Component design, development, and testing of an inductive voltage adder (IVA) system for Jupiter
Jupiter is a proposed 15-20 MJ laboratory X-ray source. It would store /spl sim/100 MJ in the Marx generators and deliver /spl sim/500 TW to drive high power z-pinch implosions. The pulsed power requirements for Jupiter were evaluated by a national review panel which concluded that the modular IVA technology as used in HERMES III is capable of meeting these requirements. Modularity of construction permits design verification with less than a full size system and offers the flexibility to meet changing requirements. A program to validate this approach at the required power levels has begun with the construction and testing of components that will comprise a full scale IVA generator module. The IVA module will provide a nominal 10 MV, 1.8 MA, 100 ns FWHM output pulse and will consist of four submodules. Each submodule is composed of a Marx generator, two intermediate energy storage capacitors (ISCs) four pulse forming lines (PFLs), one voltage adder cavity (VAC), plus other associated switches and hardware. A conceptual design for this IVA module has been completed. Initial designs for the ISC, PFL, and their gas switches are also complete and hardware has been procured. Testing of these components is underway at Sandia National Laboratories. Discussions of these designs and results of tests are presented in this paper.
A high-voltage multistage laser-triggered gas switch
This paper describes the development and testing of an SF/sub 6/-insulated, multistage laser-triggered gas switch for use in the Hermes-III accelerator at Sandia National Laboratories. Twenty of these switches are used in Hermes III to transfer energy from intermediate energy storage water-dielectric capacitors to the pulse-forming lines (PFLs) and to provide the overall synchronization of the accelerator. The gas switches operate in an oil environment, are charged to a peak voltage between 2.2 MV and 2.4 MV in approx.1 ..mu..s, and are laser triggered with a root-mean-square (rms) jitter equal to or less than 2 ns. Both the triggered and untriggered performance of the switch have been investigated. A summary of the development tests are presented together with initial results from Hermes III.
Germination ecology of Central Asian Stipa spp: differences among species, seed provenances, and the importance of field studies
Stipa-species are wide-spread in Central Asia, but sexual reproduction in the dry steppes is rare. To facilitate conservation and restoration of these important rangelands, we studied germination characteristics of three common Mongolian Stipa-species under field- and lab conditions. Seeds of Stipa krylovii, Stipa gobica and Stipa glareosa were sown at the study site in Southern Mongolia over two consecutive years during which period tests were carried out to ascertain whether competition or herbivory are the main constraints of seedling establishment. In addition, we tested germination and seed viability in the laboratory under two different temperature regimes (20/10°C and 8/4°C), as well as the effect of cold-stratification. The lab experiments also included S. krylovii seeds originating from three climatically different provenances. None of the three Stipa-species seedlings emerged during the first 2 years of the field study. However, after an unusually intense rain event in the third year, 3% of S. krylovii, 0.6% of S. glareosa and 0.1% of S. gobica seeds germinated in the study plots. The factors ‘sowing-year’ and ‘vegetation’ significantly affected seedling emergence, whereas grazing had no effect at all. Under laboratory conditions a high percentage of viable seeds of S. gobica and S. glareosa germinated at both incubation temperatures, and cold-stratification had no effect on germination or viability. Germination of S. krylovii seeds required warmer temperatures and cold-stratification had a positive effect. Such evidence for dormancy was more pronounced in seeds from the moister, northern provenances. Germination of Stipa-species in the field is rare and only possible under exceptionally moist conditions. Conservation should thus concentrate on steppe conservation rather than on restoration. Where artificial reseeding is necessary, differences among species and also among different seed provenances should be taken into account.