT tokamak. It is found that the runaway current generation following provoked disruptions depends on both the toroidal magnetic field and the plasma current. The conversion efficiency of pre-disruptive plasma currents into runaway currents is in the ranges of 30% to 60% in J-TEXT. The runaway currents can be avoided by the intensive gas puffing of H2 due to the low multiplication factor in J-TEXT.

  14. Simulation of runaway electrons, transport affected by J-TEXT resonant magnetic perturbation

    NASA Astrophysics Data System (ADS)

    Jiang, Z. H.; Wang, X. H.; Chen, Z. Y.; Huang, D. W.; Sun, X. F.; Xu, T.; Zhuang, G.

    2016-09-01

    The topology of a magnetic field and transport properties of runaway electrons can be changed by a resonant magnetic perturbation field. The J-TEXT magnetic topology can be effectively altered via static resonant magnetic perturbation (SRMP) and dynamic resonant magnetic perturbation (DRMP). This paper studies the effect of resonant magnetic perturbation (RMP) on the confinement of runaway electrons via simulating their drift orbits in the magnetic perturbation field and calculating the orbit losses for different runaway initial energies and different runaway electrons, initial locations. The model adopted is based on Hamiltonian guiding center equations for runaway electrons, and the J-TEXT magnetic turbulences and RMP are taken into account. The simulation indicates that the loss rate of runaway electrons is sensitive to the radial position of electrons. The loss of energetic runaway beam is dominated by the shrinkage of the confinement region. Outside the shrinkage region of the runaway electrons are lost rapidly. Inside the shrinkage region the runaway beam is confined very well and is less sensitive to the magnetic perturbation. The experimental result on the response of runaway transport to the application RMP indicates that the loss of runaway electrons is dominated by the shrinkage of the confinement region, other than the external magnetic perturbation.

  15. Experimental study of the runaway current in the J-TEXT Tokamak

    NASA Astrophysics Data System (ADS)

    Luo, Y. H.; Chen, Z. Y.; Zhang, X. Q.; Huang, D. W.; Jin, W.; Huang, Y. H.; Tang, Y.; Li, J. C.; Tong, R. H.; Yan, W.; Zhuang, G.

    2014-02-01

    Major plasma disruptions in tokamaks often generate runaway currents, which contain electrons with energies of several tens of megaelectron-volts (MeV). These currents can cause substantial damage when control is lost and the current hits the limiters or the vessel wall. The interaction between the runaway electrons and the impurities inside the plasma results in soft X-ray emission, which can provide detailed information about the runaway generation process and the confinement of runaway electrons. A vertical soft X-ray array at the top of Joint Texas Experimental Tokamak (J-TEXT) was used to study the runaway beams resulting from major disruptions. Runaway electron production and confinement of runaway current were observed by using soft X-ray images.

  16. Progress in Modeling Classical Nova Outbursts

    NASA Astrophysics Data System (ADS)

    Calder, A. C.; Alexakis, A.; Dursi, L. J.; Mignone, A.; Timmes, F. X.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Brown, E.; Fryxell, B.; Zingale, M.; Ricker, P.; Olson, K.

    2003-03-01

    We report on progress in modeling many facets of Classical Novae. These include magnetohydrodynamical simulations of the accretion phase (for the case of magnetic white dwarfs) and hydrodynamical simulations of the mixing of white dwarf material into the hydrogen-rich envelope by resonant gravity wave breaking at the surface of the white dwarf (See also Alexakis, et al.). We also report on initial efforts at the development of a sub-grid enrichment model based on these results as well as results of one-dimensional simulations with mixing length convection of the enrichment process exploring the long-term behavior of the enriched region. Finally, we present two-dimensional simulations of the onset and development of convection in nova precursor models and during the runaway. This work was supported by the DOE ASCI/Alliances program at the University of Chicago under grant No. B341495.

  17. Dual and Multiple Diagnosis Among Substance Using Runaway Youth#

    PubMed Central

    Slesnick, Natasha; Prestopnik, Jillian

    2008-01-01

    Although research on runaway and homeless youth is increasing, relatively little is known about the diagnostic profile of runaway adolescents. The current study examined patterns of psychiatric dual and multiple diagnosis among a sample (N = 226) of treatment-engaged substance-abusing youth (ages 13 to 17) who were residing at a runaway shelter. As part of a larger treatment outcome study, the youths’ psychiatric status was assessed using the DSM-IV based computerized diagnostic interview schedule for children [CDISC; (1)]. The majority of the youth in our sample met criteria for dual or multiple diagnosis (60%) with many having more than one substance-use diagnosis (56%). The severity of mental-health and substance-use problems in this sample of substance-abusing runaways suggests the need for continued development of comprehensive services. The range and intensity of diagnoses seen indicates a need for greater focus on treatment development and strategies to address their multiple areas of risk. PMID:15768577

  18. Theory of runaway current sustainment by lower-hybrid waves

    SciTech Connect

    Liu, C.S.; Chan, V.S.; Bhadra, D.K.; Harvey, R.W.

    1982-05-24

    A mechanism is proposed whereby high--phase-velocity lower-hybrid waves can interact with lower--parallel-velocity electrons through nonlinearly excited plasma waves. Significant steady-state current can be sustained by the rf after the Ohmic field is turned off in a tokamak provided the initial electron distribution is in the runaway regime with density below a critical value.

  19. Successful Transitions of Runaway/Homeless Youth from Shelter Care

    ERIC Educational Resources Information Center

    Nebbitt, Von E.; House, Laura E.; Thompson, Sanna J.; Pollio, David E.

    2007-01-01

    Previous research indicates that runaway and homeless youth often achieve positive outcomes after shelter stays however few studies have examined how these outcomes are achieved. This study employs qualitative methods to explicate this phenomenon. Twenty-five providers and 21 youth from four shelters participated in this study. Youth were…

  20. Low Simulated Radiation Limit for Runaway Greenhouse Climates

    NASA Technical Reports Server (NTRS)

    Goldblatt, Colin; Robinson, Tyler D.; Zahnle, Kevin J.; Crisp, David

    2013-01-01

    Terrestrial planet atmospheres must be in long-term radiation balance, with solar radiation absorbed matched by thermal radiation emitted. For hot moist atmospheres, however, there is an upper limit on the thermal emission which is decoupled from the surface temperature. If net absorbed solar radiation exceeds this limit the planet will heat uncontrollably, the so-called \\runaway greenhouse". Here we show that a runaway greenhouse induced steam atmosphere may be a stable state for a planet with the same amount of incident solar radiation as Earth has today, contrary to previous results. We have calculated the clear-sky radiation limits at line-by-line spectral resolution for the first time. The thermal radiation limit is lower than previously reported (282 W/sq m rather than 310W/sq m) and much more solar radiation would be absorbed (294W/sq m rather than 222W/sq m). Avoiding a runaway greenhouse under the present solar constant requires that the atmosphere is subsaturated with water, and that cloud albedo forcing exceeds cloud greenhouse forcing. Greenhouse warming could in theory trigger a runaway greenhouse but palaeoclimate comparisons suggest that foreseeable increases in greenhouse gases will be insufficient to do this.

  1. Conditions for electron runaway under leader breakdown of long gaps

    SciTech Connect

    Ul'yanov, K. N.

    2008-04-15

    An original hydrodynamic model in which inelastic collisions in the equations of motion and energy balance play a decisive role is developed and applied to simulate electron avalanches in strong electric fields. The mean energy and drift velocity of electrons, as well as the ionization coefficient and electric field in a wide range of mean electron energies, are determined for helium and xenon. A criterion is derived for the runaway of the average electron in discharges with ionization multiplication. It is shown that runaway can take place at any value of E/p, provided that the momentum mean free path exceeds the gap length. The voltage corresponding to electron runaway is found for helium, xenon, and air as a function of the electric field, the electron mean energy, and the parameter pd. Conditions for the formation of a precursor in electronegative gases are analyzed. It is shown that the presence of a precursor with a high electric conductance is necessary for the formation of a new leader step. The voltage and time ranges corresponding to efficient electron runaway and X-ray generation during leader breakdown in air are determined.

  2. Runaway House: A Youth-Run Service Project.

    ERIC Educational Resources Information Center

    Butler, Dodie; And Others

    This booklet describes Special Approaches in Juvenile Assistance (SAJA), a nonprofit corporation that consists of: (1) the Runaway House, a temporary shelter and counseling program for people under the age of 18 who have run away from home; (2) two foster group homes in which the workers and young people share responsibility for cooking, cleaning…

  3. Gang Involvement and Membership among Homeless and Runaway Youth.

    ERIC Educational Resources Information Center

    Yoder, Kevin A.; Whitbeck, Les B.; Hoyt, Dan R.

    2003-01-01

    Assessed the extent of gang involvement among homeless and runaway youth, comparing gang members, gang-involved youth (not members), and non-gang youth on several dimensions. Interview data indicated that 15.4 percent of the youth were gang members and 32.2 percent were involved in gangs. These youth reported more family problems and school…

  4. Successful Transitions of Runaway/Homeless Youth from Shelter Care

    ERIC Educational Resources Information Center

    Nebbitt, Von E.; House, Laura E.; Thompson, Sanna J.; Pollio, David E.

    2007-01-01

    Previous research indicates that runaway and homeless youth often achieve positive outcomes after shelter stays however few studies have examined how these outcomes are achieved. This study employs qualitative methods to explicate this phenomenon. Twenty-five providers and 21 youth from four shelters participated in this study. Youth were…

  5. Experiential Therapy with Homeless, Runaway and Street Youth.

    ERIC Educational Resources Information Center

    Kallander, Karin; Levings, Laura

    This paper describes the services and activities of the Orion Center, a drop-in day-use facility for homeless and runaway youth in Seattle (Washington). Orion Center uses experiential therapy and adventure-based activities to develop trust, promote fun and relationship building, and facilitate growth and healing among this homeless population. A…

  6. Gang Involvement and Membership among Homeless and Runaway Youth.

    ERIC Educational Resources Information Center

    Yoder, Kevin A.; Whitbeck, Les B.; Hoyt, Dan R.

    2003-01-01

    Assessed the extent of gang involvement among homeless and runaway youth, comparing gang members, gang-involved youth (not members), and non-gang youth on several dimensions. Interview data indicated that 15.4 percent of the youth were gang members and 32.2 percent were involved in gangs. These youth reported more family problems and school…

  7. Runaway electrons and mitigation studies in MST tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Goetz, J. A.; Chapman, B. E.; Almagri, A. F.; Cornille, B. S.; Dubois, A.; McCollam, K. J.; Munaretto, S.; Sovinec, C. R.

    2016-10-01

    Studies of runaway electrons generated in low-density MST tokamak plasmas are being undertaken. The plasmas have Bt <= 0.14 T, Ip <= 50 kA, q (a) = 2.2 , and an electron density and temperature of about 5 ×1017m-3 and 150 eV. Runaway electrons are detected via x-ray bremsstrahlung emission. The density and electric field thresholds for production and suppression have been previously explored with variations in gas puffing for density control. Runaway electrons are now being probed with resonant magnetic perturbations (RMP's). An m = 3 RMP strongly suppresses the runaway electrons and initial NIMROD modeling shows that this may be due to degradation of flux surfaces. The RMP is produced by a poloidal array of 32 saddle coils at the narrow vertical insulated cut in MST's thick conducting shell, with each RMP having a single m but a broad n spectrum. While a sufficiently strong m = 3 RMP suppresses the runaway electrons, an RMP with m = 1 and comparable amplitude has little effect. The impact of the RMP's on the magnetic topology of these plasmas is being studied with the nonlinear MHD code NIMROD. With an m = 3 RMP, stochasticity is introduced in the outer third of the plasma but no such flux surface degradation is observed with an m = 1 RMP. NIMROD also predicts regularly occurring MHD activity similar to that observed in the experiment. These studies have also been done in q (a) = 2.7 plasmas and analysis and modeling is ongoing. This work supported by USDoE.

  8. Runaway transient simulation of a model Kaplan turbine

    NASA Astrophysics Data System (ADS)

    Liu, S.; Zhou, D.; Liu, D.; Wu, Y.; Nishi, M.

    2010-08-01

    The runaway transient is a typical transient process of a hydro power unit, where the rotational speed of a turbine runner rapidly increases up to the runaway speed under a working head as the guide vanes cannot be closed due to some reason at the load rejection. In the present paper, the characteristics of the runaway transient of a model Kaplan turbine having ns = 479(m-kW) is simulated by using a time-dependent CFD technique where equation of rotational motion of runner, continuity equation and unsteady RANS equations with RNG k-epsilon turbulence model are solved iteratively. In the calculation, unstructured mesh is used to the whole flow passage, which consists of several sub-domains: entrance, casing, stay vanes + guide vanes, guide section, runner and draft tube. And variable speed sliding mesh technique is used to exchange interface flow information between moving part and stationary part, and three-dimensional unstructured dynamic mesh technique is also adopted to ensure mesh quality. Two cases were treated in the simulation of runaway transient characteristics after load rejection: one is the rated operating condition as the initial condition, and the other is the condition at the maximum head. Regarding the runaway speed, the experimental speed is 1.45 times the initial speed and the calculation is 1.47 times the initial for the former case. In the latter case, the experiment and the calculation are 1.67 times and 1.69 times respectively. From these results, it is recognized that satisfactorily prediction will be possible by using the present numerical method. Further, numerical results show that the swirl in the draft-tube flow becomes stronger in the latter part of the transient process so that a vortex rope will occur in the draft tube and its precession will cause the pressure fluctuations which sometimes affect the stability of hydro power system considerably.

  9. Multi-instrumental observations of the 2014 Ursid meteor outburst

    NASA Astrophysics Data System (ADS)

    Moreno-Ibáñez, Manuel; Trigo-Rodríguez, Josep M.; Madiedo, José María; Vaubaillon, Jérémie; Williams, Iwan P.; Gritsevich, Maria; Morillas, Lorenzo G.; Blanch, Estefanía; Pujols, Pep; Colas, François; Dupouy, Philippe

    2017-06-01

    The Ursid meteor shower is an annual shower that usually shows little activity. However, its Zenith hourly rate sometimes increases, usually either when its parent comet, 8P/Tuttle, is close to its perihelion or its aphelion. Outbursts when the comet is away from perihelion are not common and outbursts when the comet is close to aphelion are extremely rare. The most likely explanation offered to date is based on the orbital mean motion resonances. The study of the aphelion outburst of 2000 December provided a means of testing that hypothesis. A new aphelion outburst was predicted for 2014 December. The SPanish Meteor Network, in collaboration with the French Fireball Recovery and InterPlanetary Observation Network, set up a campaign to monitor this outburst and eventually retrieve orbital data that expand and confirm previous preliminary results and predictions. Despite unfavourable weather conditions over the south of Europe over the relevant time period, precise trajectories from multistation meteor data recorded over Spain were obtained, as well as orbital and radiant information for four Ursid meteors. The membership of these four meteors to the expected dust trails that were to provoke the outburst is discussed, and we characterize the origin of the outburst in the dust trail produced by the comet in the year ad 1392.

  10. YOUNG AGN OUTBURST RUNNING OVER OLDER X-RAY CAVITIES

    SciTech Connect

    Bogdán, Ákos; Van Weeren, Reinout J.; Kraft, Ralph P.; Forman, William R.; Randall, Scott; Jones, Christine; Giacintucci, Simona; Churazov, Eugene; O'Dea, Christopher P.; Baum, Stefi A.; Noell-Storr, Jacob

    2014-02-20

    Although the energetic feedback from active galactic nuclei (AGNs) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of AGN heating remain elusive. Here, we study NGC 193—a nearby lenticular galaxy—based on X-ray (Chandra) and radio (Very Large Array and Giant Meter-wave Radio Telescope) observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced ∼78 Myr ago by a weaker AGN outburst, while the outer cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr) and 4-8 times more powerful outburst. Combining this with the observed morphology of NGC 193, we conclude that NGC 193 likely represents the first example of a second, more powerful, AGN outburst overrunning an older, weaker outburst. These results help us to understand how the outburst energy is dissipated uniformly in the core of galaxies, and therefore may play a crucial role in resolving how AGN outbursts suppress the formation of large cooling flows at cluster centers.

  11. Young AGN Outburst Running over Older X-Ray Cavities

    NASA Astrophysics Data System (ADS)

    Bogdan, Akos; van Weeren, Reinout Johannes; Kraft, Ralph; Forman, William; Scott, Randall; Giacintucci, Simona; Churazov, Eugene; O'Dea, Christopher; Baum, Stefi; Noell-Storr, Jacob; Jones, Christine

    2015-08-01

    Although the energetic feedback from active galactic nuclei (AGNs) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of AGN heating remain elusive. Here, we study NGC 193 -- a nearby lenticular galaxy in a group -- based on X-ray and radio observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced about 78 Myr ago by a weaker AGN outburst, while the outer cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr) and 4-8 times more powerful outburst. Combining this with the observed morphology of NGC 193, we conclude that NGC 193 likely represents the first example of a second, more powerful, AGN outburst overrunning an older, weaker outburst. These results help us to understand how the outburst energy is dissipated uniformly in the core of galaxies, and therefore may play a crucial role in resolving how AGN outbursts suppress the formation of large cooling flows at cluster centers.

  12. GIANT OUTBURSTS IN Be/X-RAY BINARIES

    SciTech Connect

    Martin, Rebecca G.; Nixon, Chris; Armitage, Philip J.; Lubow, Stephen H.; Price, Daniel J.

    2014-08-01

    Be/X-ray binary systems exhibit both periodic (Type I) X-ray outbursts and giant (Type II) outbursts, whose origins have remained elusive. We suggest that Type II X-ray outbursts occur when a highly misaligned decretion disk around the Be star becomes eccentric, allowing the compact object companion to capture a large amount of material at periastron. Using three-dimensional smoothed particle hydrodynamics simulations, we model the long-term evolution of a representative Be/X-ray binary system. We find that periodic (Type I) X-ray outbursts occur when the neutron star is close to periastron for all disk inclinations. Type II outbursts occur for large misalignment angles and are associated with eccentricity growth which occurs on a timescale of about 10 orbital periods. Mass capture from the eccentric decretion disk results in an accretion disk around the neutron star whose estimated viscous time is long enough to explain the extended duration of Type II outbursts. Previous studies suggested that the outbursts are caused by a warped disk but our results suggest that this is not sufficient; the disk must be both highly misaligned and eccentric to initiate a Type II accretion event.

  13. Statistical analysis of properties of dwarf novae outbursts

    NASA Astrophysics Data System (ADS)

    Otulakowska-Hypka, Magdalena; Olech, Arkadiusz; Patterson, Joseph

    2016-08-01

    We present a statistical study of all measurable photometric features of a large sample of dwarf novae during their outbursts and superoutbursts. We used all accessible photometric data for all our objects to make the study as complete and up to date as possible. Our aim was to check correlations between these photometric features in order to constrain theoretical models which try to explain the nature of dwarf novae outbursts. We managed to confirm a few of the known correlations, that is the Stolz and Schoembs relation, the Bailey relation for long outbursts above the period gap, the relations between the cycle and supercycle lengths, amplitudes of normal and superoutbursts, amplitude and duration of superoutbursts, outburst duration and orbital period, outburst duration and mass ratio for short and normal outbursts, as well as the relation between the rise and decline rates of superoutbursts. However, we question the existence of the Kukarkin-Parenago relation but we found an analogous relation for superoutbursts. We also failed to find one presumed relation between outburst duration and mass ratio for superoutbursts. This study should help to direct theoretical work dedicated to dwarf novae.

  14. Prevalence and clinical correlates of explosive outbursts in Tourette Syndrome

    PubMed Central

    Chen, Kevin; Budman, Cathy L.; Herrera, Luis Diego; Witkin, Joanna E.; Weiss, Nicholas T.; Lowe, Thomas L.; Freimer, Nelson B.; Reus, Victor I.; Mathews, Carol A.

    2012-01-01

    The aim of this study was to examine the prevalence and clinical correlates of explosive outbursts in two large samples of individuals with TS, including one collected primarily from non-clinical sources. Participants included 218 TS-affected individuals who were part of a genetic study (N=104 from Costa Rica (CR) and N=114 from the US). The relationship between explosive outbursts and comorbid attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), tic severity, and prenatal and perinatal complications were examined using regression analyses. Twenty percent of participants had explosive outbursts, with no significant differences in prevalence between the CR (non-clinical) and the US (primarily clinical) samples. In the overall sample, ADHD, greater tic severity, and lower age of tic onset were strongly associated with explosive outbursts. ADHD, prenatal exposure to tobacco, and male gender were significantly associated with explosive outbursts in the US sample. Lower age of onset and greater severity of tics were significantly associated with explosive outbursts in the CR sample. This study confirms previous studies that suggest that clinically significant explosive outbursts are common in TS and associated with ADHD and tic severity. An additional potential risk factor, prenatal exposure to tobacco, was also identified. PMID:23040794

  15. Prevalence and clinical correlates of explosive outbursts in Tourette syndrome.

    PubMed

    Chen, Kevin; Budman, Cathy L; Diego Herrera, Luis; Witkin, Joanna E; Weiss, Nicholas T; Lowe, Thomas L; Freimer, Nelson B; Reus, Victor I; Mathews, Carol A

    2013-02-28

    The aim of this study was to examine the prevalence and clinical correlates of explosive outbursts in two large samples of individuals with Tourette syndrome (TS), including one collected primarily from non-clinical sources. Participants included 218 TS-affected individuals who were part of a genetic study (N=104 from Costa Rica (CR) and N=114 from the US). The relationships between explosive outbursts and comorbid attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), tic severity, and prenatal and perinatal complications were examined using regression analyses. Twenty percent of participants had explosive outbursts, with no significant differences in prevalence between the CR (non-clinical) and the US (primarily clinical) samples. In the overall sample, ADHD, greater tic severity, and lower age of tic onset were strongly associated with explosive outbursts. ADHD, prenatal exposure to tobacco, and male gender were significantly associated with explosive outbursts in the US sample. Lower age of onset and greater severity of tics were significantly associated with explosive outbursts in the CR sample. This study confirms previous studies that suggest that clinically significant explosive outbursts are common in TS and associated with ADHD and tic severity. An additional potential risk factor, prenatal exposure to tobacco, was also identified.

  16. V1331 Cyg- An outburst of results

    NASA Astrophysics Data System (ADS)

    Choudhary, Arpita; Stecklum, Bringfried; Stapelfeldt, Karl

    2013-07-01

    FU Orionis objects are a class of young stars with large brightness outbursts in the optical. The outbursts lead to strong increase in luminosity due to enhanced accretion and dust removal by the accompanying wind. All FUors have large infrared excess emission from circumstellar dust, and some drive bipolar jets and outflows. V1331 Cyg is a pre-outburst FUor candidate: At distance of ~ 550 pc, at the border of the dark cloud LDN 981. It is associated with an arc-like reflection nebula. It has two nested rings of 9000 and 3300 AU radii respectively, encircled by an expanding CO ring. The HST-WFPC2 imaging was done in 2000 and 2009. The first epoch images were obtained for F606W and F814W filters. The second epoch observations were deeper with one more filter, F450W introduced. Wind-driven expansion has an imprint on the colour profile of the ring, the study of which will be the next step to do. There is a missing ring section to the NW not due to extinction by the dark cloud but represent a shadow, originating close to the star. Our PSF -subtracted planetary camera frames disclosed a knot at ~0.4" from the star in the same direction. Also our analysis of archival Subaru coronagraphic H-band imaging reveals scattered light associated with this feature which was not seen before. Both findings suggest increased height of the matter at distances of ~300 AU which casts the shadow. This might be related to planet formation in the circumstellar disk. The scattering knot is associated with two spiral arms which stretch further out. The UKIDSS JHK images show faint reddened stars in the gap, confirming the presence of dense matter from probably both the protostellar environment and the molecular cloud. Herschel and SCUBA data confirm that V1331 Cyg is the most luminous object in the surroundings, ONLY possible young stellar candidate responsible for the outflow. Narrow-band imaging in the Hα and [SII] line revealed a bipolar outflow, presumed to have a substantial

  17. Runaway and pregnant: risk factors associated with pregnancy in a national sample of runaway/homeless female adolescents.

    PubMed

    Thompson, Sanna J; Bender, Kimberly A; Lewis, Carol M; Watkins, Rita

    2008-08-01

    Homeless youth are at particularly high risk for teen pregnancy; research indicates as many as 20% of homeless young women become pregnant. These pregnant and homeless teens lack financial resources and adequate health care, resulting in increased risk for low-birth-weight babies and high infant mortality. This study investigated individual and family-level predictors of teen pregnancy among a national sample of runaway/homeless youth in order to better understand the needs of this vulnerable population. Data from the Runaway/Homeless Youth Management Information System (RHY MIS) provided a national sample of youth seeking services at crisis shelters. A sub-sample of pregnant females and a random sub-sample (matched by age) of nonpregnant females comprised the study sample (N = 951). Chi-square and t tests identified differences between pregnant and nonpregnant runaway females; maximum likelihood logistic regression identified individual and family-level predictors of teen pregnancy. Teen pregnancy was associated with being an ethnic minority, dropping out of school, being away from home for longer periods of time, having a sexually transmitted disease, and feeling abandoned by one's family. Family factors, such as living in a single parent household and experiencing emotional abuse by one's mother, increased the odds of a teen being pregnant. The complex problems associated with pregnant runaway/homeless teens create challenges for short-term shelter services. Suggestions are made for extending shelter services to include referrals and coordination with teen parenting programs and other systems of care.

  18. Outburst of the Cataclysmic Variable 1514-24 GW Lib

    NASA Astrophysics Data System (ADS)

    Templeton, Matthew R.

    2007-04-01

    The cataclysmic variable 1514-24 GW Lib is in outburst (Rod Stubbings, Drouin, Victoria, Australia, visual magnitude 13.8, 2007 April 12.4938 UT), the first outburst observed since its discovery on 1983 August 10 UT. V-band time series photometry and visual observations are urgently requested for GW Lib [the brightest of the accreting pulsating white dwarf systems; the outburst provides the opportunity to see how pulsations change with temperature, according to Dr. Paula Szkody, University of Washington]. Data reported to the AAVSO may be found at www.aavso.org.

  19. EUVE photometry of SS Cygni: Dwarf nova outbursts and oscillations

    SciTech Connect

    Mauche, C.W.

    1995-05-15

    The authors present EUVE Deep Survey photometry and AAVSO optical measurements of the 1993 August and 1994 June/July outbursts of the dwarf nova SS Cygni. The EUV and optical light curves are used to illustrate the different response of the accretion disk to outbursts which begin at the inner edge and propagate outward, and those which begin at the outer edge and propagate inward. Furthermore, the authors describe the properties of the quasi-coherent 7--9 s sinusoidal oscillations in the EUV flux detected during the rise and plateau stages of these outbursts.

  20. Runaway Signatures in the Transport Description of Solar Wind Electrons: A New Quantitative Steady Electron Runaway Model (SERM)

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Salem, C. S.

    2016-12-01

    A new model for solar wind electrons provides an explanation for the origin of the non-thermal core-halo-strahl-superhalo VDF ubiquitously observed in the solar wind. Such kurtotic VDF's should be as common as the gradient induced occurrence of finite parallel electric fields that enforce quasi-neutrality in astrophysical plasmas. The velocity space separatrix of coulomb runaway predicts the observed scaling of the break point energy at 1AU of the electron VDF between thermal and suprathermal components and agrees well with the tabulations of its variation with radius. SERM quantitatively reproduces: 14 year IMP archives of the fraction of supra thermal electrons and the observed variation of the supra thermal density with local (nearly asymptotic) solar wind speed; the observed inverse correlation between halo density fraction and Th/Tc; and the reported, but theoretically unusual relative slippage of the core and halo that supports the heat flux. Requirements for quasi-neutrality (in the presence of runaways) lead to a quantitative non-local specification of the required supra thermal density fraction and the lowest even Legendre order approximate VDF that is symmetric, but kurtotic in the proton rest frame. The Stokes drift of the thermals suggested by runaway physics requires a counter drift of the non-locally returning suprathermals which determine the observed heat flux and thermal force contributions and the lowest order odd Legendre dependence of the VDF. The strahl is recovered as an extreme part of the non-local suprathermals. "Direct'' runaways caused by the parallel electric field are identified as an omnipresent source for the observed sunward portion of the non-thermal VDF. The source of the super halo electrons is suggested to be mirrored runaways produced at the base of the corona with subsequent near isotropization in the interplanetary medium.

  1. Experimental and theoretical analysis of a method to predict thermal runaway in Li-ion cells

    NASA Astrophysics Data System (ADS)

    Shah, Krishna; Chalise, Divya; Jain, Ankur

    2016-10-01

    Thermal runaway is a well-known safety concern in Li-ion cells. Methods to predict and prevent thermal runaway are critically needed for enhanced safety and performance. While much work has been done on understanding the kinetics of various heat generation processes during thermal runaway, relatively lesser work exists on understanding how heat removal from the cell influences thermal runaway. Through a unified analysis of heat generation and heat removal, this paper derives and experimentally validates a non-dimensional parameter whose value governs whether or not thermal runaway will occur in a Li-ion cell. This parameter is named the Thermal Runaway Number (TRN), and comprises contributions from thermal transport within and outside the cell, as well as the temperature dependence of heat generation rate. Experimental data using a 26650 thermal test cell are in good agreement with the model, and demonstrate the dependence of thermal runaway on various thermal transport and heat generation parameters. This parameter is used to predict the thermal design space in which the cell will or will not experience thermal runaway. By combining all thermal processes contributing to thermal runaway in a single parameter, this work contributes towards a unified understanding of thermal runaway, and provides the fundamental basis for design tools for safe, high-performance Li-ion batteries.

  2. Behaviour of runaway electrons in the HL-2A plasmas with LHCD and ECCD

    NASA Astrophysics Data System (ADS)

    Zhu, J. X.; Yao, L. M.; Zhang, Y. P.; Yang, J. W.; Yang

    2015-12-01

    > The behaviour of runaway electrons have been investigated in lower hybrid current drive (LHCD) and electron cyclotron current drive (ECCD) plasmas as well as the LHCD only plasmas in the HL-2A tokamak. The fast electrons generated by lower hybrid waves (LHWs) and electron cyclotron waves (ECWs) can act as a seed population for runaway electrons. In the LHCD only discharges, a large number of runaway electrons are produced after the termination of lower hybrid (LH) power by conversion of fast electrons into runaway electrons due to the fast electron tail which extends above the runaway critical energy. However, in contrast to LHCD only discharges, during the simultaneous application of LHCD and ECCD discharges, runaway electrons cannot be created by the termination of LH power when the ECCD is on duty. The runaway production is observed to be enhanced until the EC power termination. The loop voltage increase due to the termination of EC power gives rise to a decline in the critical runaway energy, which leads to some of the energetic fast electrons converting into runaway electrons via the acceleration from the toroidal electric field. That is, the fast electrons created by waves can be accelerated into the runaway regime due to the Dreicer process.

  3. A POWERFUL AGN OUTBURST IN RBS 797

    SciTech Connect

    Cavagnolo, K. W.; McNamara, B. R.; Wise, M. W.; Nulsen, P. E. J.; Gitti, M.; Brueggen, M.; Rafferty, D. A.

    2011-05-10

    Utilizing {approx}50 ks of Chandra X-Ray Observatory imaging, we present an analysis of the intracluster medium (ICM) and cavity system in the galaxy cluster RBS 797. In addition to the two previously known cavities in the cluster core, the new and deeper X-ray image has revealed additional structure associated with the active galactic nucleus (AGN). The surface brightness decrements of the two cavities are unusually large and are consistent with elongated cavities lying close to our line of sight. We estimate a total AGN outburst energy and mean jet power of {approx}(3-6) x 10{sup 60} erg and {approx}(3-6) x 10{sup 45} erg s{sup -1}, respectively, depending on the assumed geometrical configuration of the cavities. Thus, RBS 797 is apparently among the most powerful AGN outbursts known in a cluster. The average mass accretion rate needed to power the AGN by accretion alone is {approx}1 M{sub sun} yr{sup -1}. We show that accretion of cold gas onto the AGN at this level is plausible, but that Bondi accretion of the hot atmosphere is probably not. The brightest cluster galaxy (BCG) harbors an unresolved, non-thermal nuclear X-ray source with a bolometric luminosity of {approx}2 x 10{sup 44} erg s{sup -1}. The nuclear emission is probably associated with a rapidly accreting, radiatively inefficient accretion flow. We present tentative evidence that star formation in the BCG is being triggered by the radio jets and suggest that the cavities may be driving weak shocks (M {approx} 1.5) into the ICM, similar to the process in the galaxy cluster MS 0735.6+7421.

  4. Theoretical determination of the strength characteristics of multilayer materials intended for nuclear and thermonuclear engineering

    NASA Astrophysics Data System (ADS)

    Vitkovskii, I. V.; Leshukov, A. Yu.; Romashin, S. N.; Shorkin, V. S.

    2015-12-01

    A method is developed to estimate the integrity of multilayer structures. This method is based on the version of the theory of adhesion and cohesion interactions of structure elements that only takes into account their thermomechanical properties. The structures to be studied are the material of the multilayer wall of the liquid-metal thermonuclear reactor blanket and a heat-resistant magnet wire with a bimetallic conductor, which is the base of the windings of the magnetohydrodynamic machines and electric motors intended for operation at high temperatures under ionizing radiation in, e.g., the machines and facilities in nuclear and thermonuclear reactors.

  5. The Pulsating, Accreting White Dwarf in GW Lib after Outburst

    NASA Astrophysics Data System (ADS)

    Szkody, Paula

    The first known pulsating white dwarf in an accreting close binary system (GW Lib) underwent an outburst in April, 2007. We aim to follow the pulsation spectrum as the white dwarf cools back to to its quiescent temperature from its heating due to the outburst which should take about 3 years. As it cools, it should re-enter the instability strip and we can witness changes in the driving mechanism and detect modes that are excited by the temperature changes. The higher pulse amplitude in UV vs optical and the available time-tag mode makes GALEX the instrument of choice. The data in 2008 will be combined with our DOT time in May, June 2007 to provide coverage of the largest cooling that takes place in the year following outburst. Since the few known systems only outburst every 20-30 yrs, this is the first opportunity to accomplish a study of this type."

  6. ON THE EVOLUTION OF ACCRETION RATES IN COMPACT OUTBURST SOURCES

    SciTech Connect

    Mandal, Samir; Chakrabarti, Sandip K. E-mail: chakraba@bose.res.in

    2010-02-20

    Spectra in outburst sources are found to become soft in viscous timescales before going back to hard as in the pre-outburst phase. By using two component accretion disks we show that major characteristics of the spectral evolution can be reproduced. We find that the outburst is possibly caused by a sudden rise in viscosity which gradually converts the sub-Keplerian flow into a Keplerian flow. The decline of the viscosity reduces the Keplerian accretion rate, and the system goes back to hard states. We discuss the genesis of the characteristic shape of the hardness-intensity diagram and reproduce this for the well-known outburst source GRO J1655-40.

  7. New Outburst of Centaur Comet (60558) 174P/Echeclus

    NASA Astrophysics Data System (ADS)

    Choi, Young-Jun; Ishiguro, Masateru; Moon, Hong-Kyu

    2015-03-01

    We report observations of new outburst of Centaur (60558) 174P/Echeclus, using Suprime-Cam of Subaru tele-scope. The outburst was detected by Jager on May 30, 2011 (Jaeger et al., 2011). We made several follow-up observations for this outburst with 1m telescope at Mt. Lemon Optical Astronomy Observatory located in US and 60cm telescope at Sobaeksan Optical Astronomy Observatory in Korea. The very first presence of coma around (60558) 2000 EC98 has been detected by Choi and Weissman (2006) on 2005 December 30.50 UT with the Palomar 5m telescope. Soon after, the object was given the periodic comet designa-tion 174P/Echeclus. We will present the characterstics and discuss the reason of this recursive outburst.

  8. The September 1996 outbursts of Comet Hale-Bopp

    NASA Astrophysics Data System (ADS)

    Larson, S. M.; Samarasinha, N.; Tao, J.; Hergenrother, C.

    2000-10-01

    Digitally enhanced pre-perihelion groundbased images of Comet Hale-Bopp taken in September 1996 show intersting morphology resulting from at least two outbursts. During that apparition, the coma was dominated by radial ``porcupine" morphology. However, a 2 magnitude outburst starting on 1996 September 9.5 UT (Tao et al., 2000, Plan. Sp. Sci. 48, 153-161) resulted in two expanding dust shells with apparent expansion speeds of 112 and 225 m/s and an arc in the NW quadrant. This morphology is very similar to that seen in post-perihelion NICMOS images of a similar outburst on 1997 August 27 (see Campins et al., DPS 2000 abstract). Similar, but less pronounced outburst activity can be seen later in the month and include evidence for ejection of discrete fragments. We explore the possible mechanisms for the observed morphology. This work is supported in part by the NASA Planetary Atmospheres Program.

  9. The First Six Outbursting Cool DA White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Bell, K. J.; Hermes, J. J.; Montgomery, M. H.; Winget, D. E.; Gentile Fusillo, N. P.; Raddi, R.; Gänsicke, B. T.

    2017-03-01

    Extensive observations from the Kepler spacecraft have recently revealed a new outburst phenomenon operating in cool pulsating DA (hydrogen atmosphere) white dwarfs (DAVs). With the introduction of two new outbursting DAVs from K2 Fields 7 (EPIC 229228364) and 8 (EPIC 220453225) in these proceedings, we presently know of six total members of this class of object. We present the observational commonalities of the outbursting DAVs: (1) outbursts that increase the mean stellar flux by up to ≍15%, last many hours, and recur irregularly on timescales of days; (2) effective temperatures that locate them near the cool edge of the DAV instability strip; and (3) rich pulsation spectra with modes that are observed to wander in amplitude/frequency.

  10. Physical Mechanism of Comet (and Asteroid) Outbursts: The Movie

    NASA Astrophysics Data System (ADS)

    Hartmann, W. K.

    2015-07-01

    A film made during impact experiments at NASA Ames illustrates a mechanism in which regolith can become gas charged and then erupt to create outbursts as observed on comets (and "asteroids" such as 2060 Chiron).

  11. Deciphering Outburst Flood Discharges from the Morphology of Hesperian Canyons

    NASA Astrophysics Data System (ADS)

    Lapotre, M. G. A.; Lamb, M. P.; Williams, R. M.

    2014-07-01

    We model the hydraulics of outburst floods over canyon escarpments. We show that canyons only maintain a constant width under a certain hydraulic regime. We combine the hydraulic model to an erosion law to constrain paleodischarges at Echus Chasma.

  12. Theoretical z -pinch scaling relations for thermonuclear-fusion experiments.

    PubMed

    Stygar, W A; Cuneo, M E; Vesey, R A; Ives, H C; Mazarakis, M G; Chandler, G A; Fehl, D L; Leeper, R J; Matzen, M K; McDaniel, D H; McGurn, J S; McKenney, J L; Muron, D J; Olson, C L; Porter, J L; Ramirez, J J; Seamen, J F; Speas, C S; Spielman, R B; Struve, K W; Torres, J A; Waisman, E M; Wagoner, T C; Gilliland, T L

    2005-08-01

    implosion time tau(i). For an accelerator coupled to a double-pinch-driven hohlraum that drives the implosion of an ICF fuel capsule, we find that the accelerator power and energy required to achieve high-yield fusion scale as tau(i)0.36 and tau(i)1.36, respectively. Thus the accelerator requirements decrease as the implosion time is decreased. However, the x-ray-power and thermonuclear-yield efficiencies of such a coupled system increase with tau(i). We also find that increasing the anode-cathode gap of the pinch from 2 to 4 mm increases the requisite values of P(a) and E(a) by as much as a factor of 2.

  13. Particle Injection in the Cir X-1 radio outbursts

    NASA Technical Reports Server (NTRS)

    Sanchez, J. G.; Paredes, J. M.

    1996-01-01

    A particle injection model has been applied to the radio outbursts of the X-ray binary Circinus X-1. The radio outbursts of this system have often been observed to exhibit a double peaked structure, i.e., with two apparent consecutive maxima. We show here that particle injection models can account for such observed behavior provided that a time variable particle injection rate is adopted.

  14. Outburst of the recurrent nova V745 Sco

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.

    2014-02-01

    The outburst of the recurrent nova V745 Sco (Nova Sco 1937) by Rod Stubbings (Tetoora Road, VIC, Australia) at visual magnitude 9.0 on 2014 February 6.694 UT is reported. This recurrent nova is fading quickly. Follow-up observations of all types (visual, CCD, DSLR) are strongly encouraged, as is spectroscopy; fast time-series of this nova may be useful to detect possible flaring activity as was observed during the outburst of U Scorpii in 2010. Coincident time-series by multiple observers would be most useful for such a study, with a V-filter being preferred. Observations reported to the AAVSO International Database show V745 Sco at visual mag. 10.2 on 2014 Feb. 07.85833 UT (A. Pearce, Nedlands, W. Australia). Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. Previous outbursts occurred in 1937 and 1989. The 1937 outburst was detected in 1958 (in decline at magnitude 11.0 on 1937 May 11.1 UT; outburst had occurred within the previous 19 days) by Lukas Plaut on plates taken by Hendrik van Gent at the Leiden Observatory; the object was announced as Nova Sco 1937 and later assigned the GCVS name V745 Sco. The 1989 outburst was detected on 1989 August 1.55 UT by Mati Morel (MMAT, Thornton, NSW, Australia) at visual magnitude 10.4 and in decline. Dr. Bradley Schaefer (Louisiana State University) reports (2010ApJS..187..275S) in his comprehensive analysis of the 10 known galactic recurrent novae (including V745 Sco) that the median interval between recurrent novae outbursts is 24 years. The interval since the 1989 outburst of V745 Sco is 24.10 years. See the Alert Notice for additional visual and multicolor photometry and for more details.

  15. Note: Measurement of the runaway electrons in the J-TEXT tokamak

    SciTech Connect

    Chen, Z. Y.; Zhang, Y.; Zhang, X. Q.; Luo, Y. H.; Jin, W.; Li, J. C.; Chen, Z. P.; Wang, Z. J.; Yang, Z. J.; Zhuang, G.

    2012-05-15

    The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5-5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau following the disruptions.

  16. Observation of runaway electrons by infrared camera in J-TEXT

    SciTech Connect

    Tong, R. H.; Chen, Z. Y. Zhang, M.; Huang, D. W.; Yan, W.; Zhuang, G.

    2016-11-15

    When the energy of confined runaway electrons approaches several tens of MeV, the runaway electrons can emit synchrotron radiation in the range of infrared wavelength. An infrared camera working in the wavelength of 3-5 μm has been developed to study the runaway electrons in the Joint Texas Experimental Tokamak (J-TEXT). The camera is located in the equatorial plane looking tangentially into the direction of electron approach. The runaway electron beam inside the plasma has been observed at the flattop phase. With a fast acquisition of the camera, the behavior of runaway electron beam has been observed directly during the runaway current plateau following the massive gas injection triggered disruptions.

  17. The space frequency and origin of the runaway O and B stars

    SciTech Connect

    Stone, R.C. )

    1991-07-01

    Determinations of space frequency for runaway O and B stars are in very poor agreement, and many possible sources of systematic errors have been put forward. This paper investigates these sources, as well as others, and presents means for determining unbiased (true) space frequencies. When corrected for major sources of systematic error, space frequency determinations for the runaway O stars are in very good agreement but less so for the B-type runaways. The true space frequencies of runaway O and B stars are, respectively, 46 percent and 4 percent, as discussed in this paper. The former value is very supportive, along with other arguments presented in this paper, for runaway O stars being produced from supernova explosions in massive binaries. The origin of the B-type runaways is less clear. 89 refs.

  18. Observation of runaway electrons by infrared camera in J-TEXT.

    PubMed

    Tong, R H; Chen, Z Y; Zhang, M; Huang, D W; Yan, W; Zhuang, G

    2016-11-01

    When the energy of confined runaway electrons approaches several tens of MeV, the runaway electrons can emit synchrotron radiation in the range of infrared wavelength. An infrared camera working in the wavelength of 3-5 μm has been developed to study the runaway electrons in the Joint Texas Experimental Tokamak (J-TEXT). The camera is located in the equatorial plane looking tangentially into the direction of electron approach. The runaway electron beam inside the plasma has been observed at the flattop phase. With a fast acquisition of the camera, the behavior of runaway electron beam has been observed directly during the runaway current plateau following the massive gas injection triggered disruptions.

  19. Suppression of runaway generation by SMBI in disruptions in J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Huang, Duwei; Chen, Zhongyong; Tong, Ruihai; Yan, Wei; Wang, Shenyang; Wei, Yunong; Ma, Tiankui; Zhuang, Ge; J-TEXT Team

    2015-11-01

    Runaway current generated in ITER disruption can lead to severe damage at plasma facing components. The generation and suppression of runaway electrons have been investigated in the J-TEXT tokamak. Runaway current was created with rapid argon injection by a massive gas injection (MGI) valve. Supersonic molecular beam injection (SMBI) as a highly efficient fueling method can provide a high beam velocity and deep penetration depth. A small amount of hydrogen injected by SMBI during the quiescent plasma current flattop can induce magnetic penetration, and then cause plasma instability which increases runaway electron loss rapidly. SMBI has been used to mitigate disruption generated runaway electrons in the J-TEXT tokamak. It is found that SMBI of hydrogen during plasma disruption can efficiently suppress runaway generation. Corresponding author

  20. Note: Measurement of the runaway electrons in the J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Chen, Z. Y.; Zhang, Y.; Zhang, X. Q.; Luo, Y. H.; Jin, W.; Li, J. C.; Chen, Z. P.; Wang, Z. J.; Yang, Z. J.; Zhuang, G.

    2012-05-01

    The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5-5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau following the disruptions.

  1. Note: measurement of the runaway electrons in the J-TEXT tokamak.

    PubMed

    Chen, Z Y; Zhang, Y; Zhang, X Q; Luo, Y H; Jin, W; Li, J C; Chen, Z P; Wang, Z J; Yang, Z J; Zhuang, G

    2012-05-01

    The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5-5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau following the disruptions.

  2. Observation of runaway electrons by infrared camera in J-TEXT

    NASA Astrophysics Data System (ADS)

    Tong, R. H.; Chen, Z. Y.; Zhang, M.; Huang, D. W.; Yan, W.; Zhuang, G.

    2016-11-01

    When the energy of confined runaway electrons approaches several tens of MeV, the runaway electrons can emit synchrotron radiation in the range of infrared wavelength. An infrared camera working in the wavelength of 3-5 μm has been developed to study the runaway electrons in the Joint Texas Experimental Tokamak (J-TEXT). The camera is located in the equatorial plane looking tangentially into the direction of electron approach. The runaway electron beam inside the plasma has been observed at the flattop phase. With a fast acquisition of the camera, the behavior of runaway electron beam has been observed directly during the runaway current plateau following the massive gas injection triggered disruptions.

  3. Turbulent fluctuations and the excitation of Z Cam outbursts

    NASA Astrophysics Data System (ADS)

    Ross, Johnathan; Latter, Henrik N.

    2017-09-01

    Z Cam variables are a subclass of dwarf nova that lie near a global bifurcation between outbursting ('limit cycle') and non-outbursting ('standstill') states. It is believed that variations in the secondary star's mass-injection rate instigate transitions between the two regimes. In this paper, we explore an alternative trigger for these transitions: stochastic fluctuations in the disc's turbulent viscosity. We employ simple one-zone and global viscous models which, though inappropriate for detailed matching to observed light curves, clearly indicate that turbulent disc fluctuations induce outbursts when the system is sufficiently close to the global bifurcation point. While the models easily produce the observed 'outburst/dip' pairs exhibited by Z Cam and Nova-like variables, they struggle to generate long trains of outbursts. We conclude that mass transfer variability is the dominant physical process determining the overall Z Cam standstill/outburst pattern, but that viscous stochasticity provides an additional ingredient explaining some of the secondary features observed.

  4. Constraining models of accretion outbursts in low-mass YSOs}

    NASA Astrophysics Data System (ADS)

    Ninan, J. P.; Ojha, D. K.; Ghosh, S. K.; Bhatt, B. C.

    Young low-mass stars, which are still undergoing accretion, have been found to undergo sudden outbursts in short period of time. They are believed to be due to sudden increase of typically ˜2 orders of magnitude in mass infall rate. Classically these objects are classified as FUors and EXors. FUors undergo long duration outbursts for several decades of typical magnitude δ m ˜ 4-5, while EXors undergo short duration outbursts for few months to years of typical magnitude δ m ˜ 2-3 and they might occur repeatedly. From the number count of FUors, it is estimated that every low-mass stars, on a minimum, undergo FUors kind of outburst in its early life. We present our study on three such rare outbursts in optical and near-infrared wavebands using long-term observations with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Observatory telescope. Using the current available models and the constrains on it, we can deduce to understand the physical process driving the outburst.

  5. Runaway Electrification of Friable Self-Replicating Granular Matter

    PubMed Central

    2013-01-01

    We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palmlike structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter. PMID:24041221

  6. Runaway Stars in the Galactic Halo: Their Origin and Kinematics

    NASA Astrophysics Data System (ADS)

    Duarte de Vasconcelos Silva, Manuel

    2012-03-01

    Star formation in the Milky Way is confined to star-forming regions (OB associ- ation, HII regions, and open clusters) in the Galactic plane. It is usually assumed that these regions are found preferably along spiral arms, as is observed in other spiral galaxies. However, young early-type stars are often found at high Galactic latitudes, far away from their birthplaces in the Galactic disc. These stars are called runaway stars, and it is believed that they were ejected from their birth- places early in their lifetimes by one of two mechanisms: ejection from a binary system following the destruction of the massive companion in a supernova type II event (the binary ejection mechanism), or ejection from a dense cluster following a close gravitational encounter between two close binaries (the dynamical ejection mechanism). The aims of our study were: to improve the current understanding of the nature of high Galactic latitude runaway stars, in particular by investigating whether the theoretical ejection mechanisms could explain the more extreme cases; to show the feasibility of using high Galactic latitude stars as tracers of the spiral arms. The main technique used in this investigation was the tracing of stellar orbits back in time, given their present positions and velocities in 3D space. This technique allowed the determination of the ejection velocities, flight times and birthplaces of a sample of runaway stars. In order to obtain reasonable velocity estimates several recent catalogues of proper motion data were used. We found that the evolutionary ages of the vast majority of runaway stars is consistent with the disc ejection scenario. However, we identified three outliers which would need flight times much larger then their estimated ages in order to reach their present positions in the sky. Moreover, the ejection velocity distribution appears to be bimodal, showing evidence for two populations of runaway stars: a "low" velocity population (89 per cent of the

  7. Fast Thermal Shutdown of Tokamak Discharges Without Runaway Electron Avalanching

    SciTech Connect

    Bakhtiari, M.; Yoshino, R.; Nishida, Y

    2002-03-15

    The possibility of using massive quantities of injected deuterium with and without additional admixture of lesser quantities of higher-Z impurities to effect fast thermal shutdown of a tokamak discharge without causing runaway electron avalanching is systematically studied. It is found that various combinations of deuterium alone and deuterium with impurities (helium, nitrogen, argon, and krypton) can provide acceptable runaway-free thermal shutdown. The admixture of impurities cited reduces the quantity of deuterium needed and also reduces the radiative cooling time needed for the plasma to reach final thermal equilibrium, where radiation losses balance ohmic input. In contrast, the addition of neon does not appreciably reduce deuterium quantity or promote faster cooling. This difference relative to the other impurity studies can be understood from the radiation versus plasma temperature characteristics for neon.

  8. All-optical runaway evaporation to Bose-Einstein condensation

    NASA Astrophysics Data System (ADS)

    Clément, J.-F.; Brantut, J.-P.; Robert-de-Saint-Vincent, M.; Nyman, R. A.; Aspect, A.; Bourdel, T.; Bouyer, P.

    2009-06-01

    We demonstrate runaway evaporative cooling directly with a tightly confining optical-dipole trap and achieve fast production of condensates of 1.5×105 R87b atoms. Our scheme uses a misaligned crossed-beam far off-resonance optical-dipole trap (MACRO-FORT). It is characterized by independent control of the trap confinement and depth allowing forced all-optical evaporation in the runaway regime. Although our configuration is particularly well suited to the case of R87b atoms in a 1565 nm optical trap, where an efficient initial loading is possible, our scheme is general and will allow all-optical evaporative cooling at constant stiffness for every optically trappable atomic or even molecular species.

  9. Mechanism of generation of runaway electrons in a lightning leader

    NASA Astrophysics Data System (ADS)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2014-06-01

    A mechanism is analyzed of the electric field enhancement in a lightning leader up to the level permitting runaway of low-energy electrons. The ionization wave propagation in the preionized domain in front of the leader makes it possible to overcome the limitation imposed on the field intensity by transversal expansion of the leader front. By means of numerical simulations, it is demonstrated that, at the final stage of formation of a new leader step, generation of an electric field is possible in the channels of the streamer zone ahead of the new step with intensity sufficient for electron runaway and, consequently, for producing the X-ray and γ-ray pulses observed in correlation with the lightning leader steps.

  10. Perceived self-image of escapist and throwaway runaways.

    PubMed

    Peretti, P O; Purham, C

    1994-03-01

    It has been estimated that several million youngsters run away from home every year in the USA. The present research was conducted to determine the extent to which the escapist and throwaway runaways perceived their self-image. It focused on variables the runaways perceived as the most significant for them regarding perception of self. Results indicated that escapists tend to perceive themselves with greater self-worth, self-confidence, and self-motivation than did the throwaways. The latter Ss tend to perceive themselves with greater self-acceptance and self-depression compared to the former group, while both S groups had no significant difference in their perceptions of self-reliance.

  11. Suppression of x-rays generated by runaway electrons in ATF

    SciTech Connect

    Rasmussen, D.A.; England, A.C.; Eberle, C.C.; Devan, W.R.; Harris, J.H.; Jernigan, T.C.; Kindsfather, R.R.; Morris, R.N.; Murakami, M.; Neilson, G.H.

    1987-01-01

    X-ray emission from runaway electrons on ATF is a serious issue. Runaway suppression techniques used on Heliotron-E are not adequate for ATF. Three approaches have been developed to suppress runaway production. Monitoring devices have been installed in occupied areas and personnel access and exposure will be limited. Additional shielding will be added as required. These systems will be ready for installation and testing on ATF prior to commissioning or first plasma operation.

  12. Results from computational and experimental modeling of runaway electron damage on plasma facing components

    SciTech Connect

    Niemer, K.A.; Gilligan, J.G.; Croessmann, C.D.

    1994-11-01

    The purpose of this research was to extend the theoretical and experimental knowledge of runaway electron damage-impact-bombardment on plasma facing components and materials in magnetic fusion devices. The emphasis of this work involved computational modeling and experimental studies to investigate runaway electron energy deposition and thermal response in plasma facing materials. The goals were: (1) to develop a computational model to study and analyze runaway electron damage; (2) to characterize runaway electron parameters; and (3) to perform experiments to analyze runaway electron damage. These goals were accomplished by first assembling the PTA code package. PTA is a unique application of PATRAN, the Integrated TIGER Series (ITS), and ABAQUS for modeling high energy electron impact on magnetic fusion materials and components. The PTA code package provides a three-dimensional, time dependent, computational code package which predicts material response from runaway bombardment under most runaway conditions (i.e., electron energy, incident angle, energy density, and deposition time). As part of this research, PTA was used to study energy deposition and material response in several design applications, to analyze damaged material, and to analyze several experiments. Runaway electron characterization was determined through parametric studies, analysis of damaged materials, and analysis of experimental results. Characterization provided information on electron energy, incident angle, current, deposition time, and volume of material impacted by runaway electrons. Finally an experiment was performed on the Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory to study runaway electron damage. The experiment provided information on the runaway electron energy and current in ATF, as well as supplemented the existing experimental knowledge of runaway electron damage.

  13. Detection of runaway electrons - a journey 100 years long

    NASA Astrophysics Data System (ADS)

    Chilingarian, Ashot

    2013-04-01

    In the beginning of last century C.T.R. Wilson proposes that strong electrical field of the thunderclouds might accelerate electrons to very high energies. However, this and many other electromagnetic processes in our atmosphere are poorly understood till now; the key questions about the thundercloud electrification and lightning initiation remain unanswered. During recent decades several observations of gamma ray, electron and neutron fluxes correlated with thunderstorms were reported. Nonetheless, the origin of these fluxes is under debate till now. The direct registration of the particle showers initiated by the runaway electrons (the most popular theory) was missing. We present the experimental evidence of the microsecond duration electron bursts originated from runaway electrons accelerated in thunderclouds. The first direct experimental observation of the RREA process was made at Aragats in 2009 with a network of 16 plastic scintillators distributing on the area of ~ 1000 m2 registering 8-fold enhancement of particle showers during maximal flux of TGE. The statistical analysis of ~200 detected particle showers reveals their systematic difference from the Extensive Air Shower (EAS) events: the density was much lower and spatial spread of the electrons was much more uniform (particle distribution in EAS has characteristic bell-like form). The particle showers from the thunderclouds were named - Cloud extensive showers (CESs). A SEC phenomenon is very rare: only 3 largest TGEs from 300 were accompanied by SEC observation. CESs originated from individual runaway electrons accelerated in the cloud just above the detector. RREA (CES) phenomenon is very local and depends on the height of cloud above detector and on the strength of electric field in it. Both parameters are fast changing and only during several minutes cascades from runaway electrons can be developed enough to cover several thousand square meters of surface. Only very suitable location and large sizes

  14. Breakdown and discharges in dense gases governed by runaway electrons

    SciTech Connect

    Babich, L.P.

    1996-03-01

    The phenomenon of runaway electrons (REs) at high values of the ratio field intensity/gas number density {ital E}/{ital N} and {ital N} up to the Loshmidt number {ital N}{sub {ital L}}{approx_equal}2.7{times}10{sup 19} cm{sup {minus}3} is described. REs are shown to govern the breakdown and discharges at such condition. {copyright} {ital 1996 American Institute of Physics.}

  15. Outbursts In Symbiotic Binaries (FUSE 2000)

    NASA Technical Reports Server (NTRS)

    Kenyon, Scott J.; Sonneborn, George (Technical Monitor)

    2002-01-01

    During the past year, we made good progress on analysis of FUSE observations of the symbiotic binary Z And. For background, Z And is a binary system composed of a red giant and a hot component of unknown status. The orbital period is roughly 750 days. The hot component undergoes large-scale eruptions every 10-20 yr. An outburst began several years ago, triggering this FUSE opportunity. First, we obtained an excellent set of ground-based optical data in support, of the FUSE observations. We used FAST, a high throughput low resolution spectrograph on the 1.5-m telescope at Mt. Hopkins, Arizona. A 300 g/ mm grating blazed at 4750 A, a 3 in. slit, and a thinned Loral 512 x 2688 CCD gave us spectra covering 3800-7500 A at a resolution of 6 A. The wavelength solution for each spectrum has a probable error of +/- 0.5 A or better. Most of the resulting spectra have moderate signal-to-noise, S/.N approx. greater than 30 per pixel. The time coverage for these spectra is excellent. Typically, we acquired spectra every 1-2 nights during dark runs at Mt. Hopkins. These data cover most of the rise and all of the decline of the recent outburst. The spectra show a wealth of emission lines, including H I, He I, He II, [Fe V11], and the Raman scattering bands at 6830 A and 7088 A. The Raman bands and other high ionization features vary considerably throughout the outburst. These features will enable us to correlate variations in the FUSE spectra with variations in the optical spectra. Second, we began an analysis of FUSE spectra of Z And. We have carefully examined the spectra, identifying real features and defects. We have identified and measured fluxes for all strong emission lines, including the O VI doublet at 1032 A and 1038 A. These and several other strong emission lines display pronounced P Cygni absorption components indicative of outgrowing gas. We will attempt to correlate these velocities with similar profiles observed on optical spectra. The line velocities - together

  16. Relativistic runaway breakdown in low-frequency radio

    NASA Astrophysics Data System (ADS)

    Füllekrug, Martin; Roussel-Dupré, Robert; Symbalisty, Eugene M. D.; Chanrion, Olivier; Odzimek, Anna; van der Velde, Oscar; Neubert, Torsten

    2010-01-01

    The electromagnetic radiation emitted by an electron avalanche beam resulting from relativistic runaway breakdown within the Earth's atmosphere is investigated. It is found from theoretical modeling with a computer simulation that the electron beam emits electromagnetic radiation which is characterized by consecutive broadband pulses in the low-frequency radio range from ˜10 to 300 kHz at a distance of ˜800 km. Experimental evidence for the existence of consecutive broadband pulses is provided by low-frequency radio observations of sprite-producing lightning discharges at a distance of ˜550 km. The measured broadband pulses occur ˜4-9 ms after the sprite-producing lightning discharge, they exhibit electromagnetic radiation which mainly spans the frequency range from ˜50 to 350 kHz, and they exhibit complex waveforms without the typical ionospheric reflection of the first hop sky wave. Two consecutive pulses occur ˜4.5 ms and ˜3 ms after the causative lightning discharge and coincide with the sprite luminosity. It is concluded that relativistic runaway breakdown within the Earth's atmosphere can emit broadband electromagnetic pulses and possibly generates sprites. The source location of the broadband pulses can be determined with an interferometric network of wideband low-frequency radio receivers to lend further experimental support to the relativistic runaway breakdown theory.

  17. Formation of runaway stars in a star-cluster potential

    NASA Astrophysics Data System (ADS)

    Ryu, Taeho; Leigh, Nathan W. C.; Perna, Rosalba

    2017-09-01

    We study the formation of runaway stars due to binary-binary (2+2) interactions in young star-forming clusters and/or associations. This is done using a combination of analytic methods and numerical simulations of 2+2 scattering interactions, both in isolation and in a homogeneous background potential. We focus on interactions that produce two single stars and a binary, and study the outcomes as a function of the depth of the background potential, within a range typical of cluster cores. As reference parameters for the observational properties, we use those observed for the system of runaway stars AE Aur and μ Col and binary ι Ori. We find that the outcome fractions have no appreciable dependence on the depth of the potential, and neither do the velocities of the ejected single stars. However, as the potential gets deeper and a larger fraction of binaries remain trapped, two binary populations emerge, with the escaped component having higher speeds and shorter semimajor axes than the trapped one. Additionally, we find that the relative angles between the ejected products are generally large. In particular, the angle between the ejected fastest star and the escaped binary is typically ≳120°-135°, with a peak at around 160°. However, as the potential gets deeper, the angle distribution becomes broader. Finally, we discuss the implications of our results for the interpretation of the properties of the runaway stars AE Aur and μ Col.

  18. Effects of energetic runaway electron penetration in plasma facing materials

    SciTech Connect

    Kawamura, T.

    1994-12-31

    Runaway electrons generated in a tokamak have severe, interactions with plasma facing materials of the first wall. They primarily contribute intense energy deposition on a material surface and give a severe heat shock to material components. Energetic runaway electrons penetrating in materials splendidly generate X-ray photons by Bremsstrahlung, and electrons of energy range beyond a few MeV lead to gamma ray photon production. In this paper the penetrations of energetic runaway electrons with energy exceeding a few MeV in graphite and other materials are quantitatively analyzed. The slowing down process and generation of gamma ray photons by Bremsstrahlung in materials are estimated. The neutron emission and radioactive isotope {sup 11}C production due to the giant resonance reaction {sup 12}C ({gamma}, n) {sup 11}C are quantitatively analyzed. A preliminary report on this process was presented at the first ISFNT in Tokyo. In this paper more comprehensive and quantitative estimations on this process are presented. The energy deposition profile in materials due to energetic electron penetration is also discussed.

  19. Probability and critical electric field for electron runaway

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Brennan, Dylan; Boozer, Allen; Bhattacharjee, Amitava

    2015-11-01

    It is very important that we understand the physics of the runaway electron avalanche, both due to the need for runaway mitigation in disruptions in ITER, and the pure scientific merit. In this work we developed a new method to obtain the probability of an electron in momentum space to run away, by solving a time-independent PDE, alleviating the need for Monte-Carlo simulation. This PDE turns out to be adjoint to the electron kinetic equation. The new method is applied to calculate the avalanche growth rate and the threshold electric field. The results show that in the presence of synchrotron radiation and pitch angle scattering, the threshold electric field for the avalanche growth will increase to a value that is higher than the Connor-Hastie electric field. A series of kinetic simulations are conducted which confirms the findings. We also did a time-dependent simulation with increasing plasma density to simulate the gas-puffing runaway electron experiments in DIII-D, and the hard X-ray signal result shows qualitative agreement with the experiments for the threshold electric field.

  20. An analytic method for identifying dynamically formed runaway stars

    NASA Astrophysics Data System (ADS)

    Ryu, Taeho; Leigh, Nathan W. C.; Perna, Rosalba

    2017-09-01

    In this paper, we study the three-body products (two single stars and a binary) of binary-binary (2+2) scattering interactions. This is done using a combination of analytic methods and numerical simulations of 2+2 scattering interactions, both in isolation and in a homogeneous background potential. We analytically derive a simple formula relating the angle between the velocity vectors of the two ejected single stars and the orbital separation of the remaining binary. We compare our analytic formulation to numerical scattering simulations and illustrate that the agreement is excellent, both in isolation and in a homogeneous background potential. Our results are ideally suited for application to the GAIA data base, which is expected to identify many hundred runaway stars. The analytic relation presented here has the potential to identify runaway stars formed dynamically with high confidence. Finally, by applying our method to the runaways AE Aur and μ Col, we illustrate that it can be used to constrain the history of the background potential, which was denser than the presently observed density in the case of the Trapezium cluster.

  1. THE NATURE OF THE HYPER-RUNAWAY CANDIDATE HIP 60350

    SciTech Connect

    Irrgang, Andreas; Przybilla, Norbert; Heber, Ulrich; Fernanda Nieva, M.; Schuh, Sonja

    2010-03-01

    Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B star HIP 60350 to determine which runaway scenario-a supernova explosion disrupting a binary system or dynamical interaction in star clusters-may be responsible for HIP 60350's peculiar orbit. Based on a non-local thermodynamic equilibrium approach, a high-resolution optical echelle spectrum was examined to revise spectroscopic quantities and for the first time to perform a differential chemical abundance analysis with respect to the B-type star 18 Peg. The results together with proper motions from the Hipparcos Catalog further allowed the three-dimensional kinematics of the star to be studied numerically. The abundances derived for HIP 60350 are consistent with a slightly supersolar metallicity agreeing with the kinematically predicted place of birth {approx}6 kpc away from the Galactic center. However, they do not exclude the possibility of an alpha-enhanced abundance pattern expected in the case of the supernova scenario. Its outstanding high Galactic rest-frame velocity of 530 +- 35 km s{sup -1} is a consequence of ejection in the direction of Galactic rotation and slightly exceeds the local Galactic escape velocity in a standard Galactic potential. Hence, HIP 60350 may be unbound to the Galaxy.

  2. An impact-induced, stable, runaway climate on Mars

    NASA Astrophysics Data System (ADS)

    Segura, Teresa L.; McKay, Christopher P.; Toon, Owen B.

    2012-07-01

    Large asteroid and comet impacts on Mars, such as the one that formed the Argyre basin, delivered considerable amounts of kinetic energy to the planet and raised the surface temperature hundreds of degrees. The impact that formed the Argyre basin occurred 3.8-3.9 byr ago (Werner, S.C. [2008]. Icarus 195, 45-60; Fassett, C.I., Head, J.W. [2011]. Icarus 211, 1204-1214), during the time of formation of fluvial features on the early martian surface, and was capable of causing global-scale precipitation and warming of the surface. Dual solutions to the climate of early Mars, one cold like present Mars and the other in a hot runaway state, exist for the pressure range of 0.006-1 bar of CO2, and for water inventories 6.5 bars or greater. A large impact event may have pushed Mars to a long-lasting hot runaway state. The runaway state would persist until escape processes reduced water vapor and forced the planet to return to a cold climate.

  3. Runaway stars as cosmic ray injectors inside molecular clouds

    NASA Astrophysics Data System (ADS)

    del Valle, M. V.; Romero, G. E.; Santos-Lima, R.

    2015-03-01

    Giant molecular clouds (GMCs) are a new population of gamma-ray sources, being the target of cosmic rays (CRs) - locally accelerated or not. These clouds host very young stellar clusters where massive star formation takes place. Eventually, some of the stars are ejected from the clusters, becoming runaway stars. These stars move supersonically through the cloud and develop bowshocks where particles can be accelerated up to relativistic energies. As a result, the bowshocks present non-thermal emission, and inject relativistic protons in the cloud. These protons diffuse in the GMC interacting with the matter. We present a model for the non-thermal radiation generated by protons and secondary pairs accelerated in the bowshocks of massive runaway stars within young GMCs. We solve the transport equation for primary protons and secondary pairs as the stars move through the cloud. We present non-thermal emissivity maps in radio and in gamma-rays as a function of time. We obtain X-ray luminosities of the order of ˜1032 erg s-1 and gamma-ray luminosities ˜1034 erg s-1. We conclude that, under some assumptions, relativistic protons from massive runaway stars interacting with matter in GMCs give rise to extended non-thermal sources.

  4. Parametric upconversion of lower hybrid wave by runaway electrons in tokamak

    SciTech Connect

    Kuley, Animesh; Tripathi, V. K.

    2010-06-15

    A kinetic formalism of parametric decay of a large amplitude lower hybrid pump wave into runaway electron mode and an upper sideband mode is investigated. The pump and the sideband exert a ponderomotive force on runaway electrons, driving the runaway mode. The density perturbation associated with the latter beats with the oscillatory velocity due to the pump to produce the sideband. The finite parallel velocity spread of the runaway electrons turns the parametric instability into a stimulated Compton scattering process where growth rate scales as the square of the pump amplitude. The large phase velocity waves thus generated can potentially generate relativistic electrons.

  5. Destabilization of magnetosonic-whistler waves by a relativistic runaway beam

    SciTech Connect

    Fueloep, T.; Pokol, G.; Helander, P.; Lisak, M.

    2006-06-15

    Magnetosonic-whistler waves may be destabilized by runaway electrons both in fusion and astrophysical plasmas. A linear instability growth rate of these waves in the presence of a runaway avalanche is calculated both perturbatively and by numerical solution of the full dispersion equation. The local threshold of the instability depends on the fraction of runaways, the magnetic field, and the temperature of the background plasma. The quasilinear analysis shows that the main result of the instability is the scattering of the electrons in pitch-angle. It appears possible that this instability could explain why the number of runaway electrons generated in tokamak disruptions depends on the strength of the magnetic field.

  6. Monte Carlo simulations of the supernova ejection mechanism for the runaway stars

    SciTech Connect

    Leonard, P.J.T.; Dewey, R.J.

    1992-08-01

    Monte Carlo simulations of supernova explosions in a realistic population of binary systems have been carried out for the purpose of studying the production of runaway stars. Contrary to previous studies, we find that the lowest mass runaways attain the highest velocities, and that there is no low-mass cutoff in the mass spectrum of the runaways. The vast majority of runaways with masses {ge} 5 M{circle_dot} have velocities < 200 km s{sup {minus}1}. An asymmetric kick during the explosion of 100--200 km s{sup {minus}1} is not enough to disrupt most of the binary systems; thus the majority of the runaways are expected to possess neutron star companions. For runaways with velocities > 50 km s{sup {minus}1}, most of these companions will be in eccentric orbits with periods < 10 days. Only {approx_equal} 1% of the supernova-ejected runaways should be normal binaries consisting of main-sequence stars. Such binaries axe produced when the distant component of a dose triple system is the first star to explode. Finally, only one 0-type runaway with a velocity {ge} 50 km s{sub {minus}1} is produced by every 10 to 15 binaries with O-type primaries, and thus the supernova ejection mechanism predicts that < 10% of all 0-type stars should be runaways.

  7. Monte Carlo simulations of the supernova ejection mechanism for the runaway stars

    SciTech Connect

    Leonard, P.J.T. ); Dewey, R.J. )

    1992-01-01

    Monte Carlo simulations of supernova explosions in a realistic population of binary systems have been carried out for the purpose of studying the production of runaway stars. Contrary to previous studies, we find that the lowest mass runaways attain the highest velocities, and that there is no low-mass cutoff in the mass spectrum of the runaways. The vast majority of runaways with masses {ge} 5 M{circle dot} have velocities < 200 km s{sup {minus}1}. An asymmetric kick during the explosion of 100--200 km s{sup {minus}1} is not enough to disrupt most of the binary systems; thus the majority of the runaways are expected to possess neutron star companions. For runaways with velocities > 50 km s{sup {minus}1}, most of these companions will be in eccentric orbits with periods < 10 days. Only {approx equal} 1% of the supernova-ejected runaways should be normal binaries consisting of main-sequence stars. Such binaries axe produced when the distant component of a dose triple system is the first star to explode. Finally, only one 0-type runaway with a velocity {ge} 50 km s{sub {minus}1} is produced by every 10 to 15 binaries with O-type primaries, and thus the supernova ejection mechanism predicts that < 10% of all 0-type stars should be runaways.

  8. [Human life and energy production. Prospects opened up by controlled thermonuclear fusion].

    PubMed

    Escande, D

    1997-03-18

    The massive and presently increasing energy production is going to confront mankind with a very important problem in the forthcoming decades, in particular due to the vanishing of resources and to the greenhouse effect. The share of fossil fuels in the energy production will have to decrease, and other energy sources will be needed. Among them controlled thermonuclear fusion has may assets due to its non-radioactive fuel with plentiful supply, its non radioactive and non polluting ashes, its safety, its weak environmental impact, and its irrelevance to nuclear proliferation in a normal setting. During the last three decades, physicists have made a series of steps toward the peaceful use of the dominant source of energy in the Universe. They have learned how to confine by magnetic fields plasmas at temperatures of 200 millions degrees centigrade, and they have developed several specific technologies. This way, they produced 11 million watts of nuclear power by fusing two isotopes of hydrogen. These investigations are conducted in a responsible spirit, that of ecoproduction, where possible negative consequences are anticipated, are made as low as reasonably achievable, and their management is studied. Yet several fundamental issues still have to be solved before on economically efficient industrial thermonuclear power plant be operated. A huge international collaboration involving Japan, the USA, the Russian Federation, and the European Union joined with Switzerland and Canada, is presently designing the first experimental thermonuclear reactor, the International Thermonuclear Experimental Reactor (ITER). It would cost 9 billion dollars, a cost similar to other large scientific projects. This is an important step toward an electricity producing thermonuclear reactor that would be both safe and respectful of human health and of environment.

  9. Runaway and Pregnant: Risk Factors Associated with Pregnancy in a National Sample of Runaway/Homeless Female Adolescents

    PubMed Central

    Thompson, Sanna J.; Bender, Kimberly A.; Lewis, Carol M.; Watkins, Rita

    2009-01-01

    Purpose Homeless youth are at particularly high risk for teen pregnancy; research indicates as many as 20% of homeless young women become pregnant. These pregnant and homeless teens lack financial resources and adequate health care, resulting in increased risk for low– birth-weight babies and high infant mortality. This study investigated individual and family-level predictors of teen pregnancy among a national sample of runaway/homeless youth in order to better understand the needs of this vulnerable population. Methods Data from the Runaway/Homeless Youth Management Information System (RHY MIS) provided a national sample of youth seeking services at crisis shelters. A sub-sample of pregnant females and a random sub-sample (matched by age) of nonpregnant females comprised the study sample (N= 951). Chi-square and t tests identified differences between pregnant and nonpregnant runaway females; maximum likelihood logistic regression identified individual and family-level predictors of teen pregnancy. Results Teen pregnancy was associated with being an ethnic minority, dropping out of school, being away from home for longer periods of time, having a sexually transmitted disease, and feeling abandoned by one's family. Family factors, such as living in a single parent household and experiencing emotional abuse by one's mother, increased the odds of a teen being pregnant. Conclusions The complex problems associated with pregnant runaway/homeless teens create challenges for short-term shelter services. Suggestions are made for extending shelter services to include referrals and coordination with teen parenting programs and other systems of care. PMID:18639785

  10. The Runaway Greenhouse Effect on Earth and other Planets

    NASA Technical Reports Server (NTRS)

    Rabbette, Maura; Pilewskie, Peter; McKay, Christopher; Young, Robert

    2001-01-01

    Water vapor is an efficient absorber of outgoing longwave infrared radiation on Earth and is the primary greenhouse gas. Since evaporation increases with increasing sea surface temperature, and the increase in water vapor further increases greenhouse warming, there is a positive feedback. The runaway greenhouse effect occurs if this feedback continues unchecked until all the water has left the surface and enters the atmosphere. For Mars and the Earth the runaway greenhouse was halted when water vapor became saturated with respect to ice or liquid water respectively. However, Venus is considered to be an example of a planet where the runaway greenhouse effect did occur, and it has been speculated that if the solar luminosity were to increase above a certain limit, it would also occur on the Earth. Satellite data acquired during the Earth Radiation Budget Experiment (ERBE) under clear sky conditions shows that as the sea surface temperature (SST) increases, the rate of outgoing infrared radiation at the top of the atmosphere also increases, as expected. Over the pacific warm pool where the SST exceeds 300 K the outgoing radiation emitted to space actually decreases with increasing SST, leading to a potentially unstable system. This behavior is a signature of the runaway greenhouse effect on Earth. However, the SST never exceeds 303K, thus the system has a natural cap which stops the runaway. According to Stefan-Boltzmann's law the amount of heat energy radiated by the Earth's surface is proportional to (T(sup 4)). However, if the planet has a substantial atmosphere, it can absorb all infrared radiation from the lower surface before the radiation penetrates into outer space. Thus, an instrument in space looking at the planet does not detect radiation from the surface. The radiation it sees comes from some level higher up. For the earth#s atmosphere the effective temperature (T(sub e)) has a value of 255 K corresponding to the middle troposphere, above most of the

  11. The Runaway Greenhouse Effect on Earth and other Planets

    NASA Technical Reports Server (NTRS)

    Rabbette, Maura; Pilewskie, Peter; McKay, Christopher; Young, Robert

    2001-01-01

    Water vapor is an efficient absorber of outgoing longwave infrared radiation on Earth and is the primary greenhouse gas. Since evaporation increases with increasing sea surface temperature, and the increase in water vapor further increases greenhouse warming, there is a positive feedback. The runaway greenhouse effect occurs if this feedback continues unchecked until all the water has left the surface and enters the atmosphere. For Mars and the Earth the runaway greenhouse was halted when water vapor became saturated with respect to ice or liquid water respectively. However, Venus is considered to be an example of a planet where the runaway greenhouse effect did occur, and it has been speculated that if the solar luminosity were to increase above a certain limit, it would also occur on the Earth. Satellite data acquired during the Earth Radiation Budget Experiment (ERBE) under clear sky conditions shows that as the sea surface temperature (SST) increases, the rate of outgoing infrared radiation at the top of the atmosphere also increases, as expected. Over the pacific warm pool where the SST exceeds 300 K the outgoing radiation emitted to space actually decreases with increasing SST, leading to a potentially unstable system. This behavior is a signature of the runaway greenhouse effect on Earth. However, the SST never exceeds 303K, thus the system has a natural cap which stops the runaway. According to Stefan-Boltzmann's law the amount of heat energy radiated by the Earth's surface is proportional to (T(sup 4)). However, if the planet has a substantial atmosphere, it can absorb all infrared radiation from the lower surface before the radiation penetrates into outer space. Thus, an instrument in space looking at the planet does not detect radiation from the surface. The radiation it sees comes from some level higher up. For the earth#s atmosphere the effective temperature (T(sub e)) has a value of 255 K corresponding to the middle troposphere, above most of the

  12. Nucleosynthesis in the Classical Nova Outburst

    NASA Astrophysics Data System (ADS)

    Starrfield, Sumner

    2010-02-01

    Classical Novae are the consequences of the accretion of hydrogen-rich material onto white dwarfs in close binary stellar systems. They are the third largest stellar explosions that occur in a galaxy after Gamma-ray Bursts and Supernovae but are far more common. They are well studied in the Solar neighborhood and in nearby galaxies so that a large number now have measured chemical abundances of their ejected gases. Of importance to this meeting, our simulations show that the temperatures reached in the explosions sample the same conditions as realized in terrestrial laboratory measurements; therefore, no extrapolations are necessary. As a result, we have been doing new calculations that test the effects of new reaction rates on predictions of the observed properties of the outburst. We will show the results of these simulations and, in addition, the effects of including reaction rates that were not previously included in the calculations. We will also show how the evolution and properties of the explosion depends on the initial assumed composition of the accreting material and the characteristics of the white dwarf. Finally, the connection with Supernovae of Type Ia, the explosions currently being used the study the evolution of the universe, is that they are thought to be the consequences of the accretion of helium rich material onto a white dwarf. The results of new simulations of these events will be presented. )

  13. Multiband Microvariability of BL Lac During Outburst

    NASA Astrophysics Data System (ADS)

    Clements, S. D.; Carini, M. T.; Noble, J. C.

    1998-01-01

    The blazar BL Lac recently underwent a major outburst. A search for microvariability was made with the 0.76 m telescope at the University of Florida's Rosemary Hill Observatory. Nearly 300 CCD observations in V and R were made over ten nights in July. During that time, BL Lac varied by more than 1.5 magnitudes and exhibited substantial microvariability. In fact, it exhibited microvariability each of the eight nights multiple exposures were made, being most active when brightest on July 29. On this night, four mini-flares were seen within 7 hours. During one of these flares, BL Lac brightened by more than 0.5 magnitude in less than 2.5 hours. The variations in V and R were simultaneous within the limits of the observations. However, the V and R magnitudes did not always change at the same rate. On July 3, BL Lac brightened in R faster than in V. Then on July 4, it dimmed in V faster than in R. Yet over the ten nights observed, BL Lac became bluer as it brightened. Another interesting difference between the V and R data was seen on July 4 when a mini-flare was seen in V but not in R. Clearly, while the V and R variations are highly correlated, there are compelling differences. Here we present these observations and discuss them in relation to models intended to explain microvariability. The authors gratefully acknowledge the support of NASA grant NCC5-228.

  14. 2014-2015 Multiple Outbursts of 15P/Finlay

    NASA Astrophysics Data System (ADS)

    Ishiguro, Masateru; Kuroda, Daisuke; Hanayama, Hidekazu; Kwon, Yuna Grace; Kim, Yoonyoung; Lee, Myung Gyoon; Watanabe, Makoto; Akitaya, Hiroshi; Kawabata, Koji; Itoh, Ryosuke; Nakaoka, Tatsuya; Yoshida, Michitoshi; Imai, Masataka; Sarugaku, Yuki; Yanagisawa, Kenshi; Ohta, Kouji; Kawai, Nobuyuki; Miyaji, Takeshi; Fukushima, Hideo; Honda, Satoshi; Takahashi, Jun; Sato, Mikiya; Vaubaillon, Jeremie J.; Watanabe, Jun-ichi

    2016-12-01

    Multiple outbursts of a Jupiter-family comet (JFC), 15P/Finlay, occurred from late 2014 to early 2015. We conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 January 15.6-15.7. The gas, consisting mostly of C2 and CN, and dust particles expanded at speeds of 1110 ± 180 m s-1 and 570 ± 40 m s-1 at a heliocentric distance of 1.0 au. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity β max = 1.6 ± 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 108-109 kg of dust particles (assumed to be 0.3 μm-1 mm) were ejected through each outburst. Although the total mass is three orders of magnitude smaller than that of the 17P/Holmes event observed in 2007, the kinetic energy per unit mass (104 J kg-1) is equivalent to the estimated values of 17P/Holmes and 332P/2010 V1 (Ikeya-Murakami), suggesting that the outbursts were caused by a similar physical mechanism. From a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15P/Finlay-class outbursts occur >1.5 times annually and inject dust particles from JFCs and Encke-type comets into interplanetary space at a rate of ˜10 kg s-1 or more.

  15. 45 CFR 1351.10 - What is the purpose of the Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... existing or proposed community-based runaway and homeless youth projects to provide temporary shelter and care to runaway or otherwise homeless youth who are in need of temporary shelter, counseling...

  16. 45 CFR 1351.10 - What is the purpose of the Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... existing or proposed community-based runaway and homeless youth projects to provide temporary shelter and care to runaway or otherwise homeless youth who are in need of temporary shelter, counseling...

  17. 45 CFR 1351.10 - What is the purpose of the Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... existing or proposed community-based runaway and homeless youth projects to provide temporary shelter and care to runaway or otherwise homeless youth who are in need of temporary shelter, counseling...

  18. Very rare outburst of the symbiotic variable AG Peg

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.

    2015-06-01

    The symbiotic variable AG Peg is in outburst, the first one observed since its only known outburst, which occurred in 1860-1870. Currently at visual/V magnitude 7.2 (B=7.8), it is an excellent target for visual, PEP, CCD, and DSLR observers and spectroscopists. The current outburst began after 2015 May 27 UT (T. Markham, Leek, Staffordshire, England, from the BAAVSS online database) and was underway by June 13.90 (A. Kosa-Kiss, Salonta, Romania). AG Peg has a very interesting history. Regarding the 1860-1870 outburst, data collected by E. Zinner (Merrill, 1959, S&T, 18, 9, 490) show AG Peg slowly brightening from visual magnitude 9.2 in 1821 to 8.0 in 1855, then at 6.2 in 1860 and brightening to 6.0 in 1870, then in decline at 6.8 by 1903, and continuing to decline slowly ( 6.9 in 1907, 8.0 in 1920, 8.3 in 1940). Observations in the AAVSO International Database since July 1941 show that the decline has continued without interruption from an average magnitude of 7.7 to an average magnitude of 8.8-9.0 by mid-January 2015. The AAVSO data since 1941 also show the periodic 0.4-magnitude variations ( 825 days) that have been present since the 1920s. Thus, after taking about 10 years to brighten from its minimum magnitude of about 9 to its maximum magnitude of 6.0, and then fading gradually over 140-145 years, AG Peg is now in outburst again. There are no observations of the 1860-1870 outburst that show the outburst's beginning. This time, however, in 2015, the opportunity is here to follow the outburst itself closely and learn just what this system does during outburst. Observations in all bands and visual observations are strongly encouraged. AG Peg is bright enough to be a very good PEP target. For spectroscopists, AG Peg has an extremely complex spectrum that undergoes substantial changes and would make a very interesting target. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (https://www.aavso.org/vsp). Observations should be

  19. HOPS 383: AN OUTBURSTING CLASS 0 PROTOSTAR IN ORION

    SciTech Connect

    Safron, Emily J.; Megeath, S. Thomas; Booker, Joseph; Fischer, William J.; Furlan, Elise; Rebull, Luisa M.; Stutz, Amelia M.; Stanke, Thomas; Billot, Nicolas; Tobin, John J.; Ali, Babar; Allen, Lori E.; Watson, Dan M.; Wilson, T. L.

    2015-02-10

    We report the dramatic mid-infrared brightening between 2004 and 2006 of Herschel Orion Protostar Survey (HOPS) 383, a deeply embedded protostar adjacent to NGC 1977 in Orion. By 2008, the source became a factor of 35 brighter at 24 μm with a brightness increase also apparent at 4.5 μm. The outburst is also detected in the submillimeter by comparing APEX/SABOCA to SCUBA data, and a scattered-light nebula appeared in NEWFIRM K{sub s} imaging. The post-outburst spectral energy distribution indicates a Class 0 source with a dense envelope and a luminosity between 6 and 14 L{sub ⊙}. Post-outburst time-series mid- and far-infrared photometry show no long-term fading and variability at the 18% level between 2009 and 2012. HOPS 383 is the first outbursting Class 0 object discovered, pointing to the importance of episodic accretion at early stages in the star formation process. Its dramatic rise and lack of fading over a 6 year period hint that it may be similar to FU Ori outbursts, although the luminosity appears to be significantly smaller than the canonical luminosities of such objects.

  20. A Simple, Unifying Model of the Extreme Ultraviolet Spectra of Dwarf Novae in Outburst

    SciTech Connect

    Mauche, C W

    2003-12-31

    A simple model of the boundary layer and accretion disk wind of dwarf novae in outburst is briefly described and applied to the Chandra Low Energy Transmission Grating spectra of WZ Sge and SS Cyg in outburst.

  1. Assessing glacial lake outburst flood risk

    NASA Astrophysics Data System (ADS)

    Kougkoulos, Ioannis; Cook, Simon; Jomelli, Vincent; Clarke, Leon; Symeonakis, Elias

    2017-04-01

    Glaciers across the world are thinning and receding in response to atmospheric warming. Glaciers tend to erode subglacial basins and deposit eroded materials around their margins as lateral-frontal terminal moraines. Recession into these basins and behind impounding moraines causes meltwater to pond as proglacial and supraglacial lakes. Consequently, there has been a general trend of increasing number and size of these lakes associated with glacier melting in many mountainous regions around the globe, in the last 30 years. Glacial lake outburst floods (GLOFs) then may occur where the glacial lake dam (ice, rock, moraine, or combination thereof) is breached, or overtopped, and thousands of people have lost their lives to such events in the last few decades, especially in the Andes and in the Himalaya. Given the ongoing and arguably increasing risk posed to downstream communities, and infrastructure, there has been a proliferation of GLOF studies, with many seeking to estimate GLOF hazard or risk in specific regions, or to identify 'potentially dangerous glacial lakes'. Given the increased scientific interest in GLOFs, it is timely to evaluate critically the ways in which GLOF risk has been assessed previously, and whether there are improvements that can be made to the ways in which risk assessment is achieved. We argue that, whilst existing GLOF hazard and risk assessments have been extremely valuable they often suffer from a number of key shortcomings that can be addressed by using different techniques as multi-criteria decision analysis and hydraulic modelling borrowed from disciplines like engineering, remote sensing and operations research.

  2. Family Risk Factors and Prevalence of Dissociative Symptoms among Homeless and Runaway Youth

    ERIC Educational Resources Information Center

    Tyler, Kimberly A.; Cauce, Ana Mari; Whitbeck, Les

    2004-01-01

    Objective: To examine family risk factors associated with dissociative symptoms among homeless and runaway youth. Method: Three hundred and twenty-eight homeless and runaway youth were interviewed using a systematic sampling strategy in metropolitan Seattle. Homeless young people were interviewed on the streets and in shelters by outreach workers…

  3. Runaway electron beam generation and mitigation during disruptions at JET-ILW

    NASA Astrophysics Data System (ADS)

    Reux, C.; Plyusnin, V.; Alper, B.; Alves, D.; Bazylev, B.; Belonohy, E.; Boboc, A.; Brezinsek, S.; Coffey, I.; Decker, J.; Drewelow, P.; Devaux, S.; de Vries, P. C.; Fil, A.; Gerasimov, S.; Giacomelli, L.; Jachmich, S.; Khilkevitch, E. M.; Kiptily, V.; Koslowski, R.; Kruezi, U.; Lehnen, M.; Lupelli, I.; Lomas, P. J.; Manzanares, A.; De Aguilera, A. Martin; Matthews, G. F.; Mlynář, J.; Nardon, E.; Nilsson, E.; Perez von Thun, C.; Riccardo, V.; Saint-Laurent, F.; Shevelev, A. E.; Sips, G.; Sozzi, C.; contributors, JET

    2015-09-01

    Disruptions are a major operational concern for next generation tokamaks, including ITER. They may generate excessive heat loads on plasma facing components, large electromagnetic forces in the machine structures and several MA of multi-MeV runaway electrons. A more complete understanding of the runaway generation processes and methods to suppress them is necessary to ensure safe and reliable operation of future tokamaks. Runaway electrons were studied at JET-ILW showing that their generation dependencies (accelerating electric field, avalanche critical field, toroidal field, MHD fluctuations) are in agreement with current theories. In addition, vertical stability plays a key role in long runaway beam formation. Energies up to 20 MeV are observed. Mitigation of an incoming runaway electron beam triggered by massive argon injection was found to be feasible provided that the injection takes place early enough in the disruption process. However, suppressing an already accelerated runaway electron beam in the MA range was found to be difficult even with injections of more than 2 kPa.m3 high-Z gases such as krypton or xenon. This may be due to the presence of a cold background plasma weakly coupled to the runaway electron beam which prevents neutrals from penetrating in the electron beam core. Following unsuccessful mitigation attempts, runaway electron impacts on beryllium plasma-facing components were observed, showing localized melting with toroidal asymmetries.

  4. Propensity for Violence among Homeless and Runaway Adolescents: An Event History Analysis

    ERIC Educational Resources Information Center

    Crawford, Devan M.; Whitbeck, Les B.; Hoyt, Dan R.

    2011-01-01

    Little is known about the prevalence of violent behaviors among homeless and runaway adolescents or the specific behavioral factors that influence violent behaviors across time. In this longitudinal study of 300 homeless and runaway adolescents aged 16 to 19 at baseline, the authors use event history analysis to assess the factors associated with…

  5. Comparison of Family Therapy Outcome with Alcohol-Abusing, Runaway Adolescents

    ERIC Educational Resources Information Center

    Slesnick, Natasha; Prestopnik, Jillian L

    2009-01-01

    Treatment evaluation for alcohol problem, runaway adolescents and their families is rare. This study recruited primary alcohol problem adolescents (N = 119) and their primary caretakers from two runaway shelters and assigned them to (a) home-based ecologically based family therapy (EBFT), (b) office-based functional family therapy (FFT), or (c)…

  6. Model Experiment of Thermal Runaway Reactions Using the Aluminum-Hydrochloric Acid Reaction

    ERIC Educational Resources Information Center

    Kitabayashi, Suguru; Nakano, Masayoshi; Nishikawa, Kazuyuki; Koga, Nobuyoshi

    2016-01-01

    A laboratory exercise for the education of students about thermal runaway reactions based on the reaction between aluminum and hydrochloric acid as a model reaction is proposed. In the introductory part of the exercise, the induction period and subsequent thermal runaway behavior are evaluated via a simple observation of hydrogen gas evolution and…

  7. Propensity for Violence among Homeless and Runaway Adolescents: An Event History Analysis

    ERIC Educational Resources Information Center

    Crawford, Devan M.; Whitbeck, Les B.; Hoyt, Dan R.

    2011-01-01

    Little is known about the prevalence of violent behaviors among homeless and runaway adolescents or the specific behavioral factors that influence violent behaviors across time. In this longitudinal study of 300 homeless and runaway adolescents aged 16 to 19 at baseline, the authors use event history analysis to assess the factors associated with…

  8. RUNAWAY STARS AND THE ESCAPE OF IONIZING RADIATION FROM HIGH-REDSHIFT GALAXIES

    SciTech Connect

    Conroy, Charlie; Kratter, Kaitlin M.

    2012-08-20

    Approximately 30% of all massive stars in the Galaxy are runaways with velocities exceeding 30 km s{sup -1}. Their high speeds allow them to travel {approx}0.1-1 kpc away from their birthplace before they explode at the end of their several Myr lifetimes. At high redshift, when galaxies were much smaller than in the local universe, runaways could venture far from the dense inner regions of their host galaxies. From these large radii, and therefore low column densities, much of their ionizing radiation is able to escape into the intergalactic medium. Runaways may therefore significantly enhance the overall escape fraction of ionizing radiation, f{sub esc}, from small galaxies at high redshift. We present simple models of the high-redshift runaway population and its impact on f{sub esc} as a function of halo mass, size, and redshift. We find that the inclusion of runaways enhances f{sub esc} by factors of Almost-Equal-To 1.1-8, depending on halo mass, galaxy geometry, and the mechanism of runaway production, implying that runaways may contribute 50%-90% of the total ionizing radiation escaping from high-redshift galaxies. Runaways may therefore play an important role in reionizing the universe.

  9. Model Experiment of Thermal Runaway Reactions Using the Aluminum-Hydrochloric Acid Reaction

    ERIC Educational Resources Information Center

    Kitabayashi, Suguru; Nakano, Masayoshi; Nishikawa, Kazuyuki; Koga, Nobuyoshi

    2016-01-01

    A laboratory exercise for the education of students about thermal runaway reactions based on the reaction between aluminum and hydrochloric acid as a model reaction is proposed. In the introductory part of the exercise, the induction period and subsequent thermal runaway behavior are evaluated via a simple observation of hydrogen gas evolution and…

  10. Comparison of Family Therapy Outcome with Alcohol-Abusing, Runaway Adolescents

    ERIC Educational Resources Information Center

    Slesnick, Natasha; Prestopnik, Jillian L

    2009-01-01

    Treatment evaluation for alcohol problem, runaway adolescents and their families is rare. This study recruited primary alcohol problem adolescents (N = 119) and their primary caretakers from two runaway shelters and assigned them to (a) home-based ecologically based family therapy (EBFT), (b) office-based functional family therapy (FFT), or (c)…

  11. Family Risk Factors and Prevalence of Dissociative Symptoms among Homeless and Runaway Youth

    ERIC Educational Resources Information Center

    Tyler, Kimberly A.; Cauce, Ana Mari; Whitbeck, Les

    2004-01-01

    Objective: To examine family risk factors associated with dissociative symptoms among homeless and runaway youth. Method: Three hundred and twenty-eight homeless and runaway youth were interviewed using a systematic sampling strategy in metropolitan Seattle. Homeless young people were interviewed on the streets and in shelters by outreach workers…

  12. Parents, Teachers, and Peers and Early Adolescent Runaway in Hong Kong

    ERIC Educational Resources Information Center

    Cheung, Chan-Kiu; Liu, Suk-Ching; Lee, Tak-Yan

    2005-01-01

    Parental monitoring, teacher support, classmate support, and friend relationship presumably affect adolescents' runaway from home. According to social control theory, social control based on conventional social norms would prevent adolescent runaway, but association with friends may erode such control. This expectation appears to hold true in a…

  13. 30 CFR 57.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Protection against moving or runaway railroad equipment. 57.9302 Section 57.9302 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad...

  14. 30 CFR 57.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Protection against moving or runaway railroad equipment. 57.9302 Section 57.9302 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad...

  15. 30 CFR 56.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Protection against moving or runaway railroad... MINES Loading, Hauling, and Dumping Safety Devices, Provisions, and Procedures for Roadways, Railroads, and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad...

  16. 30 CFR 56.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Protection against moving or runaway railroad... MINES Loading, Hauling, and Dumping Safety Devices, Provisions, and Procedures for Roadways, Railroads, and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad...

  17. Risk Factors for Cigarette, Alcohol, and Marijuana Use among Runaway Youth Utilizing Two Services Sectors

    ERIC Educational Resources Information Center

    Thompson, Sanna J.; Zittel-Palmara, Kimberley M.; Forehand, Gregory

    2005-01-01

    The high rates of substance use among American adolescents are challenging; however, runaway youth are at particularly high-risk for substance use. Runaway youth utilizing two service sectors, emergency crisis shelters and juvenile detention centers, were recruited to evaluate differences in risk factors associated with substance use. Findings…

  18. 30 CFR 57.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Protection against moving or runaway railroad equipment. 57.9302 Section 57.9302 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad equipment...

  19. 30 CFR 56.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Protection against moving or runaway railroad... MINES Loading, Hauling, and Dumping Safety Devices, Provisions, and Procedures for Roadways, Railroads, and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad equipment...

  20. 30 CFR 56.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Protection against moving or runaway railroad... MINES Loading, Hauling, and Dumping Safety Devices, Provisions, and Procedures for Roadways, Railroads, and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad equipment...