|Fast Electron-Ion Coupling in Warm Dense Copper|
|Friday, 24 June 2011 17:01|
The Warm Dense Matter regime falls in between condensed matter and plasma, where it is defined by temperatures of ~ 104-105 K (~ 1-10 eV) and near solid densities. Studying this superheated solid or strongly coupled plasma can provide key understandings about non-equilibrium phase transitions and energy relaxation processes, related to phenomena found in astrophysics, inertial confinement fusion, as well as applied processes such as laser machining and ablation. Quantitative Warm Dense Matter studies are difficult due to the transient nature of the high-energy-density system. An LBNL-LLNL joint team used a femtosecond laser to heat copper nano-foils isochorically, and probed the warm dense copper with x-rays from Advanced Light Source before substantial expansion happens.
The experimental team based at Lawrence Berkeley National Lab, Byoung-ick Cho, Kyle Engelhorn, Chris Weber, Hae Ja Lee, Jun Feng, Pavel Ni, Yuan Ping, Art Nelson, Roger Falcone and Philip Heimann, measured the copper 2p x-ray absorption spectrum with picosecond time resolution. The theoretical team based at Lawrence Livermore National Lab, Alfredo Correa, Tadashi Ogitsu, David Prendergast and Richard Lee provided calculated x-ray absorption spectra derived from first-principles Density Functional Theory (DFT) simulations.
The temperature of the copper sample ranged from 5000 to 10000 K and was determined by comparing the measured x-ray absorption spectrum with the simulations. It is found that the time history of electron temperature is consistent with calculations using an enhanced e-ion coupling parameter. As a result, the electrons and ions reach equilibrium faster than one would expect from the behavior of copper under ambient conditions. This finding may impact all transport properties of copper in the warm dense regime.
Work performed on ALS Beamline 6.0.2
Citation: B. I. Cho, K. Engelhorn, A. A. Correa, T. Ogitsu, C. P. Weber, H. J. Lee, J. Feng, P. A. Ni,Y. Ping, A. J. Nelson, D. Prendergast, R.W. Lee, R.W. Falcone, and P. A. Heimann, "The Electron Structure of Warm Dense Copper,"Physical Review Letters 106, 167601 (2011).
This project was supported by DOE BES funding at LBNL and LDRD program at LLNL.