Abstract Details
Equation of State Measurements of Warm Dense Matter Heated by Laser Accelerated MeV Protons
Author: Gilliss M Dyer
Requested Type: Oral Only
Submitted: 2009-04-21 16:57:05
Co-authors: B.I. Cho, A. Bernstein, A. Dalton T. Ditmire, R Shepherd, H. Chen, Y. Ping, K. Widmann, J. Bonelie, L. Elberson, P. Rambo, J. Schwartz, M. Geissel, E. Brambrink, B. Atherton, A. Edens
Contact Info:
The University of Texas at Austin
2511 Speedway
Austin, tx 78712
USA
Abstract Text:
We present experimental results testing equation of state models of aluminum in the difficult thermodynamic regime of warm dense matter (WDM). By way of energetic protons generated with an ultrafast, ultra-intense laser pulse, we have flash-heated a several-micron thick aluminum foil sample to temperatures around 20 eV on a timescale of several picoseconds, faster than the dissociation time of the foil. We probed the heated foil using two simultaneous, independent, time-resolved measurements: the thermal emission, measured using a streaked optical pyrometer (SOP), and the free expansion into vacuum, measured using a chirped-pulse interferometer (CPI).
Our experiment was performed on the Titan laser at Lawrence Livermore National Laboratory. The laser delivered on target 100 J in a 600-700 ps pulse at a wavelength of 1054 nm. Our targets consisted of flat source and sample foils, separated by 400 micron of vacuum. The laser irradiated an Al or Au source foil to generate a pulse of ~MeV protons, through the process of target normal sheath acceleration. The protons traversed the vacuum gap to rapidly heat the full thickness of the Al sample foil. The SOP and CPI measured, respectively, the temperature and expansion of the rear side of the sample foil. The SOP consisted of an absolutely calibrated optical system, which imaged the heated self-emission of the sample rear surface through a 470 nm band-pass interference filter and onto the slit of a fast, high dynamic range streak camera. The CPI used a 100 ps linearly chirped pulse as a probe, which reflected off the surface of the heated and expanding sample and was imaged into an interferometer and then onto the slit of a high-resolution spectrometer. With careful calibration of the spectrum and chirp, this diagnostic allowed us to determine the time history of expansion of the heated foil.
We compared our data to simulations made in in HYADES, a 1-D radiative Lagrangian hydrocode using different widely used equation of state models. Each EOS model predicts a slightly different relationship between the SOP and CPI signals, and we compare this to the data. We will present these comparisons for the LEOS, SESAME #3718 and XEOS equation of state tables, and discuss the utility of this technique as a test of equation of state models for warm dense matter.
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