LLE Review 142

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Highlights

This volume of the LLE Review, covering January–March 2015, features “Alpha Heating and Burning Plasmas in Inertial Confinement Fusion.” This article estimates the level of alpha heating and determines the onset of the burning-plasma regime, which are essential to finding the path toward thermonuclear ignition. The onset of the burning-plasma regime inside the hot spot of current implosions at the National Ignition Facility requires a fusion yield of ~50 kJ.

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

• Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy are presented. The shadowgraphy technique uses time-resolved images of soft x rays (>1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. The article discusses the methods used to accurately measure the ablation-front radius, image-to-image timing, and absolute timing.
• The mechanical characterization of optical oxide thin films that is performed using nano-indentation is discussed. The results are explained based on the deposition conditions used. Of the four single-layer thin films tested, alumina was observed to demonstrate the highest values of nano-indentation hardness and elastic modulus.
• The thermal fluctuations in hybrid superconductor/ferromagnetic NbN/NiCu bilayers are discussed, as well as in pure superconducting NbN 2-D nanostripes to understand the origin of dark counts in superconducting nanostripes when operated as single-photon detectors.
• Both numerical and experimental results show that a phase modulator, acting as a time lens in the Fourier-lens configuration, can induce spectral broadening, narrowing, or shifts depending on the phase of the modulator cycle. Numerical simulations show that the pulse spectrum could be compressed by a factor of 8 for a 30-rad phase shift. Experimentally, spectral shifts over a 1.35-nm range and spectral narrowing and broadening by a factor of 2 were demonstrated using a lithium niobate phase modulator with a maximum phase shift of 16 rad at a 10-GHz modulation frequency.
• The macrostructure of chemical-vapor–deposited (CVD) zinc sulfide (ZnS) substrates is characterized by cone-like structures that start growing at the early stages of deposition. This article describes the magnetorheological finishing (MRF) process of polishing four CVD ZnS substrates, manufactured by four different vendors, with conventional magnetorheological (MR) fluid at pH 10 and zirconia-coated–CI (carbonyl iron) MR fluids at pH 4, 5, and 6. The surface-texture evolution of the substrates as they were MRF polished with the different fluids is reported. The performances of the zirconia-coated–CI MR fluid at pH 4 are shown to be significantly higher than that of the same fluid at pH levels of 5 and 6 and moderately higher than that of a conventional MR fluid at pH 10.