Exploring Astrophysical Magnetohydrodynamics Using High-power Laser Facilities

Transcription

1 Exploring Astrophysical Magnetohydrodynamics Using High-power Laser Facilities Mario Manuel Einstein Fellows Symposium Harvard-Smithsonian Center for Astrophysics October 28 th, 2014 Ø Collimation and propagation dynamics in magnetized flows Ø Radiative and reverse-radiative shock systems Ø Collisionless shock interactions Ø Instabilities in plasma RT, RM, KH, MRI, MTI Ø Equation of state planetary and stellar interiors Ø Relativistic electron-positron plasmas Ø Nucleosynthesis - relevant Gamow energies in a thermal plasma

2 Exploring Astrophysical Magnetohydrodynamics Using High-power Laser Facilities log n H [cm -3 ] log T[K] Gamma-Ray Bursts Big Bang 1 Gbar P total = 1 Mbar 60 M sun Short Pulse Laser Plasmas 1 Mbar Sun P gas = 1 Gbar Supernova Progenitors Brown Dwarf HED regime (P>1 Mbar) log kt[ev] 2 Giant Planet log [g/cm 3 ] Mario Manuel Einstein Fellows Symposium Harvard-Smithsonian Center for Astrophysics October 28 th, 2014 Accesible Region *Adapted from NRC committee on HEDP (2003)

3 Scaled experiments provide a complimentary technique to investigate the dynamics in some astrophysical systems 3 Ø High-power laser facilities provide a unique opportunity to generate physical conditions similar to those in various astrophysical systems Ø Laboratory results are directly scalable when similarity and geometric conditions hold between the two systems Ø Experiments also allow for detailed benchmark comparisons with numerical calculations in relevant dynamic regimes

4 Magnetohydrodynamic (MHD) equations describe both laboratory and astrophysical systems 4 Continuity Momentum Energy Field Evolution ρ t + ρv = 0 $ ρ& v % t + v v ' ) = p + 1 ( B) B ( µ 0 p t γ p ρ ρ t + v p γ p ρ v ρ = 0 B t = v B ( ) [1] Ryutov, ApJ 518 (1999) [2] Ryutov, POP 8 (2001) [3] Drake, High-energy-density physics (2006), ch 10 [4] Remington, RMP 78 (2006) [5] Falize, ApJ 730 (2011)

5 Multiple dimensionless parameters determine the validity of using the MHD equations to describe system dynamics 5 Ø The system exhibits fluid-like behavior Ø Energy flow by particle heat conduction is negligible Ø Energy flow by radiation flux is negligible Ø Viscous dissipation is negligible l mfp L <<1 Pe >>1 Pe γ >>1 Re >>1 Ø Magnetic field diffusion is negligible Re m >>1 Astrophysical systems are large and fulfill these criteria in many cases!

6 Multiple dimensionless parameters determine the validity of using the MHD equations to describe system dynamics 6 Ø The system exhibits fluid-like behavior Ø Energy flow by particle heat conduction is negligible Ø Energy flow by radiation flux is negligible Ø Viscous dissipation is negligible l mfp L <<1 Pe >>1 Pe γ >>1 Re >>1 Ø Magnetic field diffusion is negligible Re m >>1 Two MHD systems evolve similarly when the Euler number (Eu) and magnetization (µ) are similar. Eu v * β 1 p * ρ * µ p * B * ( ) 2

7 Magnetized plasma jets are prominent in young stellar objects with a wide range of parameters 7 Physical condition Constraint Stellar Jets Experiment Viscosity plays minor role Reynolds ~ ~ Magnetic diffusion plays minor role Supersonic flow Thermal compared to magnetic pressure Ram compared to magnetic pressure Magnetic Reynolds Mach number ~ ~ ~ ~10 0 Thermal ~ ~ plasma β th Ram ~ ~ plasma β ram Curran et al., Mon. Not. R. Astron. Soc. 382 (2007); Carrasco-Gonzalez et al., Science 330 (2010); Ferreira AA 452 (2006); Reipurth ARAA 39 (2001)

8 Recent work by colleagues investigated astrophysical jets under similar laboratory-created environments 8 Ciardi et al., PRL 110 (2013); Albertazzi et al., Science 346 (2014)

9 Laser-irradiated cones create collimated plasma flows 9 y z θ c ~80 expanding plasma τ~10 ns E~ J ~600 µm spot x z ~1.5 mm 90-µm-thick plastic cone plasma jet collimates on-axis

10 Optical diagnostics and proton radiography characterized plasma flows 10 Shadowography/ Schlieren Interferometry Long Pulse 10 ns, ~600 µm spot B max ~5 T Probe Beam

11 Collimated jets formed at varying drive energies 11 E 180 J n e [10 18 #/cc] E 330 J n e [10 18 #/cc] 1 mm 1 mm Free electron density is reduced at lower energies, but bulk jet characteristics are roughly constant: - collimated diameter is ~500 µm - average axial velocity is ~45 µm/ns

12 Complete disruption of the collimated jet was observed with an applied 5-T B-field along the jet axis 12 B = 0 T B = 5 T mm 1 mm 0 n e [10 18 #/cc] 0 n e [10 18 #/cc] Ø A tapered hollow cavity is observed in processed interferograms Ø The cavity wall is ~300 µm thick and tapers from ~3 mm to ~2 mm in diameter

13 Simulations* of similar systems predict cavity formation prior to magnetized jet collimation PHYSICAL REVIEW LETTERS PRL 110, (2013) 13 week e 11 JANUA Drive B FIG. 2 (color online). *Ciardi et al. PRL 110 (2013) Color maps correspond to the logarithmic density in g cm"1. Panels (a), (c), and (e) show a cut thr

14 Simulations* of similar systems predict cavity formation prior to magnetized jet collimation PRL 110, (2013) PHYSICAL REVIEW LETTERS 14 week ending 11 JANUARY 2013 Ø Purely expanding plasma Ø Cavity bounded by shock envelope Ø Radial collimation (pinching) Ø frozen-in magnetic field compresses at the shock Ø S t a n d i n g c o n i c a l s h o c k collimates a jet beam FIG. 2 (color online). Color maps correspond to the logarithmic density in g cm"1. Panels (a), (c), and (e) show a cut through the middle of the computational domain in the xz plane. Contour lines in panel (a) correspond to Mma ¼ 1 (dashed) and Mma ¼ 10 (solid). Velocity vectors are shown in panel (c), while in panel (e) the contours are for the magnetic field intensity in MG. Panel (b) is a zoom over the conical shock region depicted in (c), and shows additionally the region where the flow is submagnetosonic, Mma < 1 (dashed line). Panel (d) is a cut perpendicular to the jet at z ¼ 17 mm. Panel (f) shows the profiles on axis of density, " & 106 (g cm"3 ), axial velocity, vz ðkm=sþ, and ion and electron temperatures (ev). Induced Current Inward Force Fr jθ Bz collimation of a (magnetically or thermally driven) wind is the consequence of the inertia of a dense, toruslike circumstellar envelope, which focuses the flow in the polar direction, forming prolate, wind-blown cavities, and jets [28 31]. show for(2013) the first time that an axial *CiardiOur et results al. PRL 110 magnetic field and it is potentially susceptible to firehose instability, which may disrupt the flow through long (axial) wavelength, helical-like distortions (e.g., Ref. [33]). The condition of growth requires anisotropic pressures, Pk " P? > B2 =4!, where the parallel Pk and perpendicular P?

15 Cavity formation in our experiments appears similar to previous predictions 15 T [ev] V [µm/ns] Cone Target Flat Target ~1 ~400 ~50 ~100 Re m ~1 ~100 B = 5 T mm Ø Purely expanding plasma ü Cavity bounded by shock envelope ü Radial collimation (pinching) Ø frozen-in magnetic field compresses at the shock β ~1 ~1 n e [10 18 #/cc]? Standing conical shock collimates a jet beam Different plasma parameters and initial conditions yielded similar behavior.

16 Central jet disruption and shock envelope formation may be simply caused by induction 16 Ø Induced toroidal current acts to oppose the change in flux B = 5 T Ø Direction of radial velocity sets the direction of toroidal current j θ (r) = 2π η B z v r dr F r j θ B z The J B force did not permit axial collimation but still formed an envelope from the radially expanding plasma

17 Cavity formation is very sensitive to the plasma-β 17 B = 2 T B = 0 T B = 5 T 1 mm In the stellar analog to these systems, collimated outflows from the star may be disrupted by the background field.

18 Scaled experiments provide a complimentary technique to investigate some astrophysical systems 18 Ø High-power laser facilities provide a unique opportunity to generate physical conditions similar to those in various astrophysical systems Ø Laboratory results are directly scalable when similarity and geometric conditions hold between the two systems Ø Experiments also allow for detailed benchmark comparisons with numerical calculations in relevant dynamic regimes