Electron distribution anisotropy in laser-produced plasmas from x-ray line polarization measurements

We report the first measurements of significant polarization of the He-like emission in a laser-produced plasma. From these measurements we infer a negative second-order (i.e., oblate) anisotropy of the electron velocity distribution function in the energy deposition region. This result is in agreement with our kinetic Fokker-Planck calculations which indicate non-Maxwell behavior and strong anisotropy due to nonlocal electron heat flow.