Science.gov

Sample records for outburst thermonuclear runaways

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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).

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  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. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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)

  9. 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.

  10. Stability of Beta Limited Thermonuclear Burn.

    DTIC Science & Technology

    1980-01-28

    wunboeJ e burn stability of a thermonuclear reacting plasma Is examined under the assumption that a bum equilibrium exists due to the rapid Increase...of loss rate with plasma beta once a critical beta value is exceeded, it is found that perturbations about equilibrium generally result in a rapidly...exceeded, in order to establish a thermonuclear burn equilibrium , it is necessary that plasma losses increase sufficiently rapidly with temperature. In

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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)

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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…

  4. 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…

  5. 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…

  6. 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.

  7. 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.

  8. 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)

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  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. 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…

  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. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.).

  5. 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.).

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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).

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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…

  9. 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

  10. 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.

  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. 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.

  13. 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.

  14. 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.

  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

    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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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)].

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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…

  16. 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.

  17. 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.

  18. 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.}

  19. 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.

  20. 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.

  1. 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

  2. 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…

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  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. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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…

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  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. 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

  18. 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.}

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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%.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  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. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  1. 30 CFR 56.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Protection against moving or runaway railroad..., and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  2. 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..., and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  3. 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..., and Loading and Dumping Sites § 56.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  4. 30 CFR 57.9302 - 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..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  5. 30 CFR 57.9302 - Protection against moving or runaway railroad equipment.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Protection against moving or runaway railroad..., Railroads, and Loading and Dumping Sites § 57.9302 Protection against moving or runaway railroad equipment. Stopblocks, derail devices, or other devices that protect against moving or runaway rail equipment shall...

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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. 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.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. 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...

  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. 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.

  15. 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

  16. 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.

  17. 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

  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. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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…

  4. 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.

  5. 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.

  6. 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.

  7. 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…

  8. 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.

  9. 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.

  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. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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).

  3. 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."

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  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. 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.

  16. 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

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.}

  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. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. [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.

  15. 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

  16. 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.

  17. 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.

  18. 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...

  19. 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...

  20. 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...

  1. X-ray observations of dwarf nova outbursts

    NASA Astrophysics Data System (ADS)

    Wheatley, P.

    Dwarf novae are semi-detached binary stars in which a white dwarf accretes material lost by a red dwarf. Accretion occurs via an accretion disk which is apparently unstable, resulting in dramatic optical outbursts (systems typically brighten by a factor 100). Dwarf nova outbursts occur infrequently (weeks to years) and unpredictably, making them difficult targets for most astronomical observatories. Consequently our understanding is based largely on optical monitoring by amateur astronomers, and observations at other wavelengths are rare and usually sketchy. While optical photometry does provide a good probe of the outer accretion disk, most of the accretion luminosity is liberated in X-rays and the EUV in the inner accretion disk and at its boundary with the white dwarf. High-energy observations allow us to study the response of these inner regions to the varying accretion rate through the outburst cycle. In this talk I review recent X-ray observations of dwarf nova outbursts. RXTE has played an extremely important role in this field because it is the only X-ray observatory with sufficient scheduling flexibility to respond rapidly to outbursts and to make frequent monitoring observations.

  2. 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.

  3. 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…

  4. 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…

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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.

  10. 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…

  11. 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)…

  12. 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…

  13. 78 FR 64153 - Direct Certification and Certification of Homeless, Migrant and Runaway Children for Free School...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-28

    ... of Homeless, Migrant and Runaway Children for Free School Meals; Approval of Information Collection... Homeless, Migrant and Runaway Children for Free School Meals was published on April 25, 2011. The ICR for... collection OMB Control Number 0584-0585. The Office of Management and Budget (OMB) cleared the...

  14. 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.

  15. Largescale Long-term particle Simulations of Runaway electrons in Tokamaks

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Qin, Hong; Wang, Yulei

    2016-10-01

    To understand runaway dynamical behavior is crucial to assess the safety of tokamaks. Though many important analytical and numerical results have been achieved, the overall dynamic behaviors of runaway electrons in a realistic tokamak configuration is still rather vague. In this work, the secular full-orbit simulations of runaway electrons are carried out based on a relativistic volume-preserving algorithm. Detailed phase-space behaviors of runaway electrons are investigated in different timescales spanning 11 orders. A detailed analysis of the collisionless neoclassical scattering is provided when considering the coupling between the rotation of momentum vector and the background field. In large timescale, the initial condition of runaway electrons in phase space globally influences the runaway distribution. It is discovered that parameters and field configuration of tokamaks can modify the runaway electron dynamics significantly. Simulations on 10 million cores of supercomputer using the APT code have been completed. A resolution of 107 in phase space is used, and simulations are performed for 1011 time steps. Largescale simulations show that in a realistic fusion reactor, the concern of runaway electrons is not as serious as previously thought. This research was supported by National Magnetic Connement Fusion Energy Research Project (2015GB111003, 2014GB124005), the National Natural Science Foundation of China (NSFC-11575185, 11575186) and the GeoAlgorithmic Plasma Simulator (GAPS) Project.

  16. 45 CFR 1351.20 - What are the additional requirements under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Runaway and Homeless Youth Program grant? 1351.20 Section 1351.20 Public Welfare Regulations Relating to... HOMELESS YOUTH PROGRAM Additional Requirements § 1351.20 What are the additional requirements under a Runaway and Homeless Youth Program grant? (a) To improve the administration of the Runaway and...

  17. 45 CFR 1351.15 - What costs are supportable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Homeless Youth Program grant? 1351.15 Section 1351.15 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.15 What costs are supportable under a Runaway and...

  18. 45 CFR 1351.16 - What costs are not allowable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Homeless Youth Program grant? 1351.16 Section 1351.16 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.16 What costs are not allowable under a Runaway...

  19. 45 CFR 1351.15 - What costs are supportable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Homeless Youth Program grant? 1351.15 Section 1351.15 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.15 What costs are supportable under a Runaway and...

  20. 45 CFR 1351.15 - What costs are supportable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Homeless Youth Program grant? 1351.15 Section 1351.15 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.15 What costs are supportable under a Runaway and...

  1. 45 CFR 1351.20 - What are the additional requirements under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Runaway and Homeless Youth Program grant? 1351.20 Section 1351.20 Public Welfare Regulations Relating to... HOMELESS YOUTH PROGRAM Additional Requirements § 1351.20 What are the additional requirements under a Runaway and Homeless Youth Program grant? (a) To improve the administration of the Runaway and...

  2. 45 CFR 1351.12 - Who gets priority for the award of a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Homeless Youth Program grant? 1351.12 Section 1351.12 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.12 Who gets priority for the award of a Runaway...

  3. 45 CFR 1351.11 - Who is eligible to apply for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Homeless Youth Program grant? 1351.11 Section 1351.11 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.11 Who is eligible to apply for a Runaway and...

  4. 45 CFR 1351.16 - What costs are not allowable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Homeless Youth Program grant? 1351.16 Section 1351.16 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.16 What costs are not allowable under a Runaway...

  5. 45 CFR 1351.11 - Who is eligible to apply for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Homeless Youth Program grant? 1351.11 Section 1351.11 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.11 Who is eligible to apply for a Runaway and...

  6. 45 CFR 1351.16 - What costs are not allowable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Homeless Youth Program grant? 1351.16 Section 1351.16 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.16 What costs are not allowable under a Runaway...

  7. 45 CFR 1351.16 - What costs are not allowable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Homeless Youth Program grant? 1351.16 Section 1351.16 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.16 What costs are not allowable under a Runaway...

  8. 45 CFR 1351.20 - What are the additional requirements under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Runaway and Homeless Youth Program grant? 1351.20 Section 1351.20 Public Welfare Regulations Relating to... HOMELESS YOUTH PROGRAM Additional Requirements § 1351.20 What are the additional requirements under a Runaway and Homeless Youth Program grant? (a) To improve the administration of the Runaway and...

  9. 45 CFR 1351.12 - Who gets priority for the award of a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Homeless Youth Program grant? 1351.12 Section 1351.12 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.12 Who gets priority for the award of a Runaway...

  10. 45 CFR 1351.12 - Who gets priority for the award of a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Homeless Youth Program grant? 1351.12 Section 1351.12 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.12 Who gets priority for the award of a Runaway...

  11. 45 CFR 1351.11 - Who is eligible to apply for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Homeless Youth Program grant? 1351.11 Section 1351.11 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.11 Who is eligible to apply for a Runaway and...

  12. 45 CFR 1351.15 - What costs are supportable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Homeless Youth Program grant? 1351.15 Section 1351.15 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.15 What costs are supportable under a Runaway and...

  13. 45 CFR 1351.12 - Who gets priority for the award of a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Homeless Youth Program grant? 1351.12 Section 1351.12 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.12 Who gets priority for the award of a Runaway...

  14. 45 CFR 1351.11 - Who is eligible to apply for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Homeless Youth Program grant? 1351.11 Section 1351.11 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.11 Who is eligible to apply for a Runaway and...

  15. 45 CFR 1351.12 - Who gets priority for the award of a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Homeless Youth Program grant? 1351.12 Section 1351.12 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.12 Who gets priority for the award of a Runaway...

  16. 45 CFR 1351.20 - What are the additional requirements under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Runaway and Homeless Youth Program grant? 1351.20 Section 1351.20 Public Welfare Regulations Relating to... HOMELESS YOUTH PROGRAM Additional Requirements § 1351.20 What are the additional requirements under a Runaway and Homeless Youth Program grant? (a) To improve the administration of the Runaway and...

  17. 45 CFR 1351.15 - What costs are supportable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Homeless Youth Program grant? 1351.15 Section 1351.15 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.15 What costs are supportable under a Runaway and...

  18. 45 CFR 1351.16 - What costs are not allowable under a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Homeless Youth Program grant? 1351.16 Section 1351.16 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.16 What costs are not allowable under a Runaway...

  19. 45 CFR 1351.11 - Who is eligible to apply for a Runaway and Homeless Youth Program grant?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Homeless Youth Program grant? 1351.11 Section 1351.11 Public Welfare Regulations Relating to Public Welfare... FOR CHILDREN, YOUTH AND FAMILIES, FAMILY AND YOUTH SERVICES BUREAU RUNAWAY AND HOMELESS YOUTH PROGRAM Runaway and Homeless Youth Program Grant § 1351.11 Who is eligible to apply for a Runaway and...

  20. CFD research on runaway transient of pumped storage power station caused by pumping power failure

    NASA Astrophysics Data System (ADS)

    Zhang, L. G.; Zhou, D. Q.

    2013-12-01

    To study runaway transient of pumped storage power station caused by pumping power failure, three dimensional unsteady numerical simulations were executed on geometrical model of the whole flow system. Through numerical calculation, the changeable flow configuration and variation law of some parameters such as unit rotate speed,flow rate and static pressure of measurement points were obtained and compared with experimental data. Numerical results show that runaway speed agrees well with experimental date and its error was 3.7%. The unit undergoes pump condition, brake condition, turbine condition and runaway condition with flow characteristic changing violently. In runaway condition, static pressure in passage pulses very strongly which frequency is related to runaway speed.

  1. Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons

    SciTech Connect

    Pokol, G. I.; Kómár, A.; Budai, A.; Stahl, A.; Fülöp, T.

    2014-10-15

    Runaway electrons with strongly anisotropic distributions present in post-disruption tokamak plasmas can destabilize the extraordinary electron (EXEL) wave. The present work investigates the dynamics of the quasi-linear evolution of the EXEL instability for a range of different plasma parameters using a model runaway distribution function valid for highly relativistic runaway electron beams produced primarily by the avalanche process. Simulations show a rapid pitch-angle scattering of the runaway electrons in the high energy tail on the 100–1000 μs time scale. Due to the wave-particle interaction, a modification to the synchrotron radiation spectrum emitted by the runaway electron population is foreseen, exposing a possible experimental detection method for such an interaction.

  2. Observation of runaway electron beams by visible color camera in the Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Shi, Yuejiang; Fu, Jia; Li, Jiahong; Yang, Yu; Wang, Fudi; Li, Yingying; Zhang, Wei; Wan, Baonian; Chen, Zhongyong

    2010-03-01

    The synchrotron radiation originated from the energetic runaway electrons has been measured by a visible complementary metal oxide semiconductor camera working in the wavelength ranges of 380-750 nm in the Experimental Advanced Superconducting Tokamak [H. Q. Liu et al., Plasma Phys. Contr. Fusion 49, 995 (2007)]. With a tangential viewing into the plasma in the direction of electron approach on the equatorial plane, the synchrotron radiation from the energetic runaway electrons was measured in full poloidal cross section. The synchrotron radiation diagnostics provides a direct pattern of the runaway beam inside the plasma. The energy and pitch angle of runaway electrons have been obtained according to the synchrotron radiation pattern. A stable shell shape of synchrotron radiation has been observed in a few runaway discharges.

  3. Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field

    NASA Astrophysics Data System (ADS)

    Gurevich, A. V.; Mesyats, G. A.; Zybin, K. P.; Yalandin, M. I.; Reutova, A. G.; Shpak, V. G.; Shunailov, S. A.

    2012-08-01

    The generation of an avalanche of runaway electrons is demonstrated for the first time in a laboratory experiment. Two flows of runaway electrons are formed sequentially in an extended air discharge gap at the stage of delay of a pulsed breakdown. The first, picosecond, runaway electron flow is emitted in the cathode region where the field is enhanced. Being accelerated in the gap, this beam generates electrons due to impact ionization. These secondary electrons form a delayed avalanche of runaway electrons if the field is strong enough. The properties of the avalanche correspond to the existing notions about the runaway breakdown in air. The measured current of the avalanche exceeds up to an order the current of the initiating electron beam.

  4. Observation of the avalanche of runaway electrons in air in a strong electric field.

    PubMed

    Gurevich, A V; Mesyats, G A; Zybin, K P; Yalandin, M I; Reutova, A G; Shpak, V G; Shunailov, S A

    2012-08-24

    The generation of an avalanche of runaway electrons is demonstrated for the first time in a laboratory experiment. Two flows of runaway electrons are formed sequentially in an extended air discharge gap at the stage of delay of a pulsed breakdown. The first, picosecond, runaway electron flow is emitted in the cathode region where the field is enhanced. Being accelerated in the gap, this beam generates electrons due to impact ionization. These secondary electrons form a delayed avalanche of runaway electrons if the field is strong enough. The properties of the avalanche correspond to the existing notions about the runaway breakdown in air. The measured current of the avalanche exceeds up to an order the current of the initiating electron beam.

  5. Structure of the runaway electron loss during induced disruptions in TEXTOR

    SciTech Connect

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

    2015-10-15

    The loss of runaway electrons during an induced disruption is recorded by a synchrotron imaging technique using a fast infrared CCD camera. The loss is predominantly diffuse. During the “spiky-loss phase”, when the runaway beam moves close to the wall, a narrow channel between the runaway column and a scintillator probe is formed and lasts until the runaway beam is terminated. In some cases, the processed images show a stripe pattern at the plasma edge. A comparison between the MHD dominated disruptions and the MHD-free disruption is performed. A new mechanism of plasma disruptions with the runaway electron generation and a novel model which reproduces many characteristic features of the plasma beam evolution during a disruption is briefly described.

  6. Observation of the loss of pre-disruptive runaway electrons in KSTAR ohmic plasma disruptions

    NASA Astrophysics Data System (ADS)

    Cheon, MunSeong; Kim, Junghee; An, YoungHwa; Seo, Dongcheol; Kim, Hyunseok

    2016-12-01

    A newly-developed fast neutron detector revealed a close relationship between the loss of pre-disruptive runaway electrons and the plasma disruption in KSTAR ohmic plasmas. It is observed that a burst of photoneutrons is generated exactly before the start of thermal quenches, indicating a bunch of runaway electrons which had existed before the disruption impacts the first wall at the time. The loss of runaway electrons could be identified also as a decrease in the measured electron temperature, forming a typical two-stage thermal quench trace. From the MHD pattern in the neutron signal during a low-q disruption, it could be identified that pre-disruptive runaway electrons are localized in the plasma, especially on the q  =  2 drift surface. These new findings suggest the pre-disruptive runaway electrons might play an important role in the plasma disruption mechanism.

  7. Structure of the runaway electron loss during induced disruptions in TEXTOR

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    The loss of runaway electrons during an induced disruption is recorded by a synchrotron imaging technique using a fast infrared CCD camera. The loss is predominantly diffuse. During the "spiky-loss phase", when the runaway beam moves close to the wall, a narrow channel between the runaway column and a scintillator probe is formed and lasts until the runaway beam is terminated. In some cases, the processed images show a stripe pattern at the plasma edge. A comparison between the MHD dominated disruptions and the MHD-free disruption is performed. A new mechanism of plasma disruptions with the runaway electron generation and a novel model which reproduces many characteristic features of the plasma beam evolution during a disruption is briefly described.

  8. Observation of runaway electron beams by visible color camera in the Experimental Advanced Superconducting Tokamak

    SciTech Connect

    Shi Yuejiang; Fu Jia; Li Jiahong; Yang Yu; Wang Fudi; Li Yingying; Zhang Wei; Wan Baonian; Chen Zhongyong

    2010-03-15

    The synchrotron radiation originated from the energetic runaway electrons has been measured by a visible complementary metal oxide semiconductor camera working in the wavelength ranges of 380-750 nm in the Experimental Advanced Superconducting Tokamak [H. Q. Liu et al., Plasma Phys. Contr. Fusion 49, 995 (2007)]. With a tangential viewing into the plasma in the direction of electron approach on the equatorial plane, the synchrotron radiation from the energetic runaway electrons was measured in full poloidal cross section. The synchrotron radiation diagnostics provides a direct pattern of the runaway beam inside the plasma. The energy and pitch angle of runaway electrons have been obtained according to the synchrotron radiation pattern. A stable shell shape of synchrotron radiation has been observed in a few runaway discharges.

  9. Observation of runaway electron beams by visible color camera in the Experimental Advanced Superconducting Tokamak.

    PubMed

    Shi, Yuejiang; Fu, Jia; Li, Jiahong; Yang, Yu; Wang, Fudi; Li, Yingying; Zhang, Wei; Wan, Baonian; Chen, Zhongyong

    2010-03-01

    The synchrotron radiation originated from the energetic runaway electrons has been measured by a visible complementary metal oxide semiconductor camera working in the wavelength ranges of 380-750 nm in the Experimental Advanced Superconducting Tokamak [H. Q. Liu et al., Plasma Phys. Contr. Fusion 49, 995 (2007)]. With a tangential viewing into the plasma in the direction of electron approach on the equatorial plane, the synchrotron radiation from the energetic runaway electrons was measured in full poloidal cross section. The synchrotron radiation diagnostics provides a direct pattern of the runaway beam inside the plasma. The energy and pitch angle of runaway electrons have been obtained according to the synchrotron radiation pattern. A stable shell shape of synchrotron radiation has been observed in a few runaway discharges.

  10. The production and confinement of runaway electrons with impurity killer pellets in DIII-D

    SciTech Connect

    Evans, T.E.; Taylor, P.L.; Whyte, D.G.

    1998-12-01

    Prompt runaway electron bursts, generated by rapidly cooling DIII-D plasmas with argon killer pellets, are used to test a recent knock-on avalanche theory describing the growth of multi-MeV runaway electron currents during disruptions in tokamaks. Runaway current amplitudes, observed during some but not all DIII-D current quenches, are consistent with growth rates predicted by the theory assuming a pre-current quench runaway electron density of approximately 10{sup 15} m{sup {minus}3}. Argon killer pellet modeling yields runaway densities of between 10{sup 15}--10{sup 16} m{sup {minus}3} in these discharges. Although knock-on avalanching appears to agree rather well with the measurements, relatively small avalanche amplification factors combined with uncertainties in the spatial distribution of pellet mass and cooling rates make it difficult to unambiguously confirm the proposed theory with existing data.

  11. Electromagnetic waves destabilized by runaway electrons in near-critical electric fields

    SciTech Connect

    Komar, A.; Pokol, G. I.; Fueloep, T.

    2013-01-15

    Runaway electron distributions are strongly anisotropic in velocity space. This anisotropy is a source of free energy that may destabilize electromagnetic waves through a resonant interaction between the waves and the energetic electrons. In this work, we investigate the high-frequency electromagnetic waves that are destabilized by runaway electron beams when the electric field is close to the critical field for runaway acceleration. Using a runaway electron distribution appropriate for the near-critical case, we calculate the linear instability growth rate of these waves and conclude that the obliquely propagating whistler waves are most unstable. We show that the frequencies, wave numbers, and propagation angles of the most unstable waves depend strongly on the magnetic field. Taking into account collisional and convective damping of the waves, we determine the number density of runaways that is required to destabilize the waves and show its parametric dependences.

  12. Sexual Health Information Seeking Online Among Runaway and Homeless Youth.

    PubMed

    Barman-Adhikari, Anamika; Rice, Eric

    2011-06-01

    Research shows runaway and homeless youth are reluctant to seek help from traditional health providers. The Internet can be useful in engaging this population and meeting their needs for sexual health information, including information about HIV and other sexually transmitted infections (STIs). Using a sample of homeless youth living in Los Angeles, California in June 2009, this study assesses the frequency with which runaway and homeless youth seek sexual health information via the Internet, and assesses which youth are more likely to engage in seeking health information from online sources. Drawing from Andersen's (1968) health behavior model and Pescosolido's (1992) network episode model, we develop and refine a model for seeking online sexual health information among homeless youth. Rather than testing the predicative strength of a given model, our aim is to identify and explore conceptually driven correlates that may shed light on the characteristics associated with these help seeking behaviors among homeless youth. Analyses using multivariate logistic regression models reveal that among the sample of youth, females and gay males most frequently seek sexual health information online. We demonstrate the structure of social network ties (e.g., connection with parents) and the content of interactions (e.g., e-mail forwards of health information) across ties are critical correlates of online sexual health information seeking. Results show a continued connection with parents via the Internet is significantly associated with youth seeking HIV or STI information. Similarly for content of interactions, more youth who were sent health information online also reported seeking HIV information and HIV-testing information. We discuss implications for intervention and practice, focusing on how the Internet may be used for dissemination of sexual health information and as a resource for social workers to link transient, runaway, and homeless youth to care.

  13. Runaway electrons preionized diffuse discharges at high pressure

    NASA Astrophysics Data System (ADS)

    Tarasenko, Victor F.; Lomaev, Mikhail I.; Sorokin, Dmitry A.

    2010-09-01

    Breakdown of the gaps with a non-uniform electric field filled with nitrogen and air as well as with other gases under high-voltage nanosecond pulses was investigated. It is shown that conditions of obtaining a diffuse discharge without a source of additional ionization are extended at the voltage pulse duration decreasing. A volume discharge is formed due to the gap pre-ionization by runaway electrons and X-ray quanta. At a negative polarity of the electrode with a small radius of curvature, a volume (diffuse) discharge formation is determined by pre-ionization with runaway electrons which are generated due to the electric field amplification near the cathode and in the gap. At a positive polarity of the electrode with a small radius of curvature, the X-ray radiation, generated at the runaway electrons braking at the anode and in the gap, is of great importance in a volume discharge formation. A runaway electrons preionized diffuse discharge (REP DD) has two characteristic stages. In the first stage, the ionization wave overlaps the gap during a fraction of a second. The discharge current is determined by the conductivity current in the dense plasma of the ionization wave and the displacement current in the remaining part of the gap. The second stage of the discharge can be related to the anomalous glow discharge with a high specific input power. During the second stage, the gap voltage decreases and the cathode spots formed as a result of explosive electron emission can participate in the electron emission from the cathode. At the increase of the voltage pulse duration and specific input power, the REP DD transforms into a spark discharge form. A REP DD is easily realized in various gases and at different pressures; see [1] and references in [1]. At pressure decrease was obtained the anode electrons beam current to rise (up to ~2 kA/cm2 in helium). At the REP DD, the anode is influenced by the plasma of a dense nanosecond discharge with the specific input power

  14. Runaway electron beam control for longitudinally pumped metal vapor lasers

    NASA Astrophysics Data System (ADS)

    Kolbychev, G. V.; Kolbycheva, P. D.

    1995-08-01

    Physics and techniques for producing of the pulsed runaway electron beams are considered. The main obstacle for increasing electron energies in the beams is revealed to be a self- breakdown of the e-gun's gas-filled diode. Two methods to suppress the self-breakdown and enhance the volumetric discharge producing the e-beam are offered and examined. Each of them provides 1.5 fold increase of the ceiling potential on the gun. The methods also give the ways to control several guns simultaneously. Resulting in the possibility of realizing the powerful longitudinal pumping of metal-vapor lasers on self-terminated transitions of atoms or ions.

  15. The comet 17P/Holmes 2007 outburst: the early motion of the outburst material

    NASA Astrophysics Data System (ADS)

    Montalto, M.; Riffeser, A.; Hopp, U.; Wilke, S.; Carraro, G.

    2008-03-01

    Context: On October 24, 2007 the periodic comet 17P/Holmes underwent an astonishing outburst that increased its apparent total brightness from magnitude V~17 up to V~2.5 in roughly two days. In this contribution we report on Wendelstein 0.8 m telescope (WST) photometric observations of the early evolution stages of the outburst. Aims: We studied the evolution of the structure morphology and its kinematic and provide an estimate of the ejected dust mass. Methods: We analyzed 126 images of the comet in the BVRI photometric bands spread between October 26, 2007 and November 20, 2007. The bright comet core appeared to be separated from a quickly expanding dust cloud in all the data, and the bulk of the cloud was contained in the field of view of our instrument during the days soon after the outburst, allowing precise estimates both of the separation velocities of the two luminous baricenters and of the expansion velocity of the dust cloud. The ejected dust mass was derived on the basis of differential photometry on background stars occulted by the moving cloud. Results: The two cores were moving apart from each other at a relative, projected constant velocity of (9.87±0.07) arcsec/day (0.135±0.001 km s-1). In the inner regions of the dust cloud we observed a linear increase in size at a mean constant velocity of (14.6±0.3) arcsec/day (0.200±0.004 km s-1). Evidence of a radial velocity gradient in the expanding cloud was also found. Our estimate for the expanding coma's mass was approximately 10-2-1 comet's mass, implying a significant disintegration event. Conclusions: We interpret our observations in the context of an explosive scenario that was more probably triggered by some internal instability processes rather than by an impact with an asteroidal body. Due to the peculiar characteristics of this event, further observations and investigations are necessary to bring the nature of the physical processes that determined it to light. Based on observations taken at

  16. A Review of Cometary Outbursts at Large Heliocentric Distances

    NASA Astrophysics Data System (ADS)

    Gronkowski, P.; Wesołowski, M.

    2016-11-01

    The outbursts of comets, sudden large increases in their luminosity, are still very interesting and mysterious signs of activity of this celestial bodies. Most of the cometary outbursts are taking place at heliocentric distances where sublimation of water ice plays an important role in the activity of comets. However, the phenomenon is also observed far away from the Sun (i.e. ≃5-20 au) where the sublimation of water ice is negligible and the activity of comets is dominated by more volatile chemicals. Not only typical comets show `cometary-like' activity but also Centaurs. In addition to the long-term changes in brightness related to heliocentric distances and short-periodic variations connected with the rotation of the nucleus, they also exhibit a random variations in luminosity which are similar to the cometary outbursts. Paper presents an overview of the most likely hypotheses and models which try to explain this phenomenon.

  17. Spectrophotometric observations of P/Schwassmann-Wachmann 1 during outburst

    NASA Technical Reports Server (NTRS)

    Cochran, A. L.; Barker, E. S.; Cochran, W. D.

    1980-01-01

    Spectra of Comet Schwassmann-Wachmann 1 were obtained on November 26-27, 1978 and February 15, 1979 using the Cassegrain Digicon spectrograph, and on February 21-23, 1979 using the IDS spectrograph of McDonald Observatory. All spectra were obtained while the comet was in an extended series of outburst (12th-13th mag). The spectra were predominantly reflected solar light, indicating the outburst was very rich in dust. Weak emission between 4000 and 4050 A, and between 4240 and 4290 A was detected in November 1978 and is probably due to CO(+). These outbursts, and the detection of CO(+), indicate that comets are not inactive at distances as great as 6 AU.

  18. Oscillations During Thermonuclear X-ray Bursts: A New Probe of Neutron Stars

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    Observations of thermonuclear (also called Type 1) X-ray bursts from neutron stars in low mass X-ray binaries (LMXB) with the Rossi X-ray Timing Explorer (RXTE) have revealed large amplitude, high coherence X-ray brightness oscillations with frequencies in the 300 - 600 Hz range. Substantial spectral and timing evidence point to rotational modulation of the X-ray burst flux as the cause of these oscillations, and it is likely that they reveal the spin frequencies of neutron stars in LMXB from which they are detected. Here we review the status of our knowledge of these oscillations and describe how they can be used to constrain the masses and radii of neutron stars as well as the physics of thermonuclear burning on accreting neutron stars.

  19. Compression and combustion of non-cryogenic targets with a solid thermonuclear fuel for inertial fusion

    NASA Astrophysics Data System (ADS)

    Gus'kov, S. Yu.; Zmitrenko, N. V.; Sherman, V. E.

    2013-04-01

    Variants of a target with a solid thermonuclear fuel in the form of deuterium-tritium hydrides of light metals for an inertial fusion have been proposed. The laser-pulse-induced compression of non-cryogenic targets, as well as ignition and combustion of such targets, has been examined. The numerical calculations show that, despite a decrease in the caloric content of the fuel and an increase in the energy losses on intrinsic radiation in the target containing deuterium-tritium hydrides of light metals as compared to the target containing deuterium-tritium ice, the non-cryogenic target can ensure the fusion gain sufficient for its use in the energy cycle of a thermonuclear power plant based on the inertial plasma confinement method.

  20. Compression and combustion of non-cryogenic targets with a solid thermonuclear fuel for inertial fusion

    SciTech Connect

    Gus'kov, S. Yu.; Zmitrenko, N. V.; Sherman, V. E.

    2013-04-15

    Variants of a target with a solid thermonuclear fuel in the form of deuterium-tritium hydrides of light metals for an inertial fusion have been proposed. The laser-pulse-induced compression of non-cryogenic targets, as well as ignition and combustion of such targets, has been examined. The numerical calculations show that, despite a decrease in the caloric content of the fuel and an increase in the energy losses on intrinsic radiation in the target containing deuterium-tritium hydrides of light metals as compared to the target containing deuterium-tritium ice, the non-cryogenic target can ensure the fusion gain sufficient for its use in the energy cycle of a thermonuclear power plant based on the inertial plasma confinement method.

  1. Water outburst activity in Comet 17P/Holmes

    NASA Astrophysics Data System (ADS)

    de Almeida, Amaury A.; Boice, Daniel C.; Picazzio, Enos; Huebner, Walter F.

    2016-08-01

    Cometary outbursts are sporadic events whose mechanisms are not well known where the activity and consequently the brightness can increase hundreds of thousands of times within a few hours to several days. This indicates a dramatic departure from thermal equilibrium between the comet and interplanetary space and is usually documented by ;light curves;. In a typical cometary outburst, the brightness can increase by 2-5 magnitudes (Whitney, 1955; Gronkowski and Wesolowski, 2015). In only 42 h, Comet 17P/Holmes was reported to brighten from a magnitude of about 17 to about 2.4 at the height of the burst, representing the largest known outburst by a comet. We present the H2O production rate of Holmes for the megaburst occurring between 23 and 24 October 2007. For this, we selected more than 1900 photometric observations from the International Comet Quarterly Archive of Photometric Data (Green, 2007) and use the Semi-Empirical Method of Visual Magnitudes (SEMVM; de Almeida et al., 2007). We clearly show that the comet achieved an average water production rate of 5 × 1029 molecules s-1, corresponding to a water gas loss rate of 14,960 kg s-1, in very good agreement with Schleicher (2009) who derived the water production rate using OH measurements on 1 Nov 2007 (about 8 days after the outburst). We discuss possible physical processes that might cause cometary outbursts and propose a new qualitative mechanism, the Pressurized Obstructed Pore (POP) model. The key feature of POP is the recrystallization of water in the surface regolith as it cools, plugging pores and blocking the release of subsurface gas flow. As the interior gas pressure increases, an outburst is eventually triggered. POP is consistent with current observations and can be tested in the future with observations (e.g., Rosetta in situ measurements) and detailed simulations.

  2. Glacial lake inventory and lake outburst potential in Uzbekistan.

    PubMed

    Petrov, Maxim A; Sabitov, Timur Y; Tomashevskaya, Irina G; Glazirin, Gleb E; Chernomorets, Sergey S; Savernyuk, Elena A; Tutubalina, Olga V; Petrakov, Dmitriy A; Sokolov, Leonid S; Dokukin, Mikhail D; Mountrakis, Giorgos; Ruiz-Villanueva, Virginia; Stoffel, Markus

    2017-03-16

    Climate change has been shown to increase the number of mountain lakes across various mountain ranges in the World. In Central Asia, and in particular on the territory of Uzbekistan, a detailed assessment of glacier lakes and their evolution over time is, however lacking. For this reason we created the first detailed inventory of mountain lakes of Uzbekistan based on recent (2002-2014) satellite observations using WorldView-2, SPOT5, and IKONOS imagery with a spatial resolution from 2 to 10m. This record was complemented with data from field studies of the last 50years. The previous data were mostly in the form of inventories of lakes, available in Soviet archives, and primarily included localized in-situ data. The inventory of mountain lakes presented here, by contrast, includes an overview of all lakes of the territory of Uzbekistan. Lakes were considered if they were located at altitudes above 1500m and if lakes had an area exceeding 100m(2). As in other mountain regions of the World, the ongoing increase of air temperatures has led to an increase in lake number and area. Moreover, the frequency and overall number of lake outburst events have been on the rise as well. Therefore, we also present the first outburst assessment with an updated version of well-known approaches considering local climate features and event histories. As a result, out of the 242 lakes identified on the territory of Uzbekistan, 15% are considered prone to outburst, 10% of these lakes have been assigned low outburst potential and the remainder of the lakes have an average level of outburst potential. We conclude that the distribution of lakes by elevation shows a significant influence on lake area and hazard potential. No significant differences, by contrast, exist between the distribution of lake area, outburst potential, and lake location with respect to glaciers by regions.

  3. A Deep Search for Prompt Radio Emission from Thermonuclear Supernovae with the Very Large Array

    NASA Astrophysics Data System (ADS)

    Chomiuk, Laura; Soderberg, Alicia M.; Chevalier, Roger A.; Bruzewski, Seth; Foley, Ryan J.; Parrent, Jerod; Strader, Jay; Badenes, Carles; Fransson, Claes; Kamble, Atish; Margutti, Raffaella; Rupen, Michael P.; Simon, Joshua D.

    2016-04-01

    Searches for circumstellar material around Type Ia supernovae (SNe Ia) are some of the most powerful tests of the nature of SN Ia progenitors, and radio observations provide a particularly sensitive probe of this material. Here, we report radio observations for SNe Ia and their lower-luminosity thermonuclear cousins. We present the largest, most sensitive, and spectroscopically diverse study of prompt ({{Δ }}t≲ 1 years) radio observations of 85 thermonuclear SNe, including 25 obtained by our team with the unprecedented depth of the Karl G. Jansky Very Large Array. With these observations, SN 2012cg joins SN 2011fe and SN 2014J as an SN Ia with remarkably deep radio limits and excellent temporal coverage (six epochs, spanning 5-216 days after explosion, implying \\dot{M}/{v}w≲ 5× 10-9 M⊙) yr-1/(100 km s-1), assuming ɛB = 0.1 and ɛe = 0.1). All observations yield non-detections, placing strong constraints on the presence of circumstellar material. We present analytical models for the temporal and spectral evolution of prompt radio emission from thermonuclear SNe as expected from interaction with either wind-stratified or uniform density media. These models allow us to constrain the progenitor mass loss rates, with limits in the range of \\dot{M}≲ 10-9-10-4 M⊙ yr-1, assuming a wind velocity of vw = 100 km s-1. We compare our radio constraints with measurements of Galactic symbiotic binaries to conclude that ≲10% of thermonuclear SNe have red giant companions.

  4. Frontiers in propulsion research: Laser, matter-antimatter, excited helium, energy exchange thermonuclear fusion

    NASA Technical Reports Server (NTRS)

    Papailiou, D. D. (Editor)

    1975-01-01

    Concepts are described that presently appear to have the potential for propulsion applications in the post-1990 era of space technology. The studies are still in progress, and only the current status of investigation is presented. The topics for possible propulsion application are lasers, nuclear fusion, matter-antimatter annihilation, electronically excited helium, energy exchange through the interaction of various fields, laser propagation, and thermonuclear fusion technology.

  5. Experimental Study of Coal and Gas Outbursts Related to Gas-Enriched Areas

    NASA Astrophysics Data System (ADS)

    Tu, Qingyi; Cheng, Yuanping; Guo, Pinkun; Jiang, Jingyu; Wang, Liang; Zhang, Rong

    2016-09-01

    A coal and gas outburst can lead to a catastrophic failure in a coal mine. These outbursts usually occur where the distribution of coal seam gas is abnormal, commonly in tectonic belts. To study the effects of the abnormal distribution of this gas on outbursts, an experimental apparatus to collect data on simulated coal seam outbursts was constructed. Experiments on specimens containing discrete gas-enriched areas were run to induce artificial gas outbursts and further study of these outbursts using data from the experiment was conducted. The results suggest that more gas and outburst energy are contained in gas-enriched areas and this permits these areas to cause an outburst easily, even though the gas pressure in them is lower. During mining, the disappearance of the sealing effect of a coal pillar establishes the occurrence conditions for an outburst. When the enriched gas and outburst energy in the gas-enriched area is released suddenly, a reverse unloading wave and a high gas pressure gradient are formed, which have tension effects on the coal. Under these effects, the fragmentation degree of the coal intensifies and the intensity of the outburst increases. Because a high gas pressure gradient is maintained near the exposed surface and the enriched energy release reduces the coal strength, the existence of a gas-enriched area in coal leads to a faster outburst and the average thickness of the spall is smaller than where is no gas-enriched area.

  6. VizieR Online Data Catalog: Historical outbursts of OJ287 (Hudec+, 2013)

    NASA Astrophysics Data System (ADS)

    Hudec, R.; Basta, M.; Pihajoki, P.; Valtonen, M.

    2013-08-01

    We report on historical optical outbursts in the OJ287 system in 1900 and 1913, detected on archival astronomical plates of the Harvard College Observatory. The 1900 outburst is reported for the first time. The first recorded outburst of the periodically active quasar OJ287 described before was observed in 1913. Up to now the information on this event was based on three points from plate archives. We used the Harvard plate collection, and added another seven observations to the light curve. The light curve is now well covered and allows one to determine the beginning of the outburst quite accurately. The outburst was longer and more energetic than the standard 1983 outburst. Should the system be strictly periodic, the period determined from these two outbursts would be 11.665yr. However, this does not match the 1900 outburst or other prominent outbursts in the record. On the other hand, the precessing binary black hole model of Lehto and Valtonen (1996ApJ...460..207L) can explain these and other known outbursts in OJ287. Finally, we discuss the upper limits for the expected 1906 outburst and the 1910 outburst, which was observed. (1 data file).

  7. Rocket propulsion by thermonuclear micro-bombs ignited with intense relativistic electron beams.

    NASA Technical Reports Server (NTRS)

    Winterberg, F.

    1971-01-01

    Discussion of a method for the ignition of a thermonuclear microbomb by means of an intense relativistic electron beam with regard to its potential application to rocket propulsion. With such a system, exhaust velocities up to 1000 km/sec, corresponding to a specific impulse of 100,000 sec, seem to be within the realm of possibility. The rocket is propelled by a chain of thermonuclear microbombs exploded in a concave magnetic mirror produced by superconducting field coils. The magnetic pressure of the field reflects the fireball generated by the explosion. For the large capacitor bank required to generate the intense relativistic electron beam, a desirable lightweight design may be possible through use of ferroelectric materials. Because of the high cost of the T-D and He 3-D thermonuclear material, the system has to be optimized by minimizing the T-D and He 3-D consumption by a proper TD and He 3-D fuel to hydrogen propellant mass ratio, leading to a larger total system mass than would be absolutely necessary.

  8. Vaporization in Comets; outbursts from Comet Schwassmann-Wachmann 1

    NASA Technical Reports Server (NTRS)

    Cowan, J. J.; Ahearn, M. F.

    1982-01-01

    Revised estimates are presented which show that the total mass and kinetic energy in a typical Comet P/Schassmann-Wachmann 1 outburst are lower than previously estimated, and that this mass is comparable to the mass of gas vaporized, as inferred from recent observations of CO(+) in this comet. The storage of energy suggested by many authors is therefore not neccessary. A simple equilibrium vaporization of CO2 or CO which is suddenly exposed, on a nucleus that is otherwise primarily composed of H2O, is proposed. Under these conditions, calculations of the variation of vaporization with rotational phase indicate that the mechanism can quantitatively produce outbursts of the size observed.

  9. The Post-outburst Pulsations of GW Librae

    NASA Astrophysics Data System (ADS)

    Chote, P.; Mukadam, A. S.; Aungwerojwit, A.; Szkody, P.; Gänsicke, B. T.; Sullivan, D. J.; Poshyachinda, S.; Reichart, D. E.; Haislip, J. B.; Moore, J. P.

    2017-03-01

    We present new observations of GW Librae obtained between 2012 and 2016. GW Librae was the first accreting white dwarf to be discovered with non-radial pulsations, which were wiped out in 2007 when a dwarf nova outburst heated the surface of the WD outside the instability strip. In the years that followed, we have seen pulsations return with periods near 280 and 1200 seconds, but find that their periods and amplitudes vary on timescales longer than a few hours. Some of these changes are found to correlate with changes in the mysterious 2/3/4 hour modulation that has been seen both before and after the outburst.

  10. The response of Jupiter's magnetosphere to an outburst on Io.

    PubMed

    Brown, M E; Bouchez, A H

    1997-10-10

    A 6-month-long monitoring campaign of the Io plasma torus and neutral cloud was conducted to determine the characteristics of their interaction. During the observations, a large outburst of material from Io-inferred to be caused by the eruption of a volcanic plume on Io-caused a transient increase in the neutral cloud and plasma torus masses. The response of the plasma torus to this outburst shows that the interaction between Io and Jupiter's magnetosphere is stabilized by a feedback mechanism in which increases in the plasma torus mass cause a nonlinear increase in loss from the plasma torus, limiting plasma buildup.

  11. Influence of stochastic magnetic fields on the confinement of runaway electrons and thermal electron energy in tokamaks

    SciTech Connect

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

    1980-07-01

    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 dislaced 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.

  12. Quantification of Lithium-ion Cell Thermal Runaway Energetics

    SciTech Connect

    Orendorff, Christopher J.; Lamb, Joshua; Steele, Leigh Anna Marie; Spangler, Scott Wilmer; Langendorf, Jill Louise

    2016-01-01

    Much of what is known about lithium-ion cell thermal runaway energetics has been measured and extrapolated from data acquired on relatively small cells (< 3 Ah). This work is aimed at understanding the effects of cell size on thermal runaway energetics on cells from 3 to 50 Ah of both LiFePO4 (LFP) and LiNi0.80Co0.15Al0.05O2 (NCA) chemistries. Results show that for both LFP and NCA cells, the normalized heating rate (W/Ah) increases roughly linearly for cells from 3-38 Ah while the normalized total heat released (kJ/Ah) is relatively constant over that cell size range. The magnitude of the normalized heating rate is on the order of 2x greater for NCA relative to LFP chemistries for 2-3 Ah cells, while that difference is on the order of 10x for 30-40 Ah cells. The total normalized heat release is ~ 15-20% greater for NCA relative to LFP cells across the entire size range studied 3-38 Ah.

  13. Runaway electron behavior in the Frascati Tokamak Upgrade (FTU)

    NASA Astrophysics Data System (ADS)

    Popovic, Zana; Martin-Solis, Jose Ramon; Esposito, Basilio; Marocco, Daniele; Causa, Federica; Buratti, Paolo; Boncagni, Luca; Carnevale, Daniele; Gospodarczyk, Mateusz

    2016-10-01

    Several recent experiments in the FTU tokamak are dedicated to the study of runaway electrons (RE), both in the flattop and disruption phases of the discharge. Experiments have been carried out to evaluate the threshold electric field for RE generation during the flattop of ohmic discharges. The measured threshold electric field during RE electron generation and suppression experiments for a wide range of plasma parameters is found to be 2-5 times larger than predicted by the relativistic collisional theory, ER = nee3ln Λ/4 πɛ02 mec2, and is consistent with an increase of the critical field due to the RE synchrotron radiation. Runaway evolution has been numerically simulated using a test particle model including toroidal electric field acceleration, collisions and synchrotron radiation losses. Estimates of RE energy distribution are consistent with the measurements of two recently installed RE diagnostics: HXR-camera and RE Imaging and Spectroscopy (REIS) system. Supported by MINECO (Spain), Projects ENE2012-31753.

  14. Density dependence triggers runaway selection of reduced senescence.

    PubMed

    Seymour, Robert M; Doncaster, C Patrick

    2007-12-01

    In the presence of exogenous mortality risks, future reproduction by an individual is worth less than present reproduction to its fitness. Senescent aging thus results inevitably from transferring net fertility into younger ages. Some long-lived organisms appear to defy theory, however, presenting negligible senescence (e.g., hydra) and extended lifespans (e.g., Bristlecone Pine). Here, we investigate the possibility that the onset of vitality loss can be delayed indefinitely, even accepting the abundant evidence that reproduction is intrinsically costly to survival. For an environment with constant hazard, we establish that natural selection itself contributes to increasing density-dependent recruitment losses. We then develop a generalized model of accelerating vitality loss for analyzing fitness optima as a tradeoff between compression and spread in the age profile of net fertility. Across a realistic spectrum of senescent age profiles, density regulation of recruitment can trigger runaway selection for ever-reducing senescence. This novel prediction applies without requirement for special life-history characteristics such as indeterminate somatic growth or increasing fecundity with age. The evolution of nonsenescence from senescence is robust to the presence of exogenous adult mortality, which tends instead to increase the age-independent component of vitality loss. We simulate examples of runaway selection leading to negligible senescence and even intrinsic immortality.

  15. MULTIWAVELENGTH OBSERVATIONS OF THE RUNAWAY BINARY HD 15137

    SciTech Connect

    McSwain, M. Virginia; Aragona, Christina; Marsh, Amber N.; Roettenbacher, Rachael M.; De Becker, Michael; Roberts, Mallory S. E.; Boyajian, Tabetha S.; Gies, Douglas R.; Grundstrom, Erika D. E-mail: cha206@lehigh.edu E-mail: rmr207@lehigh.edu E-mail: malloryr@gmail.com E-mail: gies@chara.gsu.edu

    2010-03-15

    HD 15137 is an intriguing runaway O-type binary system that offers a rare opportunity to explore the mechanism by which it was ejected from the open cluster of its birth. Here, we present recent blue optical spectra of HD 15137 and derive a new orbital solution for the spectroscopic binary and physical parameters of the O star primary. We also present the first XMM-Newton observations of the system. Fits of the EPIC spectra indicate soft, thermal X-ray emission consistent with an isolated O star. Upper limits on the undetected hard X-ray emission place limits on the emission from a proposed compact companion in the system, and we rule out a quiescent neutron star (NS) in the propeller regime or a weakly accreting NS. An unevolved secondary companion is also not detected in our optical spectra of the binary, and it is difficult to conclude that a gravitational interaction could have ejected this runaway binary with a low mass optical star. HD 15137 may contain an elusive NS in the ejector regime or a quiescent black hole with conditions unfavorable for accretion at the time of our observations.

  16. KORC: A Kinetic Orbit Runaway Electrons code for tokamak disruptions

    NASA Astrophysics Data System (ADS)

    Carbajal Gomez, Leopoldo; Del-Castillo-Negrete, Diego; Spong, Donald; Seal, Sudip; Baylor, Larry

    2016-10-01

    Runaway electrons (RE) resulting from the violent termination of tokamak plasmas pose a serious threat to ITER due to the very high energies they can reach and deposit on the plasma facing components. Most of the current modelling of RE in fusion tokamak plasmas rely on reduced models such as the bounce-average and the test particle equations. In some scenarios, the radiation losses in these models might lead to uncertainties in the RE parameters that determine their confinement and energy limit. In order to study this in detail we have developed a new Kinetic Orbit Runaway electrons Code (KORC). KORC follows the dynamics of ensembles of relativistic electrons in the 6D phase space fully resolving gyro-motion under the influence of the Lorentz force, the Landau-Lifshiftz consistent formulation of the Abraham-Lorentz-Dirac force for radiation damping, and collisions with impurities and the background plasma. KORC is parallelized using open MP/MPI, and benefits from a modified relativistic leap-frog method along with an operator splitting scheme for solving the RE dynamics in different magnetic fields. The code is robust, conservative, and shows nearly linear strong scaling. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

  17. Massive runaway stars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Pflamm-Altenburg, J.; Kroupa, P.

    2011-01-01

    Using archival Spitzer Space Telescope data, we identified for the first time a dozen runaway OB stars in the Small Magellanic Cloud (SMC) through the detection of their bow shocks. The geometry of detected bow shocks allows us to infer the direction of motion of the associated stars and to determine their possible parent clusters and associations. One of the identified runaway stars, AzV 471, was already known as a high-velocity star on the basis of its high peculiar radial velocity, which is offset by ≃ 40 km s-1 from the local systemic velocity. We discuss implications of our findings for the problem of the origin of field OB stars. Several of the bow shock-producing stars are found in the confines of associations, suggesting that these may be “alien” stars contributing to the age spread observed for some young stellar systems. We also report the discovery of a kidney-shaped nebula attached to the early WN-type star SMC-WR3 (AzV 60a). We interpreted this nebula as an interstellar structure created owing to the interaction between the stellar wind and the ambient interstellar medium.

  18. Physical Mechanism of Comet Outbursts: The Movie

    NASA Astrophysics Data System (ADS)

    Hartmann, William K.

    2014-11-01

    predicted for the Deep Impact experiment in Comet Tempel 1.The film is posted on the Planetary Science Institute website, www.psi.edu/hartmann. [1] Hartmann, W. K. 1993 Physical Mechanism of Comet Outbursts: An Experimental Result. Icarus 104, 226-233.

  19. Maverick Comet Splits during Dramatic Outburst

    NASA Astrophysics Data System (ADS)

    1996-01-01

    New ESO Observations of P/Schwassmann-Wachmann 3 A few months ago, Periodic Comet Schwassmann-Wachmann 3 underwent a dramatic and completely unexpected, thousand-fold brightening. At that time, the cause for this interesting event was unknown. However, observations with the two largest ESO telescopes have now shown that the ``dirty snowball'' nucleus of this comet has recently split into at least four individual pieces [1]. There is little doubt that the outburst and the splitting event(s) are closely related and that the greatly increased dust and gas production is due to ``fresh'' material of the icy cometary nucleus becoming exposed to the surrounding space for the first time. A Comet with a Troubled History Comet Schwassmann-Wachmann 3 was discovered on May 2, 1930, on a photographic plate obtained at the Hamburg Observatory (Germany) by two astronomers at this institution, Arnold Schwassmann and Arthur Arno Wachmann. The subsequent observations showed that the comet moved in an elliptical orbit with a revolution period of somewhat more than 5 years. Great efforts were expended to observe the comet during the next returns, but it was not recovered until nearly 50 years and eight revolutions later, when its faint image was found of a plate obtained in August 1979 with a telescope at the Perth Observatory in Western Australia. It was missed in 1984, but was sighted again in 1989 and most recently in 1994. Thus this comet has only been observed during four out of thirteen approaches since 1930. While this may be partly due to a less advantageous location in the sky at some returns, it is also a strong indication that the comet behaves unpredictably and must have a quite variable brightness. For the sake of convenience this comet is often referred to as ``SW-3'' by professional astronomers. Recent orbital calculations have shown that it was inserted into the present, short-period orbit by the strong gravitational pull of Jupiter during several, relatively close

  20. Experimental observation of increased threshold electric field for runaway generation due to synchrotron radiation losses in the FTU tokamak

    SciTech Connect

    Martin-Solis, Jose Ramon; Sanchez, Raul; Esposito, Basilio

    2010-01-01

    The threshold electric field for runaway generation has been investigated during runaway suppression experiments by means of electron-cyclotron-resonance heating in the flattop phase of FTU discharges. Runaway suppression has been experimentally found to occur at electric fields substantially larger than those predicted by the relativistic collisional theory of runaway generation, E{sub R} = n{sub e}e{sup 3}ln{Lambda}/4{pi}{var_epsilon}{sub 0}{sup 2}m{sub e}c{sup 2}. These experimental results are consistent with an increase of the critical electric field due to the electron synchrotron radiation losses. No runaway electrons are found in FTU experiments below the radiation threshold. These results support evidence for a new threshold electric field for runaway generation that accounts for the effect of the synchrotron losses, and which should be considered when making predictions on runaway generation and mitigation in devices such as ITER.

  1. Dramatic Outburst Reveals Nearest Black Hole

    NASA Astrophysics Data System (ADS)

    2000-01-01

    Scientists have discovered the closest black hole yet, a mere 1,600 light years from Earth. Its discovery was heralded by four of the most dramatic rapid X-ray intensity changes ever seen from one star. Astronomers from the Massachusetts Institute of Technology (MIT) and the National Science Foundation's National Radio Astronomy Observatory (NRAO) announced their findings at the American Astronomical Society's meeting in Atlanta. The black hole in the constellation Sagittarius, along with a normal star dubbed V4641 Sgr, form a violent system that briefly flooded part of our Milky Way Galaxy with X-rays and ejected subatomic particles moving at nearly the speed of light one day last September. At the peak of its X-ray output, V4641 Sgr was the brightest X-ray emitter in the sky. Astronomers call this type of system an X-ray nova because it suddenly becomes a bright source of X-rays, but this object shows characteristics never seen in an X-ray nova. "V4641 Sgr turns on and off so fast that it seems to represent a new subclass of X-ray novae," said Donald A. Smith, postdoctoral associate in MIT's Center for Space Research. Smith worked on data from this object with MIT principal research scientist Ronald Remillard and NRAO astronomer Robert Hjellming. "In X-rays, the intensity rose by a factor of more than 1,000 in seven hours, then dropped by a factor of 100 in two hours," Remillard said. The radio emission was seen as an image of an expanding "jet" of particles shooting out from the binary system. After reaching a maximum, the radio intensity dropped by a factor of nearly 40 within two days. "Radio telescopes give us a quick glimpse of something moving at a fantastically high velocity," Hjellming said. Black holes harbor enormous gravitational force that can literally rip the gas away from a nearby star. This transfer of gas is visible in many forms of radiation. Both orbiting X-ray telescopes and ground-based radio and optical telescopes saw the outburst of V4641

  2. Thermonuclear Processes as a Principal Source of the Earth's Internal Energy

    NASA Astrophysics Data System (ADS)

    Terez, E. I.; Terez, I. E.

    2011-12-01

    A cosmological model of the formation of the Solar System is presented. It is shown that the main source of the Earth's energy is delivered from the thermonuclear processes in the inner Earth's core consisting of metallic hydrides. Several theoretical studies showed that under low temperature (T<104 K) and sufficiently high density of plasma, the characteristics of nuclear synthesis could be explained only with some adjustments to a thermonuclear synthesis theory. By building a diagram of the mass luminosity for the giant planets and the Earth, Wang Hong-Zhang (1990) illustrated that this diagram was similar to the one corresponding to stars. This could have only one explanation-the energy is due to the thermonuclear reactions and the energy rate is increasing exponentially with temperature and pressure. In the local areas where thermonuclear reactions occur in the Earth core, one should expect a sharp increase in temperature which causes of the dissolution of hydrides, e.g. release of hydrogen from the hydride-ionic form to the proton gas in large quantities (Larin, 2005). The pressure in this zone would sharply rise, and this would cause expulsion of the streams of the hydrogen plasma outside of the Earth's core. As a result of the Earth rotation and existence of the Coriolis' acceleration, the hydrogen plumes (more exactly, the proton gas) characterized by a high electrical conductivity twirl in spirals in the outer core of the Earth. These spirals form solenoid and, as a result, create the dipole magnetic field of the Earth. The suggest hypothesis of the thermonuclear nature of the Earth's energy flux is a main reason for the endogenic geodynamic and tectonic processes in the Earth's history. This hypothesis is supported by known experimental facts, and it opens new ways to study not only our planet but other planets of the Solar System. One should note that according to accepted concepts, the dipole magnetic field could exist in planets with a sufficient

  3. A NEW CONDITION FOR THE TRANSITION FROM RUNAWAY TO OLIGARCHIC GROWTH

    SciTech Connect

    Ormel, C. W.; Dullemond, C. P.; Spaans, M. E-mail: dullemon@mpia.de

    2010-05-01

    Accretion among macroscopic bodies of {approx}km size or larger is enhanced significantly due to gravitational focusing. Two regimes can be distinguished. Initially, the system experiences runaway growth, in which the gravitational focusing factors increase, and bodies at the high-mass tail of the distribution grow fastest. However, at some point, the runaway body dynamically heats its environment, gravitational focusing factors decrease, and runaway growth passes into oligarchic growth. Based on the results of recent simulations, we reconsider the runaway growth-oligarchy transition. In contrast to oligarchy, we find that runaway growth cannot be approximated with a two-component model (of small and large bodies) and that the criterion of Ida and Makino, which is frequently adopted as the start of oligarchy, is not a sufficient condition to signify the transition. Instead, we propose a new criterion based on timescale arguments. We then find a larger value for the runaway growth-oligarchy transition: from several hundreds of km in the inner disk regions up to {approx}10{sup 3} km for the outer disk. These findings are consistent with the view that runaway growth has been responsible for the size distribution of the present-day Kuiper Belt objects. Our finding, furthermore, outlines the proper initial conditions at the start of the oligarchy stage.

  4. Visible imaging and spectroscopy of disruption runaway electrons in DIII-D

    SciTech Connect

    Yu, J. H.; Hollmann, E. M.; Moyer, R. A.; Commaux, N.; Jernigan, T. C.; Eidietis, N. W.; Humphreys, D. A.; James, A. N.

    2013-04-15

    The first visible light images of synchrotron emission from disruption runaway electrons are presented. The forward-detected continuum radiation from runaways is identified as synchrotron emission by comparing two survey spectrometers and two visible fast cameras viewing in opposite toroidal directions. Analysis of the elongation of 2D synchrotron images of oval-shaped runaway beams indicates that the velocity pitch angle v{sub Up-Tack }/v{sub ||} ranges from 0.1 to 0.2 for the detected electrons, with energies above 25 MeV. Analysis of synchrotron intensity from a camera indicates that the tail of the runaway energy distribution reaches energies up to 60 MeV, which agrees with 0D modeling of electron acceleration in the toroidal electric field generated during the current quench. A visible spectrometer provides an independent estimate of the upper limit of runaway electron energy which is roughly consistent with energy determined from camera data. Synchrotron spectra reveal that approximately 1% of the total post-thermal quench plasma current is carried by the detected high-energy runaway population with energies in the range of 25-60 MeV; the bulk of the plasma current thus appears to be carried by relativistic electrons with energy less than 25 MeV. In addition to stable oval shapes, runaway beams with other shapes and internal structure are sometimes observed.

  5. Runaway-electron formation and electron slide-away in an ITER post-disruption scenario

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Mitigation of runaway electrons is one of the outstanding issues for the reliable operation of ITER and other large tokamaks, and accurate estimates for the expected runaway- electron energies and current are needed. Previously, linearized tools (which assume the runaway population to be small) have been used to study the runaway dynamics, but these tools are not valid in the cases of most interest, i.e. when the runaway population becomes substantial. We study runaway-electron formation in a post-disruption ITER plasma using the newly developed non-linear code NORSE, and describe a feedback mechanism by which a transition to electron slide-away can be induced at field strengths significantly lower than previously expected. If the electric field is actively imposed using the control system, the entire electron population is quickly converted to runaways in the scenario considered. We find the time until the feedback mechanism sets in to be highly dependent on the details of the mechanisms removing heat from the thermal electron population.

  6. Effect of magnetic and electrostatic fluctuations on the runaway electron dynamics in tokamak plasmas

    SciTech Connect

    Martin-Solis, J.R.; Sanchez, R.; Esposito, B.

    1999-10-01

    A test particle description of the runaway dynamics [J.R. Mart{acute i}n-Sol{acute i}s {ital et al.}, Phys. Plasmas {bold 5}, 2370 (1998)] is extended to investigate the behavior of runaway electrons in the presence of fluctuations of electric and magnetic fields. The interaction with the fluctuations is accounted for via a friction force with an effective {open_quotes}collision{close_quotes} frequency determined by the fluctuation induced radial diffusion coefficient. It is shown that both the runaway generation process and the maximum runaway energy can be noticeably affected by magnetic fluctuations. The test particle model is then used to discuss a proposed runaway control scheme via induced magnetic turbulence, with particular emphasis to situations like major disruptions, where a large number of runaway electrons and high runaway energies are expected. It is found that the efficiency of such scheme can in some cases be jeopardized by drift orbit effects as well as by the coexistence of stochastic magnetic regions with good magnetic surfaces. {copyright} {ital 1999 American Institute of Physics.}

  7. The runaway greenhouse: implications for future climate change, geoengineering and planetary atmospheres.

    PubMed

    Goldblatt, Colin; Watson, Andrew J

    2012-09-13

    The ultimate climate emergency is a 'runaway greenhouse': a hot and water-vapour-rich atmosphere limits the emission of thermal radiation to space, causing runaway warming. Warming ceases only after the surface reaches approximately 1400 K and emits radiation in the near-infrared, where water is not a good greenhouse gas. This would evaporate the entire ocean and exterminate all planetary life. Venus experienced a runaway greenhouse in the past, and we expect that the Earth will in around 2 billion years as solar luminosity increases. But could we bring on such a catastrophe prematurely, by our current climate-altering activities? Here, we review what is known about the runaway greenhouse to answer this question, describing the various limits on outgoing radiation and how climate will evolve between these. The good news is that almost all lines of evidence lead us to believe that is unlikely to be possible, even in principle, to trigger full a runaway greenhouse by addition of non-condensible greenhouse gases such as carbon dioxide to the atmosphere. However, our understanding of the dynamics, thermodynamics, radiative transfer and cloud physics of hot and steamy atmospheres is weak. We cannot therefore completely rule out the possibility that human actions might cause a transition, if not to full runaway, then at least to a much warmer climate state than the present one. High climate sensitivity might provide a warning. If we, or more likely our remote descendants, are threatened with a runaway greenhouse, then geoengineering to reflect sunlight might be life's only hope. Injecting reflective aerosols into the stratosphere would be too short-lived, and even sunshades in space might require excessive maintenance. In the distant future, modifying Earth's orbit might provide a sustainable solution. The runaway greenhouse also remains relevant in planetary sciences and astrobiology: as extrasolar planets smaller and nearer to their stars are detected, some will be in

  8. A fast optical outburst of the quasar CTA102

    NASA Astrophysics Data System (ADS)

    Jorstad, Svetlana; Larionov, Valeri; Mokrushina, Anna

    2016-10-01

    The quasar CTA102 is being in an active state at gamma-ray and optical wavelengths since 2015, with prominent gamma-ray and optical outbursts observed in the beginning of 2016 (see www.bu.edu/blazars/VLBA_GLAST/cta102.html).

  9. Herschel observations of Circinus X-1 during outburst and quiescence

    SciTech Connect

    Harrison, Thomas E.; Gelino, Dawn M.; Buxton, Michelle; Fost, Tyler E-mail: dawn@ipac.caltech.edu E-mail: tyler.fost@gmail.com

    2014-07-01

    We have used the Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging REceiver instruments on the Herschel Space Observatory to observe Cir X-1 both in and out of outburst. We detected Cir X-1 during outburst at 70 μm. Unfortunately, a cold background source dominates Cir X-1 at longer wavelengths. We have assembled optical and infrared (IR) data for Cir X-1 to model its spectral energy distribution (SED) in both quiescence and outburst and find that in both states it is consistent with a heavily reddened, 10,000 K blackbody. We believe this behavior is completely consistent with previous suggestions that these outbursts are due to accretion disk events, not unlike those of dwarf novae. To explore the behavior of other low-mass X-ray binaries with reported synchrotron jets, we have extracted and/or compiled optical and near- and mid-IR data sets for five such systems to construct their SEDs. The Z-source GX 349+2 and the black hole system GRS 1915+105 have strong and variable mid-IR excesses that suggest synchrotron emission. The other Z-sources have rather weak (or no) IR excesses that can be explained as reddened blackbody spectra with the addition of either synchrotron or bremsstrahlung components.

  10. Minor Outburst of 0324+43 GK Persei

    NASA Astrophysics Data System (ADS)

    Mattei, Janet A.

    1992-07-01

    GK Per is undergoing an minor outburst, currently around ~11.8. A group of astronomers from the University of Texas have requested observers to keep a close eye on GK Per. Recent observations of the supernove in NGC 4411B approximate 13.5 magnitude.

  11. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.

  12. Exploration of the Variety of Outburst Modes of Transient Neutron Star LMXBS

    NASA Astrophysics Data System (ADS)

    Bailyn, Charles

    Recent work on transient LMXBs containing neutron stars, particularly Aql X-1, has shown that outbursts are of three types. In addition to the traditional large outbursts, there are also low intensity outbursts, in which no high X-ray state occurs, and short "mini- outbursts" seen in the optical, which are not accompanied by any X-ray flux detectable by the RXTE/ASM. The absence of good triggers from the ASM means that little is known about the non-traditional outburst modes. Here we propose to use our ongoing optical monitoring to trigger PCA observations of ALL outbursts of Aql X-1 and Cen X-4, particularly those which do not evolve into strong X-ray outbursts.

  13. A DOUBLE-PEAKED OUTBURST OF A 0535+26 OBSERVED WITH INTEGRAL, RXTE, AND SUZAKU

    SciTech Connect

    Caballero, I.; Barragan, L.; Wilms, J.; Kreykenbohm, I.; Ferrigno, C.; Klochkov, D.; Suchy, S.; Santangelo, A.; Staubert, R.; Zurita Heras, J. A.; Kretschmar, P.; Fuerst, F.; Rothschild, R.; Finger, M. H.; Camero-Arranz, A.; Makishima, K.; Enoto, T.; Iwakiri, W.; and others

    2013-02-20

    The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in 2009 August. It is the fourth in a series of normal outbursts associated with the periastron, but is unusual because it presented a double-peaked light curve. The two peaks reached a flux of {approx}450 mCrab in the 15-50 keV range. We present results of the timing and spectral analysis of INTEGRAL, RXTE, and Suzaku observations of the outburst. The energy-dependent pulse profiles and their evolution during the outburst are studied. No significant differences with respect to other normal outbursts are observed. The centroid energy of the fundamental cyclotron line shows no significant variation during the outburst. A spectral hardening with increasing luminosity is observed. We conclude that the source is accreting in the sub-critical regime. We discuss possible explanations for the double-peaked outburst.

  14. Li-ion battery thermal runaway suppression system using microchannel coolers and refrigerant injections

    DOEpatents

    Bandhauer, Todd M.; Farmer, Joseph C.

    2016-11-08

    A battery management system with thermally integrated fire suppression includes a multiplicity of individual battery cells in a housing; a multiplicity of cooling passages in the housing within or between the multiplicity of individual battery cells; a multiplicity of sensors operably connected to the individual battery cells, the sensors adapted to detect a thermal runaway event related to one or more of the multiplicity of individual battery cells; and a management system adapted to inject coolant into at least one of the multiplicity of cooling passages upon the detection of the thermal runaway event by the any one of the multiplicity of sensors, so that the thermal runaway event is rapidly quenched.

  15. Quenching electron runaway in positive high-voltage-impulse discharges in air by laser filaments.

    PubMed

    Eto, S; Zhidkov, A; Oishi, Y; Miki, M; Fujii, T

    2012-03-15

    Strong hard (ε>100 keV) x rays being observed from impulse atmospheric discharges with maximal voltages from U=0.5 to 0.9 MV just before the breakdown were completely stopped with the use of femtosecond-laser-filament plasma. Runaway electrons generating such x rays and being estimated to achieve their maximal energy, ε~U, near the positive electrode disappear if a laser filament plasma is ignited perpendicularly to the runaway near the positive electrode. A preheating mechanism for formation of the electron runaway in air is proposed.

  16. Particle-in-cell simulations of the runaway breakdown of nitrogen

    SciTech Connect

    Levko, D.; Krasik, Ya. E.

    2012-12-01

    The runaway breakdown initiated by a mono-energetic beam of runaway electrons propagating through a cathode-anode gap filled with nitrogen at atmospheric pressure is studied using the one-dimensional particle-in-cell numerical model. It is shown that the breakdown is strongly influenced by the amplitude of the beam, its duration, and the electric field in the vicinity of the cathode. In addition, the simulation results showed that, in spite of the formation of rather dense plasma inside the cathode-anode gap by runaway electrons, the electric field is not screened because of frequent electron-neutral collisions.

  17. Suppression of runaway electron generation by massive helium injection after induced disruptions on TEXTOR

    NASA Astrophysics Data System (ADS)

    Lvovskiy, A.; Koslowski, H. R.; Zeng, L.; Zeng

    2015-10-01

    > Disruptions with runaway electron generation have been deliberately induced by injection of argon using a disruption mitigation valve. A second disruption mitigation valve has been utilised to inject varying amounts of helium after a short time delay. No generation of runaway electrons has been observed when more than a critical amount of helium has been injected no later than 5 ms after the triggering of the first valve. The required amount of helium for suppression of runaway electron generation is up to one order of magnitude lower than the critical density according to Connor & Hastie (1975) and Rosenbluth & Putvinski (1997).

  18. Black Hole X Ray Nova Outburst with XTE and HST

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph; Haswell, Carole

    1998-01-01

    We obtained multiwavelength coverage of the soft X-ray transient. GRO J1655-40 during its 1996 outburst, using HST (Hubble Space Telescope), RXTE (Rossi X Ray Timing Explorer), CGRO (Compton Gamma Ray Observatory), and ground-based facilities. This outburst was qualitatively different from other SXT (Soft X Ray Telescope) outbursts and from previous outbursts of this source. The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with with the standard disk instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. Based on the strength of the 2175-A interstellar absorption feature, we constrain the reddening to be E(B - V) = 1.2 plus or minus 0.1, a result which is consistent with the known properties of the source and with the strength of other interstellar absorption lines. After this dereddening we find that the spectra are dominated by a component peaking in the optical, with the expected v (sup l/3) disk spectrum seen only in the ultraviolet. Bowen fluorescence lines of NIII and OIII are also seen, as well as possible P Cyg profiles in the ultraviolet resonance lines. These features suggest an accretion-disk wind. The X-ray spectra broadly resemble the high/soft state commonly seen in black hole candidates, but evolve through two substates.

  19. After runaway: The trans-Hill stage of planetesimal growth

    SciTech Connect

    Lithwick, Yoram

    2014-01-01

    When planetesimals begin to grow by coagulation, they first enter an epoch of runaway, during which the biggest bodies grow faster than all the others. The questions of how runaway ends and what comes next have not been answered satisfactorily. We show that runaway is followed by a new stage—the 'trans-Hill stage'—that commences when the bodies that dominate viscous stirring ('big bodies') become trans-Hill, i.e., when their Hill velocity matches the random speed of the small bodies they accrete. Subsequently, the small bodies' random speed grows in lockstep with the big bodies' sizes, such that the system remains in the trans-Hill state. Trans-Hill growth is crucial for determining the efficiency of growing big bodies, as well as their growth timescale and size spectrum. Trans-Hill growth has two sub-stages. In the earlier one, which occurs while the stirring bodies remain sufficiently small, the evolution is collisionless, i.e., collisional cooling among all bodies is irrelevant. The efficiency of forming big bodies in this collisionless sub-stage is very low, ∼10α << 1, where α ∼ 0.005(a/AU){sup –1} is the ratio between the physical size of a body and its Hill radius. Furthermore, the size spectrum is flat (equal mass per size decade, i.e., q = 4). This collisionless trans-Hill solution explains results from previous coagulation simulations for both the Kuiper Belt and the asteroid belt. The second trans-Hill sub-stage commences once the stirring bodies grow big enough (>α{sup –1} × the size of the accreted small bodies). After that time, collisional cooling among small bodies controls the evolution. The efficiency of forming big bodies rises and the size spectrum becomes more top heavy. Trans-Hill growth can terminate in one of two ways, depending on the sizes of the small bodies. First, mutual accretion of big bodies can become significant and conglomeration proceeds until half of the total mass is converted into big bodies. This mode of growth

  20. Synchrotron and collisional damping effects on runaway electron distributions

    NASA Astrophysics Data System (ADS)

    Paz-Soldan, C.; Eidietis, N.; Pace, D.; Cooper, C.; Shiraki, D.; Commaux, N.; Hollmann, E.; Moyer, R.; Granetz, R.; Embreus, O.; Fulop, T.; Stahl, A.; Wilkie, G.; Aleynikov, P.; Brennan, D. P.; Liu, C.

    2016-10-01

    Validated models of runaway electron (RE) dissipation are required to confidently approve safe ITER Q = 10 operation. DIII-D experiments using quiescent REs are exploring the importance of synchrotron and collisional damping terms to RE dissipation. New time and energy-resolved measurements of RE bremsstrahlung hard X-ray (HXR) emission reveal stark differences between high and low energy REs as damping terms are varied. Previously reported anomalously high RE dissipation only applies to low energy REs. At high energy (where synchrotron effects are strongest) low synchrotron damping cases reach higher peak RE energy despite weaker particle confinement. Low-energy RE decay is observed concurrently with high-energy RE growth. RE dissipation models predict bump-on-tail distributions whose properties depend on the damping terms. Measured HXR spectra are very broad, as expected for bump-on-tail distributions. Work supported by the U.S. DOE under DE-FC02-04ER54698.

  1. Ionization rate in the presence of runaway electrons

    SciTech Connect

    Bulanov, S.V.; Lontano, M.; Sasorov, P.V.

    1997-04-01

    The role of a fast electron population, produced by the strong electric field driving the axial current in a capillary discharge, can be essential in order to justify the appreciable concentration of highly charged C ions (C{sup 5+}, C{sup 6+}) as observed in many experiments with low electron temperature. Under the assumption that a quasistationary state is established during the discharge, the runaway electron distribution function is determined analytically for Z{sub eff}{gt}1, following the approximated method developed by Lebedev [A. N. Lebedev, Sov. Phys. JETP {bold 21}, 931 (1965)]. The strong enhancement of the ionization rate, due to the presence of an electron tail in the energy range of the ionization potential, is then demonstrated. {copyright} {ital 1997 American Institute of Physics.}

  2. Laser action in runaway electron pre-ionized diffuse discharges

    NASA Astrophysics Data System (ADS)

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Viktor F.; Suslov, Alexei I.

    2015-12-01

    Formation features of run-away electron preionized diffuse discharge (REP DD) and REP DD properties in different experimental conditions are studied. It was shown that sufficient uniformity of REP DD allows its application as an excitation source of lasers on different gas mixtures at elevated pressure. Promising results of REP DD application for development of gas lasers are shown. Stimulated radiation in the IR, visible and UV spectral ranges was obtained in the diffuse discharge. Ultimate efficiency of non-chain HF(DF) chemical and nitrogen lasers on mixtures of SF6 with H2(D2) and N2 was achieved. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at λ = 337,1 nm. Long-pulse operation of rare gas halide lasers was achieved.

  3. Optical characteristics of red sprites produced by runaway air breakdown

    SciTech Connect

    Yukhimuk, V.; Roussel-Dupre, R.A.; Symbalisty, E.M.; Taranenko, Y.

    1998-05-01

    The results of numerical calculations of intensity and spectra of optical emissions from red sprites produced by runaway air breakdown in the atmosphere are presented. It is shown that the optical emissions from red sprites consist of two components: (1) short-term (t{approx}0.3{endash}2thinspms) emissions produced as a result of dissipation of an energetic electron beam in air; (2) long-term (t{approx}2{endash}10thinspms) emissions produced by a population of low-energy electrons in an electric field. The long-term optical emissions are calculated for all low-energy electrons, including the secondary low-energy electrons produced by the relativistic electron beam, ambient background electrons, and electrons produced as a result of regular breakdown. The theoretical results are compared with observational data. {copyright} 1998 American Geophysical Union

  4. r-MODE Runaway and Rapidly Rotating Neutron Stars

    NASA Astrophysics Data System (ADS)

    Stergioulas, Nikolaos; Kokkotas, Kostas D.; Andersson, Nils; Jones, David Ian

    2002-12-01

    We present a simple spin evolution model that predicts that rapidly rotating accreting neutron stars will mainly be confined to a narrow range of spin-frequencies; P = 1.5 - 5 ms. This is in agreement with current observations of both neutron stars in the Low-Mass X-ray Binaries and millisecond radio pulsars. The main ingredients in the model are: i) the instability of r-modes above a critical spin rate, ii) thermal runaway due to heat released as viscous damping mechanisms counteract the r-mode growth, and iii) a revised estimate of the strength of dissipation due to the presence of a viscous boundary layer at the base of the crust in an old and relatively cold neutron star...

  5. Thermal Runaway during Intermediate-Depth Earthquake Rupture

    NASA Astrophysics Data System (ADS)

    Prieto, German; Florez, Manuel; Barrett, Sarah; Beroza, Gregory; Pedraza, Patricia; Blanco, Jose; Poveda, Esteban

    2014-05-01

    Intermediate-depth earthquakes occur at depths of 50 to 300 km in subducting lithosphere. Despite their ubiquity in earthquake catalogs, their physical mechanism remains unclear because ambient temperatures and pressures are expected to lead to ductile, rather than brittle deformation. There are two leading explanations for the physical mechanism that enables these earthquakes. In the first, high pore pressure from metamorphic dehydration reactions in the subducting slab reduces the effective normal stress sufficiently to enable frictional failure. In the second, slow deformation generates heat, which leads to weakening, further deformation, and a self-localizing thermal shear runaway. We use the nest of intermediate-depth earthquakes under Bucaramanga, Colombia as recorded by the digital RSNC (Red Sísmica Nacional de Colombia) regional seismic network to explore these two possibilities. We observe a combination of high stress drop and low radiation efficiency for Mw 4-5 earthquakes in the Bucaramanga Nest that points to the importance of thermal effects. If we assume a cm-scale fault-zone width, this combination implies a temperature increase of 600-1,000ºC during earthquake failure, which suggests that substantial shear heating, and possibly partial melting, occurs during intermediate-depth earthquake failure. Our observations support thermal shear runaway as the mechanism for intermediate-depth earthquakes. This mechanism could help explain differences in their behavior, such as the paucity of aftershocks, compared to shallow earthquakes. Although we have inferred these mechanisms for intermediate depth earthquakes, it's likely that they would apply for rapid deformation on the deep extensions of fault zones as well - particularly during large earthquakes, such as the 2012 Mw 8.6 strike-slip event off Sumatra, which is inferred to have ruptured well into the oceanic mantle.

  6. Acceleration of runaway electrons and Joule heating in solar flares

    SciTech Connect

    Holman, G.D.

    1985-06-15

    The electric-field acceleration of electrons out of a thermal plasma and the simultaneous Joule heating of the plasma are studied. Acceleration and heating time scales are derived and compared, and upper limits are obtained on the acceleration volume and the rate at which electrons can be accelerated. These upper limits, determined by the maximum magnetic-field strength observed in flaring regions, place stringent restrictions on the acceleration process. The implications of these results for the microwave and hard X-ray emission from solar flares are examined. The major conclusions are: (1) The simple electric-field acceleration of electrons is found, in agreement with Spicer, to be incapable of producing a large enough electron flux to explain the bulk of the observed hard X-ray emission from solar flares as nonthermal bremsstrahlung. For the bulk of the X-ray emission to be nonthermal, at least 10/sup 4/ oppositely directed current channels are required, or an acceleration mechanism that does not result in a net current in the acceleration region is required. (2) lf the bulk of the X-ray emission is thermal, a single current sheet can yield the required heating and acceleration time scales and the required electron energies for the microwave emission. This is accomplished with an electric field that is much smaller than the Dreicer field (E/sub D//Eroughly-equal10--50). (3) The rise time of the nonthermal emission is determined by the time needed to generate the required number of runaway electrons rather than by the time needed to accelerate the electrons to the required energies, which is generally a much shorter time scale. (4) The acceleration of enough electrons to produce a microwave flare requires the resupply of electrons to both the current sheet and the runaway region of velocity space.

  7. Dynamics of runaway tails with time-dependent sub-Dreicer dc fields in magnetized plasmas

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Vlahos, L.

    1987-01-01

    The evolution of runaway tails driven by sub-Dreicer time-dependent dc fields in a magnetized plasma are studied numerically using a quasi-linear code based on the Ritz-Galerkin method and finite elements. It is found that the runaway tail maintained a negative slope during the dc field increase. Depending on the values of the dc electric field at t = 0 and the electron gyrofrequency to the plasma frequency ratio the runaway tail became unstable to the anomalous Doppler resonance or remained stable before the saturation of the dc field at some maximum value. The systems that remained stable during this stage became unstable to the anomalous Doppler or the Cerenkov resonances when the dc field was kept at the saturation level or decreased. Once the instability is triggered, the runaway tail is isotropized.

  8. A study of Stark broadening for the diagnostic of runaway electrons in ITER

    NASA Astrophysics Data System (ADS)

    Rosato, J.; Pandya, S. P.; Logeais, Ch.; Meireni, M.; Hannachi, I.; Reichle, R.; Barnsley, R.; Marandet, Y.; Stamm, R.

    2017-03-01

    We investigate the Stark broadening of hydrogen lines in tokamak edge plasma conditions in the presence of a beam of relativistic "runaway" electrons. The possibility for a diagnostic involving passive spectroscopy is discussed.

  9. Interaction of runaway electrons with lower hybrid waves via anomalous Doppler broadening

    NASA Astrophysics Data System (ADS)

    Martín-Solís, J. R.; Sánchez, R.; Esposito, B.

    2002-05-01

    Due to the relativistic decrease of the electron cyclotron frequency, a cyclotron resonance may appear between runaway electrons and lower hybrid waves. A single particle description of the runaway dynamics [J. R. Martín-Solís et al., Phys. Plasmas 5, 2370 (1998)] is extended to analyze the effect of the interaction of runaway electrons with lower hybrid waves via anomalous Doppler broadening. The conditions under which the resonant interaction can play a role in limiting the runaway energy are established and it is shown that, under typical lower hybrid current drive operation parameters, an efficient wave-particle coupling may occur. Observations of a fast pitch angle scattering event during the current decay phase of Ohmic discharges in the Toroidal Experiment for Technically Oriented Research (TEXTOR) [R. J. E. Jaspers, Ph.D. thesis, Technical University Eindhoven (1995)] are interpreted in terms of such interaction.

  10. Dynamics of runaway tails with time-dependent sub-Dreicer dc fields in magnetized plasmas

    SciTech Connect

    Moghaddam-Taaheri, E.; Vlahos, L.

    1987-10-01

    The evolution of runaway tails driven by sub-Dreicer time-dependent dc fields in a magnetized plasma are studied numerically using a quasilinear code based on the Ritz--Galerkin method and finite elements. It is found that the runaway tail maintained a negative slope during the dc field increase. Depending on the values of the dc electric field at t = 0 and the electron gyrofrequency to the plasma frequency ratio the runaway tail became unstable to the anomalous Doppler resonance or remained stable before the saturation of the dc field at some maximum value. The systems that remained stable during this stage became unstable to the anomalous Doppler or the C-hacekerenkov resonances when the dc field was kept at the saturation level or decreased. Once the instability is triggered, the runaway tail is isotropized.

  11. Cyclotron-absorption measurement of the runaway-electron distribution in a tokamak

    SciTech Connect

    Zvonkov, A.V.; Suvorov, E.V.; Timofeev, A.V.; Fraiman, A.A.

    1983-03-01

    The distribution function of runaway electrons in a tokamak can be determined in the slightly relativistic region from measurements of the absorption coefficient corresponding to electron cyclotron waves. The plasma should be probed in the vertical direction.

  12. Stimulation of high-frequency breakdown of gas in Uragan-3M torsatron by runaway electrons

    NASA Astrophysics Data System (ADS)

    Tarasov, I. K.; Tarasov, M. I.; Sitnikov, D. A.; Pashnev, V. K.; Lytova, M. A.

    2016-01-01

    In experiments on confinement and heating of plasma in the Uragan-3M torsatron, the method of high-frequency breakdown of the working gas is used. In these experiments, in conditions of a relatively stable magnetic field, the rf power supplied to the setup chamber has a frequency close to the ion-cyclotron frequency. Such a method of gas breakdown is not always sufficiently reliable. In our experiments, preliminary ionization of the working gas by the run-away electron beam is used for stabilizing the breakdown. This work contains the results of experiments on enhancement of the runaway electron beam and on the interaction of the runaway electron beam in the Uragan-3M torsatron with the HF electromagnetic pump field. This enables us to formulate a number of recommendations for using spontaneously formed beams of accelerated particles for stimulating the rf breakdown. Our results confirm the possibility of gas breakdown by runaway electrons.

  13. Runaway electron damage to the Tore Supra Phase III outboard pump limiter

    SciTech Connect

    Nygren, R.; Lutz, T.; Walsh, D.; Martin, G.; Chatelier, M.; Loarer, T.; Guilhem, D.

    1996-08-01

    Operation of the Phase III outboard pump limiter (OPL) in Tore Supra in 1994 was terminated prematurely when runaway electrons during the current decay following a disruption pierced leading edge tube on the electron side and caused a water leak. The location, about 20 mm outside the last closed flux surface during normal operation, and the infrared (IR) images of the limiter indicate that the runaways moved in large outward steps, i.e. tens of millimeters, in one toroidal revolution. For plasma (runaway) currents in the range of 155 to 250 kA, the drift orbits open to the outside. Basic trajectory computations suggest that such motion is possible under the conditions present for this experiment. Activation measurements made on sections of the tube to indicate the area of local damage are presented here. An understanding of this event may provide important guidance regarding the potential damage from runaways in future tokamaks.

  14. Alternative approaches to the design of targets for a hybrid thermonuclear station

    SciTech Connect

    Basov, N G; Lebo, I G; Rozanov, Vladislav B; Feoktistov, L P; Tishkin, V F

    1998-04-30

    Targets with low degrees of compression, such as those with internal energy deposition, two-stage conical targets for lasers emitting pulses of duration of the order of 100 ns, and multilayer shell targets for short-pulse long-wavelength CO{sub 2} and CO lasers may prove acceptable for hybrid thermonuclear reactors with high values (of the order of 10{sup 3}) of the gain in the blanket. Estimates and one-dimensional calculations of the compression of such targets are reported for the laser radiation energy range 0.2-2 MJ. (interaction of laser radiation with matter. laser plasma)

  15. Fermi-GBM detection of a thermonuclear burst from 4U 1608-52

    NASA Astrophysics Data System (ADS)

    Jenke, P.; Linares, M.; Connaughton, V.; van der Horst, A. J.; Camero-Arranz, A.; Finger, M.; Wilson-Hodge, C.; Kouveliotou, C.

    2012-05-01

    We report the detection with Fermi-GBM (daily CTIME data, 12-25 keV band) of an X-ray burst from a location consistent with the neutron star low-mass X-ray binary and thermonuclear burster 4U 1608-52. The burst peak occurred on May 2, 2012 at 06:47:54 UTC. The Fermi-GBM location of the burst is R.A.(J2000) = 241.3 deg, DEC(J2000) = -51.1 deg (1.8 deg from 4U 1608-52) with a 1 sigma error of 4.7 deg.

  16. Thermonuclear reaction rate of 18Ne(α ,p ) 21Na from Monte Carlo calculations

    NASA Astrophysics Data System (ADS)

    Mohr, P.; Longland, R.; Iliadis, C.

    2014-12-01

    The 18Ne(α ,p ) 21Na reaction impacts the break-out from the hot CNO cycles to the r p process in type-I x-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches.

  17. FROM THE HISTORY OF PHYSICS: The extraordinarily beautiful physical principle of thermonuclear charge design (on the occasion of the 50th anniversary of the test of RDS-37 — the first Soviet two-stage thermonuclear charge)

    NASA Astrophysics Data System (ADS)

    Goncharov, German A.

    2005-11-01

    On 22 November 1955, the Semipalatinsk test site saw the test of the first domestic two-stage thermonuclear RDS-37 charge. The charge operation was based on the principle of radiation implosion. The kernel of the principle consists in the radiation generated in a primary A-bomb explosion and confined by the radiation-opaque casing propagating throughout the interior casing volume and flowing around the secondary thermonuclear unit. The secondary unit experiences a strong compression under the irradiation, with a resulting nuclear and thermonuclear explosion. The RDS-37 explosion was the strongest of all those ever realized at the Semipalatinsk test site. It produced an indelible impression on the participants in the test. This document-based paper describes the genesis of the ideas underlying the RDS-37 design and reflects the critical moments in its development. The advent of RDS-37 was an outstanding accomplishment of the scientists and engineers of our country.

  18. Effects of FU Orionis Outbursts on Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Bodenheimer, Peter

    1997-01-01

    In the early stages of work under this grant, we developed simulations to match the light curves of the three best studied systems: FU Ori, V1515 Cyg, & V1057 Cyg (Bell et al. 1995). We compared the details of model results to observations to test the validity of the thermal ionization instability model for outburst. In this paper, we were able to answer several of the key objections to the accretion disk outburst model for the FU Orionis phenomenon (eg. Herbig 1989). The declines in line width and reddening observed in V1057 Cyg following peak light had been used as arguments against the disk instability model. We showed these effects to be natural consequences of the slow outward progression and limited radial excursion of the ionization front during outburst. By the end of the grant period, we had begun combining the inner and outer disk models to derive the radiation expected in the planet forming region of the disk. A crucial step in this was the development of a radiative transfer model of the complete inner and outer disk system (Turner, Bodenheimer, & Bell 1997). In this work, wavelength dependent opacities were used to synthesize images and spectral energy distributions of FU Ori objects. New detailed opacities provided by Alexander (1995) allowed the resolution of coarse features such as silicate emission lines. Data for the fits were taken from the time dependent simulations in Bell et al. (1995) to which was added the effect of disk to disk or "self"-reprocessing which accounts for the illumination of the outer disk by the inner disk (Bell 1998). Through the course of work on this grant we have made considerable progress in computing detailed models of both the active outburst region of the disk and the outer quiescent disk. We have begun an investigation into the effects of a cocooning envelope. Direct comparisons with observations lend confidence that the basic underlying assumptions of the outburst model are reasonable. We are now ready to build upon

  19. The Effect of a Tectonic Stress Field on Coal and Gas Outbursts

    PubMed Central

    An, Fenghua; Cheng, Yuanping

    2014-01-01

    Coal and gas outbursts have always been a serious threat to the safe and efficient mining of coal resources. Ground stress (especially the tectonic stress) has a notable effect on the occurrence and distribution of outbursts in the field practice. A numerical model considering the effect of coal gas was established to analyze the outburst danger from the perspective of stress conditions. To evaluate the outburst tendency, the potential energy of yielded coal mass accumulated during an outburst initiation was studied. The results showed that the gas pressure and the strength reduction from the adsorbed gas aggravated the coal mass failure and the ground stress altered by tectonics would affect the plastic zone distribution. To demonstrate the outburst tendency, the ratio of potential energy for the outburst initiation and the energy consumption was used. Increase of coal gas and tectonic stress could enhance the potential energy accumulation ratio, meaning larger outburst tendency. The component of potential energy for outburst initiation indicated that the proportion of elastic energy was increased due to tectonic stress. The elastic energy increase is deduced as the cause for a greater outburst danger in a tectonic area from the perspective of stress conditions. PMID:24991648

  20. From Planetesimals to Planets in Turbulent Protoplanetary Disks. I. Onset of Runaway Growth

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hiroshi; Tanaka, Hidekazu; Okuzumi, Satoshi

    2016-02-01

    When planetesimals grow via collisions in a turbulent disk, stirring through density fluctuation caused by turbulence effectively increases the relative velocities between planetesimals, which suppresses the onset of runaway growth. We investigate the onset of runaway growth in a turbulent disk through simulations that calculate the mass and velocity evolution of planetesimals. When planetesimals are small, the average relative velocity between planetesimals, {v}{{r}}, is much greater than their surface escape velocity, {v}{{esc}}, so that runaway growth does not occur. As planetesimals become large via collisional growth, {v}{{r}} approaches {v}{{esc}}. When {v}{{r}}≈ 1.5{v}{{esc}}, runaway growth of the planetesimals occurs. During the oligarchic growth subsequent to runaway growth, a small number of planetary embryos produced via runaway growth become massive through collisions with planetesimals with radii of that at the onset of runaway growth, {r}{{p,run}}. We analytically derive {r}{{p,run}} as a function of the turbulent strength. Growing ∼ 10 {M}\\oplus embryos that are suitable to become the cores of Jupiter and Saturn requires {r}{{p,run}}∼ 100 km, which is similar to the proposed fossil feature in the size distribution of main belt asteroids. In contrast, the formation of Mars as quickly as suggested from Hf-W isotope studies requires small planetesimals at the onset of runaway growth. Thus, the conditions required to form Mars, Jupiter, and Saturn and the size distribution of the main-belt asteroids indicate that the turbulence increased in amplitude relative to the sound speed with increasing distance from the young Sun.

  1. Runaway electrons in a magnetized plasma in an rf electric field

    SciTech Connect

    Razdorskii, V.G.

    1982-01-01

    Runaway electrons may appear during electron-cyclotron heating of a plasma. In a constant magnetic field crossed with an rf electric field an effective acceleration of plasma electrons across the magnetic field takes place. When Coulomb collisions are taken into account, this acceleration gives rise to a stream of runaway electrons. The current in this stream is determined as a function of the amplitude of the electric field and the plasma parameters.

  2. Laser action in xenon pumped by pulsed beams of runaway electrons

    SciTech Connect

    Kolbychev, G.V.; Samyshkin, E.A.

    1983-02-01

    A report is given of the use of pulsed beams of runaway electrons for the pumping of gas lasers. Electron beams were generated inside a laser chamber. The average energy of these electrons was 1--4 keV. Lasing was observed as a result of the 3d/sub 2/--2p/sub 7/ transition in xenon. An analysis was made of the possibility of using runaway-electron beams in other types of gas laser.

  3. Spontaneous emission near the electron plasma frequency in a plasma with a runaway electron tail

    NASA Technical Reports Server (NTRS)

    Freund, H. P.; Lee, L. C.; Wu, C. S.

    1978-01-01

    Spontaneous emission of radiation with frequencies near the electron plasma frequency is studied for a plasma which consists of both thermal and runaway electrons. It is found that a substantial enhancement of the spontaneous radiation intensity can occur in this frequency regime via a Cherenkov resonance with the runaway electrons. Numerical analysis indicates that, for reasonable estimates of densities and energies, the plasma-frequency radiation can attain levels greater than the peak thermal emission at the second gyroharmonic.

  4. Influence of the angular scattering of electrons on the runaway threshold in air

    NASA Astrophysics Data System (ADS)

    Chanrion, O.; Bonaventura, Z.; Bourdon, A.; Neubert, T.

    2016-04-01

    The runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare the outcome of different Fokker-Planck and Monte Carlo models with increasing complexity in the description of the scattering. The results show that the inclusion of the stochastic nature of collisions smooths the probability to run away around the threshold. Furthermore, we observe that a significant number of electrons diffuse out of the runaway regime when we take into account the diffusion in angle due to the scattering. Those results suggest using a runaway threshold energy based on the Fokker-Planck model assuming the angular equilibrium that is 1.6 to 1.8 times higher than the one proposed by [1, 2], depending on the magnitude of the ambient electric field. The threshold also is found to be 5 to 26 times higher than the one assuming forward scattering. We give a fitted formula for the threshold field valid over a large range of electric fields. Furthermore, we have shown that the assumption of forward scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation.

  5. Control of post-disruption runaway electron beams in DIII-D

    SciTech Connect

    Eidietis, N. W.; Humphreys, D. A.; Strait, E. J.; VanZeeland, M. A.; Wesley, J. C.; Commaux, N.; Jernigan, T. C.; Hollmann, E. M.; Moyer, R. A.; Yu, J. H.

    2012-05-15

    Recent experiments in the DIII-D tokamak have demonstrated real-time control and dissipation of post-disruption runaway electron (RE) beams. In the event that disruption avoidance, control, and mitigation schemes fail to avoid or suppress RE generation, active control of the RE beam may be an important line of defense to prevent the rapid, localized deposition of RE beam energy onto vulnerable vessel sections. During and immediately after the current quench, excessive radial compression of the runaway beams is avoided by a combination of techniques, improving the likelihood of the beams surviving this dynamic period without a fast termination. Once stabilized, the runaway beams are held in a steady state (out to the ohmic flux limit) with the application of active plasma current and position controls. Beam interaction with the vessel wall is minimized by avoiding distinct thresholds for enhanced wall interaction at small and large radii, corresponding to inner wall and outer limiter interaction, respectively. Staying within the 'safe zone' between those radial thresholds allows for the sustainment of long-lived, quiescent runaway beams. The total beam energy and runaway electron population are then dissipated gradually by a controlled ramp-down of the runaway current.

  6. Numerical investigation of the methods for reducing the runaway electron beam divergence

    NASA Astrophysics Data System (ADS)

    Lisenkov, V. V.; Shklyaev, V. A.

    2016-08-01

    We have performed a comparative numerical analysis of two methods for reducing the runaway electron beam divergence using an external magnetic field or a dielectric tube. The generation of runaway electrons takes place in an inhomogeneous medium that consists of a hot channel (spark channel, laser torch, etc.) surrounded by air under normal conditions. The model makes it possible to consistently calculate the formation of a subnanosecond gas discharge and the generation of accelerated electrons under these conditions. The possibility of effectively decreasing the runaway electron beam divergence using an external magnetic field, as well as a dielectric tube, has been demonstrated. However, the number of runaway electrons in the case with the tube is considerably smaller than in the case with the magnetic field due to the fact that some runaway electrons settle on the tube walls. The energy spectra of the runaway electrons significantly differ in these cases, which can be explained by the differences in the dynamics of the discharge formation.

  7. Modeling of runaway electron damage for the design of tokamak plasma facing components

    SciTech Connect

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

    1990-04-01

    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 three dimensional, time dependent, computational code package used to predict energy deposition, temperature rise, and damage on tokamak first wall and limiter materials form runaway electron impact. Two experiments were modeled to validate the PTA code package. The first experiment tested the thermal and structural response from high energy electron impact on different fusion materials, and the second experiment simulated runaway electrons scattering through a plasma facing surface (graphite) into an internal structure (copper). 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, resistant to runaway electron damage. 9 refs., 7 figs.

  8. Control of post-disruption runaway electron beams in DIII-D

    SciTech Connect

    Eidietis, N. W.; Commaux, Nicolas JC; Hollmann, E. M.; Humphrey, D. A.; Jernigan, T. C.; Moyer, R.A.; Strait, E. J.; Van Zeeland, M. A.; Wesley, J. C.

    2012-01-01

    Recent experiments in the DIII-D tokamak have demonstrated real-time control and dissipation of post-disruption runaway electron (RE) beams. In the event that disruption avoidance, control, and mitigation schemes fail to avoid or suppress RE generation, active control of the RE beam may be an important line of defense to prevent the rapid, localized deposition of RE beam energy onto vulnerable vessel sections. During and immediately after the current quench, excessive radial compression of the runaway beams is avoided by a combination of techniques, improving the likelihood of the beams surviving this dynamic period without a fast termination. Once stabilized, the runaway beams are held in a steady state (out to the ohmic flux limit) with the application of active plasma current and position controls. Beam interaction with the vessel wall is minimized by avoiding distinct thresholds for enhanced wall interaction at small and large radii, corresponding to inner wall and outer limiter interaction, respectively. Staying within the 'safe zone' between those radial thresholds allows for the sustainment of long-lived, quiescent runaway beams. The total beam energy and runaway electron population are then dissipated gradually by a controlled ramp-down of the runaway current.

  9. Experiments in DIII-D toward achieving rapid shutdown with runaway electron suppression

    SciTech Connect

    Hollmann, E. M.; Commaux, Nicolas JC; Eidietis, N. W.; Evans, T. E.; Humphreys, D. A.; James, A. N.; Jernigan, T. C.; Parks, P. B.; Strait, E. J.; Wesley, J. C.; Yu, J.H.; Austin, M. E.; Baylor, Larry R; Brooks, N. H.; Izzo, V. A.; Jackson, G. L.; Van Zeeland, M. A.; Wu, W.

    2010-01-01

    Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well as toward achieving complete collisional suppression of these runaway electrons via massive delivery of impurities. Runaway acceleration and amplification appear to be well explained using the zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling using a Dreicer seed term, however, appears to be too small to explain the initial runaway seed formation. Up to 15% of the line-average electron density required for complete runaway suppression has been achieved in the middle of the current quench using optimized massive gas injection with multiple small gas valves firing simultaneously. The novel rapid shutdown techniques of massive shattered pellet injection and shell pellet injection have been demonstrated for the first time. Experiments using external magnetic perturbations to deconfine runaways have shown promising preliminary results. (C) 2010 American Institute of Physics. [doi:10.1063/1.3309426

  10. Fokker-Planck simulation of runaway electron generation in disruptions with the hot-tail effect

    NASA Astrophysics Data System (ADS)

    Nuga, H.; Yagi, M.; Fukuyama, A.

    2016-06-01

    To study runaway electron generation in disruptions, we have extended the three-dimensional (two-dimensional in momentum space; one-dimensional in the radial direction) Fokker-Planck code, which describes the evolution of the relativistic momentum distribution function of electrons and the induced toroidal electric field in a self-consistent manner. A particular focus is placed on the hot-tail effect in two-dimensional momentum space. The effect appears if the drop of the background plasma temperature is sufficiently rapid compared with the electron-electron slowing down time for a few times of the pre-quench thermal velocity. It contributes to not only the enhancement of the primary runaway electron generation but also the broadening of the runaway electron distribution in the pitch angle direction. If the thermal energy loss during the major disruption is assumed to be isotropic, there are hot-tail electrons that have sufficiently large perpendicular momentum, and the runaway electron distribution becomes broader in the pitch angle direction. In addition, the pitch angle scattering also yields the broadening. Since the electric field is reduced due to the burst of runaway electron generation, the time required for accelerating electrons to the runaway region becomes longer. The longer acceleration period makes the pitch-angle scattering more effective.

  11. Experiments in DIII-D toward achieving rapid shutdown with runaway electron suppression

    SciTech Connect

    Hollmann, E. M.; James, A. N.; Yu, J. H.; Izzo, V. A.; Commaux, N.; Jernigan, T. C.; Baylor, L. R.; Eidietis, N. W.; Parks, P. B.; Wesley, J. C.; Brooks, N. H.; Jackson, G. L.; Zeeland, M. A. van; Wu, W.; Evans, T. E.; Humphreys, D. A.; Strait, E. J.; Austin, M. E.

    2010-05-15

    Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well as toward achieving complete collisional suppression of these runaway electrons via massive delivery of impurities. Runaway acceleration and amplification appear to be well explained using the zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling using a Dreicer seed term, however, appears to be too small to explain the initial runaway seed formation. Up to 15% of the line-average electron density required for complete runaway suppression has been achieved in the middle of the current quench using optimized massive gas injection with multiple small gas valves firing simultaneously. The novel rapid shutdown techniques of massive shattered pellet injection and shell pellet injection have been demonstrated for the first time. Experiments using external magnetic perturbations to deconfine runaways have shown promising preliminary results.

  12. New large outburst of 29P/Schwassmann-Wachmann 1

    NASA Astrophysics Data System (ADS)

    Kidger, Mark

    2010-04-01

    Mark Kidger reports on behalf of the "Observadores_cometas Group" that a major new outburst of Comet 29P/Schwassmann-Wachmann has occurred two days before the Herschel Space Observatory is due to observe the comet. The outburst was first reported on 2010 Apr. 16, 19:22UT at R=12.8 in a 10" square aperture by Estevé Cortés and the Grup d'Astronomia de Mataró (MPC A06, Mataró, Spain), having been last seen at R=16.18 by José Ramón Vidal (MPC 945, Gijón, Spain) on 2010 Apr.

  13. Intranight Variability During the 1997 Outburst of BL Lac

    NASA Astrophysics Data System (ADS)

    Clements, Sandra D.; Carini, Michael T.; Noble, John C.

    1998-02-01

    The blazar BL Lac underwent a major outburst this summer. To search for intranight variability during the outburst, observations of BL Lac were made with the 30 inch telescope at the University of Florida's Rosemary Hill Observatory. During ten nights in July, nearly 300 CCD observations were made. BL Lac was seen to vary by more than 1.5 magnitudes over those ten nights. Substantial intranight variability was also observed. For example, on July 29, BL Lac increased in brightness by more than 0.5 magnitude in less than 2.5 hours. The observations of BL Lac taken in July are reported here and discussed in relation to the models intended to explain intranight variability.

  14. Swift/BAT detects an outburst from UX Ari

    NASA Astrophysics Data System (ADS)

    Krimm, H. A.; Barthelmy, S. D.; Baumgartner, W.; Cummings, J.; Gehrels, N.; Lien, A. Y.; Markwardt, C. B.; Palmer, D.; Sakamoto, T.; Stamatikos, M.; Ukwatta, T.

    2014-02-01

    The RS Canum Venaticorum type variable star UX Ari is currently in outburst as detected in the Swift/BAT hard X-ray transient monitor in the 15-50 keV band. The current outburst began on 2014 February 14 (MJD 56702) when it had a count rate of 0.004 +/- 0.002 ct/s/cm^2 (~20 mCrab). It continued to brighten, reaching a rate of 0.013 +/- 0.003 ct/s/cm^2 (~60 mCrab) on 2014 February 17. It has since faded somewhat, with a rate of 0.005 +/- 0.002 ct/s/cm^2 (~20 mCrab) on 2014 February 19.

  15. Model Atmospheres for Novae in Outburst: Summary of Research

    NASA Technical Reports Server (NTRS)

    Hauschildt, Peter H.

    1999-01-01

    This paper presents a final report and summary of research on Model Atmospheres for Novae in Outburst. Some of the topics include: 1) Detailed NLTE (non-local thermodynamic equilibrium) Model Atmospheres for Novae during Outburst: II. Modeling optical and ultraviolet observations of Nova LMC 1988 #1; 2) A Non-LTE Line-Blanketed Stellar Atmosphere Model of the Early B Giant epsilon CMa; 3) Spectroscopy of Low Metallicity Stellar atmospheres; 4) Infrared Colors at the Stellar/Substellar Boundary; 5) On the abundance of Lithium in T CrB; 6) Numerical Solution of the Expanding Stellar Atmosphere Problem; and 7) The NextGen Model Atmosphere grid for 3000 less than or equal to T (sub eff) less than or equal to 10000K.

  16. H1743-322 in stable outburst phase

    NASA Astrophysics Data System (ADS)

    Ricci, C.; Caballero-Garcia, M.; Beckmann, V.; Miller, J. M.; Kuulkers, E.

    2008-10-01

    The Galactic black-hole candidate and X-ray transient H 1743-322 has reached a stable high flux outburst after activity in hard X-rays had been reported by INTEGRAL (Kuulkers et al. 2008, ATel #1739; Prat et al. 2008, ATel #1745) and in the radio domain by ATCA (Corbel et al. 2008, ATel #1766). Here we report about recent observations performed by INTEGRAL during the on-going outburst. Observations were performed from 2008-10-10T05:19 until 2008-10-10T11:19 and from 2008-10-10T21:34 until 2008-10-11T21:57.

  17. Multifrequency variability of OJ 287 during the expected outburst

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano

    2005-10-01

    The BL Lac object OJ 287 (z=0.306) is a highly variable blazar, which has shown optical intermittent emission with outstanding pseudo-periodic outbursts every 11-12 years. Long-term and densely-sampled light curves have been collected in the radio and optical bands since 1891. We aim at studying the spectral and temporal behaviour of OJ 287, on both long and short time scales, in the radio, mm, optical, UV and X-ray band, during the next major outburst, expected to occur in fall 2006, possibly solving some of the puzzling question about this AGN. This is a continuation of our previous XMM observations (AO4) proposed to detect the X-ray behaviour in high state. Ground-based multifrequency campaigns are already ongoing (WEBT and ENIGMA) joint with VLBI sessions.

  18. Understanding the timing behavior of magnetars during outburst

    NASA Astrophysics Data System (ADS)

    Tong, Hao

    2016-07-01

    Magnetars show various kinds of variabilities during their outbursts: (1)decreasing spin-down torque during the decrease of X-ray flux by Swift J1822.3-1606; (2) increasing spin-down torque during the decrease of X-ray flux by the Galactic center magnetar; (3) anti-glitch during an outburst of AXP 1E2259+586, etc. All these timing behaviors of magnetars can be understood uniformly in the wind braking model of magnetars. Furthermore, a possible hard X-ray cutoff at about 130 keV is found. Future spectra observations may help us to distinguish between the magnetar model and fallback disk model for AXPs and SGRs.

  19. Analysis of Tokamak Fusion Test Reactor (TFTR) Prototype of International Thermonuclear Experimental Reactor (ITER)‡

    NASA Astrophysics Data System (ADS)

    Hester, Tim; Maglich, Bogdan; Scott, Dan; Calsec Collaboration

    2015-11-01

    TFTR produced world record of 10 million watts of controlled fusion power1 (CFP-1994) was summarized in Review1. We present evidence3 that: (1) TFTR input vs. output was 40 to 10 MW i.e. a power loss. (2) Review claims no experimental evidence for thermonuclear CFP production (only a calculation). (3) Ultra-high vacuum (UHV) required for τE = 0.2 s is 10-9 torr. TFTR had no UHV pumps, resulting in 10-3 torr, restricting τE <10-6 s, << thermalization time; 0.1 s., hence DT plasma did not occur. (4) Carbon ions were presented as D-T plasma. (5) Unknown neutron detector on unexplained neutron diamagnetic effect, measured ``fusion neutron power'' without particle energy identification, energy or coincidence. (6) 8 of 9 parameters claimed were inferred not measured. Quadratic test of TFTR data results2 in zero thermonuclear fusion power contribution to 10 MW: SFP = (0 +/- 1)%. ‡ Submitted to Physics of Plasmas†

  20. On the helical instability and efficient stagnation pressure production in thermonuclear magnetized inertial fusion

    NASA Astrophysics Data System (ADS)

    Sefkow, A. B.

    2016-10-01

    Magneto-inertial fusion experiments produce thermonuclear neutrons from plasma compressed to high convergence via z-pinch. Fusion fuel contained within a cylindrical metal liner is premagnetized with an axial field and laser-preheated prior to the liner's implosion by the JxB force. Convergence greater than 40 is inferred from x-ray self-emission spectroscopy and backlit x-ray radiography. The unprecedented stability is enabled by helical modes induced in the magnetized liner, the cause of which will be discussed, because of the suppression of the ubiquitous m=0 modes of the magneto-Rayleigh-Taylor instability found in many z-pinch implosions. The plasma temperature and flux are compressed to several keV and 100 MG at stagnation, enough to magnetically trap alpha particles and provide ``bootstrap'' self-heating when scaled to larger fusion yields with DT fuel. We present quantitative comparison between experimental observables and 3D modeling in support of the interpretation that this approach to laboratory fusion can scale to larger thermonuclear yields. Namely, the implosions efficiently convert liner kinetic energy to stagnated fuel internal energy with the expected pressures of 1 Gbar and burn durations of 2 ns, in agreement with both 2D and 3D modeling. Therefore, the analysis indicates the magnetized hot-spot dynamics are not dominated by implosion instability or residual kinetic energy in our best-performing experiments, wherein laser-induced non-fuel mix into the forming hot spot is low.

  1. Stabilization of burn conditions in a thermonuclear reactor using artificial neural networks

    NASA Astrophysics Data System (ADS)

    Vitela, Javier E.; Martinell, Julio J.

    1998-02-01

    In this work we develop an artificial neural network (ANN) for the feedback stabilization of a thermonuclear reactor at nearly ignited burn conditions. A volume-averaged zero-dimensional nonlinear model is used to represent the time evolution of the electron density, the relative density of alpha particles and the temperature of the plasma, where a particular scaling law for the energy confinement time previously used by other authors, was adopted. The control actions include the concurrent modulation of the D-T refuelling rate, the injection of a neutral He-4 beam and an auxiliary heating power modulation, which are constrained to take values within a maximum and minimum levels. For this purpose a feedforward multilayer artificial neural network with sigmoidal activation function is trained using a back-propagation through-time technique. Numerical examples are used to illustrate the behaviour of the resulting ANN-dynamical system configuration. It is concluded that the resulting ANN can successfully stabilize the nonlinear model of the thermonuclear reactor at nearly ignited conditions for temperature and density departures significantly far from their nominal operating values. The NN-dynamical system configuration is shown to be robust with respect to the thermalization time of the alpha particles for perturbations within the region used to train the NN.

  2. Reevaluation of thermonuclear reaction rate of 50Fe(p, 𝜸)51Co

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Ping; He, Jian-Jun; Chai, Wan-Dong; Hou, Su-Qing; Zhang, Li-Yong

    2016-11-01

    The thermonuclear rate of the 50Fe(p, 𝜸)51Co reaction in the Type I X-ray bursts (XRBs) temperature range has been reevaluated based on a recent precise mass measurement at CSRe Lanzhou, where the proton separation energy Sp = 142±77 keV has been determined firstly for the 51Co nucleus. Comparing to the previous theoretical predictions, the experimental Sp value has much smaller uncertainty. Based on the nuclear shell model and mirror nuclear structure information, we have calculated two sets of thermonuclear rates for the 50Fe(p, 𝜸)51Co reaction by utilizing the experimental Sp value. It shows that the statistical-model calculations are not ideally applicable for this reaction primarily because of the low density of low-lying excited states in 51Co. In this work, we recommend that a set of new reaction rates based on the mirror structure of 51Cr should be incorporated in future astrophysical network calculations. Supported by Natural Science Foundation of Inner Mongolia Autonomous Region of China (2013MS0916) and National Natural Science Foundation of China (11490562, 11405228)

  3. Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures

    NASA Astrophysics Data System (ADS)

    Newton, Joseph; Longland, Richard; Iliadis, Christian

    2009-05-01

    Reliable reaction rates at high stellar temperatures are necessary for the study of advanced stellar burning stages, supernovae and x-ray bursts. We suggest a new procedure for extrapolating experimental thermonuclear reaction rates to these higher temperatures (T > 1 GK) using statistical model (Hauser-Feshbach) results. Current, generally accepted, procedures involve the use of the Gamow peak, which has been shown to be unreliable for narrow resonances at high stellar temperatures [1]. Our new approach defines the effective thermonuclear energy range (ETER) by using the 8^th, 50^th and 92^nd percentiles of the cumulative distribution of fractional resonant reaction contributions. The ETER is then used to define a reliable temperature for matching experimental rates to Hauser-Feshbach rates. The resulting matching temperature is often well above the previous result using the Gamow peak concept. Our new method should provide more accurate extrapolated rates since Hauser-Feshbach rates are more reliable at higher temperatures. These ideas are applied to 21 (p,γ), (p,α) and (α,γ) reactions on a range of A = 20-40 target nuclei and results will be presented. [0pt] [1] J. R. Newton, C. Iliadis, A. E. Champagne, A. Coc, Y. Parpottas and R. Ugalde, Phys. Rev. C 75, 045801 (2007).

  4. Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures

    NASA Astrophysics Data System (ADS)

    Newton, J. R.; Longland, R.; Iliadis, C.

    2008-08-01

    We address the problem of extrapolating experimental thermonuclear reaction rates toward high stellar temperatures (T>1 GK) by using statistical model (Hauser-Feshbach) results. Reliable reaction rates at such temperatures are required for studies of advanced stellar burning stages, supernovae, and x-ray bursts. Generally accepted methods are based on the concept of a Gamow peak. We follow recent ideas that emphasized the fundamental shortcomings of the Gamow peak concept for narrow resonances at high stellar temperatures. Our new method defines the effective thermonuclear energy range (ETER) by using the 8th, 50th, and 92nd percentiles of the cumulative distribution of fractional resonant reaction rate contributions. This definition is unambiguous and has a straightforward probability interpretation. The ETER is used to define a temperature at which Hauser-Feshbach rates can be matched to experimental rates. This matching temperature is usually much higher compared to previous estimates that employed the Gamow peak concept. We suggest that an increased matching temperature provides more reliable extrapolated reaction rates since Hauser-Feshbach results are more trustwhorthy the higher the temperature. Our ideas are applied to 21 (p,γ), (p,α), and (α,γ) reactions on A=20-40 target nuclei. For many of the cases studied here, our extrapolated reaction rates at high temperatures differ significantly from those obtained using the Gamow peak concept.

  5. Outburst Activity of the Symbiotic System AG Dra

    NASA Astrophysics Data System (ADS)

    Gális, R.; Hric, L.; Leedjärv, L.; Kundra, E.

    2015-07-01

    AG Dra is one of the best studied symbiotic systems. A period analysis of new and historical photometric data, as well as radial velocities, confirmed the presence of the two periods — about 550 days, caused by orbital motion, and around 350 days, related to pulsations of the cool component of AG Dra. In addition, the active stages change distinctively, but the outbursts recur with periods from 359 to 375 days.

  6. Stellar encounters in the context of outburst phenomena

    NASA Astrophysics Data System (ADS)

    Forgan, Duncan; Rice, Ken

    2010-02-01

    Young stellar systems are known to undergo outbursts, where the star experiences an increased accretion rate, and the system's luminosity increases accordingly. The archetype is the FU Orionis (FU Ori) outburst, where the accretion rate can increase by three orders of magnitude (and the brightness of the system by five magnitudes). The cause appears to be instability in the circumstellar disc, but there is currently some debate as to the nature of this instability (e.g. thermal, gravitational, magneto-rotational). This paper details high-resolution smoothed particle hydrodynamics (SPH) simulations that were carried out to investigate the influence of stellar encounters on disc dynamics. Star-star encounters (where the primary has a self-gravitating, marginally stable protostellar disc) were simulated with various orbital parameters to investigate the resulting disc structure and dynamics. Crucially, the simulations include the effects of radiative transfer to realistically model the resulting thermodynamics. Our results show that the accretion history and luminosity of the system during the encounter display many of the features of outburst phenomena. In particular, the magnitudes and decay times seen are comparable to those of FU Ori. There are two caveats to this assertion: the first is that these events are not expected to occur frequently enough to explain all FU Ori or EX Lupi; the second is that the inner discs of these simulations are subject to numerical viscosity, which will act to reduce the accretion rate (although it has less of an effect on the total mass accreted). In short, these results cannot rule out binary interactions as a potential source of some FU Ori-esque outbursts.

  7. EVN detection of Aql X-1 in outburst

    NASA Astrophysics Data System (ADS)

    Tudose, V.; Paragi, Z.; Miller-Jones, J.; Garrett, M.; Fender, R.; Rushton, A.; Spencer, R.

    2009-11-01

    The X-ray binary Aql X-1 has been in outburst in the last few weeks (ATEL #2288, #2296, #2299, #2302, #2303). We observed the system on 2009 November 19 between 14:30-19:00 UT at 5 GHz with the European VLBI Network (EVN) using the e-VLBI technique. The participating radio telescopes were Effelsberg (1 Gbps), Medicina (896 Mbps), Onsala 25m (1 Gbps), Torun (1 Gbps), Westerbork (1 Gbps), Yebes (896 Mbps), and Cambridge (128 Mbps).

  8. New type I outburst of GRO J1008-57

    NASA Astrophysics Data System (ADS)

    Kretschmar, P.; Kuehnel, M.; Nakajima, M.; Rothschild, R. E.; Laplace, E.; Salazar, E.; Mihara, T.; Kreykenbohm, I.; Wilson-Hodge, C. A.

    2016-01-01

    The Be X-ray binary GRO J1008-57 has begun another regular outburst. At the time of writing, daily averaged flux levels were 41 & plusmn; 11 mCrab (0.15 & plusmn; 0.04 counts/sec/cm^2, 2-20 keV) in MAXI and ~60 mCrab (~0.013 count/cm^2/s) in the Swift BAT monitor data.

  9. Disk instability and outburst properties of the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Kim, Soon-Wook; Wheeler, J. C.; Mineshige, Shin

    1992-01-01

    The present study reproduces the observed recurrence time scales and duration of the 1981-1989 dwarf nova-type outbursts of the intermediate polar GK Per with a model based on the time-dependent disk instability model. The model gives approximately symmetric (type B, inside-out) outbursts, as observed. This agreement suggests that the outbursts cannot result from a mass transfer instability. A modest variation of the mass transfer rate from the companion is sufficient to account for the variable outburst recurrence time scale. Contamination from the companion and the hot spot dominate the light from the disk except during a bright outburst. An intermediate temperature stagnation wave followed by a full heating wave is consistent with the observed rapid rise and double-peaked structure in the UV and optical light curves. It is argued that the hard X-ray efficiency is dime-dependent, and it is found to be much smaller in outburst than in quiescence.

  10. EXor Outbursts from Disk Amplification of Stellar Magnetic Cycles

    NASA Astrophysics Data System (ADS)

    Armitage, Philip J.

    2016-12-01

    EXor outbursts—moderate-amplitude disk accretion events observed in Class I and Class II protostellar sources—have timescales and amplitudes that are consistent with the viscous accumulation and release of gas in the inner disk near the dead zone boundary. We suggest that outbursts are indirectly triggered by stellar dynamo cycles, via poloidal magnetic flux that diffuses radially outward through the disk. Interior to the dead zone the strength of the net field modulates the efficiency of angular momentum transport by the magnetorotational instability. In the dead zone changes in the polarity of the net field may lead to stronger outbursts because of the dominant role of the Hall effect in this region of the disk. At the level of simple estimates we show that changes to kG-strength stellar fields could stimulate disk outbursts on 0.1 au scales, though this optimistic conclusion depends upon the uncertain efficiency of net flux transport through the inner disk. The model predicts a close association between observational tracers of stellar magnetic activity and EXor events.

  11. Two-sided conical laser target for a neutron source of a hybrid nuclear-thermonuclear reactor

    NASA Astrophysics Data System (ADS)

    Lebo, I. G.; Isaev, E. A.; Lebo, A. I.

    2017-03-01

    Numerical simulations suggest that a source of thermonuclear neutrons with a high pulse repetition rate and the number of neutrons of ~1017 per pulse, which is required for the development of nuclear-thermonuclear reactors, can be realised in the irradiation of a two-sided conical target simultaneously by a long and short laser pulses with energies of ~1 MJ and 50 kJ and durations of 100 – 250 ns and 0.1 – 1 ns. We consider the feasibility of verifying separate propositions of the proposed conception with the use of existing laser facilities.

  12. The TDF System for Thermonuclear Plasma Reaction Rates, Mean Energies and Two-Body Final State Particle Spectra

    SciTech Connect

    Warshaw, S I

    2001-07-11

    The rate of thermonuclear reactions in hot plasmas as a function of local plasma temperature determines the way in which thermonuclear ignition and burning proceeds in the plasma. The conventional model approach to calculating these rates is to assume that the reacting nuclei in the plasma are in Maxwellian equilibrium at some well-defined plasma temperature, over which the statistical average of the reaction rate quantity {sigma}v is calculated, where {sigma} is the cross-section for the reaction to proceed at the relative velocity v between the reacting particles. This approach is well-understood and is the basis for much nuclear fusion and astrophysical nuclear reaction rate data. The Thermonuclear Data File (TDF) system developed at the Lawrence Livermore National Laboratory (Warshaw 1991), which is the topic of this report, contains data on the Maxwellian-averaged thermonuclear reaction rates for various light nuclear reactions and the correspondingly Maxwellian-averaged energy spectra of the particles in the final state of those reactions as well. This spectral information closely models the output particle and energy distributions in a burning plasma, and therefore leads to more accurate computational treatments of thermonuclear burn, output particle energy deposition and diagnostics, in various contexts. In this report we review and derive the theoretical basis for calculating Maxwellian-averaged thermonuclear reaction rates, mean particle energies, and output particle spectral energy distributions for these reactions in the TDF system. The treatment of the kinematics is non-relativistic. The current version of the TDF system provides exit particle energy spectrum distributions for two-body final state reactions only. In a future report we will discuss and describe how output particle energy spectra for three- and four-body final states can be developed for the TDF system. We also include in this report a description of the algorithmic implementation of the

  13. Accretion outbursts in self-gravitating protoplanetary disks

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Nelson, Richard P. E-mail: lhartm@umich.edu E-mail: r.p.nelson@qmul.ac.uk

    2014-11-01

    We improve on our previous treatments of the long-term evolution of protostellar disks by explicitly solving disk self-gravity in two dimensions. The current model is an extension of the one-dimensional layered accretion disk model of Bae et al. We find that gravitational instability (GI)-induced spiral density waves heat disks via compressional heating (i.e., PdV work), and can trigger accretion outbursts by activating the magnetorotational instability (MRI) in the magnetically inert disk dead zone. The GI-induced spiral waves propagate well inside of the gravitationally unstable region before they trigger outbursts at R ≲ 1 AU where GI cannot be sustained. This long-range propagation of waves cannot be reproduced with the previously used local α treatments for GI. In our standard model where zero dead-zone residual viscosity (α{sub rd}) is assumed, the GI-induced stress measured at the onset of outbursts is locally as large as 0.01 in terms of the generic α parameter. However, as suggested in our previous one-dimensional calculations, we confirm that the presence of a small but finite α{sub rd} triggers thermally driven bursts of accretion instead of the GI + MRI-driven outbursts that are observed when α{sub rd} = 0. The inclusion of non-zero residual viscosity in the dead zone decreases the importance of GI soon after mass feeding from the envelope cloud ceases. During the infall phase while the central protostar is still embedded, our models stay in a 'quiescent' accretion phase with M-dot {sub acc}∼10{sup −8}--10{sup −7} M{sub ⊙} yr{sup −1} over 60% of the time and spend less than 15% of the infall phase in accretion outbursts. While our models indicate that episodic mass accretion during protostellar evolution can qualitatively help explain the low accretion luminosities seen in most low-mass protostars, detailed tests of the mechanism will require model calculations for a range of protostellar masses with some constraint on the initial core

  14. Multi-Wavelength Study of the 2008-2009 Outburst of V1647 Ori

    NASA Astrophysics Data System (ADS)

    García-Alvarez, D.; Wright, N. J.; Drake, J. J.; Abraham, P.; Anandarao, B. G.; Kashyap, V.; Kospal, A.; Kun, M.; Marengo, M.; Moor, A.; Peneva, S.; Semkov, E.; Venkat, V.; Sanz-Forcada, J.

    2011-12-01

    V1647 Ori is a young eruptive variable star, illuminating a reflection nebula (McNeil's Nebula). It underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, V1647 Ori underwent a new outburst. The observed properties of the 2003-2006 event are different in several respects from both the EXor and FUor type outbursts, and suggest that this star might represent a new class of eruptive young stars, younger and more deeply embedded than EXors, and exhibiting variations on shorter time scales than FUors. In outburst, the star lights up the otherwise invisible McNeil's nebular -- a conical cloud likely accumulated from previous outbursts. We present follow-up photometric as well as optical and near-IR spectroscopy of the nebula obtainted during the 2008-2009 outburst. We will also present results from contemporaneous X-ray observations. These multi-wavelength observations of V1647 Ori, obtained at this key early stage of the outburst, provide a snapshot of the "lighting up" of the nebula, probe its evolution through the event, and enable comparison with the 2003-2006 outburst.

  15. One-loop correction and the dilaton runaway problem

    NASA Astrophysics Data System (ADS)

    Xiu, Rulin

    1997-04-01

    We examine the one-loop vacuum structure of an effective theory of gaugino condensation coupled to the dilaton for string models in which the gauge coupling constant does not receive string threshold corrections. The new ingredients in our treatment are that we take into account the one-loop correction to the dilaton Kähler potential and we use a formulation which includes a chiral field H corresponding to the gaugino bilinear. We find through explicit calculation that supersymmetry in the Yang-Mills sector is broken by gaugino condensation. The dilaton and H field have masses on the order of the gaugino condensation scale independently of the dilaton VEV. Although the calculation performed here is at best a model of the full gaugino condensation dynamics, the result shows that the one-loop correction to the dilaton Kähler potential as well as the detailed dynamics at the gaugino condensation scale may play an important role in solving the dilaton runaway problem.

  16. Enhancer Runaway and the Evolution of Diploid Gene Expression

    PubMed Central

    Fyon, Frédéric; Cailleau, Aurélie; Lenormand, Thomas

    2015-01-01

    Evidence is mounting that the evolution of gene expression plays a major role in adaptation and speciation. Understanding the evolution of gene regulatory regions is indeed an essential step in linking genotypes and phenotypes and in understanding the molecular mechanisms underlying evolutionary change. The common view is that expression traits (protein folding, expression timing, tissue localization and concentration) are under natural selection at the individual level. Here, we use a theoretical approach to show that, in addition, in diploid organisms, enhancer strength (i.e., the ability of enhancers to activate transcription) may increase in a runaway process due to competition for expression between homologous enhancer alleles. These alleles may be viewed as self-promoting genetic elements, as they spread without conferring a benefit at the individual level. They gain a selective advantage by getting associated to better genetic backgrounds: deleterious mutations are more efficiently purged when linked to stronger enhancers. This process, which has been entirely overlooked so far, may help understand the observed overrepresentation of cis-acting regulatory changes in between-species phenotypic differences, and sheds a new light on investigating the contribution of gene expression evolution to adaptation. PMID:26561855

  17. E-ELT constraints on runaway dilaton scenarios

    SciTech Connect

    Martinelli, M.; Calabrese, E.; Martins, C.J.A.P. E-mail: erminia.calabrese@physics.ox.ac.uk

    2015-11-01

    We use a combination of simulated cosmological probes and astrophysical tests of the stability of the fine-structure constant α, as expected from the forthcoming European Extremely Large Telescope (E-ELT), to constrain the class of string-inspired runaway dilaton models of Damour, Piazza and Veneziano. We consider three different scenarios for the dark sector couplings in the model and discuss the observational differences between them. We improve previously existing analyses investigating in detail the degeneracies between the parameters ruling the coupling of the dilaton field to the other components of the universe, and studying how the constraints on these parameters change for different fiducial cosmologies. We find that if the couplings are small (e.g., α{sub b} = α{sub V} ∼ 0) these degeneracies strongly affect the constraining power of future data, while if they are sufficiently large (e.g., α{sub b} ∼> 10{sup −5}−α{sub V} ∼> 0.05, as in agreement with current constraints) the degeneracies can be partially broken. We show that E-ELT will be able to probe some of this additional parameter space.

  18. Disruptions generated runaways in the FTU high field tokamak

    NASA Astrophysics Data System (ADS)

    Poli, F. M.; Esposito, B.; Maddaluno, G.; Martin-Solis, J. R.

    2001-10-01

    Disruptions in FTU are usually accompanied by the generation of a strong pulse of photoneutrons (YN 10^12n/s), resulting from photonuclear reactions induced by the bremsstrahlung radiation emitted when runaway electrons (REs) strike the plasma facing components. Measurements of YN during major disruptions on TS [1] showed variations of three orders of magnitude when the toroidal field Bt increases from 1.8T to 3.9T. Similar results were found on JT-60 [2], where no REs are produced for low Bt (<2.2T) and a large YN was measured for higher fields (up to 4T). The range of Bt available in FTU (4T-8T) allows to extend such analysis so that useful predictions can be obtained for operation in next-step high field tokamaks (IGNITOR, ITER). The dependence of YN on Bt is investigated in several FTU disruptions. YN increases with Bt for B_t=4T-6T, while no variation is found for B_t=6T-8T: the role played by ne and Ip on such trend is discussed. [1]P.Joyer,G.Martin,Contr.Fusion and Plasma Heating,Proc.17^thEPS Conf.Amsterdam(1990) [2]R.Yoshino et al.,Nucl.Fus.39 151 (1999)

  19. Baryogenesis and gravitational waves from runaway bubble collisions

    SciTech Connect

    Katz, Andrey; Riotto, Antonio

    2016-11-07

    We propose a novel mechanism for production of baryonic asymmetry in the early Universe. The mechanism takes advantage of the strong first order phase transition that produces runaway bubbles in the hidden sector that propagate almost without friction with ultra-relativistic velocities. Collisions of such bubbles can non-thermally produce heavy particles that further decay out-of-equilibrium into the SM and produce the observed baryonic asymmetry. This process can proceed at the very low temperatures, providing a new mechanism of post-sphaleron baryogenesis. In this paper we present a fully calculable model which produces the baryonic asymmetry along these lines as well as evades all the existing cosmological constraints. We emphasize that the Gravitational Waves signal from the first order phase transition is completely generic and can potentially be detected by the future eLISA interferometer. We also discuss other potential signals, which are more model dependent, and point out the unresolved theoretical questions related to our proposal.

  20. A study of runaway electrons on a university scale generator

    NASA Astrophysics Data System (ADS)

    Ouart, Nicholas; Giuliani, John; Dasgupta, Arati; Petrov, George; Ampleford, David; Hansen, Stephanie; Safronova, Alla; Kantsyrev, Victor; Shrestha, Ishor

    2014-10-01

    Wire array implosions have produced characteristic K-shell emission. These K-alpha and K-beta photons are a result of high energy electrons removing an n = 1 bound electron from lower ionization stages (e.g. Ne-like). The motivation for studying this emission is the possibility of producing an alternative plasma radiation source with photon energies above 10 keV. However, the mechanism producing these fast runaway electrons still remains elusive. We show results from following electrons in uniform cylindrical plasma with an axial electric field and an azimuthal magnetic field. Elastic and inelastic collisions are included via Monte Carlo techniques. Comparison with experimental Zebra data previously reported will be discussed. Work supported by DOE/NNSA. This work is partially funded by Sandia LDRD Project 165733. 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 DE-AC04-94AL85000.