LLE Review 150

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Highlights

This volume of the LLE Review, covering January–March 2017, features “Laser-Driven Magnetized Liner Inertial Fusion on OMEGA,” which provides a brief overview of the development of a laser-driven MagLIF (magnetized liner inertial fusion) platform on the OMEGA laser. MagLIF was developed at the Z pulsed-power facility and is a key target concept in the U.S. Inertial Confinement Fusion Program. Laser-driven MagLIF on OMEGA is being developed to provide the first data on scaling and to allow more shots with better diagnostic access than Z, facilitating basic physics studies.

Additional highlights of research presented in this issue include the following:

• Calculations on the mitigation of cross-beam energy transfer (CBET) in OMEGA direct-drive implosions by wavelength detuning the three separate legs of the system are considered. CBET redistributes power from the ingoing central portion to the outgoing edge of OMEGA beams, increasing the root-mean-squared absorption nonuniformity by an order of magnitude and reducing total absorbed power. A wavelength shift of ±10 Å on two legs is found to be optimal for absorption and close to optimal for absorption uniformity.
• Picosecond time-resolved measurements of the shift of the 1s2p–1s² line in He-like Al as a function of electron density are reported. Temperature and density are inferred from the Al He_α complex using a nonlocal- thermodynamic-equilibrium model. The measurements are broadly consistent with an analytic line-shift model based on calculations of a self-consistent field ion-sphere model.
• The development of a 16-image Kirkpatrick–Baez (KB)–type x-ray microscope coupled to a high-speed framing camera with a temporal resolution of ~30 ps and a spatial resolution of ~6 µm is described. The new diagnostic has made it possible to accurately determine the cryogenic implosion core-emission size and shape at the peak of stagnation, which has contributed to the determination of core pressures exceeding 50 Gbar.
• A model for tritium interaction with metals that treats a metal as a composite with a high-solubility surface layer bonded to a metal lattice is presented. The equilibrium is assumed so that the ratio of tritium concentration in the surface and in the lattice depends on the relative solubilities. The model can predict the temporal evolution of tritium concentration profiles during exposure to tritium gas, during storage, and during successive decontamination efforts, and could be used to develop surfaces that are less prone to absorb tritium.
• Three-dimensional modeling with the hydrodynamic code HYDRA and the neutron tracking code IRIS3D are used to interpret neutron emission measurements. It is shown that background subtraction is important for inferring areal density from backscattered neutrons, but less important for forward-scattered neutrons, and is important for inferring ion temperature from DD neutrons, but is insignificant when inferring ion temperature from DT neutrons at the areal densities typical of OMEGA implosions. Asymmetries resulting in fluid flow in the core are shown to influence the absolute inferred ion temperatures from both reactions. Relative inferred temperatures reflect the underlying asymmetry of the implosion.