Hydrodynamic analysis of light-ion beam-driven ICF target

Myunghee Choi, Purdue University

Abstract

The hydrodynamic Rayleigh-Taylor (R-T) instability of two planar targets of tampered and untampered structures under proton beam illumination is studied. First, the analytical study for early linear regime of R-T instability is presented by using the basic formalism by Chandrasekhar in both target configurations. Second, the two-dimensional hydrodynamic responses of two planar targets at the nonlinear regime using the currently achievable proton beam parameters from Sandia are studied numerically using self-consistent, two-dimensional, particle-in-cell Fluid-Implicit-Particle code (FLIP) in three steps. In the first step, physics models of FLIP are studied and verified by comparing with the presently available experimental data of the energy loss of 1.5 MeV proton ion beam in the heated aluminum foil from KfK. The simulated code is then used to study and optimize the hydrodynamic performance of the two planar targets using 4 MeV proton beam parameters in the second step. Finally, the stability and symmetry of these two optimized planar targets are studied by introducing two kinds of nonuniformities with the larger wavelength modes: (1) at target material interface and (2) in the beam intensities of 5 TW/$cm\sp2$ and 120 TW/$cm\sp2.$ In both cases of nonuniformities described above, the case with the higher beam intensity (120 TW/$cm\sp2)$ derived more efficient target implosions in both tampered and untampered target configurations but produced much faster growth rates of bubble and spike, faster thinning rates of target layer thicknesses and thus more dangerous modes than the case of lower beam intensity (5 TW/$cm\sp2).$ The initially perturbed untampered and tampered target interfaces imploded by the uniform beam showed the broader spike and narrower bubble structure while the initially uniform untampered and tampered targets imploded by the nonuniform beam intensity showed the sharper spike and broader bubble structure throughout the implosion. It was found that the beam nonuniformity with 10% perturbed amplitude showed much slower growth rates of spike along DT/Al interface than the target material interface nonuniformity with 10% perturbed amplitude at both 5 TW/$cm\sp2$ and 120 TW/$cm\sp2.$ But, both of two nonuniformities seeded the rapidly increasing perturbation along the inner surface of DT layer within very short time (wig a few nsec) at both 5 TW/$cm\sp2$ and 120 TW/$cm\sp2$. The main differences in all calculations appeared to be the structures of bubble and spike, and the time delay in the development of their amplitudes. Therefore, these two nonuniformities with the larger wavelength (250 $\mu m)$ and amplitude (5 or 10%) seem to be large enough to destroy the symmetry of imploding target shells. (Abstract shortened by UMI.)

Degree

Ph.D.

Advisors

Choi, Purdue University.

Subject Area

Nuclear physics|Fluid dynamics|Gases

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