Accession Number:

ADA175336

Title:

Variation in the Amplitude of Perturbations on the Inner Surface of an Imploding Shell during the Coasting Phase.

Descriptive Note:

Memorandum rept. Sep 85-Jun 86,

Corporate Author:

NAVAL RESEARCH LAB WASHINGTON DC

Personal Author(s):

Report Date:

1986-11-10

Pagination or Media Count:

25.0

Abstract:

In some inertial confinement fusion target designs a spherical shell collapses on a void or compresses a small amount of gaseous material. There can be a period during which both the outside driver pressure and the inside pressure have a negligible effect on the implosion dynamics, and the motion is essentially ballistic. The changes in the aspect ratio occur mainly because of geometrical convergence. For reasonable parameters the inner surface does not begin to decelerate until shortly before convergence is complete. An approximate description of this casting phase is developed and to study the evolution of perturbations on the inner and outer surfaces of the shell in the limit where the fluid is incompressible. The two surfaces are strongly coupled as long as the shell remains thin. When the shell becomes thick compared to the inner radius, the inner and outer surface perturbations decouple. Under these conditions the surface wave action is a good adiabatic invariant, which can be used to estimate the change in the amplitude of a perturbation as a function of the shell inner radius R1. Detailed analysis confirms the adiabatic invariance argument and extends the results. We speculate that the adiabatic invariant may also be good in the case of compressible fluids.

Subject Categories:

  • Fusion Devices (Thermonuclear)

Distribution Statement:

APPROVED FOR PUBLIC RELEASE