Browsing by Author "Liang, Edison"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Conversion of ultra-intense infrared laser energy into relativistic particles
    (2010-05-04) Liang, Edison; Rice University; United States Patent and Trademark Office
    Devices and methods for producing relativistic particles are provided. The devices and methods involve collision of a thin collimated plasma layer from opposite sides with two counter-propagating ultra-intense laser (UL) electromagnetic (EM) pulses. The plasma layer is sufficiently thin so that the pulses penetrate and conjointly propagate through the plasma layer. The Lorenz force between induced skin currents and the magnetic field of the propagating pulses accelerates a number of “in-phase” plasma particles to relativistic velocities.
  • Thumbnail Image
    Item
    Multi-physics modelings and analysis for magnetized high-energy-density laser driven plasma flows
    (2020-12-04) Lu, Yingchao; Liang, Edison
    Laboratory experiments on large laser facilities have been a new way to study astrophysical phenomena and fundamental physics processes, including those related to magnetic fields. Over the past few years, two experiment platforms on OMEGA laser facility, i.e. hollow ring magnetized jet platform and shock-shear platform, have been developed to study the magnetic fields in high-energy-density laser driven plasma flows. This thesis summarizes the multi-year effort on the development of these two platforms. On the hollow ring magnetized jet platform, highly collimated jets are driven by a ring of 20 OMEGA beams. A bundle of laser beams with given individual intensity, duration and focal spot size, produces a supersonic jet of higher density, temperature and better collimation, if the beams are focused to form a circular ring pattern on a flat target instead of a single focal spot. On the shock-shear platform, counter-propagating shocks in a shock tube induces a shear layer with vortices and mix. The shock tube allows us to study the shear-induced instabilities and turbulence production under high-energy-density conditions. For both platforms, three-dimensional FLASH radiation-magnetohydrodynamics modeling is carried out to study the evolution of hydrodynamics and magnetic fields. While many experiments and observations have been carried out to study the plasmas with external magnetic fields, this thesis focus on the self-generated magnetic fields in high-energy-density plasmas. Magnetic fields are initially self-generated via the Biermann battery term. The accurate prediction and description of the late time dynamics of magnetic fields are limited by the current capability of the simulation code. For late time, non-ideal terms such as Nernst effect, magnetized heat flow and magnetic resistivity may play a significant role. In the experiments for both platforms, the hydrodynamical evolution of the plasmas was diagnosed by X-ray framing camera. Proton radiography was used to measure the line-integrated strength of magnetic fields. In the magnetized jet experiments, where the density of the plasma is low ( ρ ≲ 10^-3 g/cc ), optical Thomson scattering was used to diagnose the temperature, density and flow velocity of the jets. Synthetic proton radiography simulations, X-ray image simulations, and synthetic Thomson spectrum modelings are carried out to compare with the observable features in the experiments. The results from the simulations and experiments in this thesis have many potential applications to laboratory astrophysics, fundamental plasma physics and other areas. This thesis also summarizes the development of numerical methods for relativistic particle-in-cell simulations and analyses. Those methods significantly improves the reliability of PIC simulations and analyses in high energy density physics and high energy astrophysics.
  • Thumbnail Image
    Item
    Relativistic Shear Flow between Electron–Ion and Electron–Positron Plasmas and Astrophysical Applications
    (IOP Publishing, 2017) Liang, Edison; Fu, Wen; Böttcher, Markus
    We present particle-in-cell simulation results of relativistic shear boundary layers between electron–ion and electron–positron plasmas and discuss their potential applications to astrophysics. Specifically, we find that in the case of a fast electron–positron spine surrounded by a slow-moving or stationary electron–ion sheath, lepton acceleration proceeds in a highly anisotropic manner due to electromagnetic fields created at the shear interface. While the highest-energy leptons still produce a beaming pattern (as seen in the quasi-stationary frame of the sheath) of order 1/Γ, where Γ is the bulk Lorentz factor of the spine, for lower-energy particles, the beaming is much less pronounced. This is in stark contrast to the case of pure electron–ion shear layers, in which anisotropic particle acceleration leads to significantly narrower beaming patterns than 1/Γ for the highest-energy particles. In either case, shear-layer acceleration is expected to produce strongly angle-dependent lepton (hence, emanating radiation) spectra, with a significantly harder spectrum in the forward direction than viewed from larger off-axis angles, much beyond the regular Doppler boosting effect from a co-moving isotropic lepton distribution. This may solve the problem of the need for high (and apparently arbitrarily chosen) minimum Lorentz factors of radiating electrons, often plaguing current blazar and GRB jet modeling efforts.
  • Thumbnail Image
    Item
    Scaling of Relativistic Shear Flows with the Bulk Lorentz Factor
    (IOP Publishing, 2018) Liang, Edison; Fu, Wen; Böttcher, Markus; Roustazadeh, Parisa
    We compare Particle-in-cell simulation results of relativistic electron–ion shear flows with different bulk Lorentz factors, and discuss their implications for spine-sheath models of blazar versus gamma-ray burst (GRB) jets. Specifically, we find that most properties of the shear boundary layer scale with the bulk Lorentz factor: the lower the Lorentz factor, the thinner the boundary layer, and the weaker the self-generated fields. Similarly, the energized electron spectrum peaks at an energy near the ion drift energy, which increases with bulk Lorentz factor, and the beaming of the accelerated electrons along the shear interface gets narrower with increasing Lorentz factor. This predicts a strong correlation between emitted photon energy, angular beaming, and temporal variability with the bulk Lorentz factor. Observationally, we expect systematic differences between the high-energy emissions of blazars and GRB jets.
  • Thumbnail Image
    Item
    Time-dependent simulations of emission from the FSRQ PKS 1510−089: multiwavelength variability of external Compton and synchrotron self-Compton models
    (Royal Astronomical Society, 2012) Chen, Xuhui; Fossati, Giovanni; Bottcher, Markus; Liang, Edison
    We present results of modelling the broad-band spectral energy distribution (SED) and multiwavelength variability of the bright flat spectrum radio quasars PKS 1510−089 with our time-dependent multizone Monte Carlo/Fokker–Planck code. As the primary source of seed photons for inverse Compton scattering, we consider radiation from the broad-line region (BLR), from the hot dust of the molecular torus and the local synchrotron radiation [synchrotron self-Compton (SSC)]. We evaluate the viability of different Compton models by comparing simulated multiwavelength light curves and SEDs with one of the best observed flares by PKS 1510−089, in 2009 March. The time dependence of our code and its correct handling of light travel time effects allow us to fully take into account the effect of the finite size of the active region, and in turn to fully exploit the information carried by time-resolved observed SEDs that are becoming increasingly available since the launch of Fermi. We confirm that the spectrum adopted for the external radiation field has an important impact on the modelling of the SED, in particular for the lower energy end of the Compton component which is observed in the X-ray band, which in turn is one of the most critical bands to assess the differences between external Compton and SSC emission. In the context of the scenario presented in this paper, where the flaring is caused by the increase of the number of relativistic electrons ascribed to the effect of the interaction of a portion of the jet (blob) with a shock, we cannot firmly discriminate the three main scenarios for γ -ray emission. However, results show clearly the differences produced by a more realistic treatment of the emitting source in the shape of SEDs and their time variability over relevant, observable time-scales, and demonstrate the crucial importance of time-dependent multizone models to advance our understanding of the physics of these sources, by taking full advantage of the wealth of information offered by the high-quality data of current multiwavelength Campaigns.