OMEGA Laser-Driven Hydrodynamic Jet Experiments with Relevance to Astrophysics

Transcription

1 OMEGA Laser-Driven Hydrodynamic Jet Experiments with Relevance to Astrophysics Astronomical jets Experimental jets Instabilities 1.4 light years Ambient shocks Jet/ambient material interface 2.8 mm Collimated jet beam S. Sublett, J. P. Knauer, D. D. Meyerhofer, and A. Frank University of Rochester Laboratory for Laser Energetics 49th Annual Meeting of the American Physical Society Division of Plasma Physics Orlando, FL November 2007

2 Summary Features of the laboratory jets are consistent with an adiabatic astrophysical jet model As predicted by an adiabatic astrophysical model,* experimental bowshock morphology is constant in time and independent of input energy. Dimensionless scaling parameters place OMEGA jets in the stellar jet regime. Distinctions between double-pulsed jets and single-pulsed jets have been observed for the first time. E16230 *E. C. Ostriker et al., Astrophys. J. 557, 443 (2001).

3 Motivation Experiments detect features not routinely observed in astrophysical jets YSO: DG Tau B PPN: Calabash Optical-WFPC2 YSO: DG Tau B Infrared-NICMOS 2 observations Yellow: R-band Blue: Ha E16231 Experimental jets are imaged with multiple wavelengths that can detect both the jet and ambient shocks. OMEGA jets are viewed at the source; Astrophysical jet sources are obscured.

4 An OMEGA jet is formed by releasing material off a mid-z (Al or Ti) plug embedded in a high-z tungsten washer CH foam 100 mg/cc 2 mm 4 mm 600 nm Hole 300 nm 300 nm 125 ns E16237 The use of Al and Ti plugs allows jet and ambient features to be studied

5 Dimensionless parameters place OMEGA jets in the stellar regime Dimensionless Parameters OMEGA Experiments Young Stellar Objects Planetary Nebulae Density contrast: Jet/ambient density 5 to 20 1 to 20 ~1000 Mach number: Ratio of V s to C a 2 to 4 10 to to 100 Reynolds number: Inertial/viscous drag ~1000 ~10 13 ~10 12 Density contrast > 1 places jets in the overdense regime. Mach number > 1 places jets in the supersonic regime. Reynolds number >> 1 places jets in the unstable regime. E15245a

6 Jets are driven radially by two distinct methods Radiative Adiabatic Bow shock Jet beam Contact discontinuity Ambient medium The cocoon is able to cool, so it becomes thin and dense. Jet is driven radially by the ram pressure of the cocoon. Hot cocoon, unable to radiate, is more diffuse. Jet is driven radially by the thermal pressure of the cocoon. E16235

7 An adiabatic jet model * predicts a bow-shock morphology Cocoon R R J cap Bow shock Z Bow-shock frame The beam-cap energetics in this model account for the cocoon energy loss and, therefore, determine the ambient and jet densities, radii, and speeds. Experimental jet density, speed, and radius are determined from the radiographs. E15243a *E. C. Ostriker et al., Astrophys. J. 557, 443 (2001).

8 An adiabatic astrophysical model is fit to experimental bow-shock profiles Radial coordinates normalized to lengths Bow-shock profiles color-coded by shell Half-E 75 ns Full-E 75 ns Full-E 100 ns Full-E 125 ns x = (V s /bc a ) [(R s /R b ) 3 3(R s /R b ) + 2] R b Axial coordinates normalized to lengths 0.0 Both radial and axial bow-shock-profile coordinates were normalized to jet length. As predicted by the adiabatic astrophysical model, experimental bowshock shape is constant in time and independent of input energy. E15246a

9 Single-pulsed jets are created by seven simultaneous laser beams Cocoon R t Cocoon 100 ns 125 ns The density along the jet beam shows a dense beam cap. The cocoon has a large radius. Cocoon density is nearly the same as the jet beam density. E16233

10 Double-pulsed jets are created by three laser beams, followed 10 ns later by a second pulse of four laser beams Cocoon R t Cocoon 100 ns 125 ns The cocoon density is roughly the same as the shroud density and much less than the beam density. The cocoon radius is small compared with single-pulsed jets. Double-pulsed jets exhibit a more-uniform density along the jet beam rather than a secondary working surface. E16234 The differences in single- and double-pulsed jets are apparent within ten pulse-separation periods.

11 Summary/Conclusions Features of the laboratory jets are consistent with an adiabatic astrophysical jet model As predicted by an adiabatic astrophysical model,* experimental bowshock morphology is constant in time and independent of input energy. Dimensionless scaling parameters place OMEGA jets in the stellar jet regime. Distinctions between double-pulsed jets and single-pulsed jets have been observed for the first time. E16230 *E. C. Ostriker et al., Astrophys. J. 557, 443 (2001).