Spatially resolved temperature measurement and axial thermal transport assessment of magnetized-liner-inertial-fusion burning plasmas.

In a series of magnetized-liner-inertial-fusion experiments performed at the Z pulsed power facility of Sandia National Laboratories, beryllium liners filled with deuterium gas densities between 0.7 to 1.4 mg/cc and a tracer amount of krypton were imploded. At the collapse of the cylindrical implosion, electron temperatures in the 2-4keV range and deuterium ion number densities of ∼10^{23}cm^{-3} were expected. Spatially resolved krypton K-shell line emission was recorded with a time-integrated transmission crystal x-ray spectrometer. The spatially resolved data showed n=2→1 line emission from Be-, Li-, and He-like krypton ions and are characteristic of the highest electron temperatures achieved in the thermonuclear plasma. Detailed modeling of krypton atomic and radiation physics demonstrated that the spectrum is electron temperature dependent, thus allowing for axial temperature distributions to be extracted from the data. Additionally, the electron density (as well as the ion density) of the deuterium compressed plasma was estimated from the relative distribution of narrowband intensity between regions along the z axis. The measurement of axially resolved temperature and density distributions enabled an assessment of thermal transport along the axis of the burning plasma, showing that it proceeded at a much faster rate than local cooling by bremsstrahlung emission. Furthermore, from the pressure distribution, the rate of residual kinetic energy associated with axial plasma flow was evaluated as well.