Photographic, magnetic, and interferometric measurements of current sheet canting in a pulsed electromagnetic accelerator

The propagation speed and canting angle of current sheets in a pulsed electromagnetic accelerator were measured using three different techniques: high-speed photography, magnetic field probes, and laser interferometry. Current sheet canting may have ad-verse effects on accelerator performance. The goal of the present work is to provide a database of cant-ing angles under a variety of experimental condi-tions. Eight different propellants (hydrogen, deu-terium, helium, neon, argon, krypton, xenon, and methane) were tested in a rectangular-geometry ac-celerator, at pressures ranging from 50-400 mTorr. The photographic, magnetic, and interferometric di-agnostics were used to infer the spatial configura-tion of the current sheet by measuring the its opti-cal emission, current density, and electron density, respectively. The three techniques gave qualitative agreement; the magnetic and interferometric mea-surements gave general quantitative agreement as well. The canting angle was found to depend o

Palynological evidence for the age of the Brewer Conglomerate, Amadeus Basin, central Australia

An assemblage of spores recovered from the Undandita Member of the Brewer Conglomerate, the uppermost unit of the Pertnjara Group in the Amadeus Basin of central Australia, establishes the age of that formation as Late Devonian. Comparison with spore assemblages from sedimentary basins in Western Australia indicates that the central Australian assemblage is dateable within the post-early Frasnian to pre-late Famennian interval. Fish remains and spores previously described from the Parke Siltstone at the base of the Pertnjara Group are of probable early Frasnian age, so it now appears that the entire group was deposited during the Late Devonian. The Brewer Conglomerate is of synorogenic origin, and was deposited during uplift associated with the Alice Springs Orogeny; the spore data thus indicate that this tectonic event began in the Late Devonian. Isotopic age determinations in the Arltunga Nappe Complex and the Strangways Range of the Arunta Block have yielded Early Carboniferous dates. These possibly reflect a later stage of deformation than that which was responsible for the deformation and folding of the Brewer Conglomerate