Beam clean-up zone calculations for 2.5MV, 1.4kA experiments on DARHT-2
The injector for the second axis of the Dual-Axis Radiographic Hydrotest Facility (DARHT) produces 2 us, 2kA, 3.2 MeV electron beam with a nominal rise time of 600 ns. The injector diode is powered through a ceramic column by a Marx generator. The off-energy electrons (beam head and tail) during the rise and fall time are mismatched to the magnetic transport channel. These electrons may hit the accelerating gaps, resulting in insulator flashover or a vacuum arc. The beam cleanup zone (BCUZ) has been designed to remove low energy beam electrons and to keep mismatched charge from reaching the downstream accelerator. Eliminating the beam head requires a strongly dispersive magnetic field tune in the BCUZ. In this paper, we will present simulation results on developing a beam clean-up tune and on the beam transport through BCUZ for 2.5MeV, 1.4kA experiments on DARHT-2 using the particle-in-cell code Lsp and the envelope code Lamda. The energy loss and wall temperature rise, electron stimulated desorption due to beam scrape-off in the BCUZ and the effects of slow approach to the flat top on transport of the beam body are also investigated. In addition, the experimentally measured voltage profiles for the injector diode and the accelerating cells were used in these simulations. The current transport from Lamda calculations is compared with Lsp results.
DARHT-II commissioning status
The dual axis radiographic hydrotest facility (DARHT) at Los Alamos National Laboratory produces flash radiographs of hydrodynamic experiments using two linear induction accelerators situated on orthogonal axes. The first axis accelerator is operational and has produced radiographs of hydrodynamic experiments. The second axis accelerator, which is in the commissioning stage, will generate an 18-MeV, 2-kA, 2-/spl mu/s electron beam. These parameters are reduced during the initial phase of commissioning to /spl ges/12-MeV, /spl ges/1-kA, and /spl ges/350-ns. These reduced parameters allow lower voltages and fewer components than what will be necessary for the final machine. This paper presents experimental results of commissioning the second axis DARHT accelerator, including an overview of the pulsed power system plus electrical performance data from the 3-MV injector Marx generator and the 200-kV, 2-/spl mu/s induction accelerator cells. Beam transport data will also be presented.
Drivers of Live Cattle Price in the Livestock Trading System of Central Cameroon
Livestock production and trade are critical for the food security and welfare of rural households in sub-Saharan Africa. In Cameroon, animal trade consists mainly of live cattle commercialized through livestock markets. Identifying the factors contributing to cattle price formation is critical for designing effective policies for sustainable production and for increasing food availability. In this study, we evaluated the influence of a range of individual- and market-level factors on the price of cattle that were sold in all transactions (n = 118,017) recorded over a 12-month period from 31 livestock markets in the main cattle production area of the country. An information-theoretic approach using a generalized additive mixed-effect model was implemented to select the best explanatory model as well as evaluate the robustness of the identified drivers and the predictive ability of the model. The age and gender of the cattle traded were consistently found to be important drivers of the price (p < 0.01). Also, strong, but complex, relationships were found between cattle prices and both local human and bovine population densities. Finally, the model highlighted a positive association between the number of incoming trading connections of a livestock market and the price of the traded live cattle (p < 0.01). Although our analysis did not account for factors informing on specific phenotypic traits nor breed characteristics of cattle traded, nearly 50% of the observed variation in live cattle prices was explained by the final model. Ultimately, our model gives a large scale overview of drivers of cattle price formation in Cameroon and to our knowledge is the first study of this scale in Central Africa. Our findings represent an important milestone in designing efficient and sustainable animal health management programme in Cameroon and ensure livelihood sustainability for rural households.