Abstract Details
The Dynamics of Radiative and Non-Radiative Strong, Laser-Driven Shocks in Cluster Media
Author: Matthias Hohenberger
Requested Type: Oral Only
Submitted: 2009-04-20 08:33:51
Co-authors: D. R. Symes, J. Lazarus, R. E. Carley, H. W. Doyle, A. S. Moore, E. T. Gumbrell and R. A. Smith
Contact Info:
Imperial College London
Blackett Laboratory
London, SW7 2BW 11111
United Kingdom
Abstract Text:
Shocks and blast waves are ubiquitous features readily observed in many astrophysical phenomena and plasma physics in general. As such they have long been the subject of experimental and theoretical studies. For example, from high-resolution images of astrophysical nebulae and supernova remnants such as SN 1987A, it can be seen that rather than being spatially ‘smooth’, these systems generally exhibit an intricate structure full of turbulence. Formation of these complex structures is thought to be driven by strong shocks and blast waves, highlighting the importance of the study of these phenomena for laboratory astrophysics and, more generally, for high-energy-density plasma physics.
The rapid development of short-pulse, high-power laser systems over the last decade has made it possible to produce increasingly hot plasmas on a ~mm scale. Ultimately, this allows the systematic study of plasma environments with relevance to laboratory astrophysics, fusion research and high-energy-density physics in general with an unprecedented access to increasingly exotic plasma conditions.
Clustered gases have been shown to be an exceedingly interesting target medium for such studies as they exhibit extremely efficient absorption (~90%) when subjected to high-intensity laser radiation compared to an unclustered gas (<1%) [1]. Accordingly, a clustered gas allows for a substantial deposition of energy into the target medium even with ‘table-top’ scale laser systems, creating a low-average-density but high-temperature plasma. As such, this is the perfect tool for studying the dynamics of high-Mach-number shocks.
In this talk we will present experimental results from a recent campaign at the Rutherford Appleton Laboratory (UK) using the Vulcan Laser facility to drive high-Mach-number shocks in cluster media. Experiments were conducted to investigate the structure and propagation dynamics of cylindrical blast waves in radiative and non-radiative gases and in order to scale previous experimental data obtained at the 1J- level to significantly higher drive-energies. In addition to a comparison of shock dynamics in target media of varying Z, the presented data will focus on investigations into the onset of the radiation-driven thermal cooling instability (TCI) [2]. This instability results in oscillations of the shock propagation velocity as the shock front periodically loses energy through radiation and recovers it by propagating into radiatively pre-heated material. The studies were performed by means of a streaked Schlieren technique [3], developed to obtain single-shot shock trajectory measurements, while removing any ambiguities imposed by shot-to-shot fluctuations.
[1] T. Ditmire et al., Phys. Rev. Lett. 78, 3121 (1997)
[2] R. A. Chevalier and J. N. Imamura, AstroPhys. J. 261, 543 (1982)
[3] A. S. Moore et al., Phys. Rev. Lett. 100, 055001 (2008)
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