"Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser"

S. M. Vinko: O. Ciricosta, B. I. Cho, K. Engelhorn, H.-K. Chung, C. R. D. Brown, T. Burian, J. Chalupsky´, R. W. Falcone, C. Graves, V.Ha´jkova´, A. Higginbotham, L. Juha, J. Krzywinski, H. J. Lee, M. Messerschmidt, C. D. Murphy, Y. Ping, A. Scherz, W. Schlotter, S. Toleikis, J. J. Turner, L. Vysin, T.Wang, B.Wu, U. Zastrau, D. Zhu, R. W. Lee, P. A. Heimann, B. Nagler & J. S.Wark; Nature, 01/25/12.

Additional Authors: O. Ciricosta, B. I. Cho, K. Engelhorn, H.-K. Chung, C. R. D. Brown, T. Burian, J. Chalupsky´, R. W. Falcone, C. Graves, V.Ha´jkova´, A. Higginbotham, L. Juha, J. Krzywinski, H. J. Lee, M. Messerschmidt, C. D. Murphy, Y. Ping, A. Scherz, W. Schlotter, S. Toleikis, J. J. Turner, L. Vysin, T.Wang, B.Wu, U. Zastrau, D. Zhu, R. W. Lee, P. A. Heimann, B. Nagler & J. S.Wark

Abstract:

Matter with a high energy density (>105 joules per cm3) is prevalent throughout the Universe, being present in all types of stars1 and towards the centre of the giant planets2, 3; it is also relevant for inertial confinement fusion4. Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities5, 6. With the advent of the Linac Coherent Light Source (LCLS) X-ray laser7, high-intensity radiation (>1017 watts per cm2, previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated8. An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of 106 kelvin on inertial-confinement timescales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray–matter interactions, and illustrate the importance of electron–ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions.