Crossed-beam energy transfer in implosion experiments on OMEGA

Abstract

Radiative hydrodynamic simulations of implosion experiments on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)] show that energy transfer between crossing laser beams can reduce laser absorption by 10%–20%. A new quantitative model for the crossed-beam energy transfer has been developed, allowing one to simulate the coupling of multiple beams in the expanding corona of implosion targets. Scattered-light and bang-time measurements show good agreement with predictions of this model when nonlocal heat transport is employed. The laser absorption can be increased by narrowing laser beams and/or employing two-color light, which both reduce the crossed-beam energy transfer.

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics

“…Including LPI effects in radhydro codes is challenging: coupling a paraxial and radhydro model has been done, but is usually impractical on current computers [11]. CBET calculations either postprocess plasma conditions from a hydro simulation with no CBET [6,12], or are directly implemented "inline" in simulations that describe lasers with ray-tracing [13,14] or paraxial complex geometric optics [15]. SRS is usually treated by removing the escaping light from the incident laser, though recent work has included SRS-produced superthermal electrons in direct-drive hydrodynamic modeling [16].…”

Multiple-view spectrally resolved x-ray imaging observations of polar-direct-drive implosions on OMEGA

“…each beam had the same, averaged power and hence effects due to power imbalance were not taken into account in the calculations. Hydra's total laser energy was decreased by 20% to approximately account for cross beam energy transfer (CBET) [29,30] and other absorption effects not included in the simulations. This adjustment was also needed in order to improve the matching between simulation and experimental bang times.…”

Progress in direct-drive inertial confinement fusion

“…Crossed-beam energy transfer (CBET) [8][9][10] has been identified as a source of reduced laser absorption in direct-drive experiments [11]. Laser light that is transmitted around the target can interact with the central region of incident beams to scatter light from the Mach-1 surface, reducing the ontarget absorbed energy.…”

“…When CBET is included, the simulations are in much better agreement with the experimental measurements. CBET is modeled in 1-D simulations (including 3-D ray tracing and known focal-spot profiles) by considering pair-wise interactions of rays and calculating the energy transfer between rays using the stimulated Brillouin scattering gain rate for each pair [11]. The standard OMEGA phase plates [13] with a nominal diameter of 860 m were used in these experiments.…”

“…a e-mail: rmcc@lle.rochester.edu This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Crossed-beam energy transfer (CBET) [8][9][10] has been shown to be important in direct-drive experiments [11]. Simulations and experiments have shown that reducing the laser beam's diameter relative to the target diameter improves the laser-target coupling, increasing the implosion velocity.…”