20161012(刘畅阅读)文献阅读报告
Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet

Abstract: X-ray images show that the South-East jet in the Crab nebula changes direction every few years.To mimic the kink behaviour of the Crab jet, a laboratory experiment requires magnetic fields with the right properties:
1.The fields must have a strong azimuthal (toroidal) component generated near the target where the jet is launched.

2.The fields must be embedded in and advected with the fast moving magnetized plasma flow.

Results:

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Conclusion:
Scaled laboratory experiments and validated numerical simulation reveal that the change in direction observed in the Crab jet can be attributed to magnetic fields and theassociated MHD kink instabilities.
Reference:
*Kink instability: This kind of instability caused by the local bending of the plasma column, which will increase current induced magnetic field at one side and decrease it at the other side. Thus cause the column to bend more. Such kind of instability can be reduced by adding an external homogeneous magnetic field like above.

http://home.physics.ucla.edu/calendar/conferences/cmpd/talks/cowley.pdf

http://hibp.ecse.rpi.edu/~leij/plasma/Cylin/Cylin.html

Figures:

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2016929(韩波阅读)文献阅读报告
A higher-than-predicted measurement of iron opacity at solar interior temperatures
背景

恒星内部气体的丰度和不透明度严重影响着恒星内部结构和演化。重新对光球层光谱的研究表明CNiO等元素的丰度比以前推导的少30-50%。标准太阳模型利用新的丰度得到的太阳内部结构与星震观测得到的结果不一致。要解决这个问题则需要太阳内部物质的平均不透明度比现在使用的结果高大约15%。太阳模型和星震学差别较大的地方在太阳的辐射层和对流层的交界区域,贴的不透明度占了总的不透明度的大约四分之一。 辐射层和对流层交界区的温度范围大约为2.1 MK 密度范围为9*1022 cm-3
 
这样的状态下铁在6-16埃波段的不透明度主要由L壳层的bound-boundbound-free过程贡献。理论难点在于在上述状态下计算精确的能及布居。这个状态下谱线的滞宽未被实验检测。难于精确地处理自电离。
 

实验难点:

     

    2007年,实验在Z-facility上进行。
    Z-pinch聚集阶段预加热Fe/Mg的薄膜,薄膜表面镀了CHBe,通过控制镀膜的厚度控制Fe/Mg的膨胀,制造不同温度密度的等离子体。
    稳定阶段形成的X射线源成为背光透过等离子体。
    实验中,被照射样品的分为两部分,一半Fe/Mg加上镀膜,另一半只有镀膜。认为背光透过镀膜无衰减,一次实验便可记录被吸收和未被吸收的光谱。
    然后光透过1mm的狭缝限制谱仪的视场。后面50微米的狭缝使得信号有了空间分辨。最后通过弯晶形成能量分辨的光谱。
     

    四个状态下,实验值与SCRAM的理论值的比较。不透明度随变化的趋势相似,但是实验值更高。

    Pasted Graphic 6
     

    状态下,与OP, ATOMIC, OPAS, SCO-RCG其他理论模型的比较。所有的模型与实验值都有较大的差距。
    OPATOMIC计算时精确到能级;其他模型对于强的过程精确倒能级,而对于众多的较弱的过程则用了统计近似。
    Pasted Graphic 7
     

    讨论:

     
    一、 7-9.5Å,波长较短,连续谱占主导的波段,bound-free过程比bound-bound过程强。实验值比理论值大,原因可能是:

       
      二、 在谱线聚集的波段,实验值普遍高于各理论值,各理论模型结果之间的差异也可以达到50%.实验光谱中谱线的滞宽普遍比理论值大。原因可能是:
         
        三、 使用测得的铁的不透明度,修正后的Rosseland平均不透明度增加了7±3%。是解决前面标准太阳模型和星震理论之间差异所需要的不透明度增值的一半。
         
        四、 这个实验的结果表明可能不止辐射层和对流层交界区域的不透明度需要修正,太阳其他内部区域的不透明度也需要修正。并且NiCrTiCa等元素的L壳层引起的不透明度也需要研究。


        2016922(仝博伟阅读)

        Laboratory Modeling of Radiatively Cooled Jets Using Conical Wire Array Z-pinches

        http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.1718495
        D.J. Ampleford, S.V. Lebedev, A. Ciardi, J.P. Chittenden, S.N. Bland,
        S.C. Bott, J. Rapley, M. Sherlock, C. Jennings, A. Frank a,b, T.Gardiner a,b

        The Blackett Laboratory, Imperial College London, SW7 2BW, UK
        a Department of Physics and Astronomy, University of Rochester, Rochester NY 14627-0171 USA
        b Laboratory for Laser Energetics, University of Rochester, Rochester NY 14627-0171 USA

        Abstract. We present the results of astrophysically relevant laboratory experiments carried out on the MAGPIE pulsed power facility. Collimated, radiatively cooled outflows are observed in a number of astrophysical situations including Young Stellar Objects and Planetary Nebulae. To model these jets, highly supersonic (Mach number 20-30), radiatively cooled plasma jets are produced using conically convergent flows obtained by applying a fast rising current to a conical arrangement of fine metallic wires. Methods of varying the jet cooling length, the density contrast between jet and surrounding material and the angular momentum of the jet have been developed. We have also been able to model other observed jet features such as the deflection of jets by a side wind. Such a mechanism has been proposed to explain observations where bipolar jets are both curved in the same direction, producing a C-shaped symmetry [1]. The laboratory jets are significantly deflected without loss of collimation by the ram pressure from a photo- ionised CH wind. A new wire array design that produces a bubble, which launches a fast, short-lived jet or projectile, is also described.

        The concepts of some parameters:

        Reynolds numbers: the ratio of inertial forces to viscous forces. Reynolds numbers frequently arise when performing scaling of fluid dynamics problems, and as such can be used to determine dynamic similitude between two different cases of fluid flow. They are also used to characterize different flow regimes within a similar fluid. It could also be considered the ratio of the total momentum transfer to the molecular momentum transfer.
        Peclet numbers: It is defined to be the ratio of the rate of advection of a physical quantity by the flow to the rate of diffusion of the same quantity driven by an appropriate gradient. In the context of species or mass transfer, the Péclet number is the product of the Reynolds number and the Schmidt number. In the context of the thermal fluids, the thermal Peclet number is equivalent to the product of the Reynolds number and the Prandtl number.
        Mach number: the ratio of flow velocity past a boundary to the local speed of sound
        Cooling parameter: ratio of cooling length to jet radius.
        Density contrast: ratio of jet to ambient densities


        Conclusion:


            Figure:

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            2016914(原晓霞阅读)
            Kilotesla Magnetic Field due to a Capacitor-Coil Target Driven by High Power Laser.

            Fujioka, Shinsuke; Zhang, Zhe et al.

            Nature Scientific Reports, Volume 3, id. 1170 (2013).
            http://ads.bao.ac.cn/abs/2013NatSR...3E1170F

            References:
            1. Sagdeev, R. Z. Reviews of Plasma Physics, chap. Cooperative Phenomena and
            Shock Waves in Collisionless Plasmas, 23 (Consultants Bureau, New York, 1966).
            2. Santangelo, A. et al. A BEPPOSAX study of the pulsating transient X0115163:
            The first X-ray spectrum with four cyclotron harmonic features. Astro. Phys. J.
            Lett. 523, L85 (1999).
            3. Kopp, R. A. & Pneuman, G. W. Magnetic reconnection in the corona and the loop
            prominence phenomenon. Solar Phys. 50, 85 (1976).
            4. Masuda, S., Kosugi, T., Hara, H., Tsuneta, S. & Ogawara, Y. A loop-top hard x-ray
            source in a compact solar flare as evidence for magnetic reconection. Nature 371,
            495 (1994).
            5. Herlach, F. & Miura, N. (eds.) High Magnetic Fields: Science and Technology
            (World Scientific Pub Co Inc, Singapore, 2003).

            Abstract:Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro- and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better controlled shapes of the field are desirable. Here we have generated kilotesla magnetic fields using a capacitor-coil target, in which two nickel disks are connected by a U-turn coil. A magnetic flux density of 1.5 kT was measured using the Faraday effect 650 mm away from the coil, when the capacitor was driven by two beams from the GEKKO-XII laser (at 1 kJ (total), 1.3 ns, 0.53 or 1 µm, and 5 ×1016W/cm2).
            Pasted Graphic 1
            Figure 1 | Photographs of a capacitor-coil target from (a) its side and (b) its front.


            Pasted Graphic 3
            Figure 3 | Magnetic flux density measurement using the Faraday effect.
            Pasted Graphic 5
            Figure 5 | (a) Temporal evolution of the intensity ratio between horizontal and vertical components and the magnetic flux density using 100-mm-thick fused silica cylinder. The hatch marks in the graph represent the duration of that the probe light was blocked. (b) An x-ray streak image of the plasma generated in the target capacitor.

            Discussion:
            (1) The first important discussion issue is a validity of the Faraday rotation measurement for large B and dB/dt achieved in this experiment. B and dB/dt reach 1.5 kT and 3 kT/ns.
            (2) The second discussion issue is total energy of the magnetic field generated by the laser-driven capacitor coil. The total energy of the field were estimated to be 15 kJ.




            2016
            630日 (刘畅阅读)

            Experiments on radiative collapse in laser-produced plasmas relevant to astrophysical jets
            http://journals.aps.org/pre/abstract/10.1103/PhysRevE.62.8838
            K. Shigemori,1,2 R. Kodama,1 D. R. Farley,2 T. Koase,1 K. G. Estabrook,2 B. A. Remington,2 D. D. Ryutov,2 Y. Ochi,1
            H. Azechi,1 J. Stone,3 and N. Turner3
            1 Institute of Laser Engineering, Osaka University, Suita, Osaka, 565-0871, Japan
            2 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551
            3 Department of Astronomy, University of Maryland, College Park, Maryland 20742

            ABSTRACT:
            We report a laser experiment of astrophysical interest on radiative jet formation. Conically shaped targets are irradiated by intense laser light. An ablated plasma flow collides at the axis of the cone targets, then propagates at high Mach number, forming a jetlike structure. We measure time-resolved x-ray self-emission images from the jets. The diameter of the jet increases with decreasing atomic number of the irradiated target, suggesting that the collimation is due to radiative cooling. Two-dimensional simulations reproduce essential features of the experimental results.


            Problems and hypothesis:
            Jets are well collimated and narrow (radiative cooling is a probable reason)
            The effects of radiation in laboratory jets (varied the Z of the targets, CH, Al, Fe, and Au)

            Conclusion:
            Jets of high-Z material are more radiatively cooled and are well collimated, whereas low-Z materials jet are adiabatically expanded.
            The simulation results indicates that the radiative cooling time is important for the formation of the well-collimated jets.
            The internal Mach numbers and radiative cooling parameters of our experimental jets are relevant to those of the astrophysical jets.

            Figure:

            Pasted Graphic 3
            Pasted Graphic 4



            radiant flux (qrad): the radiant energy emitted, reflected, transmitted or received, per unit time:

            E is the radiant energy, t is the time.


            2016623
            Laboratory analogue of a supersonic accretion column in a binary star system (原晓霞阅读)

            J. E. Cross, G. Gregori, J. M. Foster, P. Graham, J. -M. Bonnet-Bidaud, C. Busschaert

            http://www.nature.com/ncomms/2016/160613/ncomms11899/full/ncomms11899.html



            AbstractFor magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B410MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100–1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.


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            (参考文献)
            1.Hartigan, P. et al. Dynamics of stellar jets in real time: third epoch hubble space telescope images of HH 1, HH 34, and HH 47. Astrophys. J. 736, 29 (2011).
            2.Wu, K. Accretion onto magnetic white dwarfs. 
            Space Sci. Rev. 93, 611–649 (2000).
            3.Dale, J. E. & Bonnell, I. A. Ionization-induced star formation—III. Effects of external triggering on the initial mass function in clusters. 
            Mon. Not. R. Astron. Soc. 422, 1352–1362(2012).

            2016526

            Monthly Notices of the Royal Astronomical Society, Volume 381, Issue 4, pp. 1727-1732.

            http://adsabs.harvard.edu/abs/2007MNRAS.381.1727K

            An investigation of FeXVI emission lines in solar and stellar extreme-ultraviole (彭吉敏阅读)

            F. P. Keenan,1 * J. J. Drake2 and K. M. Aggarwal1

            1 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University, Belfast BT7 1NN
            2 Smithsonian Astrophysical Observatory, MS 3, 60 Garden Street, Cambridge, MA 02138, USA

            Abstract

            New fully relativistic calculations of radiative rates and electron impact excitation cross-sections for FeXVI are used to determine theoretical emission-line ratios applicable to the 251-361 and 32-77Å portions of the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A comparison of the EUV results with observations from the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals excellent agreement between theory and experiment. However, for emission lines in the 32-49Å portion of the soft X-ray spectral region, there are large discrepancies between theory and measurement for both a solar flare spectrum obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and for observations of Capella from the Low-Energy Transmission Grating Spectrometer (LETGS) on the Chandra X-ray Observatory. These are probably due to blending in the solar flare and Capella data from both first-order lines and from shorter wavelength transitions detected in second and third order. By contrast, there is very good agreement between our theoretical results and the XSST and LETGS observations in the 50-77Å wavelength range, contrary to previous results. In particular, there is no evidence that the FeXVI emission from the XSST flare arises from plasma at a much higher temperature than that expected for FeXVI in ionization equilibrium, as suggested by earlier work.


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            2016512
            PhysRevLett.99.265001
            http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.99.265001 
            Supersonic-Jet Experiments Using a High-Energy Laser

            B. Loupias1,*, M. Koenig1, E. Falize2,3, S. Bouquet2,3, N. Ozaki1,4, A. Benuzzi-Mounaix1, T. Vinci1, C. Michaut3, M. Rabec le Goahec1, W. Nazarov5, C. Courtois2, Y. Aglitskiy6, A. Ya. Faenov7, and T. Pikuz7
            1LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau, France
            2CEA/DIF/DPTA BP 12, 91680 Bruyeres-le-Chatel, France
            3Laboratoire de l’Univers et de ses Théories, Observatoire de Paris, CNRS, Université Paris Diderot, Place Jules Janssen, 92190 Meudon, France
            4Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
            5School of Chemistry, University of St Andrews, Purdie Blg, St Andrews KY16 9ST, United Kingdom
            6Science Applications International Corporation, McLean, Virginia 22102, USA
            7Joint Institute for High Temperatures of RAS, Izhorskaya 13/19, Moscow, 125412, Russia

            ABSTRACT


            In this Letter, laboratory astrophysical jet experiments performed with the LULI2000 laser facility are presented. High speed plasma jets (150  kms−1) are generated using foam-filled cone targets. Accurate experimental characterization of the plasma jet is performed by measuring its time evolution and exploring various target parameters. Key jet parameters such as propagation and radial velocities, temperature, and density are obtained. For the first time, the required dimensionless quantities are experimentally determined on a single-shot basis. Although the jets evolve in vacuum, most of the scaling parameters are relevant to astrophysical conditions.

            未知


            2015
            117
            PRL 113, 105003 (2014)
            fiksel-PhysRevLett.113.105003
            Magnetic Reconnection between Colliding Magnetized Laser-Produced Plasma Plumes

            G. Fiksel,1,2,* W. Fox,3 A. Bhattacharjee,3 D. H. Barnak,1,2 P.-Y. Chang,1,2 K. Germaschewski,4
            S. X. Hu,1 and P. M. Nilson1,2
            1Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623, USA
            2Fusion Science Center for Extreme States of Matter, University of Rochester, Rochester, New York 14623, USA
            3Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
            4Space Science Center, University of New Hampshire, Durham, New Hampshire 03824, USA


            Observations of magnetic reconnection between colliding plumes of magnetized laser-produced plasma are presented. Two counterpropagating plasma flows are created by irradiating oppositely placed plastic (CH) targets with 1.8-kJ, 2-ns laser beams on the Omega EP Laser System. The interaction region between the plumes is prefilled with a low-density background plasma and magnetized by an externally applied magnetic field, imposed perpendicular to the plasma flow, and initialized with an X-type null point geometry with B ¼ 0 at the midplane and B ¼ 8 T at the targets. The counterflowing plumes sweep up and compress the background plasma and the magnetic field into a pair of magnetized ribbons, which collide, stagnate, and reconnect at the midplane, allowing the first detailed observations of a stretched current sheet in laser-driven reconnection experiments. The dynamics of current sheet formation are in good agreement with first-principles particle-in-cell simulations that model the experiments.

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            2015
            1031
            PHYSICAL REVIEW E
            91, 013110 (2015)
            Magnetized laboratory plasma jets: Experiment and simulation

            Peter Schrafel,* Kate Bell, John Greenly, Charles Seyler, and Bruce Kusse
            Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853, USA (Received 21 March 2014; published 30 January 2015)
            PhysRevE.91.013110
            Experiments involving radial foils on a 1 MA, 100 ns current driver can be used to study the ablation of thin foils and liners, produce extreme conditions relevant to laboratory astrophysics, and aid in computational code validation. This research focuses on the initial ablation phase of a 20 μm Al foil (8111 alloy), in a radial configuration, driven by Cornell University’s COBRA pulsed power generator. In these experiments ablated surface plasma (ASP) on the top side of the foil and a strongly collimated axial plasma jet are observed developing midway through the current rise. With experimental and computational results this work gives a detailed description of the role of the ASP in the formation of the plasma jet with and without an applied axial magnetic field. This 1 T field is applied by a Helmholtz-coil pair driven by a slow, 150 μs current pulse and penetrates the load hardware before arrival of the COBRA pulse. Several effects of the applied magnetic field are observed: (1) without the field extreme-ultraviolet emission from the ASP shows considerable azimuthal asymmetrywhile with the field the ASP develops azimuthal motion that reduces this asymmetry, (2) this azimuthal motion slows the development of the jet when the field is applied, and (3) with the magnetic field the jet becomes less collimated and has a density minimum (hollowing) on the axis. PERSEUS, an XMHD code, has qualitatively and quantitatively reproduced all these experimental observations. The differences between this XMHD and an MHD code without a Hall current and inertial effects are discussed. In addition the PERSEUS results describe effects we were not able to resolve experimentally and suggest a line of future experiments with better diagnostics.


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