Development of a radiative-hydrodynamics testbed using the petawatt laser facility
Many of the conditions believed to underlie astrophysical phenomena have been difficult to achieve in a laboratory setting. For example, models of supernova remnant evolution rely on a detailed understanding of the propagation of shock waves with gigabar pressures at temperatures of 1 keV or more where radiative effects can be important. Current models of gamma ray bursts posit a relativistically expanding plasma fireball with copious production of electron-positron pairs, a difficult scenario to experimentally verify. However, a new class of lasers, such as the Petawatt laser,Perry 1996 are capable of producing focused intensities greater than 1020 W/cm² where such relativistic effects can be observed and even dominate the laser-target interaction. There is ample evidence in observational data from supernova remnants of the aftermath of the passage of radiative shock or blast waves. In the early phases of supernova remnant evolution, the radially-expanding shock wave expands nearly adiabatically since it is traveling at a very high velocity as it begins to sweep up the surrounding interstellar gas. A Sedov-Taylor blast wave solution can be applied to this phase,Taylor 1950, Sedov 1959 when the mass of interstellar gas swept up by the blast greatly exceeds the mass of the stellar ejecta, or a self-similar driven wave model can be applied if the ejecta play a significant role.Chevalier 1982 As the mass of the swept up material begins to greatly exceed the mass of the stellar ejecta, the evolution transitions to a radiative phase wherein the remnant can be modeled as an interior region of ldw-density, high-pressure gas surrounded by a thin, spherical shell of cooled, dense gas with a radiative shock as its outer boundary, the pressure-driven snowplow.Blondin et al. 1998 Until recently it has not been feasible to devise laboratory experiments wherein shock waves with initial pressures in excess of several hundred Mbar and temperatures approaching 1 keV are achieved in order to validate the models of the expanding blast wave launched by a supernova in both of its phases of evolution. We report on a new experiment designed to follow the propagation of a strong blast wave launched by the interaction of an intense short pulse laser with a solid target. This blast wave is generated by the irradiation of the front surface of a layered, solid target with N 400 J of 1 pm laser radiation in a 20 ps pulse focused to a N 50 ,um diameter spot, which produces an intensity in excess of 1018 W/cm². These conditions approximate a point explosion and a blast wave is predicted to be generated with an initial pressure of several hundred megabars which decays as it travels approximately radially outward from the interaction region. We have utilized streaked optical pyrometry of the blast front to determine its time of arrival at the rear surface of the target. Applications of a self-similar Taylor-Sedov blast wave solution allows the amount of energy deposited to be estimated. By varying the parameters of the laser pulse which impinges on the target, pressures on the order of 1 Gbar with initial temperatures in excess of 1 kev are achievable. At these temperatures and densities radiative processes are coupled to the hydrodynamic evolution of the system. Short pulse lasers produce a unique environment for the study of coupled radiation-hydrodynamics in a laboratory setting.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 7987
- Report Number(s):
- UCRL-JC-131549; DP0210000; ON: DE00007987
- Resource Relation:
- Conference: Second International Workshop on Laboratory Astrophysics with Intense Lasers, Tucson, AZ, March 19-21, 1998
- Country of Publication:
- United States
- Language:
- English
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