Search Results (3 total)

Capillary channels of ≈3  cm in length and with plasma densities ≈10¹⁸  cm^-3 are a promising alternative to the much shorter, higher-density gas jets for GeV-scale laser wakefield acceleration of electrons. However, the large discrepancy between length scales of the plasma and the laser presents a major computational challenge for particle-in-cell (PIC) simulations. Methods are therefore sought that relax the need to concurrently resolve both length scales. For example, the commonly used “moving window” algorithm enables a reduction of the computational domain to a few plasma wavelengths, which is orders of magnitude smaller than the full length of the laser-plasma interaction. In addition, ponderomotive guiding center methods enable relaxation of the constraint to resolve the laser wavelength. These averaging methods split the laser-induced current into a rapidly varying part and a slowly varying envelope. The average over fast time scales is performed in a semianalytic way, leaving the evolution of the laser envelope and the plasma response to be modeled numerically. Here, we present a ponderomotive guiding center algorithm and demonstrate its applicability to model capillary channels by comparing it with fully kinetic PIC simulations.

The high stiffness and toughness of biomineralized tissues are related to the material deformation mechanisms at different levels of organization, from trabeculae and osteons at the micrometer level to the mineralized collagen fibrils at the nanometer length scale. Quantitatively little is known about the sub-micrometer deformation mechanisms under applied load. Using a parallel-fibred mineralized tissue from the turkey leg tendon as a model for the mineralized collagen fibrils, we used in situ tensile testing with synchrotron x-ray diffraction to measure the average fibril deformation with applied external strain. Diffraction peak splitting occurred at large strains, implying an inhomogeneous elongation of collagen fibrils. Scanning electron microscopy measurements lead us to conclude that the inhomogeneous mineralization in mineralized tendon is at the origin of the high fracture strain.

High-lying Rydberg states (11≤n≤34) of helium hydride have been observed. They were produced by laser excitation of a fast molecular beam and detected by field ionization. Ionization potentials, quantum defects, and the binding energy of HeH⁺ were determined. Pure rotational autoionization leads to break offs of the series. From missing lines it is concluded that B ²’) state decays by predissociation.