Implosion Of Cylindrical Shells Research Articles

Material effects on dynamics in triple-nozzle gas-puff Z pinches.

The gas-puff Z pinch has a long history with myriad applications as an efficient neutron or x-ray source. Its simplicity as a load configuration makes it suitable for studying fundamental plasma physics phenomena such as instabilities and energy transport. For example, the implosion of cylindrical shells onto a fusion fuel are inherently susceptible to instability growth on their external surfaces; if such instabilities are unmitigated, then the consequences in terms of degraded performance can be substantial. Similarly, mitigating heat transport from a hot fuel to its colder surrounding container can make fusion conditions more easily achievable. Here we have conducted a systematic study of triple-nozzle (outer liner, inner liner, fuel) gas puffs using two-dimensional (2D) magnetohydrodynamic simulations to investigate the effect of load material on the relevant dynamics. Analogous to past studies on spherical blast waves and converging shock waves, a trend emerges linking increased radiative cooling, lower adiabatic index, and increased magneto-Rayleigh-Taylor instability growth. Notably, our results suggest that, for the present configuration, Ar radiates less than both Ne and Kr during the early stages of the implosion while mass is being swept up and perturbations begin to seed instability growth. Consequently, pinches with Ar on the outer surface exhibit more stable 2D behavior. Here we also present a parameter scan of thermonuclear neutron yield, Y, as a function of peak current, I_{pk} and dopant concentration with Ne or Ar, depending on the inner liner material. Above 6 MA, our results suggest Y∝I_{pk}^{5} and even substantial mixing (10% by volume) of Ne into the fuel does not drastically reduce yield, suggesting an Ar/Ne/fuel configuration may reliably achieve DD thermonuclear yields of 10^{13}-10^{14}/cm in the 10-20 MA range.

Numerical study of implosion of shell structures

To better understand the implosion and the resultant shock wave, a series of numerical modeling and simulations were undertaken for the buckling and collapse of spherical and cylindrical shell structures. The shells were assumed to be made of steel, aluminum, and laminated fibrous composites, respectively. First, the buckling was examined for the shell structures subjected to external pressure loading without any contact with fluid media. Both static and dynamic buckling was studied. For the dynamic buckling, the speed of collapse was controlled to investigate its effect on the buckling characteristics such as buckling mode. This was achieved by decreasing the internal pressure at different rates as the structures were subjected to a constant external pressure. Then, the full implosion process associated with the collapse of shell structures was modelled and studied to understand the shock wave propagation radiated from the collapsing shell structures. The structures were initially subjected to an external water pressure equivalent to a specified water depth. Then, the collapse speed of the shells was controlled, too. Finally, the effect of an initial defect on the buckling and implosion of cylindrical shells was examined. The numerical study compared the implosion characteristics resulting from spherical and cylindrical shells, different material properties, and various controlled collapse speeds. The results suggested that there were optimal parameters which generate the maximum peak pressure during the implosion process.