Theory of induced spatial incoherence. Interim report

Technical Report · Wed Sep 16 04:00:00 EDT 1987

OSTI ID:5824756

Lehmberg, R H; Schmitt, A J; Bodner, S E

This paper describes theoretical and experimental investigations of induced spatial incoherence (ISI), a technique for achieving the smooth and controllable target beam profiles required for direct-drive laser fusion. Analytic and numerical calculations show that nonuniformities due to interference among the beamlets are smoothed by both thermal diffusion and temporal averaging. Under laser-plasma conditions of interest to ICF, average ablation pressure nonuniformities about 1% should be readily attainable. A partial ISI scheme, which allows widely-spaced beamlets to remain mutually coherent, is examined with the resulting high spatial frequency interference structure can be effectively smoothed by thermal diffusion alone. A perturbation analysis shows that the average target profile remains relatively insensitive to laser beam aberration when the scalelength of that aberration is larger than the initial beamlet width. This aberration will tend to broaden and smooth , rather than introduce any small-scale structure. The broadening is largely controllable because it depends only upon spatial averages of the aberrated quantities over the entire laser aperture; the uncontrollable perturbations can be reduced to about 1% in practical cases.

• Research Organization: Naval Research Lab., Washington, DC (USA)
• OSTI ID: 5824756
• Report Number(s): AD-A-185005/6/XAB; NRL-MR-5980
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700208* -- Fusion Power Plant Technology-- Inertial Confinement Technology
ABLATION
APERTURES
CONFINEMENT
FOCUSING
IMPLOSIONS
INCOHERENT SCATTERING
INERTIAL CONFINEMENT
LASER-PRODUCED PLASMA
OPENINGS
PELLETS
PLASMA
PLASMA CONFINEMENT
SCATTERING
SYMMETRY