Capsules with beryllium ablators have long been considered as alternatives to plastic for the National Ignition Facility laser ; now the superior performance of beryllium is becoming well substantiated . Beryllium capsules have the advantages of relative insensitivity to instability growth, low opacity, high tensile strength, and high thermal Zimmerman and W. L. h e r , Comments Plasmas Phys. Controlled Thermonucl. Fusion, 2 , 5 1 (2975)l results that particular beryllium capsule designs are several times less sensitive than the CH point design to instability growth from DT ice roughness. These capsule designs contain more ablator mass and leave some beryllium unablated at ignition. By adjusting the level of copper dopant, the unablated mass can increase or decrease, with a corresponding decrease or increase in sensitivity to perturbations . A plastic capsule with the same ablator mass as the beryllium and leaving the same unablated mass also shows this reduced perturbation sensitivity. Beryllium's low opacity permits the creation of 250 eV capsule designs. Its high tensile strength allows it to contain DT fuel at room temperature. Its high thermal conductivity simplifies cryogenic fielding.

Ionospheric plasma instabilities are usually discussed in terms of local parameters. However, because electric fields of scale size λ ≳ 1 km map along magnetic field lines, plasma populations far away from a locally unstable region may be affected by the instability process and vice versa. We present observations of electron density variations in the F1 region of the ionosphere at two locations near the magnetic equator. Oscillations in electron number density that were confined to a narrow wavelength regime were observed in a region of the ionosphere with a very weak vertical density gradient. Since magnetic flux tube interchange instabilities cannot create structure in such an environment we suggest that these are “images” of instabilities occurring elsewhere along the magnetic field line. A simple steady state theory of image formation is developed that is in good agreement with the observations. Moreover, this theory predicts a scale size dependent “effective diffusion” process in the F region that may dominate over classical cross‐field diffusion at kilometer scale sizes. Such a scale size dependent diffusion process is required to explain recent scintillation observations of decaying equatorial plumes.

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