Nuclear Instruments and Methods in Physics Research A 415 (1998) 668 — 673 Design of absolute equation of state measurements in optically thick materials by laser-driven shock waves M. Temporal*, S. Atzeni, D. Batani, M. Koenig, A. Benuzzi, B. Faral  INFN, Laboratori Nazionali di Legnaro, 35020 Legnaro, Padova, Italy  Associazione EURATOM-ENEA sulla Fusione, Centro Ricerche Frascati, C.P. 65, 00044 Frascati, Rome, Italy  Dipartimento di Fisica, Universita+ di Milano, Via Celoria 16, 20133 Milano and Istituto Nazionale di Fisica della Materia, Italy  Laboratoire pour l+Utilisation des Laser Intenses, CNRS, Ecole Polytechnique, 91128 Palaiseau, France Abstract Some aspects of the design of a target for the absolute measurement of Equation-of-State data at pressure of tens of Mbar, in optically thick materials are discussed. In the proposed experiment, a shock wave is generated in a laser- irradiated sample, and the shock velocity and the material velocity behind the shock are simultaneously measured by the optical and X-ray diagnostics. Accurate measurements require the generation of a steady, planar shock, and the detection of the motion of a shocked fluid interface by transverse radiography. One- and two-dimensional numerical fluid simulations have been performed to optimize beam and target design, in order to fulfil such requirements.  1998 Elsevier Science B.V. All rights reserved. PACS: 62.50.#p; 52.35.Tc; 52.50.Jm 1. Introduction Powerful and flexible laser facilities allow to gen- erate shock waves in matter with pressure as high as 100 Mbar [1,2], and to perform experiments [3—5] aiming to measure Equation-of-State (EOS) data. These could be helpful in validating theoret- ical models and in providing data of interest to many scientific areas, including Inertial Confine- ment Fusion (ICF). * Corresponding author. E-mail: temporal@lnl.infn.it. Equation-of-State (EOS) data of the shocked material can be evaluated from the Hugoniot equa- tions [6], expressing the conservation of mass, momentum and energy, at the shock front. For a high-pressure shock they read "  D D!u , P"P  #  Du, E"E  # u 2 , (1) and relate the pressure P, internal energy E and density  of the shocked material to the respective pre-shock values (subscripts 0). Use of Eq. (1) requires measuring two unknown quantities, such 0168-9002/98/$19.00  1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 8 ) 0 0 4 4 5 - 8