The effects of laser beam non-uniformities on x-ray conversion efficiency

Conference · Mon Nov 05 00:00:00 EST 1990

OSTI ID:6473462

Langer, S H; Estabrook, K G

High gain Inertial Confinement Fusion (ICF) targets require a highly uniform drive. In the case of direct drive, the inherent non-uniformities in a high-power glass laser beam are large enough to prevent high compression of targets. In recent years two methods for smoothing the laser drive, Induced Spatial Incoherence (ISI) and Smoothing by Spectral Dispersion (SSD), have been proposed. Both methods break the original laser beam up into many beamlets that then interfere at the target to produce an illumination pattern with large instantaneous intensity variations over a wide range of spatial scales. This interferences pattern dances around at the coherence time of the laser and averages out to produce a smooth beam on longer time scales. Indirect drive schemes shine the laser on high-Z material, usually gold, which converts the laser energy into x-rays. The x-rays are then used to drive the target. Non-uniformities in the laser beam can imprint themselves on the emitted x-rays and potentially cause problems, although the spatial transport of the x-rays to the target tends to smooth out these non-uniformities. As a result, ISI and SSD schemes are also being considered for indirect drive laser systems. We address this problem by modeling the effects on the x-ray conversion efficiency of shining a laser beam with a sinusoidal intensity modulation on a gold slab. Our principal results are that electron heat transport is quite efficient in smoothing out non-uniformities in the laser deposition before they reach the ablation surface if the spatial scale of the laser modulation is less than roughly 500 {mu}m. We also show that the gold plasma is below the Raman and Brillouin thresholds throughout the pulse.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• Sponsoring Organization: DOE/DP
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6473462
• Report Number(s): UCRL-JC-105307; CONF-9011127-10; ON: DE91004879
• Resource Relation: Conference: 32. annual meeting of the American Physical Society - Division of Plasma Physics (APS/DPP), Cincinnati, OH (USA), 12-16 Nov 1990
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
INERTIAL CONFINEMENT
X RADIATION
CONVERSION
GOLD
HEAT TRANSFER
L CODES
LASER RADIATION
LASER-PRODUCED PLASMA
PLASMA INSTABILITY
PLASMA SIMULATION
TARGETS
COMPUTER CODES
CONFINEMENT
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY TRANSFER
INSTABILITY
IONIZING RADIATIONS
METALS
PLASMA
PLASMA CONFINEMENT
RADIATIONS
SIMULATION
TRANSITION ELEMENTS
700208* - Fusion Power Plant Technology- Inertial Confinement Technology