Contrib. Plasma Phys. 45, No. 1, 61 – 69 (2005) / DOI 10.1002/ctpp.200510008 Electrical Conductivity of Noble Gases at High Pressures S. Kuhlbrodt 1 , R. Redmer ∗1 , H. Reinholz 1 , G. R¨ opke 1 , B. Holst 1 , V. B. Mintsev 2 , V. K. Gryaznov 2 , N. S. Shilkin 2 , and V. E. Fortov 2 1 Universit¨ at Rostock, Institut f¨ ur Physik, D-18051 Rostock, Germany 2 Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia Received 20 August 2004, accepted 12 November 2004 Published online 28 January 2005 Key words Electrical conductivity, composition, partially ionized plasmas. PACS 52.25.Fi, 52.25.Jm, 52.27.Gr We present experimental and theoretical results for the electrical conductivity of noble gases (He, Ne, Ar, Kr, Xe) up to high pressures where a transition from nonmetallic to metallic-like conductivities occurs. In addition, we show the behavior of the thermal conductivity and thermopower for xenon as an example. The experiments were performed using explosively driven shock waves. Different geometries allow to probe various parameter regions up to several megabars. Besides single-shock experiments along the principal Hugoniot curve, also multiple-shock experiments were performed which follow almost an isentrope. The theoretical calculations were performed within a partially ionized plasma model. The composition is determined by solving a system of mass action laws. The transport coefficients are calculated within linear response theory taking into account the relevant scattering mechanisms of electrons at different ion species, atoms, and other electrons. The general trends of the experimental results can be explained within this theoretical approach. c  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Besides hydrogen, noble gases are widely studied in plasma physics because of their simple electronic structure as closed shell systems. Especially, the electrical conductivity is of interest: Various experiments were performed measuring the electrical conductivity of helium [1, 2], neon [3], argon [2, 3, 4, 5, 6], krypton [7, 8], and xenon [2, 3, 5, 9, 10, 11, 12]. Shock waves generated by high explosives were used in these experiments to compress the gas. This technique is described in more detail in section 2; see also [13] for a recent review. A nonmetal-to-metal transition (NM-M-T) in dense hydrogen has been intensively studied [14]. It is also found in noble gas plasmas at high pressures: In static experiments using diamond anvil cells (DAC) [15, 16, 17], evidence for a NM-M-T in solid xenon was found at 130-150 GPa and room temperature. At temperatures of some 10000 K which were reached by the shock-wave experiments mentioned above, the electrical conductivity of xenon shows a drastic increase at pressures of about 100 GPa. Reflectivity measurements show also a pro- nounced increase from 5% up to 50% in the high-pressure region between 5-20 GPa and temperatures of about 30000 K [18, 19], indicating a steady rise of the density of free charge carriers as characteristic of a NM-M-T. For the calculation of the electrical and thermal conductivity as well as the thermopower, linear response theory (LRT) in the formulation of Zubarev [20] is used in this paper. It has already been applied success- fully for the calculation of transport coefficients of metal plasmas [21, 22, 23, 24]. The composition and the scattering mechanisms are treated within a partially ionized plasma (PIP) model, and a good agreement with experimental results is observed. This approach is applied here to noble gas plasmas for 10 4 K ≤ T ≤ 10 5 K and 0.001 g/cm 3 ≤  ≤ 10 g/cm 3 , i.e. for the parameter range of experiments with explosively driven shock waves. A short summary of the theoretical method is given in section 3. ∗ e-mail: ronald.redmer@uni-rostock.de, Phone: +49 381 498 6910, Fax: +49 381 498 6912 c  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim