Final LDRD Report for Feasibility Study

Remington, B ; Klein, R

Lawrence Livermore National Laboratory

关键词: Turbulent Flow;    Lawrence Livermore National Laboratory;    Photons;    99 General And Miscellaneous//Mathematics, Computing, And Information Science;    71 Classical And Quantum Mechanics, General Physics;   

DOI  :  10.2172/15009782
RP-ID  :  UCRL-TR-202367
RP-ID  :  W-7405-ENG-48
RP-ID  :  15009782

美国|英语

来源: UNT Digital Library

【 摘 要 】

Extreme conditions of density and temperature of interest to DNT are similar to conditions of low-altitude atmospheres of neutron stars. Consequently, HED experimental capabilities being developed at LLNL (NIF, petawatt lasers) will open the door to laboratory studies of neutron star atmospheres. This capability will seed a new era in the study of extreme physics generated by strongly radiation dominated flows and laser-plasma interactions for the laboratory study of distant astrophysical phenomena. Indeed as has been noted by the recent Davidsen report on Frontiers of HEDPP (p. 85) ''Accretion disks and atmospheres of neutron stars likely fall in the radiation-dominated regimes, where the radiation pressure dominates the particle pressure. Unique dynamics can ensue in such a radiation dominated plasma, especially in the presence of turbulent flows and magnetic fields. With the next generation of HED facilities such as ZR, NIF, coupled with ultra-intense laser ''heater beams'', it may become possible to create radiation-dominated plasma conditions in the laboratory relevant to neutron star (and black hole) accretion dynamics''. With the recent advent of the Rossi XTE time-resolved x-ray satellite, we have entered a new era in our ability to probe the physics and dynamics of neutron stars and black holes on rapid timescales not previously possible. With RXTE, we have diagnosed the dynamics occurring near the surface of a neutron star on timescales less than a millisecond, and have discovered a new phenomena, photon bubble instabilities, in an a accreting X-ray pulsar Centaurus X-3, some 30,000 light years across the galaxy. (Jerningan, Klein and Arons, ApJ, 2000) We in fact, predicted this instability in simulations with time-dependent 2D radiation-hydrodynamics codes that we had developed. (Klein et al. ApJ 1996a, 1996b) Strongly magnetized neutron stars accrete mass from a nearby normal star that is in orbit with the neutron star. The mass is transferred by way of an accretion disk and eventually finds its way onto the surface of the neutron star, where it is channeled by the strong magnetic fields (typically dipolar) onto polar caps that occupy a small surface ({approx}1 km{sup 2}) area on the neutron star. Photon Bubbles are a violent radiation-hydrodynamic instability whereby low density bubbles (buoyant with respect to the surrounding optically thick plasma flow) fill up with hot 10 keV radiation, grow non-linearly and cause the plasma to become turbulent. The instability occurs when the radiation force on matter exceeds the gravitational force, a regime called super Eddington accretion. As has been shown with a linear stability analysis (Arons ApJ 1992), the low density regions in the midst of surrounding optically thick gas, experience a net flux of radiation and increase in buoyancy. If the magnetic field is appreciable (B > 10{sup 8} Gauss,) a conductive increase in internal energy gives unstable growth with respect to the optically thick surrounding regions. This instability appears as an entropy mode in the accreting plasma. While some aspects of these flows are peculiar to the strongly magnetized neutron stars, most are not. Much of the phenomenology is expected in all super-Eddington flows, whether in accretion powered pulsars, low mass X-ray binaries or in the disks around black holes in active galactic nuclei. The main purpose of our feasibility grant of $75,000 for FY 2003 was to begin the study of the feasibility of generating, in a laboratory plasma, conditions that would mimic the conditions present in the low lying atmosphere of a magnetized neutron star that could potentially give rise to photon bubble instabilities, and eventually permit us to probe the physics of accreting, magnetized compact objects such as neutron stars and black holes. This would provide a unique way to explore some of the most exotic astrophysical phenomena in the universe, using powerful high energy density lasers such as NIF and petawatt laboratory platforms.